Microbiological characteristics of a sandy loam soil exposed to tebuconazole and lambda-cyhalothrin under laboratory conditions.

Changes in microbiological properties of a sandy loam soil in response to the addition of different concentrations of fungicide tebuconazole and pyrethroid insecticide lambda-cyhalothrin were assessed under laboratory conditions. To ascertain these changes, the potentially active soil microbial biomass, concentrations of ammonium and nitrate ions, numbers of total culturable bacteria, fungi, nitrogen-fixing bacteria, nitrifying and denitrifying bacteria were determined. Substrate-induced respiration (SIR) increased with time in both control (ranged from 13.7 to 23.7 mg/O(2)/kg(-1)/dry soil/h(-1)) and pesticide treated soil portions. For both pesticides, SIR values ranged from 12-13 to 23-25 mg/O(2)/kg(-1)/dry soil/h(-1) on days 1 and 28, respectively. Also, concentrations of nitrate and ammonium ions, numbers of total culturable bacteria, denitrifying bacteria, nitrogen-fixing bacteria (for the insecticide) and fungi (for the insecticide) were either unaffected or even stimulated by the pesticide treatments. The adverse impacts of the pesticides were observed for nitrate concentrations (on days 1 or 7), numbers of nitrifying bacteria (on day 1), denitrifying bacteria (for the insecticide on days 1 and 14), nitrogen-fixing bacteria (for tebuconazole on day 1) as well as numbers of fungi in tebuconazole-treated soil (on days 1 and 14).

Microbial reaction to soil contamination with Cd(II) at different temperatures.

The response of the indigenous bacterial community to the addition of single doses of Cd(II) was studied in a sandy-loam soil at 6, 20 or 30 degreesC. Soil pollution significantly reduced the number of bacteria growing on 0.1% tryptic soy agar (TSA) and those growing on 0.01% TSA especially at 30 degreesC shortly after the addition of the metal. However, an increase in cfu numbers and dominance values of metal-tolerant populations were observed at this temperature with time. In addition, changes in the kinetics of colony development were found over the period of study.

Structural diversity of microorganisms in chemically perturbed soil assessed by molecular and cytochemical approaches.

Until recently, our understanding of microbial community development in soil ecosystems exposed to different inorganic and organic pollutants has been limited to culturable microorganisms because of the techniques available. The discovery that most soil microorganisms are non-culturable but potentially viable and metabolically active accelerated the application of different culture-independent methods for structural diversity assessments of the microbial community. This review examines the results of recent studies on the impact of heavy metals and organic pollutants on the diversity of the microflora obtained with methods based on analyses of signature biomarkers such as nucleic acids and fatty acids. The application of these techniques allowed researchers to pinpoint reduction of microbial diversity in contaminated soil, and significant shifts in the community structure, leading to the dominance of only a few populations (species) and the disappearance of others, some of which were never isolated by conventional methods (e.g. an increase in Acidobacterium or a decrease in terrestrial non-thermophilic Crenarchaeota). Although the new techniques are not free from limitations, they allow the monitoring of the virtual impact of stressors on soil microorganisms and the direction of resuscitation of the microbial community during natural or induced bioremediation, especially when using combined approaches.

Microflora of technogenous wastes characterised by fatty acid profiling.

Fatty acid methyl ester (FAME) profiles obtained directly in situ have been used to estimate microbial community structure in different technogenous wastes. The effect of nutrients added, simulating the effect of plant-derived exudates on the indigenous microflora in the heaps during the reclamation process, was also studied in microcosms. The wastes such as coal-mine spoil, non-ferrous metallurgical slag and coal fly-ash were characterised by a poorly developed microflora as compared to a typical sandy loam soil. However, the most similar to the soil was the community structure in the coalmine spoil. The high content of 18: 2omega6,9 found in the metallurgical slag indicated the domination of fungi in this waste. In contrast, representatives of the Cytophaga-Flavobacterium group dominated the coal fly-ash, for which 16:1omega5c was used as the marker acid. The waste amendment resulted in changes of FAME profiles obtained. However, the changes were site-specific, indicating response of particular microbial groups to the added nutrients.

Indigenous microflora responses to introduction of cyanogenic strains of Pseudomonas fluorescens into soil.

The effects of cyanogenic Pseudomonas fluorescens strains introduced into soil on the kinetic of colony formation and bacterial community structure were investigated. About 7.8 x 10(8) and 1.2 x 10(9) cfu per g dry soil of TA1 and B2 were added to the soil portions, respectively. The parameters of colony formation by heterotrophic soil bacteria were determined. The bacterial community structure and phenotypic diversity were studied using concept of r/K strategies and echophysiological index, respectively. The physiological state of indigenous heterotrophic bacteria and gram-negative group did not change under the influence of the cyanogenic strains introduced. Phenotypic diversity of the soil bacteria also did not change significantly. However, some short-term shifts in community structure of indigenous heterotrophic bacteria were noticed. This study shows that the introduction of great numbers of cyanogenic P. fluorescens strains could be safely used as potential agents in biological control of soil-born pathogens.

Survival of lux-marked bacteria introduced into soil and the rhizosphere of bean (Phaseolus vulgaris L.).

The survival of lux-marked recombinants of Escherichia coli and Bacillus subtilis was studied in the rhizosphere of bean (Phaseolus vulgaris L.) and in bulk soil. The number of E. coli (pSB343) containing a complete lux operon did not differ significantly according to whether they were introduced into soil separately or together with a non-luminescent mutant Pseudomonas fluorescens R2fN. When genetically altered strains of E. coli and B. subtilis bearing a complete or an incomplete lux-reporter system were introduced into soil, the numbers of surviving cells were the same both in the rhizosphere and bulk soil. The insertion of lux genes into bacterial strains therefore does not affect their competitiveness and survival in the rhizosphere and bulk soil.

Effect of genetically modified Pseudomonas fluorescens introduced into soil contaminated with copper (II) on microbial community diversity in the soil and rhizosphere.

When genetically altered strains of Pseudomonas fluorescens were introduced into soil contaminated with copper in a laboratory study, they did not affect the phenotypic diversity (eco-physiological index) of indigenous microflora in the rhizosphere and bulk soil. Soil contamination with copper also did not cause shifts in the distribution of bacterial classes within the total community of heterotrophic or Gram-negative bacteria.

Effect of copper (II) on survival of Pseudomonas fluorescens and transfer of plasmid RP4 in soil.

Survival of Pseudomonas fluorescens (R2f, RP4), P. fluorescens (R2f) and plasmid RP4 transfer efficiency depended on the concentration of Cu (II) and the time of incubation. The indigenous heterotrophic bacteria were more tiolerant to Cu (II) than the introduced strains. Although transconjugants were present for the first 3 days, the frequencies of conjugation and absence of transconjugants at 14 days indicate that conjugation occurred early in the incubation and that transconjugants were unable to survive for very long.