@misc{VanDonkIanoraVos2011,
author = {Van Donk, Ellen and Ianora, Adrianna and Vos, Matthijs},
title = {Induced defences in marine and freshwater phytoplankton},
series = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe},
journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe},
number = {881},
issn = {1866-8372},
doi = {10.25932/publishup-43513},
url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-435130},
pages = {19},
year = {2011},
abstract = {Many organisms have developed defences to avoid predation by species at higher trophic levels. The capability of primary producers to defend themselves against herbivores affects their own survival, can modulate the strength of trophic cascades and changes rates of competitive exclusion in aquatic communities. Algal species are highly flexible in their morphology, growth form, biochemical composition and production of toxic and deterrent compounds. Several of these variable traits in phytoplankton have been interpreted as defence mechanisms against grazing. Zooplankton feed with differing success on various phytoplankton species, depending primarily on size, shape, cell wall structure and the production of toxins and deterrents. Chemical cues associated with (i) mechanical damage, (ii) herbivore presence and (iii) grazing are the main factors triggering induced defences in both marine and freshwater phytoplankton, but most studies have failed to disentangle the exact mechanism(s) governing defence induction in any particular species. Induced defences in phytoplankton include changes in morphology (e.g. the formation of spines, colonies and thicker cell walls), biochemistry (such as production of toxins, repellents) and in life history characteristics (formation of cysts, reduced recruitment rate). Our categorization of inducible defences in terms of the responsible induction mechanism provides guidance for future work, as hardly any of the available studies on marine or freshwater plankton have performed all the treatments that are required to pinpoint the actual cue(s) for induction. We discuss the ecology of inducible defences in marine and freshwater phytoplankton with a special focus on the mechanisms of induction, the types of defences, their costs and benefits, and their consequences at the community level.},
language = {en}
}
@misc{KehrPicchiDittmannThuenemann2011,
author = {Kehr, Jan-Christoph and Picchi, Douglas Gatte and Dittmann-Th{\"u}nemann, Elke},
title = {Natural product biosyntheses in cyanobacteria a treasure trove of unique enzymes},
series = {Beilstein journal of organic chemistry},
volume = {7},
journal = {Beilstein journal of organic chemistry},
number = {2},
publisher = {Beilstein-Institut zur F{\"o}rderung der Chemischen Wissenschaften},
address = {Frankfurt, Main},
issn = {1860-5397},
doi = {10.3762/bjoc.7.191},
pages = {1622 -- 1635},
year = {2011},
abstract = {Cyanobacteria are prolific producers of natural products. Investigations into the biochemistry responsible for the formation of these compounds have revealed fascinating mechanisms that are not, or only rarely, found in other microorganisms. In this article, we survey the biosynthetic pathways of cyanobacteria isolated from freshwater, marine and terrestrial habitats. We especially emphasize modular nonribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) pathways and highlight the unique enzyme mechanisms that were elucidated or can be anticipated for the individual products. We further include ribosomal natural products and UV-absorbing pigments from cyanobacteria. Mechanistic insights obtained from the biochemical studies of cyanobacterial pathways can inspire the development of concepts for the design of bioactive compounds by synthetic-biology approaches in the future.},
language = {en}
}
@misc{DittmannThuenemannFewerNeilan2013,
author = {Dittmann-Th{\"u}nemann, Elke and Fewer, David P. and Neilan, Brett A.},
title = {Cyanobacterial toxins biosynthetic routes and evolutionary roots},
series = {FEMS microbiology reviews},
volume = {37},
journal = {FEMS microbiology reviews},
number = {1},
publisher = {Wiley-Blackwell},
address = {Hoboken},
issn = {0168-6445},
doi = {10.1111/j.1574-6976.2012.12000.x},
pages = {23 -- 43},
year = {2013},
abstract = {Cyanobacteria produce an unparalleled variety of toxins that can cause severe health problems or even death in humans, and wild or domestic animals. In the last decade, biosynthetic pathways have been assigned to the majority of the known toxin families. This review summarizes current knowledge about the enzymatic basis for the production of the hepatotoxins microcystin and nodularin, the cytotoxin cylindrospermopsin, the neurotoxins anatoxin and saxitoxin, and the dermatotoxin lyngbyatoxin. Elucidation of the biosynthetic pathways of the toxins has paved the way for the development of molecular techniques for the detection and quantification of the producing cyanobacteria in different environments. Phylogenetic analyses of related clusters from a large number of strains has also allowed for the reconstruction of the evolutionary scenarios that have led to the emergence, diversification, and loss of such gene clusters in different strains and genera of cyanobacteria. Advances in the understanding of toxin biosynthesis and evolution have provided new methods for drinking-water quality control and may inspire the development of techniques for the management of bloom formation in the future.},
