Survival and Transport of lac-lux Marked Pseudomonas fluorescens Strain in Uncontaminated and Chemically Contaminated Soils

Degradation of 4-chlorophenol at low temperature and during extreme temperature fluctuations by Arthrobacter chlorophenolicus A6

Low average temperatures and temperature fluctuations in temperate soils challenge the efficacy of microbial strains used for clean up of pollutants. In this study, we investigated the cold tolerance of Arthrobacter chlorophenolicus A6, a microorganism previously shown to degrade high concentrations of 4-chlorophenol at 28 degrees C. Luciferase activity from a luc-tagged derivative of the strain (A6L) was used to monitor the metabolic status of the population during 4-chlorophenol degradation. The A6L strain could degrade 200-300 mug mL(-1) 4-chlorophenol in pure cultures incubated at 5 degrees C, although rates of degradation, growth and the metabolic status of the cells were lower at 5 degrees C compared to 28 degrees C. When subjected to temperature fluctuations between 5 and 28 degrees C, A6L continued to degrade 4-chlorophenol and remained active. In soil microcosm experiments, the degradation rates were significantly faster the first week at 28 degrees C, compared to 5 degrees C. However, this difference was no longer seen after 7 days, and equally low 4-chlorophenol concentrations were reached after 17 days at both temperatures. During 4-chlorophenol degradation in soil, CFU and luciferase activity values remained constant at both 5 and 28 degrees C. However, once most of the 4-chlorophenol was degraded, both values decreased by 1-1.5 logarithmic values at 28 degrees C, whereas they remained constant at 5 degrees C, indicating a high survival of the cells at low temperatures. Because of the ability of A. chlorophenolicus A6 to degrade high concentrations of 4-chlorophenol at 5 degrees C, together with its tolerance to temperature fluctuations and stress conditions found in soil, this strain is a promising candidate for bioaugmentation of chlorophenol-contaminated soil in temperate climates.

Effect of bioaugmentation on microbial transport, water infiltration, moisture loss, and surface hardness in pristine and contaminated soils

Three different soils, a clay, a pristine sandy loam and a PCB-contaminated sandy loam, were bioaugmented to determine the influence of clay content and contaminants on the transport of bacteria in unsaturated soils, using surface irrigation water as a transport medium. The results indicate that the transport of the implanted bacteria was influenced negatively more by the presence of PCBs than by the clay content of the soil. Transport was directly related to the frequency of irrigation and length of the intervals between irrigation periods, making these variables important factors to consider when applying bioaugmentation via downward percolating water. Other parameters measured after bacterial bioaugmentation were water infiltration, moisture loss, and surface hardness of these soils. Surface water infiltration was affected more by the soil clay content than by the hydrophobic contaminant. Infiltration was significantly but differently influenced by bioaugmentation, positively in clay, negatively in sandy loam, and negatively (to a lesser extent) in the PCB-contaminated sandy loam soils. Moisture loss was slower in the bioaugmented soil than in the control soils, with this difference being most pronounced in the PCB soil. High moisture loss in the bioaugmented clay soil rendered it the hardest soil for surface penetration.

A comparison of enumeration methods for culturable Pseudomonas fluorescens cells marked with green fluorescent protein

The detection of bacteria in environmental samples using genetic markers is valuable in microbial ecology. The green fluorescent protein (GFP) reporter gene was studied under nutrient starvation conditions at 4 degrees C, 23 degrees C and 30 degrees C in Pseudomonas fluorescens R2fG1 cells tagged with a red-shifted gfp. Fluorescence intensity was not significantly different in cells maintained in a buffer for at least 48 days at all the tested temperatures. gfp-Tagged R2fG1 cells were introduced into bulk soil microcosms and soil microcosms with wheat seedlings. GFP-marked cells were enumerated immediately after inoculation into soil and again in soil and root samples after 10 days. Counts of culturable colonies were obtained from drop plates using 5-microl aliquots of serial dilutions viewed with an epifluorescent microscope. Traditional spread plates (using 100-microl aliquots) and the most-probable-number (MPN) method using a spectrofluorometer were also used to enumerate the GFP-marked Pseudomonas cells in soil, rhizosphere and rhizoplane samples. Microcolonies were visualized on root surfaces under the epifluorescent microscope after immobilizing in agar and incubation for 24 h. Counts from traditional spread plates were significantly higher (P<0.05) than the population estimates of the MPN method for all treatments at any sampling time. Counts using the drop plate method, however, were not significantly different (P<0.05) except in one treatment, and provided similar estimates in half the time of spread plates and at an estimated third of the cost.

DNA in soil: adsorption, genetic transformation, molecular evolution and genetic microchip

This review examines interactions between DNA and soil with an emphasis on the persistence and stability of DNA in soil. The role of DNA in genetic transformation in soil microorganisms will also be discussed. In addition, a postulated mechanism for stabilization and elongation/assembly of primitive genetic material and the role of soil particles, salt concentrations, temperature cycling and crystal formation is examined.

Bioaugmentation as a soil bioremediation approach

The debate over the efficacy of bioaugmentation rages on, with research continuing to demonstrate that its advantages for soil bioremediation are difficult to predict; however, when it works, the results are often very encouraging. The difficulties arise from, among others, the diversity of the microorganisms used, environmental heterogeneity, and variations in the influence of critical parameters (e.g. humidity, microbial predation and "bioavailability') which, unfortunately, are not even always identified.