It is Useless to Resist: Biofilms in Metalworking Fluid Systems

Biofouling, the undesirable deposition of microorganisms on surfaces, is ubiquitous in aqueous systems. This is no different for systems running with water-miscible metalworking fluids (MWFs), which additionally contain many organic chemicals that create favorable conditions for growth and metabolism. Biofilm formation is thus inevitable, as there is no shortage of wetted surfaces in metalworking systems. Thus, biocides and biostatic compounds have always been used as ingredients in concentrates and as tank-side additives. In this study, however, we report that such elements, alone or as component of MWFs did not prevent biofilm formation and had negligible effects on pre-established laboratory biofilms. Moreover, biofilms in metalworking systems are interwoven with residues, sediments and metal swarfs generated during machining. Again, coincubation of such ‘real’ biofilms with MWFs, had no significant effect on population size – but on population composition! The implications of this finding are unclear but could provide a starting point for the treatment of biofouling, as biofilm population structure might be of importance. Finally, we show that bacteria gain function in biofilms, and that they were able to degrade a toxic amine in MWFs, a feat the same bacteria in planktonic form were incapable of.