John S. Fletcher

Polychlorinated Biphenyl (PCB)-Degrading Bacteria Associated with Trees in a PCB-Contaminated Site

ABSTRACT The abundance, identities, and degradation abilities of indigenous polychlorinated biphenyl (PCB)-degrading bacteria associated with five species of mature trees growing naturally in a contaminated site were investigated to identify plants that enhance the microbial PCB degradation potential in soil. Culturable PCB degraders were associated with every plant species examined in both the rhizosphere and root zone, which was defined as the bulk soil in which the plant was rooted. Significantly higher numbers of PCB degraders (2.7- to 56.7-fold-higher means) were detected in the root zones of Austrian pine (Pinus nigra) and goat willow (Salix caprea) than in the root zones of other plants or non-root-containing soil in certain seasons and at certain soil depths. The majority of culturable PCB degraders throughout the site and the majority of culturable PCB degraders associated with plants were identified as members of the genus Rhodococcus by 16S rRNA gene sequence analysis. Other taxa of PCB-degrading bacteria included members of the genera Luteibacter and Williamsia, which have not previously been shown to include PCB degraders. PCB degradation assays revealed that some isolates from the site have broad congener specificities; these isolates included one Rhodococcus strain that exhibited degradation abilities similar to those of Burkholderia xenovorans LB400. Isolates with broad congener specificity were widespread at the site, including in the biostimulated root zone of willow. The apparent association of certain plant species with increased abundance of indigenous PCB degraders, including organisms with outstanding degradation abilities, throughout the root zone supports the notion that biostimulation through rhizoremediation is a promising strategy for enhancing PCB degradation in situ.

Growth of PCB-degrading bacteria on compounds from photosynthetic plants

Abstract Compounds produced by photosynthetic plants were shown to support the growth of PCB-degrading bacteria, and the organisms retained their ability to metabolize PCBs. These results indicate that the rhizosphere zone surrounding the roots of some plant species may selectively foster the growth of PCB-degrading microbes. Thus, introduction of a carefully selected plant species at PCB-contaminated sites has promise as a new means of enhancing and maintaining microbial degradation of PCBs.

Release of phenols by perennial plant roots and their potential importance in bioremediation

Seventeen different plant species grown in sand culture were screened for their ability to release phenolic compounds from their roots. The concentration of phenols in the rhizosphere of each species was compared to concentrations of phenols known to support the growth of PCB-degrading bacteria (Donnelly et al. 1994). It was concluded that the concentration throughout the rhizosphere was below substrate levels, but for some plant species (i.e. mulberry) there was evidence that portions of the rhizosphere possessed levels of phenols sufficiently high enough to support microbial growth.

Influence of plant growth stage and season on the release of root phenolics by mulberry as related to development of phytoremediation technology

The phenolics released by red mulberry (Morus rubra L.) roots at different growth stages within a season were quantified and the makeup of phenols analyzed by reverse-phase high performance liquid chromatography (RP-HPLC). The data show that total phenols released into the soil solution increased continuously from an early vegetative stage to leaf senescence, indicating their accumulation in the rhizosphere. From the RP-HPLC analysis of the butanol-extractable phenolics at various growth stages, there appears to be a massive release of an assortment of less polar phenolics into the rhizosphere at the end of the season accompanying leaf senescence. The rhizosphere phenolics may create an environment suitable for the biodegradation of recalcitrant environmental pollutants, by selectively fostering the growth of some, while inhibiting the growth of other microbes.

Ecological recovery of vegetation at a former industrial sludge basin and its implications to phytoremediation.

Examination of a former industrial sludge basin containing organic pollutants showed that the basin had undergone substantial ecological recovery through natural forces following the removal of surface water in 1982. Conventional phases of ecological recovery (plant invasion and succession) have occurred, but the structure of the biodiverse plant community (51 species and 22 families) was different from that at a recovering non-polluted disturbed site. Three plant species (Bermuda grass, mulberry, and sunflower) believed to be early invaders of the basin still persist in large numbers indicating that these species are well suited to cope with normal environmental stresses at this area (i.e. seasonal drought and flood) as well as organic pollutants. There was an indication that early invaders of the site fostered disappearance of contaminants thereby creating more favorable conditions for a broader spectrum of plants to grow. Vegetation analyses of naturally vegetated hazardous waste sites hold promise as a screening device for identifying plant species and management practices worthy of further phytoremediation investigations.

Minimal organic medium for suspension cultures of Paul's scarlet rose

SummaryMaximum growth of suspension cultures of Pauls Scarlet rose has been demonstrated in a minimal organic medium possessing only 4 organic compounds: napthaleneacetic acid, kinetin, myo-inositol, and sucrose. Myo-inositol was not essential for growth, but sustained growth was reduced by 90% when it was omitted. Maximum growth required nitrate plus a supplemental amount of either NH4+or glutamine.

Involvement of mixed function oxidase systems in polychlorinated biphenyl metabolism by plant cells.

SummaryNineteen different polychlorinated biphenyl (PCB) congeners ranging in chlorine content from 2 to 6 chlorine atoms were provided to nonphotosynthetic suspension cultures of rose (Rosa sp. cv. Pauls Scarlet). After a 96 h incubation period, 11 individual congeners had been metabolized by > 10%. Provision of mixed function oxidase inhibitors (10 mM metyrapone or 0.5 mM 7,8-benzoflavone) either stopped or severely reduced the metabolism of individual congeners; whereas (inhibitors of peroxidase) (1 mM benzoate or 1 mM n-propylgallate) had minimal influence on PCB metabolism. The metabolism of PCBs by rose cultures appears to be catalyzed by a cytochrome P-450-and/or P-448-dependent enzyme system.

Assessment of published literature on the uptake, accumulation, and translocation of heavy metals by vascular plants

Abstract Assessment of published literature compiled in the UTAB Database showed that copper, zinc, cadmium, lead and nickel were the most heavily studied metals. The data analysis revealed that a broad spectrum of plants (1400 species) have been studied with 54% of all data on wild plant species. The most frequently studied plant species were Zea mays (corn), Phaseolus vulgaris (bean) and Triticum aestivum (wheat) accounting respectively for 6.0, 5.0 and 3.7 percent of the total records in UTAB.

Influence of root exposure concentration on the fate of nitrobenzene in soybean

Abstract The influence of exposure concentration on the physical and chemical fate of nitrobenzene was studied by providing 0.02, 0.2, 2.0 and 100 μg/ml to roots of intact soybean plants. The results of this study illustrate how plants may govern the physical and chemical fate of environmental pollutants, and emphasize the importance of plants as a vector for foodchain contamination even when biomagnification does not occur.

The influence of increasing chlorine content on the accumulation and metabolism of polychlorinated biphenyls (PCBs) by Paul's Scarlet Rose cells

Four radiolabled congeners of biphenyls with increasing chlorine content (biphenyl; 1-monochlorobiphenyl; 2,2′,4,4′-tetrachlorobiphenyl; and 2,2′,4,4′,5,5′-hexachlorobiphenyl) were provided to suspension cultures of rose (Rosa sp. cv. Pauls Scarlet) for 4 days. Both the kinetics of 14C exchange between the cells and medium, and the metabolism of the parent compounds depended on the chlorine content of the congeners. Analysis of both the cells and their medium showed that of the recovered radioactivity 88%, 86%, and 3% of the biphenyl, 1-PCB, and 2,2′,4,4′-PCB were metabolized respectively to polar and insoluble residue products. The 2,2′,4,4′,5,5′-PCB did not appear to be metabolized.