Abstract
BackgroundThe nontoxigenic V. cholerae El Tor strains ferment sorbitol faster than the toxigenic strains, hence fast-fermenting and slow-fermenting strains are defined by sorbitol fermentation test. This test has been used for more than 40 years in cholera surveillance and strain analysis in China. Understanding of the mechanisms of sorbitol metabolism of the toxigenic and nontoxigenic strains may help to explore the genome and metabolism divergence in these strains. Here we used comparative proteomic analysis to find the proteins which may be involved in such metabolic difference.ResultsWe found the production of formate and lactic acid in the sorbitol fermentation medium of the nontoxigenic strain was earlier than of the toxigenic strain. We compared the protein expression profiles of the toxigenic strain N16961 and nontoxigenic strain JS32 cultured in sorbitol fermentation medium, by using fructose fermentation medium as the control. Seventy-three differential protein spots were found and further identified by MALDI-MS. The difference of product of fructose-specific IIA/FPR component gene and mannitol-1-P dehydrogenase, may be involved in the difference of sorbitol transportation and dehydrogenation in the sorbitol fast- and slow-fermenting strains. The difference of the relative transcription levels of pyruvate formate-lyase to pyruvate dehydrogenase between the toxigenic and nontoxigenic strains may be also responsible for the time and ability difference of formate production between these strains.ConclusionMultiple factors involved in different metabolism steps may affect the sorbitol fermentation in the toxigenic and nontoxigenic strains of V. cholerae El Tor.
Highlights
The nontoxigenic V. cholerae El Tor strains ferment sorbitol faster than the toxigenic strains, fast-fermenting and slow-fermenting strains are defined by sorbitol fermentation test
Fructose and sorbitol metabolisms share the same pathway after the fructose-6-phosphate step, and we found no differences in fructose fermentation rates between the sorbitol fast- and slow-fermenting strains, in this study we used fructose as a control when comparing protein profiles, to exclude proteins constitutively involved in sugar metabolism
The change in pH was consistent with the sorbitol fermentation test, showing that nontoxigenic strains display positive results earlier than toxigenic strains [6]
Summary
The nontoxigenic V. cholerae El Tor strains ferment sorbitol faster than the toxigenic strains, fast-fermenting and slow-fermenting strains are defined by sorbitol fermentation test. This test has been used for more than 40 years in cholera surveillance and strain analysis in China. We found that is D-sorbitol metabolized by V. cholerae, but it is fermented at different rates by the toxigenic and nontoxigenic El Tor strains. The sorbitol fermentation test is included in the Phage-biotyping scheme, which consists of phage typing and biochemical typing and is developed in 1970s in China This scheme is used to distinguish and type the El Tor strains which are pathogenic and are potential to cause epidemic or not [6]. It is found that the O1 El Tor strains isolated from patients and environmental samples in epidemics are toxigenic and sorbitol slow-fermenting, whereas the strains isolated from environment in non-epidemic periods are nontoxigenic and fast-fermenting
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