Salt-induced Reduction of Hyperswarming Motility in Bacillus cereus MHS is Associated with Reduction in Flagellation, Nanotube Formation and Quorum Sensing Regulator plcR.

Abstract

Bacteria have been known to thrive in challenging environmental niches through diverse phenomena. Swarming is one such favourable adaptations 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. 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 increased NaCl in growth media could induce a reduction in swarming motility and pattern of MHS on Luria agar plates. This observed reduction in swarming was found to be associated with reduced flagellation and a reduction in the abundance of bacterial nanotubes. 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. 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 indicating a possible link between the bacterial nanotube formation and hyperswarming phenotype in Bacillus cereus MHS.