Protein content enhances biofilm development in Bacillus Subtilis and Escherichia coli K-12 strains

Ivo Ganchev

Abstract: Bacillus subtilis is a Gram-positive bacterium that is well known for its ability to differentiate into metabolically inactive spores that are highly resistant to environmental stresses. Cannibalism is a mechanism to delay sporulation in Bacillus subtilis. In the nature, B. subtilis cells have to compete with other organisms present in the microflora under nutritional limitation. It is interesting to raise the question regarding the behavior of B. subtilis cells in mixed cultures in medium that content different nitrogen sources. The lysed cells release nutrients that serve to feed the community, effectively delaying spore formation. The subpopulation of cells that differentiates into cannibals is the same subpopulation that produces the extracellular matrix that holds cells together in biofilms. Using this strain model, this study demonstrated the antagonistic activity of B. subtilis 170 and 168 strains against E. coli K-12. The formed biofilms by co-cultivation of B. subtilis and E. coli K-12 strains were analyzed by using of confocal scanning laser microscopy. It is known that formation of biofilms by B. subtilis is a complex process that includes secretion of surfactin, a lipopeptide antimicrobial agent or suplancin or the mechanism of cannibalism. However in addition to the competition among the cells of B. subtilis, these cells also compete with other organisms for the limited nutrients. In this work, we report the cannibalistic behavior of B. subtilis in presence of Escherichia coli in medium that content peptone, caseine, tryptone and soy casein hydrolyzate. We demonstrate that B. subtilis 170 and 168 strains lyses cells of E. coli K-12 1655 in the presence of peptone, tryptone and soy casein hydrolyzate аnd does not induce spore formation. Our experiments also suggest that B. subtilis prefers predation of E. coli to cannibalism in mixed cultures. This may offer B. subtilis a niche to survive in an environment with limited nutrients and under competition from other microorganisms.

Keywords: antagonism; B. subtilis; cannibalism; competition; E. coli K-12; multispecies biofilm; spore formation

Date published: 2020-09-04