Ecological interactions between metals and microbes that impact bioremediation

Conference · Wed Mar 17 00:00:00 EST 2004

OSTI ID:895383

Konopka, Allan; Nakatsu, Cindy

Distinct microbial communities had been found in contaminated soils that varied in their concentrations of Pb, Cr and aromatic compounds. It is difficult to distinguish between their effects as their presence is highly correlated. Microcosms were constructed in which either Pb{sup +2} or CrO{sub 4}{sup -2} was added at levels that produced acute modest or severe acute effects (50 or 90% reduction). We previously reported on changes in microbial activity and broad patterns of Bacterial community composition. These results showed that addition of an organic energy source selected for a relatively small number of phylotypes and the addition of Pb or Cr(VI) modulated the community response. We sequenced dominant phylotypes from microcosms amended with xylene and Cr(VI) and from those with the simple addition of glucose only. In both cases, the dominant selected phylotypes were diverse. We found a number of distinct Arthrobacter strains, as well as several Pseudomonas spp. In addition, the high GC-content bands belonged to members of the genera Nocardioides and Rhodococcus. The focus of amended microcosm work has now shifted to anaerobic processes. The reduction of Cr(VI) to Cr(III) as a detoxification mechanism is of greater interest, as is the specific role of particular physiological groups of anaerobes in mediating Cr(VI) detoxification. The correlation between microbial activity, community structure, and metal level has been analyzed on 150 mg of soil collected at spatial scales <1, 5, 15 and 50 cm. There was no correlation between metal content and activity level. Soils <1 cm apart could differ in activity 10-fold and extractable Pb and Cr 7-fold. Therefore, we turned to geostatistical analysis. There was spatial periodicity which is likely to reflect the heterogeneous distribution of active microbes and metal contaminants. Variograms indicated that the range of spatial dependence was up to 20 cm. To visualize the spatial relationships between the primary variate (activity) and its covariates (lead and chromium content), block kriging was used. The kriging maps suggest that areas exist where increased metal concentrations have zones of decreased metabolic microbial activity. Cr(VI) resistant bacteria have been isolated from two contaminated sites. Most isolates are Arthrobacter, Rhodococcus, or Pseudomonas spp. A chrA gene has been cloned from Arthrobacter strain CR15 isolated from Cannelton, MI. PCR-primers have been produced against conserved motifs analyzed from 8 chrA sequences. Of the 96 Cr-resistant isolates from Cannelton, 85% gave a positive reaction to these primers. In contrast, none of the 38 isolates from Seymour, IN were positive. Therefore, at least for the culturable community, a particular resistance determinant appears to be widespread at a geographical site but rare (absent) at another site. The phylogenetic relatedness of the Arthrobacter strains is being evaluated via the distribution of repetitive elements as well as genome-wide restriction fragment analysis. Work to date on the latter has also suggested that Arthrobacter genomes are small (<2.5 Mbp). Gene capture experiments demonstrated that chromate-sensitive Gram-negative bacterial strains could obtain resistance from Cr-contaminated soil. However, frequency of transfer is low (10-6-10-8). Genetic diversity of the acquired chromate resistance mechanism is being assessed.

• Research Organization: Purdue University, West Lafayette, IN
• Sponsoring Organization: USDOE Office of Science (SC)
• OSTI ID: 895383
• Report Number(s): CONF-NABIR2004-31; TRN: US200702%%830
• Resource Relation: Conference: Annual NABIR PI Meeting, March 15-17, 2004, Warrenton, VA
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
54 ENVIRONMENTAL SCIENCES
ACTIVITY LEVELS
AROMATICS
BACTERIA
BIOREMEDIATION
CHROMATES
CHROMIUM
DETOXIFICATION
ENERGY SOURCES
GENES
GENETICS
GLUCOSE
KRIGING
MICROCOSMS
PERIODICITY
PSEUDOMONAS
RHODOCOCCUS
SOILS
SPACE DEPENDENCE
STRAINS
XYLENES