language = {en}
}
@phdthesis{Meissner2014,
author = {Meissner, Sven},
title = {Implications of Microcystin Production in Microcystis aeruginosa PCC 7806},
url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-75199},
school = {Universit{\"a}t Potsdam},
pages = {VII, 141},
year = {2014},
abstract = {Cyanobacteria produce about 40 percent of the world's primary biomass, but also a variety of often toxic peptides such as microcystin. Mass developments, so called blooms, can pose a real threat to the drinking water supply in many parts of the world. This study aimed at characterizing the biological function of microcystin production in one of the most common bloom-forming cyanobacterium Microcystis aeruginosa. In a first attempt, the effect of elevated light intensity on microcystin production and its binding to cellular proteins was studied. Therefore, conventional microcystin quantification techniques were combined with protein-biochemical methods. RubisCO, the key enzyme for primary carbon fixation was a major microcystin interaction partner. High light exposition strongly stimulated microcystin-protein interactions. Up to 60 percent of the total cellular microcystin was detected bound to proteins, i.e. inaccessible for standard quantification procedures. Underestimation of total microcystin contents when neglecting the protein fraction was also demonstrated in field samples. Finally, an immuno-fluorescence based method was developed to identify microcystin producing cyanobacteria in mixed populations. The high light induced microcystin interaction with proteins suggested an impact of the secondary metabolite on the primary metabolism of Microcystis by e.g. modulating the activity of enzymes. For addressing that question, a comprehensive GC/MS-based approach was conducted to compare the accumulation of metabolites in the wild-type of Microcystis aeruginosa PCC 7806 and the microcystin deficient ΔmcyB mutant. From all 501 detected non-redundant metabolites 85 (17 percent) accumulated significantly different in either of both genotypes upon high light exposition. Accumulation of compatible solutes in the ΔmcyB mutant suggests a role of microcystin in fine-tuning the metabolic flow to prevent stress related to excess light, high oxygen concentration and carbon limitation. Co-analysis of the widely used model cyanobacterium Synechocystis PCC 6803 revealed profound metabolic differences between species of cyanobacteria. Whereas Microcystis channeled more resources towards carbohydrate synthesis, Synechocystis invested more in amino acids. These findings were supported by electron microscopy of high light treated cells and the quantification of storage compounds. While Microcystis accumulated mainly glycogen to about 8.5 percent of its fresh weight within three hours, Synechocystis produced higher amounts of cyanophycin. The results showed that the characterization of species-specific metabolic features should gain more attention with regard to the biotechnological use of cyanobacteria.},
language = {en}
}
@article{WeizIshidaQuittereretal.2014,
author = {Weiz, Annika R. and Ishida, Keishi and Quitterer, Felix and Meyer, Sabine and Kehr, Jan-Christoph and Mueller, Kristian M. and Groll, Michael and Hertweck, Christian and Dittmann-Th{\"u}nemann, Elke},
title = {Harnessing the evolvability of tricyclic microviridins to dissect protease-inhibitor interactions},
series = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition},
volume = {53},
journal = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition},
number = {14},
publisher = {Wiley-VCH},
address = {Weinheim},
issn = {1433-7851},
doi = {10.1002/anie.201309721},
pages = {3735 -- 3738},
year = {2014},
abstract = {Understanding and controlling proteolysis is an important goal in therapeutic chemistry. Among the natural products specifically inhibiting proteases microviridins are particularly noteworthy. Microviridins are ribosomally produced and posttranslationally modified peptides that are processed into a unique, cagelike architecture. Here, we report a combined rational and random mutagenesis approach that provides fundamental insights into selectivity-conferring moieties of microviridins. The potent variant microviridin J was co-crystallized with trypsin, and for the first time the three-dimensional structure of microviridins was determined and the mode of inhibition revealed.},
language = {en}
}
@misc{KehrDittmannThuenemann2015,
author = {Kehr, Jan-Christoph and Dittmann-Th{\"u}nemann, Elke},
title = {Biosynthesis and function of extracellular glycans in cyanobacteria},
url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-400121},
pages = {17},
year = {2015},
