SEQUENTIAL ENRICHMENT OF MICROBIAL-POPULATIONS EXHIBITING ENHANCED BIODEGRADATION OF CRUDE-OIL

The distribution of oil-degrading bacteria in the coastal water and se diments of Hokkaido, Japan, was surveyed. The potential of mixed micro bial populations to degrade weathered crude oil was not confined to an y ecological components (water or sediment) nor to the sampling statio ns. One microbial culture that was stable during repeated subculturing degraded 45% of the saturates and 20% of the aromatics present in cru de oil in 10 days during the initial screening. The residual hydrocarb ons in this culture were extracted by chloroform and dispersed in a fr esh seawater-based medium and subsequently inoculated with microorgani sms from the first culture. After full growth of the second culture, t he residual hydrocarbons were again extracted and dispersed in a fresh medium in which microorganisms from the second culture had been inocu lated. This sequential process was carried out six times to enrich tho se microorganisms that grew on the recalcitrant components of crude oi l. After repeated exposure of the residual crude oil to the enriched m icroorganisms, about 80% of the initially added crude oil was degraded . The cultures obtained after each enrichment cycle were kept, and the degradation of fresh crude oil by the enriched microorganisms was exa mined. The degradative activity of the enriched cultures increased as the number of enrichment cycles increased. A microbial population that had been selected six times on the residual crude oil could degrade 7 0% of the saturates and 30% of the aromatics of crude oil. Thus, growt h of a microbial population on residual crude oil improved its ability to biodegrade crude oil.