Degradation of 2-Methylisoborneol by Aquatic Bacteria

Abstract

2-Methylisoborneol (MIB) is a musty- or muddy-smelling compound which occurs in some natural waters and which is difficult to remove by conventional water treatment methods. Bacterial degradation of MIB was examined in batch culture experiments. Cultures able to metabolize MIB were enriched in a mineral salts medium supplemented with milligram-per-liter levels of the compound and were inoculated with water and sediment samples from reservoirs where MIB is seasonally produced. Bacteria from degrading cultures were isolated on R2A agar and identified as predominantly Pseudomonas spp. Degradation occurred only in cultures consisting of three or more different bacteria. MIB supported growth as the sole added carbon source at 1 to 6.7 mg/liter. MIB was also degraded at microgram-per-liter levels in sterile filtered lake water inoculated with washed bacteria and in synthetic medium supplemented with various sugars or acetate. Complete degradation of MIB took from 5 days to more than 2 weeks. Enrichment with isoborneol, a structural analog of MIB, failed as a preenrichment for MIB degraders. Isoborneol at 20 to 40 mg/liter readily supported bacterial growth, whereas MIB at 12 to 20 mg/liter took months to degrade. The relative recalcitrance of MIB compared with isoborneol may be a result of the additional methyl group in MIB.