Salt-induced reduction of hyperswarming motility in Bacillus cereus MHS is associated with reduced flagellation, reduced nanotube formation and reduction in expression of quorum sensing regulator

Bacteria have been known to thrive in challenging environmental niches through diverse phenomena. Swarming is one such favourable adaptation that could help bacteria survive extreme conditions. Therefore, targeting swarming is crucial for improving our understanding of bacterial motility and preventing related infections. Bacillus cereus, which causes food poisoning, has been shown to perform swarming, and salts like NaCl can act as a food preservative to control bacterial growth. In order to explore the possible alterations in the swarming of Bacillus cereus in the presence of salt, the present study encompasses the effect of NaCl on the swarming characteristics of a natural bacterial isolate, Bacillus cereus MHS, with a hyperswarming phenotype. Here we report that the presence of an increased amount of NaCl in growth media could induce a reduction in swarming motility and swarming pattern of MHS on Luria agar plates and the observed reduction in swarming was associated with the reduced flagellation and reduction in bacterial nanotube formation. Gene expression studies supported the phenotypic and ultrastructure observations as the expressions of bfla and ymdb genes, involved in formations of flagella and nanotubes respectively, were found to be reduced in the swarming MHS cells in the presence of increased NaCl in swarm media. It was also observed that the salt-induced reduction in swarming of MHS is associated with the reduced expression of the quorum sensing regulator gene plcR. This study first time reports the bacterial nanotubes in a Bacillus cereus strain and indicates a possible link between the bacterial nanotube formation and hyperswarming phenotype in Bacillus cereus MHS.