Characterization of heavy metal-associated bacteria from petroleum-contaminated soil and their resistogram and antibiogram analysis

The aim of the current study was to screen and identify heavy metal (chromium, cadmium, and lead) associated bacteria from petroleum-contaminated soil of district Muzaffarabad, Azad Jammu and Kashmir, Pakistan to develop ecofriendly technology for contaminated soil remediation. The petroleum-contaminated soil was collected from 99 different localities of district Muzaffarabad and the detection of heavy metals via an atomic absorption spectrometer. The isolation and identification of heavy metals-associated bacteria were done via traditional and molecular methods. Resistogram and antibiogram analysis were also performed using agar well diffusion and agar disc diffusion methods. The isolated bacteria were classified into species, i.e., B. paramycoides, B. albus, B. thuringiensis, B. velezensis, B. anthracis, B. pacificus Burkholderia arboris, Burkholderia reimsis, Burkholderia aenigmatica, and Streptococcus agalactiae. All heavy metals-associated bacteria showed resistance against both high and low concentrations of chromium while sensitive towards high and low concentrations of lead in the range of 3.0 ± 0.0 mm to 13.0 ± 0.0 mm and maximum inhibition was recorded when cadmium was used. Results revealed that some bacteria showed sensitivity towards Sulphonamides, Norfloxacin, Erythromycin, and Tobramycin. It was concluded that chromium-resistant bacteria could be used as a favorable source for chromium remediation from contaminated areas and could be used as a potential microbial filter.

Biodegradation of petroleum hydrocarbons based pollutants in contaminated soil by exogenous effective microorganisms and indigenous microbiome

Microbial remediation is an eco-friendly and promising approach for the restoration of sites contaminated by petroleum hydrocarbons (PHCs). The degradation of total petroleum hydrocarbons (TPHs), semi volatile organic compounds (SVOCs) and volatile organic compounds (VOCs) of the soil samples collected from a petrochemical site by indigenous microbiome and exogenous microbes (Saccharomyces cerevisiae ATCC 204508/S288c, Candida utilis AS2.281, Rhodotorula benthica CBS9124, Lactobacillus plantarum S1L6, Bacillus thuringiensis GDMCC1.817) was evaluated. Community structure and function of soil microbiome and the mechanism involved in degradation were also revealed. After bioremediation for two weeks, the concentration of TPHs in soil samples was reduced from 17,800 to 13,100 mg/kg. The biodegradation efficiencies of naphthalene, benzo[a]anthracene, benzo[b]fluoranthene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene, dibenzo[a,h]anthracene, 1,2,3-trichloropropane, 1,2-dichloropropane, ethylbenzene and benzene in soil samples with the addition of S. cerevisiae were 38.0%, 35.7%, 36.2%, 40.4%, 33.6%, 36.2%, 12.0%, 43.9%, 43.3% and 43.0%, respectively. The microbial diversity and community structure were improved during the biodegradation process. S. cerevisiae supplemented soil samples exhibited the highest relative abundance of the genus Acinetobacter for bacteria and Saccharomyces for yeast. The findings offer insight into the correlation between microbes and the degradation of PHC-based pollutants during the bioremediation process.

In situ synthesis of Fe-N co-doped carbonaceous nanocomposites using biogas residue as an effective persulfate activator for remediation of aged petroleum contaminated soils

Persulfate (PS)-based chemical oxidation is an effective method for the remediation of petroleum-contaminated soils, but higher concentrations of PS (3-40%) may lead to soil acidification (pH decreased by 1.8-6.2 units) and affect the microbial communities. In this study, Fe/N co-doped carbonaceous nanocomposites (Fe-N @ CN) that can efficiently activate PS were developed from biogas residue for the remediation of petroleum-contaminated soil. The as-obtained Fe-N@CN displayed that the Fe-based nanoparticles were encapsulated in graphitic nanosheets, with Fe₃C and FeN_0.0760 as the main bonding modes. The removal efficiency of total petroleum hydrocarbons (TPHs) reached 73.14% in 3 days with a PS dose of 2% and catalyst dose of 0.4%, and increased by 15.8% on adding 30 mmol/kg of β-cyclodextrin. The free-radical quenching experiment and electron paramagnetic resonance revealed that SO₄·^-,·OH, O₂·^-, and ¹O₂ were involved in the removal of TPHs. Because of the low PS dosage, the remediation process had no significant effect on the soil pH. During the remediation process, soil catalase activity was enhanced and then recovered, whereas the soil bacterial community, reflected by the operational taxonomic unit values, decreased and then recovered. TPH-degrading bacteria were produced in the Fe-N@CN/PS/soil system after chemical oxidation, further contributing to soil remediation.

