Functional Gene Diversity of Selected Indigenous Hydrocarbon-Degrading Bacteria in Aged Crude Oil

A comparative assesment of biostimulants in microbiome-based ecorestoration of polycyclic aromatic hydrocarbon polluted soil

Polycyclic aromatic hydrocarbons (PAHs) pose severe environmental and public health risks due to their harmful and persistent nature. Therefore, developing sustainable and effective methods for PAH remediation is crucial. This study explores the biostimulation potential of various nutrient supplements in enhancing the metabolic activities of indigenous oleophilic bacteria to PAH degradation and removal. The physicochemical and microbiological characterization of the soil sample obtained from the aged crude oil spill site prior to bioremediation revealed the presence of PAH and other hydrocarbons, reduced nutrient availability as well as an appreciable population of PAH degrading bacteria such as strains of Pseudomonas, Enterobacter, Kosakonia and Staphylococcus. The polluted soil treatment was conducted in six microcosms representing each nutrient supplement: casmes-CM, cocodust-CCD and osmocote-OSM slow-release fertilizers, NPK 20:10:10, casmes + cow dung - CM + CD and a control (unamended soil). Each pot contained 4 kg of soil spiked with 4% Escravos crude oil to a final concentration of 989 mg/kg of PAH, respectively. All treatments enhanced the activity of the indigenous bacteria to promote PAH removal (> 50%) after 35 days although CM + CD had the highest biostimulation effect (B. E.) of 56% with 71.77% PAH attenuation followed by NPK treatment with B. E. of 54.9% and 70.4% PAH removal, respectively. The order of degradation of PAHs from lowest to highest is: control > casmes > osmocote > cocodust > NPK > CM + CD. First-order kinetic model revealed soil microcosm amended with CM + CD had a higher k value (0.0342 day-1) and lower t½ (18.48 day) and this was relatively followed by NPK treated soil. Biostimulation is an effective bioremediation approach to PAH degradation, however, a combined nutrient regimen in the presence of PAH-degrading microbes is more potent and eco-friendly in driving this process.

Characterization the microbial diversity and functional genes in the multi-component contaminated groundwater in a petrochemical site

Microorganisms in groundwater at petroleum hydrocarbon (PHC)-contaminated sites are crucial for PHC natural attenuation. Studies mainly focused on the microbial communities and functions in groundwater contaminated by PHC only. However, due to diverse raw and auxiliary materials and the complex production processes, in some petrochemical sites, groundwater suffered multi-component contamination, but the microbial structure remains unclear. To solve the problem, in the study, a petrochemical enterprise site, where the groundwater suffered multi-component pollution by PHC and sulfates, was selected. Using hydrochemistry, 16S rRNA gene, and metagenomic sequencing analyses, the relationships among electron acceptors, microbial diversity, functional genes, and their interactions were investigated. Results showed that different production processes led to different microbial structures. Overall, pollution reduced species richness but increased the abundance of specific species. The multi-component contamination multiplied a considerable number of hydrocarbon-degrading and sulfate-reducing microorganisms, and the introduced sulfates might have promoted the biodegradation of PHC. PRACTITIONER POINTS: The compound pollution of the site changed the microbial community structure. Sulfate can promote the degradation of petroleum hydrocarbons by hydrocarbon-degrading microorganisms. The combined contamination of petroleum hydrocarbons and sulfates will decrease the species richness but increase the abundance of endemic species.

Whole genome analysis of Flavobacterium aziz-sancarii sp. nov., isolated from Ardley Island (Antarctica), revealed a rich resistome and bioremediation potential

