Microbial degradation of petroleum hydrocarbons: an environmental perspective.

Inorganic Forms of Nitrogen

Desiccation tolerance of prokaryotes.

Plants vary considerably in their physiological response to selenium (Se). Some plant species growing on seleniferous soils are Se tolerant and accumulate very high concentrations of Se (Se accumulators), but most plants are Se nonaccumulators and are Se-sensitive. This review summarizes knowledge of the physiology and biochemistry of both types of plants, particularly with regard to Se uptake and transport, biochemical pathways of assimilation, volatilization and incorporation into proteins, and mechanisms of toxicity and tolerance. Molecular approaches are providing new insights into the role of sulfate transporters and sulfur assimilation enzymes in selenate uptake and metabolism, as well as the question of Se essentiality in plants. Recent advances in our understanding of the plant's ability to metabolize Se into volatile Se forms (phytovolatilization) are discussed, along with the application of phytoremediation for the cleanup of Se contaminated environments.

Selenium in higher plants.

Acanthamoeba spp. are free-living amebae that inhabit a variety of air, soil, and water environments. However, these amebae can also act as opportunistic as well as nonopportunistic pathogens. They are the causative agents of granulomatous amebic encephalitis and amebic keratitis and have been associated with cutaneous lesions and sinusitis. Immuno compromised individuals, including AIDS patients, are particularly susceptible to infections with Acanthamoeba. The immune defense mechanisms that operate against Acanthamoeba have not been well characterized, but it has been proposed that both innate and acquired immunity play a role. The ameba's life cycle includes an active feeding trophozoite stage and a dormant cyst stage. Trophozoites feed on bacteria, yeast, and algae. However, both trophozoites and cysts can retain viable bacteria and may serve as reservoirs for bacteria with human pathogenic potential. Diagnosis of infection includes direct microscopy of wet mounts of cerebrospinal fluid or stained smears of cerebrospinal fluid sediment, light or electron microscopy of tissues, in vitro cultivation of Acanthamoeba, and histological assessment of frozen or paraffin-embedded sections of brain or cutaneous lesion biopsy material. Immunocytochemistry, chemifluorescent dye staining, PCR, and analysis of DNA sequence variation also have been employed for laboratory diagnosis. Treatment of Acanthamoeba infections has met with mixed results. However, chlorhexidine gluconate, alone or in combination with propamidene isethionate, is effective in some patients. Furthermore, effective treatment is complicated since patients may present with underlying disease and Acanthamoeba infection may not be recognized. Since an increase in the number of cases of Acanthamoeba infections has occurred worldwide, these protozoa have become increasingly important as agents of human disease.

Acanthamoeba spp. as agents of disease in humans.

A study was conducted to relate the properties of Enterobacter, Pseudomonas, Bacillus, Achromobacter, Flavobacterium, and Arthrobacter strains to their transport with water moving through soil. The bacteria differed markedly in their extent of transport; their hydrophobicity, as measured by adherence to n-octane and by hydrophobic-interaction chromatography; and their net surface electrostatic charge, as determined by electrostatic interaction chromatography and by measurements of the zeta potential. Transport of the 19 strains through Kendaia loam or their retention by this soil was not correlated with hydrophobicities or net surface charges of the cells or the presence of capsules. Among 10 strains tested, the presence of flagella was also not correlated with transport. Retention was statistically related to cell size, with bacteria shorter than 1.0 μm usually showing higher percentages of cells being transported through the soil. We suggest that more than one characteristic of bacterial cells determines whether the organisms are transported through soil with moving water.

Relationship between Cell Surface Properties and Transport of Bacteria through Soil

We developed 12 models of kinetics to describe the metabolism of organic substrates that are not supporting bacterial growth These models can be used to describe the biodegradation of organic compounds that are not supporting growth when the responsible populations are growing logistically, logarithmically, or linearly or are not increasing in numbers Nonlinear regression analysis was used to fit patterns of mineralization by two bacteria to these kinetic models Pseudomonas acidovorans mineralized 1 ng of phenol per ml while growing exponentially at the expense of uncharacterized organic carbon in a synthetic medium Phenol at a concentration of 1 ng/ml did not affect the growth of P acidovorans These data were best fit by the model that incorporates the equation for logarithmic growth and assumes a concentration of test substrate well below its Km value In the absence of a second substrate, glucose at concentrations below those supporting growth was mineralized by Salmonella typhimurium in a manner best described by pseudo first-order kinetics In the presence of different concentrations of arabinose, however, the kinetics of glucose mineralization by S typhimurium reflected linear, logistic, or logarithmic growth of the population on arabinose We conclude that the kinetics of mineralization of organic compounds at concentrations too low to support growth are best described either by the first-order model or by models that incorporate expressions for the kinetics of growth of the metabolizing population on other substrates When growth is at the expense of other substrates, the kinetics observed reflect such growth, as well as the concentration of the substrate of interest(ABSTRACT TRUNCATED AT 250 WORDS)

Models for the kinetics of biodegradation of organic compounds not supporting growth.

