Factors Influencing the Bacterial Bioremediation of Hydrocarbon Contaminants in the Soil: Mechanisms and Impacts

The discharge of hydrocarbons and their derivatives to environments due to human and/or natural activities cause environmental pollution (soil, water, and air) and affect the natural functioning of an ecosystem. To minimize or eradicate environmental pollution by hydrocarbon contaminants, studies showed strategies including physical, chemical, and biological approaches. Among those strategies, the use of biological techniques (especially bacterial biodegradation) is critically important to remove hydrocarbon contaminants. The current review discusses the insights of major factors that enhance or hinder the bacterial bioremediation of hydrocarbon contaminants (aliphatic, aromatic, and polyaromatic hydrocarbons) in the soil. The key factors limiting the overall hydrocarbon biodegradation are generally categorized as biotic factors and abiotic factors. Among various environmental factors, temperature range from 30 to 40°C, pH range from 5 to 8, moisture availability range from 30 to 90%, carbon/nitrogen/phosphorous (C/N/P; 100:20:1) ratio, and 10–40% of oxygen for aerobic degradation are the key factors that show positive correlation for greatest hydrocarbon biodegradation rate by altering the activities of the microbial and degradative enzymes in soil. In addition, the formation of biofilm and production of biosurfactants in hydrocarbon-polluted soil environments increase microbial adaptation to low bioavailability of hydrophobic compounds, and genes that encode for hydrocarbon degradative enzymes are critical for the potential of microbes to bioremediate soils contaminated with hydrocarbon pollutants. Therefore, this review works on the identification of factors for effective hydrocarbon biodegradation, understanding, and optimization of those factors that are essential and critical.

Compatibility and formulation of diesel degrading consortia using bacteria isolated from contaminated soil

Soil contamination with diesel spillage is an increasing environmental challenge that damages living ecosystems. Efficiency of single bacterium in degrading diesel oil pollutants is faced with slow performance limitation. Therefore, the use of consortia is shown to be better, due to synergism, multi-enzymatic activity and potential for diversified catabolic functionalities. This study is aimed at formulating effective bacterial consortia that can degrade diesel in polluted environments. Four diesel degrading bacteria as Bacillus subtilis, Staphylococcus aureus, Micrococcus roseus and Rhodococcus specie were isolated and used for consortia formulation. Purity testing was performed on the isolates prior to consortia formulation, before their compatibility was tested by cross-spreading them on nutrient agar. Consortia formulation was made using Bacteria resting cells in Phosphate Buffer Saline based on compatibility testing and mathematical permutations. For on their ability to survive diesel on Bushnell-Haas Agar (BHA), consortia 2, 9 and 11 showed the best results among which consortium 11 was chosen as the best, considering growths on the medium within a 72 hrs period. The growth of the organisms before consortia formulation and after was also evaluated, which suggest that the consortium perform better than individual strains. Analysis of Variance showed significant statistical differences (p<0.05) between constituents of consortia, and diesel degradation on 2% (v/v) BHA. The degradation performances of the various consortia on BHA were furthermore separated by Duncan’s Multiple Range Test. The colony counts obtained indicate that degradation was performed better by the consortia than individual strains. The findings of the study contribute towards illuminating inter-microbial relationships and microbial ecology especially within groups of diesel degrading bacteria. Further studies are imperative, to maximally harness the potentials of these bacteria for applications in large scale diesel biodegradation. Key Words: Consortia, Diesel, Bacterial Biodegradation, Haemocytometry.

Evaluation of assays for screening polycyclic aromatic hydrocarbon-degrading potential of bacteria

Within a 30-day incubation laboratory study, the polycyclic aromatic hydrocarbon (PAH) degradation profile of two bacteria, Planomicrobium sp. RNP01 and Rhodococcus sp. RNP05 were studied by three microtiter plate assays to reveal the combination of certain biological and biochemical characteristics which are reliable indicators in evaluation of bacterial biodegradation abilities. The three assays, which are hydrocarbon growth assay, 2,6-DCPIP assay and dehydrogenase activity assay revealed that Rhodococcus sp. RNP05 exhibited better potential for PAH degradation than Planomicrobium sp. RNP01. Differences between initial and final optical density and specific growth rate constants were significantly higher (r = 0.995, P < 0.05) in case of Rhodococcus sp. RNP05 on all tested substrates, as compared to Planomicrobium sp. RNP01. This was confirmed by GC-FID analyses. Dehydrogenase activity of Rhodococcus sp. RNP05 was higher (r = 0.9995, P < 0.05) than Planomicrobium sp. RNP01 and correlated positively with the hydrocarbon growth assay (r = 0.999, P < 0.05, for Rhodococcus sp. RNP05, r = 0.986, P < 0.05 for Planomicrobium sp. RNP01). This study has shown that the combination of these assays could be used for determining the bioremediation potential of PAHs in petroleum contaminated soil with the ability of screening a large number of bacterial strains.