Evaluation of bacterial strategies to promote the bioavailability of polycyclic aromatic hydrocarbons.
Polycyclic aromatic hydrocarbon (PAHs)-degrading bacteria may enhance the bioavailability of PAHs by excreting biosurfactants, by production of extracellular polymeric substances, or by forming biofilms. We tested these hypotheses in pure cultures of PAHs-degrading bacterial strains. Most of the strains did not substantially reduce the surface tension when grown on PAHs in liquid shaken cultures. Thus, pseudo-solubilization of PAHs in biosurfactant micelles seems not to be a general strategy for these isolates to enhance PAHs-bioavailability. Three semi-colloid Sphingomonas polysaccharides all increased the solubility of PAHs (Gellan 1.3- to 5.4-fold, Welan 1.8- to 6.0-fold and Rhamsan 2.4- to 9.0-fold). The increases were most pronounced for the more hydrophobic PAHs. The polysaccharide-sorbed PAHs were bioavailable. Mineralization rates of 9-[14C]-phenanthrene and 3-[14C]-fluoranthene by Sphingobium EPA505, were similar with and without sphingans, indicating that mass-transfer rates from PAHs crystals to the bulk liquid were unaffected by the polysaccharides. Biofilm formation on PAHs crystals may favor the diffusive mass transfer of PAHs from crystals to the bacterial cells. A majority of the PAHs-degraders tested formed biofilms in microtiter wells coated with PAHs crystals. For strains capable of growing on different PAHs; the more soluble the PAHs, the lower the percentage of cells attached. Biofilm formation on PAHs-sources was the predominant mechanism among the tested bacteria to overcome mass transfer limitations when growing on poorly soluble PAHs.
Johnsen
A R
AR
Department of Environmental Chemistry and Microbiology, National Environmental Research Institute, Frederiksborgvej 399, PO Box 358, 4000 Roskilde, Denmark. arj@dmu.dk
Karlson
U
U
D000873:Anthracenes / Q000378:metabolism; D001673:Biodegradation, Environmental; D018441:Biofilms / Q000254:growth & development; D001682:Biological Availability; D004058:Diffusion; D005449:Fluorenes / Q000378:metabolism; D010616:Phenanthrenes / Q000378:metabolism; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry* / Q000378:metabolism*; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis / Q000737:chemistry; D011721:Pyrenes / Q000378:metabolism; D012995:Solubility; D042301:Sphingomonadaceae / Q000254:growth & development* / Q000378:metabolism*; D013501:Surface-Active Agents / Q000378:metabolism
D000873:Anthracenes; D005449:Fluorenes; D010616:Phenanthrenes; D011084:Polycyclic Aromatic Hydrocarbons; D011135:Polysaccharides, Bacterial; D011721:Pyrenes; D013501:Surface-Active Agents; C007738:fluoranthene; C031181:phenanthrene; C048288:gellan gum; C071623:rhamsan; C068570:welan; C030984:pyrene; C034020:anthracene