Variability of communities and physiological characteristics between free-living bacteria and attached bacteria during the PAH biodegradation in a soil/water system

The biodegradation of polycyclic aromatic hydrocarbons (PAHs) via free-living and attached micro-organisms in soil/water systems was observed in order to examine the variability in the community dynamics and physiological profiles of the microorganisms. As determined by fluorescence in situ hybridization (FISH), the Domain Bacteria, consisting of three phyla alpha-, beta- and gamma-Proteobacteria, reached 41.27-56.05% of all organisms in the soil/water system for PAH biodegradation. Among the free-living species, Proteobacteria, including Brevundimonas, (Pseudomonas) diminuta, Caulobacter spp., Mycoplana bullata, Acidovorax spp. and Pseudomonas aeruginosa were found to be dominant-making up 93.51-99.80% of the population-and therefore seem to be associated with PAH biodegradation. Total plate count numbers and the count of Pseudomonas sp. present in the free-living population increased to between 10(3) and 10(6) CFU ml(-1) when clay with very low organic matter content was used as the matrix for PAH degradation. However, total plate count microbial numbers increased to only 10(1)-10(2) CFU ml(-1) using natural soil from Taichung containing 1.883% organic matter. The soil organic content (SOM) seemed to affect the mass transfer of PAH in soil, leading to the difference in PAH biodegradation. Two different approaches, which included community-level physiological profiling (CLPP) and ectoenzymatic activities, were used to explain the functional diversity between free-living and attached bacteria. The free-living and attached bacterial communities from the clay system showed proportionately greater differences using CLPP. Relatively high levels of esterases, aminopeptidases and some specific glycolysis-gluconeogenesis enzymes gave an identifiable correlation with PAH biodegradation. The differences in bacterial composition, numbers and physiological characteristics show that free-living and attached micro-organisms may play different biochemical roles in PAH degradation in soil. (c) 2007 Elsevier Masson SAS. All rights reserved.