Optimisation of cold-adapted Antarctic bacteria for diesel bioremediation under low-temperature conditions and heavy metal stress

Bacterial bioremediation represents a sustainable approach for managing diesel pollutions in Antarctica. Recent Antarctic isolation studies have focused on biodegradation at temperatures above 20°C, which is higher than the Antarctic summer temperature. Nevertheless, the potential of cold-adapted bacteria in low-temperature bioremediation have been reported in previous research. This pollution is also exacerbated by the presence of heavy metal traces, which inhibit bacterial biodegradation. Therefore, there is a significant gap in research to assess the potential of cold-adapted bacteria from Antarctica for diesel degradation and heavy metal stress tolerance at low temperatures. This study endeavoured to harness the potential of cold-adapted bacteria from the terrestrial environment of Antarctica that degrade diesel, produce biosurfactant and tolerate heavy metals at temperatures of 10°C. A total of 19 Antarctic soil samples were assessed for the potential to degrade diesel at 10°C with the best-degrading consortium, SI 20, was selected for subsequent isolation and characterisation. Fifteen efficient diesel-degrading strains (1.9-4.2 mg/mL) were identified and classified as strains AQ5-29 to AQ5-43. All strains were morphologically characterised as Gram-negative, motile, rod-shaped, catalase-, and oxidase-positive bacteria. Sequencing of the 16S rRNA gene Identified strains AQ5-35 to AQ5-41 as Pseudomonas fildesensis, while the concatenated recA-gyrB-rpoB-tpiA-16S rRNA nucleotide sequences in multilocus sequence analysis further differentiated the other six strains as Janthinobacterium lividium. Janthinobacterium lividum AQ5-29 and P. fildesensis AQ5-41 were the most effective degraders of the strains examined and exhibited potential as biosurfactant producers, evidenced by positive reactions in oil displacement (clear zone) and oil drop tests (flattened droplet), and assessment of microbial adhesion to hydrocarbon (32-92%) and emulsification index (54-58%). Physiochemical factors potentially impacting total petroleum hydrocarbon (TPH) removal of the most effective candidate (strain AQ5-29) were optimised using a combination of one-factor-at-a-time analysis and statistical response-surface methodology. The predicted optimal model conditions were pH 7.05, 0% w/v salinity, 10°C, 1.49 g/L NH4Cl, 5.67% v/v initial diesel concentration and 14.10% v/v inoculum size, leading to TH removal of 20.57 ₺ 0.90 mg/mL after a 7-d incubation. Multiple secondary kinetic regressions were also selected for kinetic analyses. The Aiba-Edwards model was the mathematically best fitting model for the growth pattern of strain AQ5-29 in diesel-enriched medium, with a maximum specific growth rate (Umax) of 0.341 h. Additionally, the effects of parallel exposure to 10 heavy metals (at 1 ppm concentration) on diesel biodegradation by the strain was evaluated. Silver and chromium had the strongest inhibitory effects on strain AQ5-29, with respective half-maximal inhibition concentrations (IC50) of 0.36 and 0.65 ppm. Conversely, a higher cobalt concentration was required to effectively reduce the strain's effectiveness, with a half-maximal effective concentration (EC50) of 5.41 ppm. The remarkable capabilities of J. lividum AQ5-29, including its ability to degrade diverse diesel concentrations at 10°C, potential for biosurfactant production and tolerance of exposure to heavy metals, collectively highlight its suitability for further considerations in the development of effective bioremediation processes in Antarctica.

Text 125119 - Full Text.pdf Download (106MB) Official URL or Download Paper: http://ethesis.upm.edu.my/id/eprint/18813

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