Response surface methodology optimisation and kinetics of diesel degradation by a cold-adapted Antarctic bacterium, Arthrobacter sp. strain AQ5-05

Petroleum hydrocarbons, notably diesel oil, are the main energy source for running amenities in the Antarctic region and are the major cause of pollution in this area. Diesel oil spills are one of the major challenges facing management of the Antarctic environment. Bioremediation using bacteria can be an effective and eco-friendly approach for their remediation. However, since the introduction of non-native organisms, including microorganisms, into the Antarctic or between the distinct biogeographical regions within the continent is not permitted under the Antarctic Treaty, it is crucial to discover native oil-degrading, psychrotolerant microorganisms that can be used in diesel bioremediation. The primary aim of the current study is to optimize the conditions for growth and diesel degradation activity of an Antarctic local bacterium, Arthrobacter sp. strain AQ5-05, using the Plackett-Burman approach and response surface method (RSM) via a central composite design (CCD) approach. Based on this approach, temperature, pH, and salinity were calculated to be optimum at 16.30 °C, pH 7.67 and 1.12% (w/v), respectively. A second order polynomial regression model very accurately represented the experimental figures’ interpretation. These optimized environmental conditions increased diesel degradation from 34.5% (at 10 °C, pH 7.00 and 1.00% (w/v) salinity) to 56.4%. Further investigation of the kinetics of diesel reduction by strain AQ5-05 revealed that the Teissier model had the lowest RMSE and AICC values. The calculated values for the Teissier constants of maximal growth rate, half-saturation rate constant for the maximal growth, and half inhibition constants (μmax, Ks, and Ki), were 0.999 h−1, 1.971% (v/v) and 1.764% (v/v), respectively. The data obtained therefore confirmed the potential application of this cold-tolerant strain in the bioremediation of diesel-contaminated Antarctic soils at low temperature

Optimisation of biodegradation conditions for waste canola oil by cold-adapted Rhodococcus sp. AQ5-07 from Antarctica

Background: The potential waste canola oil-degrading ability of the cold-adapted Antarctic bacterial strain Rhodococcus sp. AQ5-07 was evaluated. Globally, increasing waste from food industries generates serious anthropogenic environmental risks that can threaten terrestrial and aquatic organisms and communities. The removal of oils such as canola oil from the environment and wastewater using biological approaches is desirable as the thermal process of oil degradation is expensive and ineffective. Results: Rhodococcus sp. AQ5-07 was found to have high canola oil-degrading ability. Physico-cultural conditions influencing its activity were studied using one-factor-at-a-time (OFAT) and statistical optimisation approaches. Considerable degradation (78.60%) of 3% oil was achieved by this bacterium when incubated with 1.0 g/L ammonium sulphate, 0.3 g/L yeast extract, pH 7.5 and 10% inoculum at 10°C over a 72-h incubation period. Optimisation of the medium conditions using response surface methodology (RSM) resulted in a 9.01% increase in oil degradation (87.61%) when supplemented with 3.5% canola oil, 1.05 g/L ammonium sulphate, 0.28g/L yeast extract, pH 7.5 and 10% inoculum at 12.5°C over the same incubation period. The bacterium was able to tolerate an oil concentration of up to 4.0%, after which decreased bacterial growth and oil degradation were observed. Conclusions: These features make this strain worthy of examination for practical bioremediation of lipid-rich contaminated sites. This is the first report of any waste catering oil degradation by bacteria originating from Antarctica

Biosurfactant production and growth kinetics studies of the waste canola oil-degrading bacterium Rhodococcus erythropolis AQ5-07 from Antarctica

With the progressive increase in human activities in the Antarctic region, the possibility of domestic oil spillage also increases. Developing means for the removal of oils, such as canola oil, from the environment and waste “grey” water using biological approaches is therefore desirable, since the thermal process of oil degradation is expensive and ineffective. Thus, in this study an indigenous cold-adapted Antarctic soil bacterium, Rhodococcus erythropolis strain AQ5-07, was screened for biosurfactant production ability using the multiple approaches of blood haemolysis, surface tension, emulsification index, oil spreading, drop collapse and “MATH” assay for cellular hydrophobicity. The growth kinetics of the bacterium containing different canola oil concentration was studied. The strain showed β-haemolysis on blood agar with a high emulsification index and low surface tension value of 91.5% and 25.14 mN/m, respectively. Of the models tested, the Haldane model provided the best description of the growth kinetics, although several models were similar in performance. Parameters obtained from the modelling were the maximum specific growth rate (qmax), concentration of substrate at the half maximum specific growth rate, Ks% (v/v) and the inhibition constant Ki% (v/v), with values of 0.142 h−1, 7.743% (v/v) and 0.399% (v/v), respectively. These biological coefficients are useful in predicting growth conditions for batch studies, and also relevant to “in field” bioremediation strategies where the concentration of oil might need to be diluted to non-toxic levels prior to remediation. Biosurfactants can also have application in enhanced oil recovery (EOR) under different environmental conditions

