Phytoremediation potential of an Antarctic microalga for subpolar and polar applications in diesel hydrocarbon cleanup

Amidst global carbon neutrality efforts, developing sustainable biological processes is essential. Algal-based technology offers CO2 sequestration benefits but faces efficiency challenges, especially in polar regions. Diesel pollution in Antarctica, primarily from fuel spills associated with research and logistics, threatens the delicate polar ecosystem due to its persistence. Despite the recognised heavy metal sorption capacities of microalgae, their potential for remediating organic compounds like diesel in polar regions remains largely unexplored. This study investigated the remediation potential of an Antarctic microalga for diesel hydrocarbons in both controlled laboratory settings and in-situ environments. The research workflow encompassed several key phases: identifying a microalgal strain capable of degrading diesel hydrocarbons, optimising growth conditions, evaluating algal physiological changes, analysing kinetic behaviours and ecotoxicology effects of diesel, and ultimately testing different diesel types under in-situ conditions at Southern Chile. An Antarctic microalga sampled from Greenwich Island in 2016 was discovered with diesel remediation capability. Through a polyphasic taxonomic approach, this microalga named as isolate WCY_AQ5_1 was identified as Tritostichococcus sp. (OQ225631), within the redefined Stichococcus clade. Under controlled conditions at 10°C under cool white fluorescent lamps (42 µmol m−2 s−1) on a 12:12-h light–dark cycle, diesel was introduced to the algal suspension, revealing adsorption onto the cell surface via Fourier transform infrared spectroscopy, with the result of biodegradation outweighed biosorption. Gas chromatographic analysis displayed differential uptake rates of n-alkanes (C7 to C25), with efficient metabolism of medium-length, particularly n-heneicosane (C21). Mixotrophic cultivation with diesel as the carbon source induced changes in the pigment composition and intracellular lipid droplets formation. Initial screening achieved a 37.5% mass degradation at 1% v/v diesel concentration. Thereafter, parametric optimisation using one￾factor-at-a-time followed by response surface methodology (RSM) increased biomass production by 3.7-fold and improved degradation efficiency to 55.0%. The optimal condition, predicted with 0.823 g/L NaNO3, 1.35 ppt salinity, pH 6.96 and 12:12 h L/D regime, enabled greater cell tolerance and continued biomass growth across diesel concentrations ranging 1% – 6% v/v. The highest degradation was recorded for 4% v/v diesel with 67.0% efficiency. Kinetic modelling indicated the Aiba-Edwards model best described degradation and growth, suggesting inhibition at higher concentrations. Furthermore, the oxidative stress response was observed with elevated intracellular reactive oxygen species (ROS) levels, suggesting ROS-mediated diesel degradation. Exposure to diesel induced enzymatic antioxidant activity (catalase) but also triggered lipid peroxidation. Suppression of photosynthetic pigments at higher diesel concentrations likely reflects an energy-balancing mechanism in response to diesel hydrocarbon catabolism. Further experiments with different diesel types from Southern Chile and Antarctica, both in controlled laboratory settings and subpolar in-situ environments showed that winter diesel under optimal conditions closely mirrored with RSM predictions. Meanwhile, a substantial abiotic loss of hydrocarbons was noted for the in-situ study, possibly from photooxidation, which also posed risks of photoinhibition in microalgae. Indoor cultivation under partially shaded sunlight proved most feasible, achieving 77.4% total hydrocarbons mass removal (7.05 mg/mL), attributable to phytoremediation and abiotic loss. This study signifies the first confirmation of diesel remediation ability in an Antarctic microalga, with promising implications for subpolar and polar regions.

Text 125110 - Full Text.pdf Download (5MB) Official URL or Download Paper: http://ethesis.upm.edu.my/id/eprint/18809

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