Functional analysis of communities of aerobic heterotrophic bacteria from hydrocarbon-contaminated sites

Abstract

Microbial communities from soil and groundwater of oil-contaminated sites (Beelitzhof in Berlin-Nikolassee and the former Pintsch site in Hanau, both in Germany) were characterized by description of the physiological potential of arbitrary samples of 48 aerobic heterotrophic bacterial isolates. It was demonstrated that the sum of metabolic abilities, presented as a percentage of substrate-degrading microorganisms in a sample, is both site specific and reproducible. The percentage of hydrocarbon-degrading microorganisms in the communities was most strongly influenced by the diversity and amount of carbon supply (whereas after addition of mineral salts, total cell counts increased). For example, in groundwater of the waste oil-contaminated Pintsch site, only the accessible short-chain alkanes up to dodecane could be metabolized. After dosing with hydrogen peroxide, long-chain alkane-degrading bacteria were found in significant amounts among the predominant microorganisms, which was apparently due to a solubilization effect that brought the longer alkanes (and their degraders) into the groundwater. Because the addition of precultured organisms to a soil-composting windrow had no effect on the degradation pattern of its microbiota, the carbon sources available probably determined whether allochthonous bacteria would become indigenous. Although the physiological potentials of the individual bacteria complemented each other and thus determined the distinctive profile characteristic of the microbial community, the individual members could differ in their metabolic abilities, as was shown by the distribution of positive test results in different samples, and they could also differ in their taxonomic status. Evidently, the taxonomic status of the bacteria did not determine their activities: Strains of the same species showed different degradation abilities for hydrocarbon substrates. However, the taxonomic status of isolates seemed to be highly dependent on the physicochemical factors of a site (soil structure, water capacity, etc.).