Influence of Ionic Liquids on growth of Escherichia coli strain possessing β-galactosidase activity

Ionic liquids (ILs) have gained a significant attention as alternative solvents in many chemical and biological reactions. ILs have evolved as a new type of non-aqueous solvents for biocatalysis, because they can stabilize and activate enzymes. Ionic liquids to be considered as so called “green solvents” should possess only very low or no toxicity to living organism and the environment. Currently, very little is known about the biotoxicity of ionic liquids. Within this paper a relative toxicity of two ionic liquids 1,3 dimethylimidazolium methyl sulfate [MMIM][MeSO4] and 1-hexyl-3-methylimidazolium chloride [HMIM][Cl]) on the growth of Escherichia coli (E.coli) was evaluated. In this study we focused on ionic liquids, which potentially could increase activity of β-galactosidase produced by selected strain of E. coli. The inhibition of cell growth in the presence of various ionic liquids was determined using both, solid and liquid cultures. Liquid culture was incubated in culture medium with different concentrations of ionic liquids (0.1, 1, 5, 10% (v/v)). Determination of the minimal inhibitory concentration (MIC50) of ionic liquids was based on monitoring of E. coli growth by optical density measured at 600 nm using densitometer. In the second method the solid culture plate with addition of various amount of ILs has been used. The number of colonies formed on the solid culture plate was converted to colony forming units (CFUs). The obtained results have confirmed, that prescreening based on cytotoxicity tests is a key element in selection procedure of ILs for any biotechnological processes based on application of microorganisms.