Global Gene Expression Profile for Swarming Bacillus cereus Bacteria

Abstract

Bacillus cereus can use swarming to move over and colonize solid surfaces in different environments. This kind of motility is a collective behavior accompanied by the production of long and hyperflagellate swarm cells. In this study, the genome-wide transcriptional response of B. cereus ATCC 14579 during swarming was analyzed. Swarming was shown to trigger the differential expression (>2-fold change) of 118 genes. Downregulated genes included those required for basic cellular metabolism. In accordance with the hyperflagellate phenotype of the swarm cell, genes encoding flagellin were overexpressed. Some genes associated with K ؉ transport, phBC6A51 phage genes, and the binding component of the enterotoxin hemolysin BL (HBL) were also induced. Quantitative reverse transcription-PCR (qRT-PCR) experiments indicated an almost 2-fold upregulation of the entire hbl operon during swarming. Finally, BC1435 and BC1436, orthologs of liaI-liaH that are known to be involved in the resistance of Bacillus subtilis to daptomycin, were upregulated under swarming conditions. Accordingly, phenotypic assays showed reduced susceptibility of swarming B. cereus cells to daptomycin, and P spac -induced hyper-expression of these genes in liquid medium highlighted the role of BC1435 and BC1436 in the response of B. cereus to daptomycin.

Swarming: Flexible Roaming Plans

“…Transcriptome studies of Proteus and of several other bacteria have not revealed a swarm-ing-specific alteration in synthesis of these molecules (26)(27)(28). We note, however, that swarmers upregulate the synthesis of the osmoprotectants glutamate and proline in Pseudomonas aeruginosa (26), potassium uptake in Bacillus cereus (29), and a sodium/solute symporter in Vibrio parahaemolyticus (30). It is possible that these or other osmotic agents are also secreted by posttranscriptional signaling mechanisms that "sense" the surface, or as part of a general bacterial metabolic program.…”

“…No specific genes could be linked to osmolyte secretion in any organism, as discussed above, although a spike in LPS synthesis was observed in Salmonella on swarm agar (24), and upregulation of osmoprotectant or sodium/solute symporter systems was seen in several bacteria (26,29,30). Many virulence genes were upregulated either in a surface-specific manner in Salmonella (24) or in a swarming agar-specific manner in P. aeruginosa, P. mirabilis, and V. parahaemolyticus (26)(27)(28)(29)64), supporting the idea that surfaceadapted cells are more pathogenic (67,68).…”

“…The transcriptomes and proteomes of several swarming bacteria have now been analyzed, although not all of these studies made a distinction between swarming and nonswarming agar, i.e., transcriptome changes in response to surface-related alterations in metabolism that were independent of swarming (24)(25)(26)(27)(28)(29)64). Nonetheless, a general picture that emerges is that a large number of genes show differential regulation on a surface compared to that in broth (swimming conditions) but increased flagellar synthesis is observed in a swarm agar-specific manner only with P. mirabilis, V. parahaemolyticus, B. subtilis, and B. cereus, consistent with their altered swarmer cell morphologies.…”

Phages Preying on Bacillus anthracis, Bacillus cereus, and Bacillus thuringiensis: Past, Present and Future

“…Interestingly, the B. cereus ATCC 14579 prophage phBC6A51 (Table 4) genes, which mostly encode proteins with no matches in the databases, are largely up-regulated under swarming conditions [157] ( i.e. , bacterial collective motility that requires flagella to move over solid surfaces, as evidenced for some members of the B. cereus group [158,159]).…”

More than Motility: Salmonella Flagella Contribute to Overriding Friction and Facilitating Colony Hydration during Swarming

“…Among these, Bacillus subtilis displays increased flagellar numbers and cell length (14), but this morphology is not as dramatic as that seen in the robust swarmers. In a Bacillus cereus transcriptome, several genes, including flagellar genes, were seen to be differentially regulated on swarm agar (15). In B. subtilis and Proteus mirabilis, the cell envelope has been implicated as a sensor of surface conditions (16,17).…”