Shlakhter, O. | Search bioRxiv

bioRxiv2024

The impact of tropodithietic acid on microbial physiology under varying culture complexities

Research has increasingly focused on understanding marine bacterial physiology under environmentally relevant conditions. Biotic interactions have a key influence on microbial physiology and are often modeled in the lab by manipulating the complexity of microbial cultures. Notably, findings from low-complexity cultures that have been re-evaluated in more complex systems, occasionally lead to different outcomes. Here, we assess how the genomic capability of bacteria to produce secondary metabolites, specifically the antibiotic tropodithietic acid (TDA), influences microbial physiology and interactions, under varying microbial complexity. We investigate the impact of TDA production on microbial physiology across systems with increasing complexity: from bacterial mono-cultures, to bacterial co-cultures of Phaeobacter inhibens with Dinoroseobacter shibae, and a more complex tri-culture that includes both bacteria and their algal host Emiliania huxleyi. In these systems, we examine both wild-type (WT) P. inhibens bacteria and mutant bacteria with a tdaB deletion ({Delta}tdaB) that are not capable of producing TDA. This systematic approach allowed us to explore the relationship between the tdaB gene, microbial physiology, and system complexity. Our findings show that deleting the tdaB gene affected bacteria-bacteria interactions in co-cultures but not in tri-cultures with the algal host. Additionally, our data revealed that algal death was delayed in cultures containing P. inhibens {Delta}tdaB mutants compared to those with WT bacteria. Results of our study highlight the importance of microbial complexity in the study of bacterial physiology and point to the understudied role of TDA in algal-bacterial interactions. ImportanceThis study advances our understanding of marine bacterial physiology under varying levels of microbial complexity. We uncover how the production of secondary metabolites, specifically the antibiotic tropodithietic acid (TDA), influences microbial interactions. Our systematic approach, which includes bacterial mono-cultures, co-cultures, and tri-cultures involving algal hosts, allows us to evaluate the impact of the tdaB gene on microbial interactions. Notably, our findings reveal that the deletion of this gene affects bacteria-bacteria interactions in co-culture but does not have the same effect in more complex systems that include algae. Additionally, the observation that algal death is delayed in cultures with TDA-deficient bacteria underscores the significance of TDA in these interactions. Overall, our research highlights the influence of the microbial culture complexity on bacterial physiology and emphasizes the overlooked role of TDA in algal-bacterial dynamics.

microbiology↗

bioRxiv2023

Bacteria Contribute Exopolysaccharides to an Algal-Bacterial Joint Extracellular Matrix

Marine ecosystems are influenced by phytoplankton aggregation, which affects processes like marine snow formation and harmful events such as marine mucilage outbreaks. Phytoplankton secrete exopolymers, creating an extracellular matrix (ECM) that promotes particle aggregation. This ECM attracts heterotrophic bacteria, providing a nutrient-rich and protective environment. In terrestrial environments, bacterial colonization near primary producers relies on attachment and the formation of multidimensional structures like biofilms. Bacteria were observed attaching and aggregating within algal-derived exopolymers, but it is unclear if bacteria produce an ECM that contributes to this colonization. This study, using Emiliania huxleyi algae and Phaeobacter inhibens bacteria in an environmentally relevant model system, reveals a shared algal-bacterial ECM scaffold that promotes algal-bacterial aggregation. Algal exudates play a pivotal role in promoting bacterial colonization, stimulating bacterial exopolysaccharide (EPS) production, and facilitating a joint ECM formation. A bacterial biosynthetic pathway responsible for producing a succinoglycan-like compound contributing to bacterial ECM formation is identified. Genes from this pathway show increased expression in algal-rich environments. These findings highlight the underestimated role of bacteria in aggregate-mediated processes in marine environments, offering insights into algal-bacterial interactions and ECM formation, with implications for understanding and managing disturbances like marine mucilage events.

microbiology↗