Biology subjects

Teikari, J. E.

Publications and source records attributed to Teikari, J. E..

3 recordsLinked to original sources

bioRxiv2024

Microcystin shapes the Microcystis phycosphere through community filtering and by influencing cross-feeding interactions

The cyanobacterium Microcystis causes harmful algal blooms (cyanoHABs) that pose a major threat to human health and ecosystem services, particularly due to the prevalence of the potent hepatotoxin microcystin. With their pronounced EPS layer, Microcystis colonies also serve as a hub for heterotrophic phycosphere bacteria. Here, we tested the hypothesis that the genotypic plasticity in its ability to produce microcystin influences the composition and assembly of the Microcystis phycosphere microbiome. In an analysis of individual colonies of a natural Microcystis bloom, we observed a significantly reduced richness of the community in the presence of microcystin biosynthesis genes. A subsequent synthetic community experiment with 21 heterotrophic strains in co-cultivation with either the wild-type strain M. aeruginosa PCC 7806 or the microcystin-free mutant {Delta}mcyB revealed not only a tug-of-war between phototrophic and heterotrophic bacteria, but also a reciprocal dominance of two isolates of the genus Sphingomonas and Flavobacterium. In contrast, an Agrobacterium isolate thrived equally well in both consortia. In substrate utilization tests, Sphingomonas showed the strongest dependence on Microcystis exudates with a clear preference for the wild-type strain. Genome sequencing revealed a high potential for complementary cross-feeding, particularly for the Agrobacterium and Sphingomonas isolates but no potential for microcystin degradation. We postulate that strain-specific functional traits, such as the ability to perform photorespiration and to produce vitamin B12, play a crucial role in the cross-feeding interactions, and that microcystin is one of the determining factors in the Microcystis phycosphere due to its interference with inorganic carbon metabolism.

microbiology↗

bioRxiv2024

Competition and interdependence define multifaceted interactions of symbiotic Nostoc sp. and Agrobacterium sp. under inorganic carbon limitation

Cyanobacteria of the Nostoc genus are capable of forming symbiotic relationships with plants, thus transitioning to a heterotrophic lifestyle in return for providing bioavailable nitrogen to the host. The diazotrophic photoautotrophs also serve as a hub for specialized heterotrophic bacterial communities whose physiological contributions are poorly understood. By comparing the axenic strain Nostoc punctiforme PCC 73102 and the related strains Nostoc sp. KVJ2 and KVJ3, which still maintain their heterotrophic microbiome, we were able to demonstrate an almost obligate dependence of the cyanobacteria on the heterotrophic partners under carbon-limiting conditions. Detailed analysis of the intimate bilateral relationship between N. punctiforme and the isolate Agrobacterium tumefaciens Het4 using shotgun proteomics and microscopy uncovered a complex partnership characterized, among other traits, by competition for iron and facilitation for carbon. Although competitive interactions with A. tumefaciens Het4 compromise nitrogen fixation and stimulate the degradation of cyanophycin, mutualistic dependency prevails under inorganic carbon limitation. Both the absence of the high affinity bicarbonate uptake transporter SbtA and the prevalent extracarboxysomal localization of the carbon-fixing enzyme RubisCO, as detected by immunofluorescence microscopy, suggest that a weak carbon concentrating mechanism in N. punctiforme enforces a dependence on heterotrophic bacteria. Further, immunofluorescence, electron microscopic and proteomic analyses reveal a pronounced extracellular recycling of proteins under N- and C-limiting conditions. Our study shows that the pivotal influence of heterotrophic bacteria on symbiotic Nostoc strains should be considered when analyzing these cyanobacteria, especially in the free-living state. This work also sheds new light on how Nostoc benefits from the organic carbon provided by plant hosts.

microbiology↗

bioRxiv2020

Divergent gene expression responses in two Baltic Sea heterotrophic model bacteria to dinoflagellate dissolved organic matter

Phytoplankton release massive amounts of dissolved organic matter (DOM) into the water column during recurring blooms in coastal waters and inland seas. The released DOM encompasses a complex mixture of both known and unknown compounds, and is a rich nutrient source for heterotrophic bacteria. The metabolic activity of bacteria during and after phytoplankton blooms can hence be expected to reflect the characteristics of the released DOM. We therefore investigated if bacterioplankton could be used as "living sensors" of phytoplankton DOM quantity and/or quality, by applying gene expression analyses to identify bacterial metabolisms induced by DOM. We used transcriptional analysis of two Baltic Sea bacterial isolates (Polaribacter sp. BAL334 [Flavobacteriia] and Brevundimonas sp. BAL450 [Alphaproteobacteria]) growing with DOM from axenic cultures of the dinoflagellate Prorocentrum minimum. We observed pronounced differences between the two bacteria both in bacterial growth and the expressed metabolic pathways in cultures exposed to dinoflagellate DOM compared with controls. Differences in metabolic responses between the two isolates were caused both by differences in gene repertoire between them (e.g. in the SEED categories for membrane transport, motility and photoheterotrophy) and the regulation of expression (e.g. fatty acid metabolism), emphasizing the importance of separating the responses of different taxa in analyses of community sequence data. Similarities between the bacteria included substantially increased expression of genes for Ton and Tol transport systems in both isolates, which are commonly associated with uptake of complex organic molecules. Polaribacter sp. BAL334 showed stronger metabolic responses to DOM harvested from exponential than stationary phase dinoflagellates (128 compared to 26 differentially expressed genes), whereas Brevundimonas sp. BAL450 responded more to the DOM from stationary than exponential phase dinoflagellates (33 compared to 6 differentially expressed genes). These findings suggest that shifts in bacterial metabolisms during different phases of phytoplankton blooms can be detected in individual bacterial species and can provide insights into their involvement in DOM transformations.

microbiology↗