Distribution of metabolic characteristics among aerobic soil bacteria and implications for biotransformation of organic and metallic wastes .

摘要

Comingled organic and metallic pollutants challenge soil remediation efforts because of their distinct chemical and biological transformation behavior. Bioremediation of such wastes depends upon pollutant types, remediation endpoints, and microbial metabolism and habitat. This research examined relationships between habitat, cell physiology, and aerobic biotransformation of chromium and organics. It was hypothesized that the degree of soil attachment by culturable heterotrophic bacterial communities in the vadose zone correlates to chromium biosorption, reduction, and tolerance; cell surface properties; growth rate; and substrate affinity. Compared to weakly soil-associated communities, strongly-associated communities were expected to have slower growth and greater substrate affinity, hydrophobicity, and chromium tolerance. Community-level relationships were not expected to hold true at the population level, however. Instead, bacterial isolates were anticipated to exhibit cell surface properties and biotransformation behavior not necessarily linked to their original soil association or community. The research sought to identify the biotransformation potential of often-overlooked soil microorganisms and to assess their use in achieving low residual contaminant concentrations in comingled chromium wastes.;Serial elution was used to extract two variably-attached bacterial communities from noncontaminated vadose zone soil. Five microbial isolates were cultured from these consortia. Consortia and isolates were characterized with respect to: (1) cell surface hydrophobicity and charge, using solvent-, resin-, and titration-based tests; (2) the rate and extent of growth on yeast extract and salicylic acid, a model organic pollutant; (3) chromium toxicity under variable substrate conditions; (4) chromium reduction, measured via x-ray spectroscopy; and (5) the kinetics and extent of chromium biosorption.;As hypothesized, the easily-detached bacterial community (F1) was less hydrophobic than its counterpart (F3), but its isolates varied unpredictably in hydrophobicity. Furthermore, F1 exhibited faster Monod-type growth but lower affinity for yeast extract (micromax = 0.35 hr-1, Ks = 36.6 mg/L) than F3 (micromax = 0.30 hr-1, Ks = 12.2 mg/L), whereas its isolates showed growth variability. Salicylic acid generally produced non-Monod growth and increased apparent chromium toxicity. All isolates and consortia were able to sorb and reduce chromium, regardless of cell surface properties or original attachment. Chromium resistance was negatively correlated to substrate (yeast extract) affinity among isolates, positively correlated to the substrate affinity of consortia (as hypothesized), and independent of cell surface properties.