Despite being one of the most isolated regions in the world, Antarctica is at risk of increased contamination with potentially toxic elements and other toxic chemicals through anthropogenic interventions. In this study, a psychrotolerant bacterium was isolated using the lake water collected from Ardley Island (Antarctica), which can grow at temperatures between 4 and 30 °C and pH values between 6.0 and 9.0. The isolate, named AC, had protease, amylase, and lipase activities with no NaCl tolerance and could degrade 1-5% diesel fuel. Multilocus sequence analysis (MLSA) using 16S rRNA, gyrB, tuf, and rpoD genes resulted in 92.91-98.6% sequence similarities between the isolate AC and other Flavobacterium spp. Whole genome analysis indicated that the genome length of Flavobacterium sp. AC is 5.8 Mbp with a GC content of 34.04% and 1274 genes predicted. The strain AC branched independently from other Flavobacterium spp. in the phylogenetic and phylogenomic trees and ranked a new species named Flavobacterium aziz-sancarii. Genome mining identified several cold-inducible genes, including stress-associated genes such as cold-shock proteins, chaperones, carotenoid biosynthetic genes, or oxidative-stress response genes. In addition, virulence, gliding motility, and biofilm-related genes were determined. Its genome contains 35 and 88 open-reading frames related to potentially toxic element and antibiotic resistance, respectively. F. aziz-sancarii showed a remarkable tolerance of Cr and Ni, with minimal inhibitory concentration values of 2.88 and 2.81 mM, respectively. Pb, Cu, and Zn exposure resulted in moderate toxicity (2.14-2.41 mM), while Cd showed the highest inhibitory effect in bacterial growth (0.74 mM). Antibiotic susceptibility testing indicated multidrug-resistant phenotype in correlation to in silico prediction of antibiotic resistance genes. Overall, our results contribute to biodiversity of Antarctica and provide new insights into resistome profile of Antarctic microorganisms. Additionally, the diesel degradation feature of F. aziz-sancarii offers potential use for the bioremediation of hydrocarbon-contaminated polar ecosystems.

Dynamic changes in the microbial community in the surface seawater of Jiaozhou Bay after crude oil spills: An in situ microcosm study

The changes in the composition and structure of microbial communities in Jiaozhou Bay are strongly affected by marine oil pollution, but the outcomes of the microbial responses and effects of dispersant application remain unclear. Herein, we performed an in situ microcosm study to investigate the response of the indigenous microbial community under crude oil alone and combined oil and dispersant treatment in the surface seawater of a semi-enclosed marine area of Jiaozhou Bay. The dynamics of the bacterial classification based on 16s rDNA sequencing were used to assess the changes with the crude oil concentration, dispersant use, and time. The crude oil resulted in a high abundance of the genera Pseudohongiella, Cycloclasticus, Marivita, and C1-B045 from the Gammaproteobacteria and Alphaproteobacteria classes, suggesting for hydrocarbon degradation. However, the dispersant treatment was more advantageous for Pacificibacter, Marivita, and Loktanella. Besides accelerating the rate of bacterial community succession, the dispersants had significantly stronger effects on the structure of the bacterial community and the degradation functions than the oil. A higher dose of oil exposure corresponded to fewer dominant species with a high relative abundance. Our study provides information for screening potential degradation bacteria and assessing the risks that oil spills pose to marine ecosystems.

Microbiome profile of soil and rhizosphere plants growing in traditional oil mining land in Wonocolo, Bojonegoro, Indonesia

Traditional oil mining poses negative effects on the environment through pollution with crude oil. One of the traditional mining sites in Wonocolo, Bojonegoro, Indonesia was reported to contaminate the surrounding area with a high level of crude oil. Therefore, this study aims to examine the microbiome profiles of contaminated soil and the rhizosphere of naturalized plants growing at the sites. It was conducted in Wonocolo, Bojonegoro to obtain an insight into the possible remediation efforts of using indigenous hydrocarbon-degrading bacteria and naturalized plants as in situ remediation agents. The results showed that the soil located close to the oil well-contained a high level of crude oil at 24.8%, and exhibited a distinct microbiome profile compared to those located further which had lower crude oil contamination of 14.15, 10.89, and 4.9%. Soil with the highest level of crude oil contamination had a comparatively higher relative abundance of assA, an anaerobic alkene-degrading gene. Meanwhile, the rhizosphere of the two naturalized plants, Muntingia calabura, and Pennisetum purpureum, exhibited indifferent microbiome profiles compared to the soil. They were found to contain less abundant hydrocarbon-degrading genes, such as C230, PAH-RHD-GP, nahAc, assA, and alkB suggesting that these naturalized plants might not be a suitable tool for in-situ remediation.

