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

Abstract

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.

Keywords: Antarctica; biodegradation; diesel; microbial consortium; seawater.

Figure 1

Screening of bacterial consortia growth and diesel degradation obtained from Antarctic seawater samples collected in (a) 2017/18 and (b) 2018/19; all consortia grown in BH media, supplemented with 20 ppt NaCl and 1.0% initial diesel concentration as sole carbon source. Vertical bars indicate SEM of three replicates.

Figure 1

Screening of bacterial consortia growth and diesel degradation obtained from Antarctic seawater samples collected in (a) 2017/18 and (b) 2018/19; all consortia grown in BH media, supplemented with 20 ppt NaCl and 1.0% initial diesel concentration as sole carbon source. Vertical bars indicate SEM of three replicates.

Figure 2

Aerial photograph showing source location of selected consortium sample. (Source: Google.com).

Figure 3

Effect of (a) varying pH (using two buffer systems), (b) salinity (% w/v) and (c) temperature on bacterial consortium growth and diesel degradation. Vertical bars indicate SEM of three replicates.

Figure 3

Effect of (a) varying pH (using two buffer systems), (b) salinity (% w/v) and (c) temperature on bacterial consortium growth and diesel degradation. Vertical bars indicate SEM of three replicates.

Figure 4

Effects of (a) different nitrogen sources and (b) of the selected nitrogen source concentration on bacterial consortium growth and diesel degradation. Vertical bars indicate SEM of three replicates.

Figure 4

Effects of (a) different nitrogen sources and (b) of the selected nitrogen source concentration on bacterial consortium growth and diesel degradation. Vertical bars indicate SEM of three replicates.

Figure 5

Effects of initial diesel concentration (v/v) on bacterial consortium o2b growth and diesel degradation. Vertical bars indicate SEM of three replicates.

Figure 6

3D Contour plots generated by Design Expert (Stat Ease, Inc) of the significantly interacting model terms (a) A: salinity and C: NH₃NO₄ concentration, (b) B: temperature and C: NH₃NO₄ concentration, (c) B: temperature and D: diesel concentration.

Figure 6

3D Contour plots generated by Design Expert (Stat Ease, Inc) of the significantly interacting model terms (a) A: salinity and C: NH₃NO₄ concentration, (b) B: temperature and C: NH₃NO₄ concentration, (c) B: temperature and D: diesel concentration.