Metagenome-Based Exploration of Bacterial Communities Associated with Cyanobacteria Strains Isolated from Thermal Muds

Cyanobacteria constitute a pioneer colonizer of specific environments for whom settlement in new biotopes precedes the establishment of composite microbial consortia. Some heterotrophic bacteria constitute cyanobacterial partners that are considered as their cyanosphere, being potentially involved in mutualistic relationships through the exchange and recycling of key nutrients and the sharing of common goods. Several non-axenic cyanobacterial strains have been recently isolated, along with their associated cyanospheres, from the thermal mud of Balaruc-les-Bains (France) and the biofilms of the retention basin where they develop. The community structure and relationships among the members of the isolated cyanobacterial strains were characterized using a metagenomic approach combined with taxonomic and microscopic descriptions of the microbial consortia. The results provided insights into the potential role and metabolic capabilities of the microorganisms of thermal mud-associated cyanobacterial biofilms. Thus, the physical proximity, host-specificity, and genetic potential functions advocate for their complementarity between cyanobacteria and their associated microbiota. Besides these findings, our results also highlighted the great influence of the reference protein database chosen for performing functional annotation of the metagenomes from organisms of the cyanosphere and the difficulty of selecting one unique database that appropriately covers both autotroph and heterotroph metabolic specificities.

Automated summary

Cyanobacteria are pioneer colonizers in specific environments, and their settlement in new habitats precedes the establishment of complex microbial consortia. Some heterotrophic bacteria are considered as cyanobacterial partners, forming their cyanosphere and potentially involved in mutualistic relationships through nutrient exchange and sharing of common goods. This study isolated non-axenic cyanobacterial strains and their associated cyanospheres from thermal mud and biofilms in a retention basin, and used metagenomic analysis to characterize the community structure and relationships. The results provided insights into the potential roles and metabolic capabilities of the microorganisms in thermal mud-associated cyanobacterial biofilms. The study also highlighted the influence of reference protein database selection for functional annotation and the challenge of finding a single database that covers both autotroph and heterotroph metabolic specificities.