Biodegradation of Total Petroleum Hydrocarbons in Soil: Isolation and Characterization of Bacterial Strains from Oil Contaminated Soil

Resuscitation-promoting factors: Novel strategies for the bioremediation of crude oil-contaminated soils

Soil contamination with petroleum hydrocarbons is a major environmental concern. The bioremediation of these soils can be restricted because of the entry of potential microbial degraders into the viable but nonculturable (VBNC) state under unfavorable environmental conditions. Resuscitation agents can stimulate the resuscitation and growth of the bacterial population, improving their degradation capabilities. This study evaluated the efficacy of resuscitation-promoting factor (Rpf) in enhancing the biodegradation of total petroleum hydrocarbons (TPHs) in crude oil-contaminated soils, with a focus on both indigenous and augmented bacterial communities without prior resuscitation. Unlike earlier studies that focused solely on Rpf-treated populations, this study investigated the simultaneous application of Rpf and traditional biostimulation and bioaugmentation processes. Additionally, this work is the first to compare Rpf with other resuscitation agents, including supernatant Rpf (SRpf) and Micrococcus luteus. The results indicated that Rpf-supplemented biostimulation (BS + Rpf) and bioaugmentation (BAS + Rpf) processes achieved 67% and 75% degradation of 31,408 mg kg-1 TPHs within 91 days, respectively, whereas 49% and 64% degradation occured by the BS and BAS processes, respectively. Rpf stimulated the growth of bacterial populations, contributing to enhanced bioremediation of contaminated soil. Furthermore, phytotoxicity decreased with decreasing TPH concentration. These findings also demonstrated that, compared with Rpf, SRpf and M. luteus presented similar TPH removal efficiencies and seemed to be suitable alternatives to recombinant Rpf. These results provide novel insights into the activation of native bacteria by the application of resuscitation agents, demonstrating a promising approach for the bioremediation of crude oil-contaminated soils.

Revitalization of Soil Contaminated by Petroleum Products Using Materials That Improve the Physicochemical and Biochemical Properties of the Soil

One of the key challenges in environmental protection is the reclamation of soils degraded by organic pollutants. Effective revitalization of such soils can contribute to improving the climate and the quality of feed and food, mainly by eliminating harmful substances from the food chain and by cultivating plants for energy purposes. To this end, research was carried out using two sorbents, vermiculite and agrobasalt, to detoxify soils contaminated with diesel oil and unleaded gasoline, using maize as an energy crop. The research was carried out in a pot experiment. The level of soil contamination with petroleum products was set at 8 cm3 and 16 cm3 kg-1 d.m. of soil, and the dose of the revitalizing substances, i.e., vermiculite and agrobasalt, was set at 10 g kg-1 of soil. Their effect was compared with uncontaminated soil and soil without sorbents. The obtained research results prove that both diesel oil and gasoline disrupt the growth and development of Zea mays. Diesel oil destabilized plant development more than gasoline. Both products distorted the activity of soil oxidoreductases and hydrolases, with diesel oil stimulating and gasoline inhibiting. The applied sorbents proved to be useful in the soil revitalization process, as they reduced the negative effects of pollutants on Zea mays, increased the activity of soil enzymes, enhanced the value of the biochemical soil quality indicator (BA), and improved the cation exchange capacity (CEC), the sum of exchangeable base cations (EBC), pH, and the Corg content. Agrobasalt demonstrated a greater potential for improving soil physicochemical properties, inducing an average increase in CEC and EBC values of 12% and 23%, respectively, in soil under G pressure, and by 16% and 25% in DO-contaminated soil.

Biodegradation of benzo(a)pyrene by Pseudomonas strains, isolated from petroleum refinery effluent: Degradation, inhibition kinetics and metabolic pathway

Benzo(a)pyrene, a five-ring polyaromatic hydrocarbon, originating from coal tar, crude oil, tobacco, grilled foods, car exhaust etc, is highly persistent in the environment. It has been classified as a Group I carcinogen, as on its ingestion in human body, diol epoxide metabolites are generated, which bind to DNA causing mutations and eventual cancer. Among various removal methods, bioremediation is most preferred as it is a sustainable approach resulting in complete mineralization of benzo(a)pyrene. Therefore, in this study, biodegradation of benzo(a)pyrene was performed by two strains of Pseudomonas, i. e WDE11 and WD23, isolated from refinery effluent. Maximum benzo(a)pyrene tolerance was 250 mg/L and 225 mg/L against Pseudomonas sp. WD23 and Pseudomonas sp. WDE11 correspondingly. Degradation rate constants varied between 0.0468 and 0.0513/day at 50 mg/L with half-life values between 13.5 and 14.3 days as per first order kinetics, while for 100 mg/L, the respective values varied between 0.006 and 0.007 L/mg. day and 15.28-16.67 days, as per second order kinetics. The maximum specific growth rate of strains WDE11 and WD23 was 0.3512/day and 0.38/day accordingly, while concentrations over 75 mg/L had an inhibitory effect on growth. Major degradation metabolites were identified as dihydroxy-pyrene, naphthalene-1,2-dicarboxylic acid, salicylic acid, and oxalic acid, indicating benzo(a)pyrene was degraded via pyrene intermediates by salicylate pathway through catechol meta-cleavage. The substantial activity of the catechol 2,3 dioxygenase enzyme was noted during the benzo(a)pyrene metabolism by both strains with minimal catechol 1,2 dioxygenase activity. This study demonstrates the exceptional potential of indigenous Pseudomonas strains in complete metabolism of benzo(a)pyrene.