DNA-SIP identification of phenanthrene-degrading bacteria undergoing bioaugmentation and natural attenuation in petroleum-contaminated soil

DNA-stable isotope probing (SIP) with ¹³C labeled phenanthrene (PHE) as substrate was used to identify specific bacterial degraders during natural attenuation (NA) and bioaugmentation (BA) in petroleum contaminated soil. BA, with the addition of a bacterial suspension mixture named GZ, played a significant role in PHE degradation with a higher PHE removal rate (∼90%) than that of NA (∼80%) during the first 3 days, and remarkably altered microbial communities. Of the five strains introduced in BA, only two genera, particularly, Ochrobactrum, Rhodococcus were extensively responsible for PHE-degradation. Six (Bacillus sp., Acinetobacter sp., Xanthomonas sp., Conexibacter sp., Acinetobacter sp. and Staphylococcus sp.) and seven (Ochrobactrum sp., Rhodococcus sp., Alkanindiges sp., Williamsia sp., Sphingobium sp., Gillisia sp. and Massilia sp.) bacteria responsible for PHE degradation were identified in NA and BA treatments, respectively. This study reports for the first time the association of Xanthomonas sp., Williamsia sp., and Gillisia sp. to PHE degradation.

Effect of immature and mature compost addition on petroleum contaminated soils composting: kinetics

PURPOSE

The kinetic studies and effect of amendment addition on the performance of the composting process in reduction of total petroleum hydrocarbons (TPH) from petroleum contaminated soils (PCS) were investigated in the present research.

METHODS

Seven composting experiments containing various mixing ratios of PCS to unfinished compost (UC) and finished compost (FC) were set up and operated for 14 weeks. The mixing rations consisted of 1:0 (as control experiment), 1:0.3, 1:0.6, and 1:1. The initial C/N/P and moisture contents of the composting piles were adjusted to 100/5/1 and 50-55%, respectively.

RESULTS

Results showed that 50.09-79.49% of TPH was removed in the composting experiments after 14 weeks. The highest and lowest removal rates were achieved in the ratios of 1:1 and 1:0.3, respectively. Moreover, application of UC as amendments and bulking agent is more efficient than FC. The biodecomposition of TPH was fitted to the first-order kinetic with the half lives and rate constants of 5.63-11.55 days and 0.060-0.123 d^-1, respectively. The bacteria detected from the composting treatments were Staphylococcus sp., Bacillus sp., and Pseudomonas sp.

CONCLUSIONS

The study confirmed the suitability of composting process for PCS bioremediation and superiority of UC than FC as bulking agent.

Bioremediation of soil contaminated crude oil by Agaricomycetes

BACKGROUND

One of the most important environmental problems is the decontamination of petroleum hydrocarbons polluted soil, particularly in the oil-rich country. Bioremediation is the most effective way to remove these pollutants in the soil. Spent mushroom compost has great ability to decompose lignin-like pollution. The purpose of this study was the bioremediation of soil contaminated with crude oil by an Agaricomycetes.

METHODS

Soil sample amended with spent mushroom compost into 3%, 5% and 10% (w/w) with or without fertilizer. Ecotoxicity germination test was conducted with Lipidium sativa.

RESULTS

The amplified fragment (18 s rDNA) sequence of this mushroom confirmed that the strain belonged to Pleurotus ostreatus species with complete homology (100% identity). All tests experiment sets were effective at supporting the degradation of petroleum hydrocarbons contaminated soil after three months. Petroleum contaminated soil amended with Spent mushroom compost 10% and fertilizer removed 64.7% of total petroleum hydrocarbons compared control. The germination index (%) in ecotoxicity tests ranged from 60.4 to 93.8%.

CONCLUSIONS

This showed that the petroleum hydrocarbons contaminated soil amended with 10% Spent mushroom compost had higher bioremediation ability and reduced soil toxicity in less than three months.