Synergistic biodegradation of pentachlorophenol by Bacillus cereus (DQ002384), Serratia marcescens (AY927692) and Serratia marcescens (DQ002385)

Toxicity of nZVI in the growth of bacteria present in contaminated soil

The use of nano zero-valent iron (nZVI) for the remediation of degraded areas is a consolidated practice. However, the long-term reactions that occur in the environment remain unknown. This study aimed to evaluate the potential toxic effects on the growth of colony-forming units (CFUs) of Bacillus cereus and Pseudomona aeruginosa present in soil contaminated with hexavalent chromium (Cr⁶⁺) and pentachlorophenol (PCP) nanoremediated with nZVI. The treatments were natural soil (control), soil contaminated by Cr⁶⁺, soil contaminated by PCP, and soil contaminated by Cr⁶⁺ and PCP (Cr⁶⁺ and PCP), all in duplicate. The concentration of contaminants used was 100 mg/kg of soil. One of the drums of the duplicate received an injection of nZVI solution with a concentration of 50 g/kg. Analysis was performed 7, 15, 21, 30, 60, and 90 days after the nZVI injection. Temporary oscillations in the abundance of the microbiological community were observed, characterizing the adaptation of bacteria to the contaminants. The bacteria showed similar behavior. Ninety days after the injection of nZVI, the averages of the CFUs were statistically equal, with the lowest coefficient of variation and the highest concentration of CFUs occurring. The strains of B. cereus and P. aeruginosa were resistant to the concentrations of nZVI, Cr⁶⁺, and PCP. The nanoremediation of nZVI in soil contaminated by Cr⁶⁺ and PCP had no toxic effects on the population of the bacteria evaluated and did not present major disturbances in temperature, electrical conductivity, pH, and humidity over time.

Dual-response quadratic model for optimisation of electricity generation and chlorophenol degradation by electro-degradative Bacillus subtilis in microbial fuel cell system

The interactions within microbial, chemical and electronic elements in microbial fuel cell (MFC) system can be crucial for its bio-electrochemical activities and overall performance. Therefore, this study explored polynomial models by response surface methodology (RSM) to better understand interactions among anode pH, cathode pH and inoculum size for optimising MFC system for generation of electricity and degradation of 2,4-dichlorophenol. A statistical central composite design by RSM was used to develop the quadratic model designs. The optimised parameters were determined and evaluated by statistical results and the best MFC systematic outcomes in terms of current generation and chlorophenol degradation. Statistical results revealed that the optimum current density of 106 mA/m² could be achieved at anode pH 7.5, cathode pH 6.3-6.6 and 21-28% for inoculum size. Anode-cathode pHs interaction was found to positively influence the current generation through extracellular electron transfer mechanism. The phenolic degradation was found to have lower response using these three parameter interactions. Only inoculum size-cathode pH interaction appeared to be significant where the optimum predicted phenolic degradation could be attained at pH 7.6 for cathode pH and 29.6% for inoculum size.

Bacterial consortium biotransformation of pentachlorophenol contaminated wastewater

The aims of this study were (i) to compare PCP removal (100 mg L^-1) by two bacterial consortia B₁ and B₂ in sterile wastewater (STWW) and liquid mineral medium (MSM), (ii) PCP effect in biofilm formation and antimicrobial susceptibility. PCP removal was measured by high-performance liquid chromatography (HPLC) during 168 h at 30 °C. Biofilm formation was assessed with two approaches: Congo Red Agar and Microtiter-plate. Antimicrobial susceptibility was determined by the agar disc diffusion technique. The results showed that the PCP removal for consortium B₁ and B₂ after 168 h was 70 and 97.5% in STWW; 62.2 and 85.5% in MSM, respectively. In addition, PCP addition showed an increase in biofilm development especially for B₂ consortium around 3.5 nm in 100 mg L^-1 PCP. PCP added in the Muller Hinton (MH) medium and Gentamicin disc showed a clear increase in diameter of cell lysis around 2 to 4.5 cm.