In situ bioremediation of petroleum hydrocarbon–contaminated soil: isolation and application of a Rhodococcus strain

Due to low consumption and high efficiency, in situ microbial remediation of petroleum hydrocarbons (PHs)-contaminated sites in in-service petrochemical enterprises has attracted more and more attention. In this study, a degrading strain was isolated from oil depot-contaminated soil with soil extract (PHs) as the sole carbon source, identified and named Rhodococcus sp. OBD-3. Strain OBD-3 exhibited wide adaptability and degradability over a wide range of temperatures (15-37 °C), pH (6.0-9.0), and salinities (1-7% NaCl) to degrade 60.6-86.6% of PHs. Under extreme conditions (15 °C and 3-7% salinity), PHs were degraded by 60.6 ± 8.2% and more than 82.1% respectively. In OBD-3, the alkane monooxygenase genes alkB1 and alkB2 (GenBank accession numbers: MZ688386 and MZ688387) were found, which belonged to Rhodococcus by sequence alignment. Moreover, strain OBD-3 was used in lab scale remediation in which the contaminated soil with OBD-3 was isolated as the remediation object. The PHs were removed at 2,809 ± 597 mg/kg within 2 months, and the relative abundances of Sphingobium and Pseudomonas in soil increased more than fivefold. This study not only established a system for the isolation and identification of indigenous degrading strains that could efficiently degrade pollutants in the isolated environment but also enabled the isolated degrading strains to have potential application prospects in the in situ bioremediation of PHs-contaminated soils.

Microbial Resources, Fermentation and Reduction of Negative Externalities in Food Systems: Patterns toward Sustainability and Resilience

One of the main targets of sustainable development is the reduction of environmental, social, and economic negative externalities associated with the production of foods and beverages. Those externalities occur at different stages of food chains, from the farm to the fork, with deleterious impacts to different extents. Increasing evidence testifies to the potential of microbial-based solutions and fermentative processes as mitigating strategies to reduce negative externalities in food systems. In several cases, innovative solutions might find in situ applications from the farm to the fork, including advances in food matrices by means of tailored fermentative processes. This viewpoint recalls the attention on microbial biotechnologies as a field of bioeconomy and of ‘green’ innovations to improve sustainability and resilience of agri-food systems alleviating environmental, economic, and social undesired externalities. We argue that food scientists could systematically consider the potential of microbes as ‘mitigating agents’ in all research and development activities dealing with fermentation and microbial-based biotechnologies in the agri-food sector. This aims to conciliate process and product innovations with a development respectful of future generations’ needs and with the aptitude of the systems to overcome global challenges.

Poly-γ-glutamic acid bioproduct improves the coastal saline soil mainly by assisting nitrogen conservation during salt-leaching process

Salt-leaching is considered to be a major method for soil desalting in agriculture. Therefore, conservation of soil nutrition is significant to soil fertility and environment protection during the salt-leaching process. The effect of poly-γ-glutamic acid bioproduct (PGAB), which was manufactured by solid-state fermentation with the bacteria producing glutamic acid (GA) and poly-γ-glutamic acid (γ-PGA) and organic waste, on keeping nitrogen (N) during salt-leaching was investigated in this study. The isolated bacteria producing GA and γ-PGA were identified as Brevibacterium flavum and Bacillus amyloliquefaciens, respectively. After the saline soil was leached for 90 days, compared to the control, soil salinity (0-30 cm) in the PGAB treatment was decreased by 39.9%, while soil total N was significantly (P < 0.05) higher than other treatments. Furthermore, the microbial biomass N (0-30 cm) in PGAB treatment was increased by 119.5%; populations of soil total bacteria, fungi, actinomyces, nitrogen-fixing bacteria, ammonifying bacteria, nitrifying bacteria, and denitrifying bacteria and soil algae biomass were also significantly (P < 0.05) increased. In terms of physical properties, the percentage of soil aggregates with diameter > 0.25 mm was increased by 293.5%, and the soil erosion-resistance coefficient was increased by 50.0%. In conclusion, the PGAB can effectively conserve soil N during the process of salt-leaching and therefore offer a sustainable way to improve coastal saline soil.