Control of alkane monooxygenase activity and expression in Pseudomonas butanovora

Graduation date: 2008The regulation of monooxygenase enzymes has been demonstrated in bacteria that grow on methane and long chain-length alkanes (>C10). Less is known about monooxygenase regulation in short chain alkane oxidizing bacteria that grow on intermediate chain-length alkanes C2-C10. This dissertation focuses on the regulation of butane monooxygenase (BMO) expression and activity that occurred in response to alcohols, aldehydes, organic acids and O₂, in a short chain-length alkane oxidizing bacterium, Pseudomonas butanovora. Propionate and butyrate were able to inhibit and inactivate BMO while lactate and acetate had no effect on BMO activity. Inactivation of BMO by propionate was both time- and O₂-dependent, suggesting that the catalytic cycle of BMO is involved in the mechanism of propionate inactivation. Since treatment with [2-¹⁴C] propionate did not label BMO polypeptides, propionate inactivation of BMO does not follow the model of the suicide substrate, acetylene. Propane and butane were strikingly dissimilar in their ability to induce BMO in lactate-grown cells. Further studies revealed that BMO is induced by the primary alcohols (C2-C8) that are intermediate products in alkane metabolism, rather than by the alkane substrates, and that BMO is repressed by propionate, a product of odd but not even alkane metabolism. Interestingly, propionate repression of BMO was released following the induction of propionate consumption in P. butanovora suggesting that BMO expression, and alkane oxidation, are closely coupled to the ability to consume the products formed via monooxygenase activity. Because O₂ is a necessary cosubstrate for BMO catalytic turnover, and yet alcohol inducers of BMO are often formed under anoxic conditions, I hypothesized that the functional expression of BMO should be linked to the cell's ability to sense O₂. Induction of the BMO promoter was repressed during denitrification under anoxic growth on 1-butanol, and during incubation with 1-butanol at low O₂ concentrations provided that Cu was supplied in the media. These data suggest that Cu is involved in the mechanism to prevent BMO expression under conditions unfavorable for enzyme function. I propose a model in which Cu is involved in a redox linked mechanism to prevent alcohol induced BMO expression under anoxic conditions