The Love and Hate Relationship between T5SS and Other Secretion Systems in Bacteria

Segregation and mixing shape the structure and functioning of aquatic microbial communities, but their respective roles are challenging to disentangle in field studies. We explored the hypothesis that functional differences and beta diversity among stochastically assembled communities would increase in the absence of dispersal. Contrariwise, we expected biotic selection during homogenizing dispersal to reduce beta and gamma diversity as well as functional variability. This was experimentally addressed by examining the compositional and functional changes of 20 freshwater bacterial assemblages maintained at identical conditions over seven growth cycles for 34 days and subjected to two consecutive dispersal regimes. Initial dispersal limitation generated high beta diversity and led to the repeated emergence of community types that were dominated by particular taxa. Compositional stability and evenness of the community types varied over successive growth cycles, reflecting differences in functional properties. Carbon use efficiency increased during cultivation, with some communities of unique composition outperforming the replicate community types. Homogenizing dispersal led to high compositional similarity and reduced gamma diversity. While a neutral and a competition-based (Elo-rating) model together largely explained community assembly, a pseudomonad disproportionally dominated across communities, possibly due to interaction-related genomic traits. In conclusion, microbial assemblages stochastically generated by dispersal limitation can be gradually “refined” into distinct community types by subsequent deterministic processes. Segregation of communities represented an insurance mechanism for highly productive but competitively weak microbial taxa that were excluded during community coalescence. IMPORTANCE We experimentally assessed the compositional and functional responses of freshwater bacterial assemblages exposed to two consecutive dispersal-related events (dispersal limitation and homogenizing dispersal) under identical growth conditions. While segregation led to a decreased local diversity, high beta diversity sustained regional diversity and functional variability. In contrast, homogenizing dispersal reduced the species pool and functional variability of the metacommunity. Our findings highlight the role of dispersal in regulating both diversity and functional variability of aquatic microbial metacommunities, thereby providing crucial insight to predict changes in ecosystem functioning.

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Cellular response in the resilience of Microcystis aeruginosa under polyaluminum chloride exposure

Eyun,

Kim,

Park

et al. 2024

Preprint

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Polyaluminum chloride (PAC) is a flocculant commonly used to remove microalgal cells from blooming reservoir. However, some cells exposed to PAC can survive and remain suspended at the surface of eutrophic lakes, potentially reblooming in high-temperature conditions. This study investigated the cellular responses underlying the survival resilience of Microcystis in response to PAC treatment. During cell growth, we observed that exposure to low levels of PAC led to a growth pattern resembling normal conditions, whereas cells exposed to high levels of PAC experienced immediate growth inhibition, followed by cell death. Therefore, we employed RNA sequencing to investigate dynamic gene expression. At the transcriptomic level, 264 distinct genes exhibited differential expression under low PAC exposure, significantly affecting the bacterial secretion system and photosynthesis. Changes in the expression of the photosystem II antenna complex phycobilisome were subsequently reflected in changes in phycocyanin pigment production. Furthermore, we identified 223 unique genes under high PAC exposure. Notably, in type II toxin–antitoxin systems, which serve as a prokaryotic defense mechanism, several toxin genes were expressed at higher levels than antitoxin genes, promoting cell death or apoptosis. These findings bridge a gap in the understanding of cyanobacterial ecotoxicology and environmental responses, potentially enhancing biotechnological and clinical applications.

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The Love and Hate Relationship between T5SS and Other Secretion Systems in Bacteria

Cited by 3 publications

References 116 publications

Antibody-based therapy: An alternative for antimicrobial treatment in the post-antibiotic era

Antibody-based therapy: An alternative for antimicrobial treatment in the post-antibiotic era

Dispersal shapes compositional and functional diversity in aquatic microbial communities

Cellular response in the resilience of Microcystis aeruginosa under polyaluminum chloride exposure

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