THE INTERACTION WITH Setophoma terrestris HAS AN IMPACT ON THE EVOLUTION OF Bacillus sp. ANTAGONISM AND ADAPTATION

Los Cocos

Congreso; XVII Congreso Argentino de Microbiología General; 2022

SAMIGE

We have previously reported that a strain of Bacillus subtilis isolated from the rhizosphere of onion cultures undergoes a hereditary phenotypic variation after interaction with the fungus Setophoma terrestris in co-culture, a phenomenon that is manifested by a greater antagonistic capacity and the formation of robust biofilms. Through metabolomics analysis based on mass spectrometry, we observed differential profiles in B. subtilis before (pre-ST) and after (post-ST) interacting with the fungus, which revealed the paradoxical absence of surfactin and plipastatin in post-ST variants. Despite the absence of these classic antimicrobial lipopeptides, post-ST variants showed greater antifungal activity compared to pre-ST. Through comparative genomics we were able to determine that mutations in the ComQPXA quorum sensing system, especially in mutations in the comA gene, represent the genetic bases of the conversion to a post-ST variant. Here, we aim to evaluate if this phenotypic change is also manifested as a product of the interaction of other Bacillus species with S. terrestris. We tested the antagonistic activity of two different species of Bacillus, amyloliquefaciens and velezensis, against S. terrestris in co-cultures. Both bacterial strains showed activity against thefungus, with a growth inhibition of 67% for B. velezensis (Bve) and 65% for B. amyloliquefaciens (Bam).We observed a change in the macroscopic aspect of the post co-culture colonies with respect to each ancestral strain. Post-ST of Bve and Bam showed structured colonies with a mixed appearance between smooth and rough. Moreover, post-ST variants of Bve and Bam showed less swarming than their ancestors never exposed to S. terrestris in co-culture. As these phenotypic traits remain stableover time, which resembles to what we observed for B. subtilis post-ST, we decided to evaluate possible mutations in the comA gene but we found no differences in the sequences between post cocultures strains and their ancestors. These results indicate that if a hereditary phenotypic conversionindeed exists in B. amyloliquefaciens and B. velezensis, it would be independent of ComA unlike what has been described for the interaction between B. subtilis and the fungus.