abstract = {The cell surface of cyanobacteria is covered with glycans that confer versatility and adaptability to a multitude of environmental factors. The complex carbohydrates act as barriers against different types of stress and play a role in intra- as well as inter-species interactions. In this review, we summarize the current knowledge of the chemical composition, biosynthesis and biological function of exo- and lipo-polysaccharides from cyanobacteria and give an overview of sugar-binding lectins characterized from cyanobacteria. We discuss similarities with well-studied enterobacterial systems and highlight the unique features of cyanobacteria. We pay special attention to colony formation and EPS biosynthesis in the bloom-forming cyanobacterium, Microcystis aeruginosa.},
language = {en}
}
@misc{LiaimerJensenDittmannThuenemann2016,
author = {Liaimer, Anton and Jensen, John B. and Dittmann-Th{\"u}nemann, Elke},
title = {A genetic and chemical perspective on symbiotic recruitment of cyanobacteria of the genus Nostoc into the host plant Blasia pusilla L.},
series = {Frontiers in microbiology},
journal = {Frontiers in microbiology},
url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-407179},
pages = {16},
year = {2016},
abstract = {Liverwort Blasia pusilla L. recruits soil nitrogen-fixing cyanobacteria of genus Nostoc as symbiotic partners. In this work we compared Nostoc community composition inside the plants and in the soil around them from two distant locations in Northern Norway. STRR fingerprinting and 16S rDNA phylogeny reconstruction showed a remarkable local diversity among isolates assigned to several Nostoc clades. An extensive web of negative allelopathic interactions was recorded at an agricultural site, but not at the undisturbed natural site. The cell extracts of the cyanobacteria did not show antimicrobial activities, but four isolates were shown to be cytotoxic to human cells. The secondary metabolite profiles of the isolates were mapped by MALDI-TOF MS, and the most prominent ions were further analyzed by Q-TOF for MS/MS aided identification. Symbiotic isolates produced a great variety of small peptide-like substances, most of which lack any record in the databases. Among identified compounds we found microcystin and nodularin variants toxic to eukaryotic cells. Microcystin producing chemotypes were dominating as symbiotic recruits but not in the free-living community. In addition, we were able to identify several novel aeruginosins and banyaside-like compounds, as well as nostocyclopeptides and nosperin.},
language = {en}
}
@article{ReynaGonzalezSchmidPetrasetal.2016,
author = {Reyna-Gonz{\´a}lez, Emmanuel and Schmid, Bianca and Petras, Daniel and S{\"u}ssmuth, Roderich D. and Dittmann, Elke},
title = {Leader Peptide-Free In Vitro Reconstitution of Microviridin Biosynthesis Enables Design of Synthetic Protease-Targeted Libraries},
series = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition},
volume = {55},
journal = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition},
publisher = {Wiley-VCH},
address = {Weinheim},
issn = {1433-7851},
doi = {10.1002/anie.201604345},
pages = {9398 -- 9401},
year = {2016},
abstract = {Microviridins are a family of ribosomally synthesized and post-translationally modified peptides with a highly unusual architecture featuring non-canonical lactone as well as lactam rings. Individual variants specifically inhibit different types of serine proteases. Here we have established an efficient in vitro reconstitution approach based on two ATP-grasp ligases that were constitutively activated using covalently attached leader peptides and a GNAT-type N-acetyltransferase. The method facilitates the efficient in vitro one-pot transformation of microviridin core peptides to mature microviridins. The engineering potential of the chemo-enzymatic technology was demonstrated for two synthetic peptide libraries that were used to screen and optimize microviridin variants targeting the serine proteases trypsin and subtilisin. Successive analysis of intermediates revealed distinct structure-activity relationships for respective target proteases.},
language = {en}
}
@phdthesis{ReynaGonzalez2017,
author = {Reyna Gonz{\´a}lez, Emmanuel},
title = {Engineering of the microviridin post-translational modification enzymes for the production of synthetic protease inhibitors},
url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-406979},
school = {Universit{\"a}t Potsdam},
pages = {XI, 91, CI},
year = {2017},