Exhaustion of pentachlorophenol in soil microcosms with three Pseudomonas species as detoxification agents

Pentachlorophenol (PCP) is a toxic compound, which is widely used as a wood preservative product and general biocide. It is persistent in the environment and has been classified as a persistent organic pollutant to be reclaimed in many countries. Bioremediation is an emerging approach to rehabilitating areas polluted by recalcitrant xenobiotics. In the present study, we evaluated the potential of three strains of Pseudomonas (P. putida S121, P. rhizophila S211, and P. fuscovagiceae S115) as bioremediation agents in depletion and detoxification of PCP in soil microcosms. PCP removal was effectively optimized using a central-composite experimental design and response surface methodology (RSM). The optimum conditions for maximum PCP removal yield (85 ± 5%) were: 500 mg/kg PCP concentration, 10⁸ UFC/g soil inoculum size of each strain and 55 days incubation period. The bacterial strains, P. putida, P. rhizophila, and P. fuscovagiceae, showed good capability to tolerate and degrade PCP so that they could be successfully used in synergistic effect to treat PCP polluted soils.

Is Long-Term Heavy Metal Exposure Driving Carriage of Antibiotic Resistance in Environmental Opportunistic Pathogens: A Comprehensive Phenomic and Genomic Assessment Using Serratia sp. SRS-8-S-2018

The carriage of both, heavy metal and antibiotic resistance appears to be a common trait in bacterial communities native to long-term contaminated habitats, including the Savannah River Site (SRS). There is widespread soil contamination at the SRS; a United States Department of Energy (DOE) facility with long-term contamination from past industrial and nuclear weapons production activities. To further evaluate the genomic and metabolic traits that underpin metal and antibiotic resistance, a robust mercury (Hg) and uranium (U)-resistant strain- SRS-8-S-2018, was isolated. Minimum inhibitory concentration of this strain revealed resistance to Hg (10 μg/ml) and U (5 mM), the two main heavy metal contaminants at the SRS. Metabolic assessment of strain SRS-8-S-2018 using Biolog metabolic fingerprinting analysis revealed preference for carbohydrate utilization followed by polymers, amino acids, carboxy acids, and esters; this physiological activity diminished when Hg stress was provided at 1 and 3 μg/ml and completely ceased at 5 μg/ml Hg, indicating that continued release of Hg will have negative metabolic impacts to even those microorganisms that possess high resistance ability. Development of antibiotic resistance in strain SRS-8-S-2018 was evaluated at a functional level using phenomics, which confirmed broad resistance against 70.8% of the 48 antibiotics tested. Evolutionary and adaptive traits of strain SRS-8-S-2018 were further assessed using genomics, which revealed the strain to taxonomically affiliate with Serratia marcescens species, possessing a genome size of 5,323,630 bp, 5,261 proteins (CDS), 55 genes for transfer RNA (tRNA), and an average G + C content of 59.48. Comparative genomics with closest taxonomic relatives revealed 360 distinct genes in SRS-8-S-2018, with multiple functions related to both, antibiotic and heavy metal resistance, which likely facilitates the strain’s survival in a metalliferous soil habitat. Comparisons drawn between the environmentally isolated Serratia SRS-8-S-2018 with 31 other strains revealed a closer functional association with medically relevant isolates suggesting that propensity of environmental Serratia isolates in acquiring virulence traits, as a function of long-term exposure to heavy metals, which is facilitating development, recruitment and proliferation of not only metal resistant genes (MRGs) but antibiotic resistant genes (ARGs), which can potentially trigger future bacterial pathogen outbreaks emanating from contaminated environmental habitats.

