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Walking the tightrope of bioavailability: growth dynamics of PAH degraders on vapour-phase PAH.

ABSTRACT: Microbial contaminant degradation may either result in the utilization of the compound for growth or act as a protective mechanism against its toxicity. Bioavailability of contaminants for nutrition and toxicity has opposite consequences which may have resulted in quite different bacterial adaptation mechanisms; these may particularly interfere when a growth substrate causes toxicity at high bioavailability. Recently, it has been demonstrated that a high bioavailability of vapour-phase naphthalene (NAPH) leads to chemotactic movement of NAPH-degrading Pseudomonas putida (NAH7) G7 away from the NAPH source. To investigate the balance of toxic defence and substrate utilization, we tested the influence of the cell density on surface-associated growth of strain PpG7 at different positions in vapour-phase NAPH gradients. Controlled microcosm experiments revealed that high cell densities increased growth rates close (<2 cm) to the NAPH source, whereas competition for NAPH decreased the growth rates at larger distances despite the high gas phase diffusivity of NAPH. At larger distance, less microbial biomass was likewise sustained by the vapour-phase NAPH. Such varying growth kinetics is explained by a combination of bioavailability restrictions and NAPH-based inhibition. To account for this balance, a novel, integrated 'Best Equation' describing microbial growth influenced by substrate availability and inhibition is presented.

SUBMITTER: Hanzel J

PROVIDER: S-EPMC3815274 | biostudies-literature | 2012 Jan

REPOSITORIES: biostudies-literature

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Walking the tightrope of bioavailability: growth dynamics of PAH degraders on vapour-phase PAH.

Hanzel Joanna J Thullner Martin M Harms Hauke H Wick Lukas Y LY

Microbial biotechnology 20110925 1

Microbial contaminant degradation may either result in the utilization of the compound for growth or act as a protective mechanism against its toxicity. Bioavailability of contaminants for nutrition and toxicity has opposite consequences which may have resulted in quite different bacterial adaptation mechanisms; these may particularly interfere when a growth substrate causes toxicity at high bioavailability. Recently, it has been demonstrated that a high bioavailability of vapour-phase naphthale ...[more]

PMID: 21951380

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Project description:The polycyclic aromatic hydrocarbon (PAH) contamination, bacterial community, and PAH-degrading bacteria were monitored in aged PAH-contaminated soil (Neuves-Maisons [NM] soil; with a mean of 1,915 mg of 16 PAHs.kg(-1) of soil dry weight) and in the same soil previously treated by thermal desorption (TD soil; with a mean of 106 mg of 16 PAHs.kg(-1) of soil dry weight). This study was conducted in situ for 2 years using experimental plots of the two soils. NM soil was colonized by spontaneous vegetation (NM-SV), planted with Medicago sativa (NM-Ms), or left as bare soil (NM-BS), and the TD soil was planted with Medicago sativa (TD-Ms). The bacterial community density, structure, and diversity were estimated by real-time PCR quantification of the 16S rRNA gene copy number, temporal thermal gradient gel electrophoresis fingerprinting, and band sequencing, respectively. The density of the bacterial community increased the first year during stabilization of the system and stayed constant in the NM soil, while it continued to increase in the TD soil during the second year. The bacterial community structure diverged among all the plot types after 2 years on site. In the NM-BS plots, the bacterial community was represented mainly by Betaproteobacteria and Gammaproteobacteria. The presence of vegetation (NM-SV and NM-Ms) in the NM soil favored the development of a wider range of bacterial phyla (Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Verrucomicrobia, Actinobacteria, Firmicutes, and Chloroflexi) that, for the most part, were not closely related to known bacterial representatives. Moreover, under the influence of the same plant, the bacterial community that developed in the TD-Ms was represented by different bacterial species (Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Actinobacteria) than that in the NM-Ms. During the 2 years of monitoring, the PAH concentration did not evolve significantly. The abundance of gram-negative (GN) and gram-positive (GP) PAH-degrading bacteria was estimated by real-time PCR quantification of specific functional genes encoding the alpha subunit of PAH-ring hydroxylating dioxygenase (PAH-RHD(alpha)). The percentage of the PAH-RHD(alpha) GN bacterial genes relative to 16S rRNA gene density decreased with time in all the plots. The GP PAH-RHD(alpha) bacterial gene proportion decreased in the NM-BS plots but stayed constant or increased under vegetation influence (NM-SV, NM-Ms, and TD-Ms).

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Walking the tightrope of bioavailability: growth dynamics of PAH degraders on vapour-phase PAH.

Publications

Walking the tightrope of bioavailability: growth dynamics of PAH degraders on vapour-phase PAH.

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