Statistical Optimisation of Diesel Biodegradation at Low Temperatures by an Antarctic Marine Bacterial Consortium Isolated from Non-Contaminated Seawater

Hydrocarbon pollution is widespread around the globe and, even in the remoteness of Antarctica, the impacts of hydrocarbons from anthropogenic sources are still apparent. Antarctica’s chronically cold temperatures and other extreme environmental conditions reduce the rates of biological processes, including the biodegradation of pollutants. However, the native Antarctic microbial diversity provides a reservoir of cold-adapted microorganisms, some of which have the potential for biodegradation. This study evaluated the diesel hydrocarbon-degrading ability of a psychrotolerant marine bacterial consortium obtained from the coast of the north-west Antarctic Peninsula. The consortium’s growth conditions were optimised using one-factor-at-a-time (OFAT) and statistical response surface methodology (RSM), which identified optimal growth conditions of pH 8.0, 10 °C, 25 ppt NaCl and 1.5 g/L NH4NO3. The predicted model was highly significant and confirmed that the parameters’ salinity, temperature, nitrogen concentration and initial diesel concentration significantly influenced diesel biodegradation. Using the optimised values generated by RSM, a mass reduction of 12.23 mg/mL from the initial 30.518 mg/mL (4% (w/v)) concentration of diesel was achieved within a 6 d incubation period. This study provides further evidence for the presence of native hydrocarbon-degrading bacteria in non-contaminated Antarctic seawater.

Growth Optimisation and Kinetic Profiling of Diesel Biodegradation by a Cold-Adapted Microbial Consortium Isolated from Trinity Peninsula, Antarctica

Pollution associated with petrogenic hydrocarbons is increasing in Antarctica due to a combination of increasing human activity and the continent’s unforgiving environmental conditions. The current study focuses on the ability of a cold-adapted crude microbial consortium (BS24), isolated from soil on the north-west Antarctic Peninsula, to metabolise diesel fuel as the sole carbon source in a shake-flask setting. Factors expected to influence the efficiency of diesel biodegradation, namely temperature, initial diesel concentration, nitrogen source type and concentration, salinity and pH were studied. Consortium BS24 displayed optimal cell growth and diesel degradation activity at 1.0% NaCl, pH 7.5, 0.5 g/L NH4Cl and 2.0% v/v initial diesel concentration during one-factor-at-a-time (OFAT) analyses. The consortium was psychrotolerant based on the optimum growth temperature of 10‒15 °C. In conventionally optimised media, the highest total petroleum hydrocarbons (TPH) mineralisation was 85% over a 7-day incubation. Further optimisation of conditions predicted through statistical response-surface methodology (RSM) (1.0% NaCl, pH 7.25, 0.75 g/L NH4Cl, 12.5 °C and 1.75% v/v initial diesel concentration) boosted mineralisation to 95% over a 7-day incubation. A Tessier secondary model best described the growth pattern of BS24 in diesel-enriched medium, with maximum specific growth rate, μmax, substrate inhibition constant, Ki and half saturation constant, Ks, being 0.9996 h−1, 1.356% v/v and 1.238% v/v, respectively. The data obtained suggest the potential of microbial consortia such as BS24 in bioremediation applications in low-temperature diesel-polluted soils.

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.

Bioremediation of Artificial Diesel-Contaminated Soil Using Bacterial Consortium Immobilized to Plasma-Pretreated Wood Waste

Bioaugmentation is a bioremediation option based on increasing the natural in-situ microbial population that possesses the ability to degrade the contaminating pollutant. In this study, a diesel-degrading consortium was obtained from an oil-contaminated soil. The diesel-degrading consortium was grown on wood waste that was plasma-pretreated. This plasma treatment led to an increase of bacterial attachment and diesel degradation rates. On the 7th day the biofilm viability on the plasma-treated wood waste reached 0.53 ± 0.02 OD 540 nm, compared to the non-treated wood waste which was only 0.34 ± 0.02. Biofilm attached to plasma-treated and untreated wood waste which was inoculated into artificially diesel-contaminated soil (0.15% g/g) achieved a degradation rate of 9.3 mg day−1 and 7.8 mg day−1, respectively. While, in the soil that was inoculated with planktonic bacteria, degradation was only 5.7 mg day−1. Exposing the soil sample to high temperature (50 °C) or to different soil acidity did not influence the degradation rate of the biofilm attached to the plasma-treated wood waste. The two most abundant bacterial distributions at the family level were Xanthomonadaceae and Sphingomonadaceae. To our knowledge, this is the first study that showed the advantages of biofilm attached to plasma-pretreated wood waste for diesel biodegradation in soil.

Enhancement of Surfactin and Fengycin Production byBacillus mojavensisA21: Application for Diesel Biodegradation

This work concerns the study of the enhancement of surfactin and fengycin production byB. mojavensisA21 and application of the produced product in diesel biodegradation. The influences of the culture medium and cells immobilization were studied. The highest lipopeptides production was achieved after 72 hours of incubation in a culture medium containing 30 g/L glucose as carbon source and a combination of yeast extract (1 g/L) and glutamic acid (5 g/L) as nitrogen sources with initial pH 7.0 at 30°C and 90% volumetric aeration. The study of primary metabolites production showed mainly the production of acetoin, with a maximum production after 24 h of strain growth. The use of immobilized cells seemed to be a promising method for improving lipopeptides productivity. In fact, the synthesis of both lipopeptides, mainly fengycin, was greatly enhanced by the immobilization of A21 cells. An increase of diesel degradation capacity of approximately 20, 27, and 40% in the presence of 0.5, 1, and 2 g/L of produced lipopeptides, respectively, was observed. Considering these properties,B. mojavensisA21 strain producing a lipopeptide mixture, containing both surfactin and fengycin, may be considered as a potential candidate for future use in bioremediation and crop protection.