abstract = {Natural products and their derivatives have always been a source of drug leads. In particular, bacterial compounds have played an important role in drug development, for example in the field of antibiotics. A decrease in the discovery of novel leads from natural sources and the hope of finding new leads through the generation of large libraries of drug-like compounds by combinatorial chemistry aimed at specific molecular targets drove the pharmaceutical companies away from research on natural products. However, recent technological advances in genetics, bioinformatics and analytical chemistry have revived the interest in natural products. The ribosomally synthesized and post-translationally modified peptides (RiPPs) are a group of natural products generated by the action of post-translationally modifying enzymes on precursor peptides translated from mRNA by ribosomes. The great substrate promiscuity exhibited by many of the enzymes from RiPP biosynthetic pathways have led to the generation of hundreds of novel synthetic and semisynthetic variants, including variants carrying non-canonical amino acids (ncAAs). The microviridins are a family of RiPPs characterized by their atypical tricyclic structure composed of lactone and lactam rings, and their activity as serine protease inhibitors. The generalities of their biosynthetic pathway have already been described, however, the lack of information on details such as the protease responsible for cleaving off the leader peptide from the cyclic core peptide has impeded the fast and cheap production of novel microviridin variants. In the present work, knowledge on leader peptide activation of enzymes from other RiPP families has been extrapolated to the microviridin family, making it possible to bypass the need of a leader peptide. This feature allowed for the exploitation of the microviridin biosynthetic machinery for the production of novel variants through the establishment of an efficient one-pot in vitro platform. The relevance of this chemoenzymatic approach has been exemplified by the synthesis of novel potent serine protease inhibitors from both rationally-designed peptide libraries and bioinformatically predicted microviridins. Additionally, new structure-activity relationships (SARs) could be inferred by screening microviridin intermediates. The significance of this technique was further demonstrated by the simple incorporation of ncAAs into the microviridin scaffold.},
language = {en}
}
@article{MeyerMainzKehretal.2017,
author = {Meyer, Sabine and Mainz, Andi and Kehr, Jan-Christoph and Suessmuth, Roderich and Dittmann, Elke},
title = {Prerequisites of Isopeptide Bond Formation in Microcystin Biosynthesis},
series = {ChemBioChem : a European journal of chemical biology},
volume = {18},
journal = {ChemBioChem : a European journal of chemical biology},
publisher = {Wiley-VCH},
address = {Weinheim},
issn = {1439-4227},
doi = {10.1002/cbic.201700389},
pages = {2376 -- 2379},
year = {2017},
abstract = {The biosynthesis of the potent cyanobacterial hepatotoxin microcystin involves isopeptide bond formation through the carboxylic acid side chains of d-glutamate and -methyl d-aspartate. Analysis of the in vitro activation profiles of the two corresponding adenylation domains, McyE-A and McyB-A(2), either in a didomain or a tridomain context with the cognate thiolation domain and the upstream condensation domain revealed that substrate activation of both domains strictly depended on the presence of the condensation domains. We further identified two key amino acids in the binding pockets of both adenylation domains that could serve as a bioinformatic signature of isopeptide bond-forming modules incorporating d-glutamate or d-aspartate. Our findings further contribute to the understanding of the multifaceted role of condensation domains in nonribosomal peptide synthetase assembly lines.},
language = {en}
}
@phdthesis{Bolius2018,
author = {Bolius, Sarah},
title = {Microbial invasions in aquatic systems - strain identity, genetic diversity and timing},
school = {Universit{\"a}t Potsdam},
pages = {154},
year = {2018},
abstract = {Biological invasions are the dispersal and following establishment of species outside their native habitat. Due to globalisation, connectivity of regions and climate changes the number of invasive species and their successful establishment is rising. The impact of these species is mostly negative, can induce community and habitat alterations, and is one main cause for biodiversity loss. This impact is particularly high and less researched in aquatic systems and microbial organisms and despite the high impact, the knowledge about overall mechanisms and specific factors affecting invasions are not fully understood. In general, the characteristics of the habitat, native community and invader determine the invasiveness. In this thesis, I aimed to provide a better understanding of aquatic invasions focusing on the invader and its traits and identity. This thesis used a set of 12 strains of the invasive cyanobacterium Cylindrospermopsis raciborskii to examine the effect and impact of the invaders' identity and genetic diversity. Further, the effect of timing on the invasion potential and success was determined, because aquatic systems in particular undergo seasonal fluctuations. Most studies revealed a higher invasion success with increasing genetic diversity. Here, the increase of the genetic diversity, by either strain richness or phylogenetic dissimilarity, is not firstly driving the invasion, but the strain-identity. The high variability among the strains in traits important for invasions led to the highly varying strain-specific invasion success. This success was most dependent on nitrogen uptake and efficient resource use. The lower invasion success into communities comprising