In vitro synergistic effects of fisetin and norfloxacin against aquatic isolates of Serratia marcescens

Serratia marcescens is a common pathogenic bacterium that can cause infections in both humans and animals. It can cause a range of diseases, from slight wound infections to life-threatening bacteraemia and pneumonia. The emergence of antimicrobial resistance has limited the treatment of the diseases caused by the bacterium to a great extent. Consequently, there is an urgent need to develop novel antimicrobial strategies against this pathogen. Synergistic strategy is a new approach to treat the infections caused by drug-resistant bacteria. In this paper, we isolated and identified the first multi-resistant pathogenic Serratia marcescens strain from diseased soft-shelled turtles (Pelodiscus sinensis) in China. We then performed a checkerboard assay; the results showed that out of 10 tested natural products fisetin had synergistic effects against S. marcescens when combined with norfloxacin. The time-kill curve assay further confirmed the results of the checkerboard assay. We found that this novel synergistic effect could significantly reduce the dosage of norfloxacin against S. marcescens.

Pentachlorophenol degradation by Janibacter sp., a new actinobacterium isolated from saline sediment of arid land

Many pentachlorophenol- (PCP-) contaminated environments are characterized by low or elevated temperatures, acidic or alkaline pH, and high salt concentrations. PCP-degrading microorganisms, adapted to grow and prosper in these environments, play an important role in the biological treatment of polluted extreme habitats. A PCP-degrading bacterium was isolated and characterized from arid and saline soil in southern Tunisia and was enriched in mineral salts medium supplemented with PCP as source of carbon and energy. Based on 16S rRNA coding gene sequence analysis, the strain FAS23 was identified as Janibacter sp. As revealed by high performance liquid chromatography (HPLC) analysis, FAS23 strain was found to be efficient for PCP removal in the presence of 1% of glucose. The conditions of growth and PCP removal by FAS23 strain were found to be optimal in neutral pH and at a temperature of 30 °C. Moreover, this strain was found to be halotolerant at a range of 1-10% of NaCl and able to degrade PCP at a concentration up to 300 mg/L, while the addition of nonionic surfactant (Tween 80) enhanced the PCP removal capacity.

Enhanced selection of micro-aerobic pentachlorophenol degrading granular sludge

Column-type combined reactors were designed to cultivate micro-aerobic pentachlorophenol (PCP) degrading granular sludge under oxygen-limited conditions (0.1-0.2 mgL(-1)) over 39-day experimental period. Micro-aerobic granular had both anaerobic activity (SMA: 2.34 mMCH4/hg VSS) and aerobic activity (SOUR: 2.21 mMO2/hg VSS). Metabolite analysis results revealed that PCP was sequentially dechlorinated to TCP, DCP, and eventually to MCP. Methanogens were not directly involved in the dechlorination of PCP, but might played a vital role in stabilizing the overall structure of the granule sludge. For Eubacteria, the Shannon Index (2.09 in inoculated granular sludge) increased both in micro-aerobic granular sludge (2.61) and PCP-degradation granular sludge (2.55). However, for Archaea, it decreased from 2.53 to 1.85 and 1.84, respectively. Although the Shannon Index demonstrated slight difference between micro-aerobic granular sludge and PCP-degradation granular sludge, the Principal Component Analysis (PCA) indicated obvious variance of the microbial composition, revealing significant effect of micro-aerobic condition and PCP on microbial community. Furthermore, nucleotide sequencing indicated that the main microorganisms for PCP degradation might be related to Actinobacterium and Sphingomonas. These results provided insights into situ bioremediation of environments contaminated by PCP and had practical implications for the strategies of PCP degradation.

Pentachlorophenol dechlorination and simultaneous Cr6+ reduction by Pseudomonas putida SKG-1 MTCC (10510): characterization of PCP dechlorination products, bacterial structure, and functional groups

