Differential protein expression during growth on model and commercial
mixtures of naphthenic acids in Pseudomonas fluorescens Pf-5
Naphthenic acids (NAs) are carboxylic acids with the formula (CnH2n+ZO2)
and are the toxic, persistent constituents of oil sands process-affected
waters (OSPW), produced during oil sands extraction. Currently, the
proteins and mechanisms involved in NA biodegradation are unknown. Using
LC-MS/MS shotgun proteomics, we identified proteins overexpressed during
the growth of Pseudomonas fluorescens Pf5 on a model NA
(4-n-butylphenyl)-4-butanoic acid (n-BPBA) and commercial NA mixture
(Acros). By day 11, >95% of n-BPBA was degraded. With
Acros, a 17% reduction in intensity occurred with 10-18 carbon
compounds of the Z family -2 to -14 (major NA species in this mixture).
A total of 554 proteins (n-BPBA) and 631 proteins (Acros) were
overexpressed during growth on NAs; including several transporters (e.g.
ABC transporters), suggesting a cellular protective response from NA
toxicity. Several proteins associated with fatty acid, lipid and amino
acid metabolism were also overexpressed; including acyl-CoA
dehydrogenase and acyl-CoA thioesterase II, which catalyze part of the
fatty acid beta-oxidation pathway. Indeed, multiple enzymes involved in
the fatty acid oxidation pathway were upregulated. Given the presumed
structural similarity between alkyl-carboxylic acid side chains and
fatty acids, we postulate that P. fluorescens Pf-5 was using existing
fatty acid catabolic pathways (among others) during NA degradation.