further N-fixing species indicates C. raciborskii can use this advantage only without the presence of competitive species. The relief of grazing pressure, which is suggested to be more important in aquatic invasions, was only promoting the invasion when unselective and larger consumers were present. High abundances of unselective consumers hampered the invasion success. This indicates a more complex and temporal interplay of competitive and consumptive resistance mechanisms during the invasion process. Further, the fluctuation abundance and presence of competitors (= primary producers) and consumers (= zooplankton) in lakes can open certain 'invasion windows'. Remarkably, the composition of the resident community was also strain-specific affected and altered, independent of a high or low invasion success. Prior, this was only documented on the species level. Further, investigations on the population of invasive strains can reveal more about the invasion patterns and how multiple strain invasions change resident communities. The present dissertation emphasises the importance of invader-addition experiments with a community context and the importance of the strain-level for microbial invasions and in general, e.g. for community assemblies and the outcome of experiments. The strain-specific community changes, also after days, may explain some sudden changes in communities, which have not been explained yet. This and further knowledge may also facilitate earlier and less cost-intensive management to step in, because these species are rarely tracked until they reach a high abundance or bloom, because of their small size. Concluded for C. raciborskii, it shows that this species is no 'generalistic' invader and its invasion success depends more on the competitor presence than grazing pressure. This may explain its, still unknown, invasion pattern, as C. raciborskii is not found in all lakes of a region.},
language = {en}
}
@article{ColomaGaedkeSivonenetal.2019,
author = {Coloma, Sebastian and Gaedke, Ursula and Sivonen, Kaarina and Hiltunen, Teppo},
title = {Frequency of virus-resistant hosts determines experimental community dynamics},
series = {Ecology : a publication of the Ecological Society of America},
volume = {100},
journal = {Ecology : a publication of the Ecological Society of America},
number = {1},
publisher = {Wiley},
address = {Hoboken},
issn = {0012-9658},
doi = {10.1002/ecy.2554},
pages = {10},
year = {2019},
abstract = {Parasites, such as bacterial viruses (phages), can have large effects on host populations both at the ecological and evolutionary levels. In the case of cyanobacteria, phages can reduce primary production and infected hosts release intracellular nutrients influencing planktonic food web structure, community dynamics, and biogeochemical cycles. Cyanophages may be of great importance in aquatic food webs during large cyanobacterial blooms unless the host population becomes resistant to phage infection. The consequences on plankton community dynamics of the evolution of phage resistance in bloom forming cyanobacterial populations are still poorly studied. Here, we examined the effect of different frequencies of a phage-resistant genotype within a filamentous nitrogen-fixing Nodularia spumigena population on an experimental plankton community. Three Nodularia populations with different initial frequencies (0\%, 5\%, and 50\%) of phage-resistant genotypes were inoculated in separate treatments with the phage 2AV2, the green alga Chlorella vulgaris, and the rotifer Brachionus plicatilis, which formed the experimental plankton community subjected to either nitrogen-limited or nitrogen-rich conditions. We found that the frequency of the phage-resistant Nodularia genotype determined experimental community dynamics. Cyanobacterial populations with a high frequency (50\%) of the phage-resistant genotype dominated the cultures despite the presence of phages, retaining most of the intracellular nitrogen in the plankton community. In contrast, populations with low frequencies (0\% and 5\%) of the phage-resistant genotype were lysed and reduced to extinction by the phage, transferring the intracellular nitrogen held by Nodularia to Chlorella and rotifers, and allowing Chlorella to dominate the communities and rotifers to survive. This study shows that even though phages represent minuscule biomass, they can have key effects on community composition and eco-evolutionary feedbacks in plankton communities.},
language = {en}
}
@misc{BoliusMorlingWiedneretal.2020,
author = {Bolius, Sarah and Morling, Karoline and Wiedner, Claudia and Weithoff, Guntram},
title = {Genetic Identity and Herbivory Drive the Invasion of a Common Aquatic Microbial Invader},
series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
number = {971},
issn = {1866-8372},
doi = {10.25932/publishup-47433},
url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-474333},
pages = {15},
year = {2020},