Diesel in Antarctica and a bibliometric study on its indigenous microorganisms as remediation agent

Diesel acts as a main energy source to complement human activities in Antarctica. However, the increased expedition in Antarctica has threatened the environment as well as its living organisms. While more efforts on the use of renewable energy are being done, most activities in Antarctica still depend heavily on the use of diesel. Diesel contaminants in their natural state are known to be persistent, complex and toxic. The low temperature in Antarctica worsens these issues, making pollutants more significantly toxic to their environment and indigenous organisms. A bibliometric analysis had demonstrated a gradual increase in the number of studies on the microbial hydrocarbon remediation in Antarctica over the year. It was also found that these studies were dominated by those that used bacteria as remediating agents, whereas very little focus was given on fungi and microalgae. This review presents a summary of the collective and past understanding to the current findings of Antarctic microbial enzymatic degradation of hydrocarbons as well as its genotypic adaptation to the extreme low temperature

Scientometric analysis of diesel pollutions in Antarctic Territories: a review of causes and potential bioremediation approaches

Despite the continuous enforcement of Antarctic Treaty System, ATS (1961), today Antarctica is constantly plagued by hydrocarbon pollution from both legacy and present-day wastes, especially near where anthropogenic activities are the most intense. The advances of science have led to multiple breakthroughs to bolster bioremediation techniques and revamp existing laws that prevent or limit the extent of hydrocarbon pollution in Antarctica. This review serves as the extension of collective efforts by the Antarctic communities through visual representation that summarizes decades of findings (circa 2000–2020) from various fields, pertinent to the application of microbe-mediated hydrocarbons remediation. A scientometric analysis was carried out based on indexed, scientific repositories (ScienceDirect and Scopus), encompassing various parameters, including but not limited to keywords co-occurrences, contributing countries, trends and current breakthroughs in polar research. The emergence of keywords such as bioremediation, biosurfactants, petroleum hydrocarbons, biodiesel, metagenomics and Antarctic treaty policy portrays the dynamic shifts in Antarctic affairs during the last decades, which initially focused on exploration and resources exploitation before switching to scientific research and the more recent ecotourism. This review also presents the hydrocarbonoclastic microbes studied in the past, known and proposed metabolic pathways and genes related to hydrocarbon biodegradation as well as bacterial adaptations to low-temperature condition

Evaluation of heavy metal tolerance level of the Antarctic bacterial community in biodegradation of waste canola oil

Heavy metal contamination is accidentally becoming prevalent in Antarctica, one of the world’s most pristine regions. Anthropogenic as well as natural causes can result in heavy metal contamination. Each heavy metal has a different toxic effect on various microorganisms and species, which can interfere with other pollutant bioremediation processes. This study focused on the effect of co-contaminant heavy metals on waste canola oil (WCO) biodegradation by the BS14 bacterial community collected from Antarctic soil. The toxicity of different heavy metals in 1 ppm of concentration to the WCO-degrading bacteria was evaluated and further analyzed using half maximal inhibition concentration (IC50) and effective concentration (EC50) tests. The results obtained indicated that Ag and Hg significantly impeded bacterial growth and degradation of WCO, while interestingly, Cr, As, and Pb had the opposite effect. Meanwhile, Cd, Al, Zn, Ni, Co, and Cu only slightly inhibited the bacterial community in WCO biodegradation. The IC50 values of Ag and Hg for WCO degradation were found to be 0.47 and 0.54 ppm, respectively. Meanwhile, Cr, As, and Pb were well-tolerated and induced bacterial growth and WCO degradation, resulting in the EC50 values of 3.00, 23.80, and 28.98 ppm, respectively. The ability of the BS14 community to tolerate heavy metals while biodegrading WCO in low-temperature conditions was successfully confirmed, which is a crucial aspect in biodegrading oil due to the co-contamination of oil and heavy metals that can occur simultaneously, and at the same time it can be applied in heavy metal-contaminated areas

The use of response surface methodology as a statistical tool for the optimisation of waste and pure canola oil biodegradation by Antarctic soil bacteria