A study was conducted of possible reasons for acclimation of microbial communities to the mineralization of organic compounds in lake water and sewage. The acclimation period for the mineralization of 2 ng of p-nitrophenol (PNP) or 2,4-dichlorophenoxyacetic acid per ml of sewage was eliminated when the sewage was incubated for 9 or 16 days, respectively, with no added substrate. The acclimation period for the mineralization of 2 ng but not 200 ng or 2 micrograms of PNP per ml was eliminated when the compound was added to lake water that had been first incubated in the laboratory. Mineralization of PNP by Flavobacterium sp. was detected within 7 h at concentrations of 20 ng/ml to 2 micrograms/ml but only after 25 h at 2 ng/ml. PNP-utilizing organisms began to multiply logarithmically after 1 day in lake water amended with 2 micrograms of PNP per ml, but substrate disappearance was only detected at 8 days, at which time the numbers were approaching 10(5) cells per ml. The addition of inorganic nutrients reduced the length of the acclimation period from 6 to 3 days in sewage and from 6 days to 1 day in lake water. The prior degradation of natural organic materials in the sewage and lake water had no effect on the acclimation period for the mineralization of PNP, and naturally occurring inhibitors that might delay the mineralization were not present. The length of the acclimation phase for the mineralization of 2 ng of PNP per ml was shortened when the protozoa in sewage were suppressed by eucaryotic inhibitors, but it was unaffected or increased if the inhibitors were added to lake water.(ABSTRACT TRUNCATED AT 250 WORDS)

Explanations for the acclimation period preceding the mineralization of organic chemicals in aquatic environments.

Experiments were carried out to determine the breakthrough of bacteria through a saturated aquifer sand at three flow velocities and three cell concentrations. Bacteria were either suspended in deionized water or 0.01 mol L−1 NaCl solution. Bacterial transport was found to increase with flow velocity and cell concentration but was significantly retarded in the presence of 0.01 mol L−1 NaCl. A mathematical model based on the advection-dispersion equation was formulated to describe bacterial transport and retention in porous media. The transport equations for bacteria were solved using the finite difference Crank-Nicolson scheme combined with Newton-Raphson iterations. The best fit of the numerical model to the experimental data was obtained using the downhill simplex optimization technique to minimize the sum of the squares of deviations between model predictions and experimental data by varying three parameters. This numerical model was found to describe the experimental data very well under all the experimental conditions tested. An alternative model (also based on the advection-dispersion equation) was tested against all the experimental data sets, but it did not represent the experimental data as well as the model proposed in this paper.

Transport of bacteria in an aquifer sand: Experiments and model simulations

A study was conducted to determine the role of inoculum size of a bacterium introduced into nonsterile lake water in the biodegradation of a synthetic chemical The test species was a strain of Pseudomonas cepacia able to grow on and mineralize 10 ng to 30 micrograms of p-nitrophenol (PNP) per ml in salts solution When introduced into water from Beebe Lake at densities of 330 cells per ml, P cepacia did not mineralize 10 microgram of PNP per ml However, PNP was mineralized in lake water inoculated with 33 X 10(4) to 36 X 10(5) P cepacia cells per ml In lake water containing 10 microgram of PNP per ml, a P cepacia population of 230 or 120 cells per ml declined until no cells were detectable at 13 h, but when the initial density was 43 X 10(4) cells per ml, sufficient survivors remained after the initial decline to multiply at the expense of PNP The decline in bacterial abundance coincided with multiplication of protozoa Cycloheximide and nystatin killed the protozoa and allowed the bacterium to multiply and mineralize 10 microgram of PNP, even when the initial P cepacia density was 230 or 360 cells per ml The lake water contained few lytic bacteria The addition of KH2PO4 or NH4NO3 permitted biodegradation of PNP at low cell densities of P cepacia We suggest that a species able to degrade a synthetic chemical in culture may fail to bring about the same transformation in natural waters, because small populations added as inocula may be eliminated by protozoan grazing or may fail to survive because of nutrient deficiencies

M. Alexander

Papers

Relationship between Cell Surface Properties and Transport of Bacteria through Soil

Models for the kinetics of biodegradation of organic compounds not supporting growth.

Explanations for the acclimation period preceding the mineralization of organic chemicals in aquatic environments.

Transport of bacteria in an aquifer sand: Experiments and model simulations

Inoculum size as a factor limiting success of inoculation for biodegradation.