It is the first report in which a novel psychrotrophic Pseudomonas putida SKG-1 strain was evaluated for simultaneous bioremediation of pentachlorophenol and Cr(6+) under various cultural and nutritional conditions. Pentachlorophenol (PCP) dechlorination products, bacterial structure, and functional groups were characterized by gas chromatography and mass spectrometry (GC-MS), scanning electron microscope and energy dispersive X-ray spectroscopy (SEM-EDS), and Fourier-transform infrared (FTIR) techniques. The strain was extremely tolerant to excessively higher individual concentration of PCP (1,400 mg l(-1)) and Cr(6+) (4,300 mg l(-1)). Increasing concentration of PCP and Cr(6+) exerted inhibitory effect on bacterial growth and toxicants' removal. The strain exhibited growth, and concomitantly remediated both the pollutants simultaneously over a broad pH (7.0-9.0) and temperature (28-32 °C) range; maximum growth, PCP dechlorination (87.5%), and Cr(6+) removal (80.0%) occurred at optimum pH 8.0 and 30 °C (from initial PCP 100 mg l(-1) and Cr(6+) 500 mg l(-1)) under shaking (150 rpm) within 72 h incubation. Optimization of agitation (125 rpm) and aeration (0.4 vvm) in bioreactor further enhanced PCP dechlorination by ~10% and Cr(6+) removal by 2%. A direct correlation existed between growth and bioremediation of both the toxicants. Among other heavy metals, mercury exerted maximum and cobalt minimum inhibitory effect on PCP dechlorination and Cr(6+) removal. Chromate reductase activity was mainly associated with the supernatant and cytosolic fraction of bacterial cells. GC-MS analysis revealed the formation of tetrachloro-p-hydroquinone, 2,4,6-trichlorophenol, and 2,6-dichlorophenol as PCP dechlorination products. FTIR spectrometry indicated likely involvement of carbonyl and amide groups in Cr(3+) adsorption, and SEM-EDS showed the presence of chromium on P. putida surface. Thus, our promising isolate can be ecofriendly employed for biotreatment of various industrial wastes contaminated with high PCP and Cr(6+) concentrations.

Reductive dechlorination and mineralization of pentachlorophenol in biocathode microbial fuel cells

Simultaneous anaerobic and aerobic degradation pathways in two-chamber, tubular microbial fuel cells (MFCs) facilitated pentachlorophenol (PCP) mineralization by a mediator-less biocathode. PCP was degraded at a rate of 0.263 ± 0.05 mg/L-h (51.5 mg/g VSS-h) along with power generation of 2.5 ± 0.03 W/m(3). Operating the biocathode MFC at 50°C improved the PCP degradation rate to 0.523 ± 0.08 mg/L-h (103 mg/g VSS-h) and power production to 5.2 ± 0.03 W/m(3). A pH of 6.0 increased the PCP degradation rate to 0.365 ± 0.02 mg/L-h (71.5mg/g VSS-h), but reduced power. While mediators were not needed, adding anthraquinone-2,6-disulfonate increased power and PCP degradation rates. Dominant bacteria most similar to the anaerobic Desulfobacterium aniline, Actinomycetes and Streptacidiphilus, and aerobic Rhodococcus erythropolis, Amycolatopsis and Gordonia were found on the biocathode. These results demonstrate efficient degradation of PCP in biocathode MFCs and the effects of temperature, pH and mediators.

Isolation, identification and characterization of a glyphosate-degrading bacterium, Bacillus cereus CB4, from soil

A bacterial strain named CB4, with highly effective glyphosate degradation capability, was isolated from soil after enrichment. On the basis of the Biolog omniLog identification system (Biolog) and 16S ribosomal RNA (rRNA) gene sequencing methods, strain CB4 was identified as Bacillus cereus. Further experiments were carried out to optimize the growth of strain CB4 and the glyphosate degradation activity by high performance liquid chromatography (HPLC). The optimal conditions were found as follows: initial pH 6.0, incubation temperature 35°C, glyphosate concentration 6 g L(-1), inoculation amount 5% and incubation time 5 days. Under the optimal conditions, stain CB4 utilized 94.47% of glyphosate. This is the first report on B. cereus with a capacity to utilize herbicide glyphosate, and it can degrade glyphosate concentrations up to 12 g L(-1). Metabolization of glyphosate by strain B. cereus CB4 was studied. Results indicated that two concurrent pathways were capable of degrading glyphosate to AMPA, glyoxylate, sarcosine, glycine and formaldehyde as products. Glyphosate breakdown in B. cereus CB4 was achieved by the C-P lyase activity and the glyphosate oxidoreductase activity.