Hydrocarbons can cause pollution to Antarctic terrestrial and aquatic ecosystems, both through accidental release and the discharge of waste cooking oil in grey water. Such pollutants can persist for long periods in cold environments. The native microbial community may play a role in their biodegradation. In this study, using mixed native Antarctic bacterial communities, several environmental factors influencing biodegradation of waste canola oil (WCO) and pure canola oil (PCO) were optimised using established one-factor-at-a-time (OFAT) and response surface methodology (RSM) approaches. The factors include salinity, pH, type of nitrogen and concentration, temperature, yeast extract and initial substrate concentration in OFAT and only the significant factors proceeded for the statistical optimisation through RSM. High concentration of substrate targeted for degradation activity through RSM compared to OFAT method. As for the result, all factors were significant in PBD, while only 4 factors were significant in biodegradation of PCO (pH, nitrogen concentration, yeast extract and initial substrate concentration). Using OFAT, the most effective microbial community examined was able to degrade 94.42% and 86.83% (from an initial concentration of 0.5% (v/v)) of WCO and PCO, respectively, within 7 days. Using RSM, 94.99% and 79.77% degradation of WCO and PCO was achieved in 6 days. The significant interaction for the RSM in biodegradation activity between temperature and WCO concentration in WCO media were exhibited. Meanwhile, in biodegradation of PCO the significant factors were between (1) pH and PCO concentration, (2) nitrogen concentration and yeast extract, (3) nitrogen concentration and PCO concentration. The models for the RSM were validated for both WCO and PCO media and it showed no significant difference between experimental and predicted values. The efficiency of canola oil biodegradation achieved in this study provides support for the development of practical strategies for efficient bioremediation in the Antarctic environment

Statistical optimisation and kinetic studies of molybdenum reduction using a psychrotolerant marine bacteria isolated from Antarctica

The extensive industrial use of the heavy metal molybdenum (Mo) has led to an emerging global pollution with its traces that can even be found in Antarctica. In response, a reduction process that transforms hexamolybdate (Mo6+) to a less toxic compound, Mo-blue, using microorganisms provides a sustainable remediation approach. The aim of this study was to investigate the reduction of Mo by a psychrotolerant Antarctic marine bacterium, Marinomonas sp. strain AQ5-A9. Mo reduction was optimised using One-Factor-At-a-Time (OFAT) and Response Surface Methodology (RSM). Subsequently, Mo reduction kinetics were further studied. OFAT results showed that maximum Mo reduction occurred in culture media conditions of pH 6.0 and 50 ppt salinity at 15 °C, with initial sucrose, nitrogen and molybdate concentrations of 2.0%, 3.0 g/L and 10 mM, respectively. Further optimization using RSM identified improved optimum conditions of pH 6.0 and 47 ppt salinity at 16 °C, with initial sucrose, nitrogen and molybdate concentrations of 1.8%, 2.25 g/L and 16 mM, respectively. Investigation of the kinetics of Mo reduction revealed Aiba as the best-fitting model. The calculated Aiba coefficient of maximum Mo reduction rate (µmax) was 0.067 h−1. The data obtained support the potential use of marine bacteria in the bioremediation of Mo

Statistical assessment of phenol biodegradation by a metal-tolerant binary consortium of indigenous Antarctic bacteria

Since the heroic age of Antarctic exploration, the continent has been pressurized by multiple anthropogenic activities, today including research and tourism, which have led to the emergence of phenol pollution. Natural attenuation rates are very slow in this region due to the harsh environmental conditions; hence, biodegradation of phenol using native bacterial strains is recognized as a sustainable remediation approach. The aim of this study was to analyze the effectiveness of phenol degradation by a binary consortium of Antarctic soil bacteria, Arthrobacter sp. strain AQ5-06, and Arthrobacter sp. strain AQ5-15. Phenol degradation by this co-culture was statistically optimized using response surface methodology (RSM) and tolerance of exposure to different heavy metals was investigated under optimized conditions. Analysis of variance of central composite design (CCD) identified temperature as the most significant factor that affects phenol degradation by this consortium, with the optimum temperature ranging from 12.50 to 13.75 °C. This co-culture was able to degrade up to 1.7 g/L of phenol within seven days and tolerated phenol concentration as high as 1.9 g/L. Investigation of heavy metal tolerance revealed phenol biodegradation by this co-culture was completed in the presence of arsenic (As), aluminum (Al), copper (Cu), zinc (Zn), lead (Pb), cobalt (Co), chromium (Cr), and nickel (Ni) at concentrations of 1.0 ppm, but was inhibited by cadmium (Cd), silver (Ag), and mercury (Hg)

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