The regulation of transcription, which maybe also affects the expression of VCA0518 in the sorbitol fast-fermenting and slow-fermenting strains, should also be considered MtlD catalyses the transformation of mannitol-1-P to fructose-6-P, the later enters

the fructose metabolism pathway. Mannitol and sorbitol are very similar in molecular structure. In Pseudomonas fluorescens, sorbitol is transported by the mannitol PTS system and transformed by polyol dehydrogenase, TPCA-1 which has a broad substrate spectrum [14, 15]. In a previous study we confirmed the transcriptions of the N16961 VCA1046 gene in sorbitol and mannitol fermentation media [16]. Here, our results indicate that two non-sorbitol specific PTSs are involved in the V. cholerae sorbitol utilization SAHA in vitro process. This may be similar to the uptake of L-sorbose in Lactobacillus casei where L-sorbose MLN4924 cell line is mainly taken up via EIISor and EIIMan plays a secondary role [17]. In Bacillus subtilis, MtlD is required for sorbitol assimilation in addition to the gut operon [18]. Interestingly, both of these PTSs are located on chromosome II of V. cholerae. Several studies indicate that the two chromosomes of V. cholerae are heterologous and that chromosome II may be a megaplasmid captured by an ancestral V. cholerae [7]. The ability to ferment sorbitol used to GNA12 differentiate V.

cholerae strains may provide clues as to both the origins and genetic variation of the toxigenic and nontoxigenic strains. The traditional sorbitol fermentation test is a phenotypic method using phenol red as the indicator. In our study, we showed that the observed differences in sorbitol fermentation rates were the

result of changes in the production rate of formate in the fast-fermenting and slow-fermenting strains. The fact that the ratio of formate to acetic acid was not consistent between the two strains also indicated that, besides the differences early in the metabolic pathway (including the transportation and transformation of sorbitol), pyruvate catabolism could be different in sorbitol fermentation in the toxigenic and nontoxigenic strains. Both pyruvate dehydrogenase and PFL can catalyze the transformation of pyruvate to acetyl-CoA, but they have different electron acceptors and outputs. Their activities affect the relative proportion of the end products [19]. Pyruvate dehydrogenase produces CO2 in addition to acetyl-CoA, while formate is the product of PFL. In the proteomic and qRT-PCR analyses of this study, the respective expression and transcription levels of these two genes were significantly different in the fast-fermenting JS32 and slow-fermenting N16961. Consistent with this fact was that formate was produced earlier in JS32 than in N16961.