Microbial oxidation of gaseous hydrocarbons: production of alcohols and methyl ketones from their corresponding n-alkanes by methylotrophic bacteria

Abstract

Cell suspensions of methane-utilizing bacteria oxidized n-alkanes (propane, butane, pentane, and hexane) to their corresponding alcohols and methyl ketones. The product alcohols and methyl ketones accumulated extracellularly. Methanol-grown cells of methane-utilizing bacteria did not oxidize n-alkanes. The product primary alcohol was detected in a cell-free system but only in a trace amount in the whole cell system due to further oxidation. The optimum conditions for in vivo formation of secondary alcohol and methyl ketone from n-alkanes were compared between two distinct types of C1-utilizing microbes: Methylococcus capsulatus M1 (type I membrane) and Methylosinus trichosporium OB3b (type II membrane). The production of acetone or 2-butanone from n-alkanes ceased after 3 h of incubation for strain OB3b and 5 h for strain M1. The amount of these methyl ketones did not decline during 30 h of incubation. The optimum pH for the in vivo production of methyl ketones from n-alkanes by both strains was around 7.0. However, secondary alcohols were accumulated at higher amounts around pH 6.0. The optimum temperature for the in vivo production of methyl ketones from n-alkanes was around 40 degrees C for strain M1 and around 30-35 degrees C for strain OB3b. Higher accumulation of secondary alcohol was detected at 30-40 degrees C for strain M1 and 25 degrees C for strain OB3b. The alkane hydroxylation enzyme was located in the cell-free particulate fraction precipitated between 10 000 and 40 000 X g centrifugation. The yield of primary and secondary alcohols from n-alkane in the cell-free system was about equal. Evidence obtained indicates that the hydroxylation of n-alkanes (both terminal and subterminal oxidations) is also catalyzed by the methane hydroxylation - alkene epoxidation enzyme system.