Chairperson, Graduate Committee: Christine ForemanOzcan, Safiye SelenMarkus Dieser, Albert E. Parker, Narayanaganesh Balasubramanian and Christine M. Foreman were co-authors of the article, 'Quorum sensing inhibition as a promissing method to control biofilm growth in metalworking fluids' submitted to the journal 'Environmental science & technology' which is contained within this thesis.2018-12-052018-12-052018https://scholarworks.montana.edu/handle/1/14613Microbial contamination in metalworking fluid (MWF) circulation systems is a serious problem. Particularly water based MWFs promote microbial colonization despite the use of biocides. Inhibiting the quorum sensing mechanism (i.e. cell-cell communication) in bacteria is a promising approach to control and prevent biofilm formation. The objective of this study was (i) to determine the microbial community in MWFs from operational machining shops, (ii) to investigate the effect of well-known quorum sensing inhibitors on controlling biofilm formation, and (iii) to implement experimental data from selected enzymes to a computer simulation biofilm accumulation model (BAM). Planktonic and biofilm samples from two local machining shops in Bozeman, MT, were collected to determine the extent of microbial colonization. In both operations, microbial communities were dominated by Pseudomonadales (60.2-99.7%). Rapid recolonization was observed even after dumping spent MWFs and cleaning. Considering the dominance of Pseudomonadales in MWFs, the model organism Pseudomonas aeruginosa PAO1 was selected for testing the effects of quorum sensing inhibitor compounds on biofilm formation. From a variety of enzymes, natural, and chemical compounds screened for quorum sensing inhibition, Patulin (40microns) and Furanone C-30 (75microns), were found to be effective in reducing biofilm formation in MWFs when applied as single compound amendments and in combination with the polysaccharide degrading enzyme alpha-amylase from Bacillus amyloliquefaciens. Particularly Furanone C-30, as a single amendment and in combination with alpha-amylase decreased biofilm formation by 76% and 82% after 48 hours. Putatively identified homoserine lactones in MWFs treated with Furanone C-30 provided evidence for quorum sensing inhibition on biofilm formation. BAM was employed to study the effect of alpha-amylase (3 Units mL -1) on P. aeruginosa PAO1 biofilms in batch reactors for 24 and 48 hours. In the absence of alpha-amylase, biofilm thickness was predicted to be 23.11 and 31.37 microns, while its presence reduced thickness to 10.47 and 13.07 microns after 24 and 48 hours, respectively. The results presented herein highlight the potential effectiveness of quorum sensing inhibition as a strategy to reduce biofilms in MWFs.enBiofilmsPseudomonas aeruginosaMetal-workLubrication and lubricantsContamination (Technology)CellsBiological control systemsThesisCopyright 2018 by Safiye Selen Ozcan