Bacterial communities of the Black Sea exhibit activity against persistent organic pollutants in the water column and sediments

The ability of bacteria to degrade organic pollutants influences their fate in the environment, impact on the other biota and accumulation in the food web. The aim of this study was to evaluate abundance and expression activity of the catabolic genes targeting widespread pollutants, such as polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and hexachloro-cyclohexane (HCH) in the Black Sea water column and sediments. Concentrations of PAHs, PCBs and HCH were determined by gas chromatography (GC) coupled to mass spectrometry (MS) and electron capture (ECD) detectors. bphA1, PAH-RHDα, nahAc, linA and linB that encode biphenyl 2,3 dioxygenase, α-subunits of ring hydroxylating dioxygenases, naphthalene dioxygenase, dehydrochlorinase and halidohydrolase correspondently were quantified by quantitative PCR. More recalcitrant PAHs, PCBs and HCH tended to accumulate in the Black Sea environments. In water samples, 3- and 4-ringed PAHs outnumbered naphthalene, while PAHs with > 4 rings prevailed in the sediments. Congeners with 4-8 chlorines with ortho-position of the substituents were the most abundant among the PCBs. β-HCH was determined at highest concentration in water samples, and total amount of HCH exceeded its legacy Environmental Quality Standard value. bphA1, was the most numerous gene in water layers (105 copies/mL) and sediments (105 copies/mg), followed by linB and PAH-RHDα genes (103 copies/mL; 105 copies/mg). The least abundant genes were linA (103 copies/mL; 104 copies/mg) and nahAc (102 copies/mL; 104 copies/mg). The most widely distributed gene bphА1 was one of the least expressed (10-3-10-2 copies/mL; 10-1 copies/mg). The most actively expressed genes were linB (101-102 copies/mL; 103 copies/mg), PAH-RHDα (101 copies/mL; 102 copies/mg) and linA (10-1-100 copies/mL; 100 copies/mg). Interaction of bacteria with PAHs, PCBs and HCH is evidenced by high copy numbers of the catabolic genes that initiate their degradation. More persistent compounds, such as high-molecular weight PAHs or β-HCH are accumulating in the Black Sea water and sediments, albeit microbial activity is directed against them.

Factors Influencing the Bacterial Bioremediation of Hydrocarbon Contaminants in the Soil: Mechanisms and Impacts

The discharge of hydrocarbons and their derivatives to environments due to human and/or natural activities cause environmental pollution (soil, water, and air) and affect the natural functioning of an ecosystem. To minimize or eradicate environmental pollution by hydrocarbon contaminants, studies showed strategies including physical, chemical, and biological approaches. Among those strategies, the use of biological techniques (especially bacterial biodegradation) is critically important to remove hydrocarbon contaminants. The current review discusses the insights of major factors that enhance or hinder the bacterial bioremediation of hydrocarbon contaminants (aliphatic, aromatic, and polyaromatic hydrocarbons) in the soil. The key factors limiting the overall hydrocarbon biodegradation are generally categorized as biotic factors and abiotic factors. Among various environmental factors, temperature range from 30 to 40°C, pH range from 5 to 8, moisture availability range from 30 to 90%, carbon/nitrogen/phosphorous (C/N/P; 100:20:1) ratio, and 10–40% of oxygen for aerobic degradation are the key factors that show positive correlation for greatest hydrocarbon biodegradation rate by altering the activities of the microbial and degradative enzymes in soil. In addition, the formation of biofilm and production of biosurfactants in hydrocarbon-polluted soil environments increase microbial adaptation to low bioavailability of hydrophobic compounds, and genes that encode for hydrocarbon degradative enzymes are critical for the potential of microbes to bioremediate soils contaminated with hydrocarbon pollutants. Therefore, this review works on the identification of factors for effective hydrocarbon biodegradation, understanding, and optimization of those factors that are essential and critical.