Bacterial formation and metabolism of 6-hydroxyhexanoate: evidence of a potential role for omega-oxidation

Abstract

Alkane-utilizing strains of Pseudomonas spp. were found to omega-oxidize hexanoate, 6-hydroxyhexanoate, and 6-oxohexanoate to adipic acid in 5, 30, and 90% molar yields, respectively, after induction with n-hexane. 6-Hydroxyhexanoate was identified as the immediate product of hexanoate omega-hydroxylation by whole cells and was further oxidized into adipic acid and an unexpected metabolite identified as 2-tetrahydrofuranacetic acid. This same metabolite, together with adipic acid, was also detected when similarly induced cells were incubated with hexanoate or 1,6-hexanediol, but not with 6-oxohexanoate (adipic semialdehyde). Cells grown on hexanoate and incubated with 6-hydroxyhexanoate were also found to accumulate 2-tetrahydrofuranacetic acid, which was not further degraded. Utilization of 6-hydroxyhexanoate for growth was restricted to those organisms also able to utilize adipate. Similar observations were made with 1,6-hexanediol serving as the carbon source and cells obtained from one organism, Pseudomonas aeruginosa PAO, grown either on 1,6-hexanediol or 6-hydroxyhexanoate, were found to be well induced for both 6-oxohexanoate and adipate oxidation. The results indicate that 6-hydroxyhexanoate and 1,6-hexanediol are susceptible to both beta- and omega-oxidative attack; however, the former pathway appears to be of no physiological significance since it generates 2-tetrahydrofuranacetic acid as a nonmetabolizable intermediate, making omega-oxidation via adipate the exclusive pathway for degradation.