Identification and characterisation of bacterial populations of an in-use metal-working fluid by phenotypic and genotypic methodology

In-use metal-working fluids (MWFs) are vulnerable to microbial attack, resulting in untimely biodeterioration, thus rendering them less effective as coolants and lubricants. The aim of this study was to investigate the microbial diversity of in-use emulsifiable oil metal-working fluids, and use the information derived to develop strategies to improve metal-working fluid formulation and longevity, and to improve microbial exploitation for biological disposal routes using bioreactors. In-use MWF samples from five different metal-working machines were analysed using phenotypic, genotypic, and in situ detection methods to determine total background bacterial communities and the composition of enriched degraders. Of 66 bacterial isolates, 13 species from 8 genera were identified by fatty acid methyl ester (FAME) analysis. Genotypic (total) diversity, determined by denaturing gradient gel electrophoresis (DGGE), reflected the low diversity shown by FAME analysis. Both DGGE and in situ microscopy (fluorescent in situ hybridisation, FISH) revealed highly conserved microbial communities in MWF from different machines and applications.