Decoding molecular interactions in microbial communities.

Microbial communities govern numerous fundamental processes on earth. Discovering and tracking molecular interactions among microbes is critical for understanding how single species and complex communities impact their associated host or natural environment. While recent technological developments in DNA sequencing and functional imaging have led to new and deeper levels of understanding, we are limited now by our inability to predict and interpret the intricate relationships and interspecies dependencies within these communities. In this review, we highlight the multifaceted approaches investigators have taken within their areas of research to decode interspecies molecular interactions that occur between microbes. Understanding these principles can give us greater insight into ecological interactions in natural environments and within synthetic consortia.

Interplay between two bacterial actin homologs, MamK and MamK-Like, is required for the alignment of magnetosome organelles in Magnetospirillum magneticum AMB-1.

Many bacterial species contain multiple actin-like proteins tasked with the execution of crucial cell biological functions. MamK, an actin-like protein found in magnetotactic bacteria, is important in organizing magnetosome organelles into chains that are used for navigation along geomagnetic fields. MamK and numerous other magnetosome formation factors are encoded by a genetic island termed the magnetosome island. Unlike most magnetotactic bacteria, Magnetospirillum magneticum AMB-1 (AMB-1) contains a second island of magnetosome-related genes that was named the magnetosome islet. A homologous copy of mamK, mamK-like, resides within this islet and encodes a protein capable of filament formation in vitro. Previous work had shown that mamK-like is expressed in vivo, but its function, if any, had remained unknown. Though MamK-like is highly similar to MamK, it contains a mutation that in MamK and other actins blocks ATPase activity in vitro and filament dynamics in vivo. Here, using genetic analysis, we demonstrate that mamK-like has an in vivo role in assisting organelle alignment. In addition, MamK-like forms filaments in vivo in a manner that is dependent on the presence of MamK and the two proteins interact in a yeast two-hybrid assay. Surprisingly, despite the ATPase active-site mutation, MamK-like is capable of ATP hydrolysis in vitro and promotes MamK filament turnover in vivo. Taken together, these experiments suggest that direct interactions between MamK and MamK-like contribute to magnetosome alignment in AMB-1.

Compartmentalization and organelle formation in bacteria.

A number of bacterial species rely on compartmentalization to gain specific functionalities that will provide them with a selective advantage. Here, we will highlight several of these modes of bacterial compartmentalization with an eye toward describing the mechanisms of their formation and their evolutionary origins. Spore formation in Bacillus subtilis, outer membrane biogenesis in Gram-negative bacteria and protein diffusion barriers of Caulobacter crescentus will be used to demonstrate the physical, chemical, and compositional remodeling events that lead to compartmentalization. In addition, magnetosomes and carboxysomes will serve as models to examine the interplay between cytoskeletal systems and the subcellular positioning of organelles.

Sinus microbiome diversity depletion and Corynebacterium tuberculostearicum enrichment mediates rhinosinusitis.

Persistent mucosal inflammation and microbial infection are characteristics of chronic rhinosinusitis (CRS). Mucosal microbiota dysbiosis is found in other chronic inflammatory diseases; however, the relationship between sinus microbiota composition and CRS is unknown. Using comparative microbiome profiling of a cohort of CRS patients and healthy subjects, we demonstrate that the sinus microbiota of CRS patients exhibits significantly reduced bacterial diversity compared with that of healthy controls. In our cohort of CRS patients, multiple, phylogenetically distinct lactic acid bacteria were depleted concomitant with an increase in the relative abundance of a single species, Corynebacterium tuberculostearicum. We recapitulated the conditions observed in our human cohort in a murine model and confirmed the pathogenic potential of C. tuberculostearicum and the critical necessity for a replete mucosal microbiota to protect against this species. Moreover, Lactobacillus sakei, which was identified from our comparative microbiome analyses as a potentially protective species, defended against C. tuberculostearicum sinus infection, even in the context of a depleted sinus bacterial community. These studies demonstrate that sinus mucosal health is highly dependent on the composition of the resident microbiota as well as identify both a new sino-pathogen and a strong bacterial candidate for therapeutic intervention.