abstract = {Despite the increasing number of species invasions, the factors driving invasiveness are still under debate. This is particularly the case for "invisible" invasions by aquatic microbial species. Since in many cases only a few individuals or propagules enter a new habitat, their genetic variation is low and might limit their invasion success, known as the genetic bottleneck. Thus, a key question is, how genetic identity and diversity of invading species influences their invasion success and, subsequently, affect the resident community. We conducted invader-addition experiments using genetically different strains of the globally invasive, aquatic cyanobacterium Raphidiopsis raciborskii (formerly: Cylindrospermopsis raciborskii) to determine the role of invader identity and genetic diversity (strain richness) at four levels of herbivory. We tested the invasion success of solitary single strain invasions against the invader genetic diversity, which was experimentally increased up to ten strains (multi-strain populations). By using amplicon sequencing we determined the strain-specific invasion success in the multi-strain treatments and compared those with the success of these strains in the single-strain treatments. Furthermore, we tested for the invasion success under different herbivore pressures. We showed that high grazing pressure by a generalist herbivore prevented invasion, whereas a specialist herbivore enabled coexistence of consumer and invader. We found a weak effect of diversity on invasion success only under highly competitive conditions. When invasions were successful, the magnitude of this success was strain-specific and consistent among invasions performed with single-strain or multi-strain populations. A strain-specific effect was also observed on the resident phytoplankton community composition, highlighting the strong role of invader genetic identity. Our results point to a strong effect of the genetic identity on the invasion success under low predation pressure. The genetic diversity of the invader population, however, had little effect on invasion success in our study, in contrast to most previous findings. Instead, it is the interaction between the consumer abundance and type together with the strain identity of the invader that defined invasion success. This study underlines the importance of strain choice in invasion research and in ecological studies in general.},
language = {en}
}
@article{BoliusKarolineMorlingWiedneretal.2020,
author = {Bolius, Sarah and Karoline Morling, and Wiedner, Claudia and Weithoff, Guntram},
title = {Genetic Identity and Herbivory Drive the Invasion of a Common Aquatic Microbial Invader},
series = {Frontiers in Microbiology},
volume = {11},
journal = {Frontiers in Microbiology},
publisher = {Frontiers Media},
address = {Lausanne},
issn = {1664-302X},
doi = {10.3389/fmicb.2020.01598},
pages = {13},
year = {2020},
abstract = {Despite the increasing number of species invasions, the factors driving invasiveness are still under debate. This is particularly the case for "invisible" invasions by aquatic microbial species. Since in many cases only a few individuals or propagules enter a new habitat, their genetic variation is low and might limit their invasion success, known as the genetic bottleneck. Thus, a key question is, how genetic identity and diversity of invading species influences their invasion success and, subsequently, affect the resident community. We conducted invader-addition experiments using genetically different strains of the globally invasive, aquatic cyanobacterium Raphidiopsis raciborskii (formerly: Cylindrospermopsis raciborskii) to determine the role of invader identity and genetic diversity (strain richness) at four levels of herbivory. We tested the invasion success of solitary single strain invasions against the invader genetic diversity, which was experimentally increased up to ten strains (multi-strain populations). By using amplicon sequencing we determined the strain-specific invasion success in the multi-strain treatments and compared those with the success of these strains in the single-strain treatments. Furthermore, we tested for the invasion success under different herbivore pressures. We showed that high grazing pressure by a generalist herbivore prevented invasion, whereas a specialist herbivore enabled coexistence of consumer and invader. We found a weak effect of diversity on invasion success only under highly competitive conditions. When invasions were successful, the magnitude of this success was strain-specific and consistent among invasions performed with single-strain or multi-strain populations. A strain-specific effect was also observed on the resident phytoplankton community composition, highlighting the strong role of invader genetic identity. Our results point to a strong effect of the genetic identity on the invasion success under low predation pressure. The genetic diversity of the invader population, however, had little effect on invasion success in our study, in contrast to most previous findings. Instead, it is the interaction between the consumer abundance and type together with the strain identity of the invader that defined invasion success. This study underlines the importance of strain choice in invasion research and in ecological studies in general.},
