Heavy metal pollution is a principle source of environmental contamination. We analyzed heavy metal impacted soil microbial communities and found that, in general, although lead adversely affected biomass, metabolic activity, and diversity, autochthonous lead- and cadmium-resistant isolates were found. In several metal-stressed soils, the microbial community consisted of two populations, either resistant or sensitive to lead. Additionally, a lead-resistant isolate was isolated from a control soil with no known previous exposure to lead, suggesting widespread lead resistance. Lead-resistant genera isolated included Pseudomonas, Bacillus, Corynebacterium, and Enterobacter species. Plasmids, ranging from 5 to 260 kb, were not detected through standard purifications from lead-resistant isolates. Positive correlations existed between antibiotic resistance and isolation habitat for lead-resistant strains, microbial metabolic activity and soil type, soluble lead concentration and microbial diversity, and arsenic concentration and total or viable cell concentrations.

The persistence of synthetic herbicides such as 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and its release in massive amounts as a herbicide (Agent Orange) have created toxicological problems in many countries. In nature, 2,4,5-T is slowly degraded by cooxidation and is not utilized as a sole source of carbon and energy. The technique of plasmid-assisted molecular breeding has led to the development of bacterial strains capable of totally degrading 2,4,5-T by using it as their sole source of carbon at high concentrations (greater than 1 mg/ml). Spectrophotometry and gas chromatography reveal various intermediates during growth of the culture with 2,4,5-T.

A p id, terned pAC25, specifying biodegradation of 3-chlorobenzoate in a strain of Pseudomonas putida has been characterized. During growth of the plasmid-harboring cells with 3-chlorobenzoate, there was an accumulation of 3chlorocatechol and fl-chloromuconic acid as intermediates and release of more than 80% of the chlorine in the form of inorganic chloride. The plasmid had a mean molecular mass of 68 x 106 daltons and was transmissible to a number of Pseudomonas species such as P. aeruginosa, P. putida strain PpG1, and P. putida strain PRS1. Transfer of pAC25 to various catechol-negative mutants of P. putida strain PRS1 showed that the chromosomally coded pyrocatechase was not complemented by the plasmid-specified pyrocatechase, which appeared to be specific for the chlorinated catechols. In contrast to benzoate, which was metabolized by the ortho pathway through ,B-ketoadipate as an intermediate, the plasmid specified ortho cleavage of the the chlorocatechols through maleylacetate as an intermediate.

No abstract

Basalt aquifers are common in many parts of Canada and the United States; however, little is known about their microbial ecology. Microbial populations were characterized at a basalt aquifer with 7 m of clay and silt in the vadose zone and a saturated zone extending from 7 to 500 m. Planktonic total counts and viable counts were 1.7 × 105 and 2.3 × 104 cells/mL, while sessile total counts and viable counts were 1.9 × 107 and 1.7 × 105 cells/g, respectively. Some of the physical and chemical habitat conditions measured were pH (7.1), Eh (135 mV), dissolved O2 (4.1 mg/L), temperature (10 °C), NH4+ (4 μM), NO3− (253 μM), Fe (0.17 μM), and Mn (36 nM). Variation in physical and chemical variables correlated with depth and the region of the aquifer sampled. One hundred forty-nine random isolates of the dominant culturable bacteria from groundwater and subsurface cores were submitted to phenotypic analysis on the basis of antibiotic responses. The resultant dominant bacteria were Gram-negative, mesophilic heterotrophs. Cluster analysis revealed at least 14 discernible clusters containing representatives from the genera Pseudomonas, Bacillus, Acinetobacter, Arthrobacter, Micrococcus, and Clavibacter. Centrotype representatives were selected from each cluster and tentatively identified.Key words: basalt aquifer bacterial ecology.