Selecting inocula for the biodegradation of organic compounds at low concentrations

Abstract

The inability of many organisms to degrade pollutants at low concentrations is a problem when selecting inocula for bioremediation of sites with these low concentrations. Thus, a study was conducted to determine the effect of low concentrations of p-nitrophenol (PNP) on growth of four PNP-degrading bacteria and their abilities to metabolize low concentrations of the compound in culture and samples from an oligotrophic lake. PNP did not increase the growth rates of Flavobacterium sp. M4, Pseudomonas sp. K, Flavobacterium sp. M1, and Pseudomonas sp. SP3 at concentrations of less than 2, 4, 10, and 100 ng/ml, respectively, when it was the sole added carbon source in culture, but it stimulated multiplication at higher concentrations. In liquid culture with the nitro compound as sole added carbon source, the four bacteria extensively mineralized PNP at 50 and 100 ng/ml, and three of the four degraded much of the substrate at 25 ng/ml. Pseudomonas sp. SP3 mineralized more than 20% but the two Flavobacterium strains converted less than 10% of the substrate to C02 at 10 ng/ml, and none of the three mineralized more than 5% at 1 and 5 ng PNP/ml. Under conditions where more than 99% of the radioactivity from (14)C-PNP added at 1 ng/ml remained in solution, two of the isolates formed organic products. Pseudomonas sp. K had no activity at 1, 5, and 10 ng/ml. In contrast, when each of the bacteria was separately inoculated into samples of water from an oligotrophic lake and from a well in which PNP was not biodegraded, the bacteria were able to mineralize as little as 1 ng PNP/ml. The addition to a salts solution of 10 ng of glucose per ml resulted in mineralization of PNP at concentrations too low to be mineralized when the nitro compound was the sole source of added carbon. Bacteria may thus be able to mineralize substrates in natural waters at concentrations below those suggested by tests conducted in culture media, possibly because of the availability of other carbon sources for the bacteria.

Estimation of the Yield Coefficient of Pseudomonas sp. Strain DP-4 with a Low Substrate (2,4-Dichlorophenol [DCP]) Concentration in a Mineral Medium from Which Uncharacterized Organic Compounds Were Eliminated by a Non-DCP-Degrading Organism

“…The results obtained in this study with DP-4 suggest that the biodegradation of extremely low concentrations of chemicals may be controlled by the presence of higher concentrations of other available substrates, as a number of studies have reported (7,12,25). The data also suggest that the inoculation of microorganisms to enhance the biodegradation of chemicals in polluted natural environments will not always give satisfactory results, because the concentrations of available substrates for microorganisms are generally extremely low in natural environments (11).…”

“…In order to enhance the biodegradation of chemicals of environmental concern, the inoculation of microorganisms capable of degrading the chemicals has been reported (7,12). However, the attempts did not always produce desired results.…”

Activity Assay of Bacterial Mixed Culture in Biological Treatment of Organochloropesticides

“…concentration of the pesticide must not be so high as to be toxic, nor so low such that biodegradation does not proceed due to a lack of induction of appropriate degradative enzymes and uptake mechanisms, failure to induce sufficient enzyme activities, or problems in providing \ sufficient energy even for cell maintenance. [7,15] Figure ( …”

Rhizosphere Ecology of Xenobiotic-Degrading Microorganisms

“…Among the various xenobiotics that may have enhanced degradation in the rhizosphere, atrazine is a particularly good candidate since, like most hydrophobic compounds, it accumulates on clay and organic matter in the upper soil horizon occupied by plant roots. At normal application rates, it is present at relatively low concentrations that may preclude the growth and maintenance of an effective dégrader population size (48). This latter problem is particularly problematic for atrazine, which has a highly oxidized triazine ring that provides no energy for microbial growth (49) Thus atrazine-degrader organisms can only acquire energy by utilizing carbon in the side chains attached to the ring or by growth on other carbon compounds contained in soil organic matter or root exudates.…”