language = {en}
}
@phdthesis{Krumbholz2021,
author = {Krumbholz, Julia},
title = {Identification of chemical mediators that regulate the specialized metabolism in Nostoc punctiforme},
doi = {10.25932/publishup-54024},
url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-540240},
school = {Universit{\"a}t Potsdam},
pages = {xxiii, 187},
year = {2021},
abstract = {Specialized metabolites, so-called natural products, are produced by a variety of different organisms, including bacteria and fungi. Due to their wide range of different biological activities, including pharmaceutical relevant properties, microbial natural products are an important source for drug development. They are encoded by biosynthetic gene clusters (BGCs), which are a group of locally clustered genes. By screening genomic data for genes encoding typical core biosynthetic enzymes, modern bioinformatical approaches are able to predict a wide range of BGCs. To date, only a small fraction of the predicted BGCs have their associated products identified. The phylum of the cyanobacteria has been shown to be a prolific, but largely untapped source for natural products. Especially multicellular cyanobacterial genera, like Nostoc, harbor a high amount of BGCs in their genomes. A main goal of this study was to develop new concepts for the discovery of natural products in cyanobacteria. Due to its diverse setup of orphan BGCs and its amenability to genetic manipulation, Nostoc punctiforme PCC 73102 (N. punctiforme) appeared to be a promising candidate to be established as a model organism for natural product discovery in cyanobacteria. By utilizing a combination of genome-mining, bioactivity-screening, variations of culture conditions, as well as metabolic engineering, not only two new polyketides were discovered, but also first-time insights into the regulation of the specialized metabolism in N. punctiforme were gained during this study. The cultivation of N. punctiforme to very high densities by utilizing increasing light intensities and CO2 levels, led to an enhanced metabolite production, causing rather complex metabolite extracts. By utilizing a library of CFP reporter mutant strains, each strain reporting for one of the predicted BGCs, it was shown that eight out of 15 BGCs were upregulated under high density (HD) cultivation conditions. Furthermore, it could be demonstrated that the supernatant of an HD culture can increase the expression of four of the influenced BGCs, even under conventional cultivation conditions. This led to the hypothesis that a chemical mediator encoded by one of the affected BGCs is accumulating in the HD supernatant and is able to increase the expression of other BGCs as part of a cell-density dependent regulatory circuit. To identify which of the BGCs could be a main trigger of the presumed regulatory circuit, it was tried to activate four BGCs (pks1, pks2, ripp3, ripp4) selectively by overexpression of putative pathway-specific regulatory genes that were found inside the gene clusters. Transcriptional analysis of the mutants revealed that only the mutant strain targeting the pks1 BGC, called AraC_PKS1, was able to upregulate the expression of its associated BGC. From an RNA sequencing study of the AraC_PKS1 mutant strain, it was discovered that beside pks1, the orphan BGCs ripp3 and ripp4 were also upregulated in the mutant strain. Furthermore, it was observed that secondary metabolite production in the AraC_PKS1 mutant strain is further enhanced under high-light and high-CO2 cultivation conditions. The increased production of the pks1 regulator NvlA also had an impact on other regulatory factors, including sigma factors and the RNA chaperone Hfq. Analysis of the AraC_PKS1 cell and supernatant extracts led to the discovery of two novel polyketides, nostoclide and nostovalerolactone, both encoded by the pks1 BGC. Addition of the polyketides to N. punctiforme WT demonstrated that the pks1-derived compounds are able to partly reproduce the effects on secondary metabolite production found in the AraC_PKS1 mutant strain. This indicates that both compounds are acting as extracellular signaling factors as part of a regulatory network. Since not all transcriptional effects that were found in the AraC_PKS1 mutant strain could be reproduced by the pks1 products, it can be assumed that the regulator NvlA has a global effect and is not exclusively specific to the pks1 pathway. This study was the first to use a putative pathway specific regulator for the specific activation of BGC expression in cyanobacteria. This strategy did not only lead to the detection of two novel polyketides, it also gave first-time insights into the regulatory mechanism of the specialized metabolism in N. punctiforme. This study illustrates that understanding regulatory pathways can aid in the discovery of novel natural products. The findings of this study can guide the design of new screening strategies for bioactive compounds in cyanobacteria and help to develop high-titer production platforms for cyanobacterial natural products.},
language = {en}
}