Viable but nonculturable state of Escherichia coli, Pseudomonas putida and Lactococcus lactis during exposure to toxic chemicals, as revealed by headspace gas chromatography and indirect conductivity techniques

Abstract

The bioconversion of water-immiscible chemicals by microbes may occur through viable but nonculturable cells (VBNC) and the evaluation of such cellular activity is important for a deeper understanding of the metabolic process. In this study, the metabolic CO2 production in a bacteria interface emulsion, consisting of bacteria, chitosan and solvent, has been monitored using headspace gas chromatography (GC) and indirect conductivity (IC). The results from GC in comparison to the standard culture technique revealed the presence of VBNC state when E. coli DH5α and P. putida F1 were in contact with nhexane. L. lactis IO-1 was the most sensitive strain, but the VBNC cells were obvious in the case of soybean and n-decane. Although GC showed better detection sensitivity, the IC technique was more practical and cost-effective. Therefore, GC and IC could be extremely simple and useful methods for monitoring the VBNC state of bacteria, which generally stems from environmental stresses.

Keywords

• gas chromatography
• indirect conductivity
• metabolic activity
• viable but nonculturable (vbnc)
• emulsion