Biodegradation最新文献

Endocrine-disrupting phthalates (EDPs) are widely used as plasticizers for the manufacture of different plastics and polyvinyl chloride by providing flexibility and mechanical strength. On the other hand, they are categorized under priority pollutants list due to their threat to human health and the environment. This study examined biodegradation of a mixture of dimethyl, diethyl, dibutyl, benzyl butyl, di-2-ethylhexyl, and di-n-octyl phthalates using a CSTB (continuous stirred tank bioreactor) operated under batch, fed-batch, continuous, and continuous with biomass recycle operation modes. For operating the CSTB under biomass recycle mode, microfiltration using an indigenous tubular ceramic membrane was employed. Ecotoxicity assessment of the treated water was carried out to evaluate the toxicity removal efficiency by the integrated bioreactor system. From the batch experiments, the EDPs cumulative degradation values were 90 and 75% at 1250 and 1500 mg/L total initial concentration of the mixture, respectively, whereas complete degradation was achieved at 750 mg/L. In the fed-batch study, 93% degradation was achieved at 1500 mg/L total initial concentration of the mixture. In continuous operation mode, 94 and 85% degradation efficiency values were achieved at 43.72 and 52.08 mg/L⋅h inlet loading rate of phthalate mixture. However, continuous feeding with 100% biomass recycle revealed complete degradation at 41.67 mg/L⋅h inlet loading rate within the 84 h operation period. High seed germination index and low mortality percentage of brine shrimps observed with phthalate degraded water from the integrated bioreactor system revealed its excellent potential in the treatment and toxicity removal of phthalates contaminated environment.

Biodegradability standards measure ultimate biodegradation of polymers by exposing the material under test to a natural microbial inoculum. Available tests developed by the International Organization for Standardization (ISO) use inoculums sampled from different environments e.g. soil, marine sediments, seawater. Understanding whether each inoculum is to be considered as microbially unique or not can be relevant for the interpretation of tests results. In this review, we address this question by consideration of the following: (i) the chemical nature of biodegradable plastics (virtually all biodegradable plastics are polyesters) (ii) the diffusion of ester bonds in nature both in simple molecules and in polymers (ubiquitous); (iii) the diffusion of decomposers capable of producing enzymes, called esterases, which accelerate the hydrolysis of esters, including polyesters (ubiquitous); (iv) the evidence showing that synthetic polyesters can be depolymerized by esterases (large and growing); (v) the evidence showing that these esterases are ubiquitous (growing and confirmed by bioinformatics studies). By combining the relevant available facts it can be concluded that if a certain polyester shows ultimate biodegradation when exposed to a natural inoculum, it can be considered biodegradable and need not be retested using other inoculums. Obviously, if the polymer does not show ultimate biodegradation it must be considered recalcitrant, until proven otherwise.

Di-2-ethylhexyl phthalate (DEHP) is used as a plasticizer in making plastics and released from landfills. This study attempted to degrade DEHP using microbial isolates. Isolates of Bacillus spp. were tested for their efficacy in degrading DEHP. Degradation was assessed using liquid chromatography-mass spectrometry (LC–MS). The most efficient DEHP degradation was achieved by Bacillus firmus MP04, which has been identified as Bacillus firmus MP04. This strain was found to use DEHP as the sole source of carbon without carbon source supplementation. Full factorial design was used to optimize the conditions for DEHP degradation which revealed the suitability of pH 7, 5% salt concentration, 20 to 37 °C temperature, and yeast extract as a nitrogen source. LC–MS elucidated the possible degradation mechanism via benzoic acid formation. However, prolonged incubation formed a typical compound denatonium benzoate due to reactions with other compounds. As maximum degradation was achieved in 4 days, prolonged incubation is not suggested. It can be concluded that new strain Bacillus firmus MP04 is the most efficient strain among all the tested strains for DEHP degradation.

The early stages of municipal solid waste degradation in landfills are complex harmonies of physical, biological, and chemical interactions that all work in concert to degrade trash into smaller and more stable materials. While many approaches have been taken to understand parts of this process, this new work attempted to simulate the early stages of landfills in controlled laboratory environments while observing the impacts of food waste content at different concentrations. This was completed by operating landfill lysimeters in a laboratory for approximately 1000 days, simulating landfill interior conditions while measuring the gas and liquid byproducts to study the impact of food waste presence in these environments. Metagenomic analysis after the experiment identified over 18,000 individual species and allowed comparison with past studies while also surveying microorganisms present in landfills. Similar populations found in past studies suggested the current experiments successfully replicated landfill conditions. While food waste diversion had a discernable impact on gas production, it did not show a clear and consistent impact on the microbiomes identified in this study.

Currently dairy processing by-products, such as whey, still propose a significant threat to the environment if unproperly disposed. Microalgal bioconversion of such lactose containing substrates can be used for production of valuable microalgae-derived bio-products as well as for significant reduction of environmental risks. Moreover, it could significantly reduce microalgae biomass production costs, being a significant obstacle in commercialization of many microalgae species. This review summarizes current knowledge on the use of lactose containing substrates, e.g. whey, for the production of value-added products by microalgae, including information on producer cultures, fermentation methods and cultivation conditions, bioprocess productivity and ability of microalgal cultures to produce β-galactosidases. It can be stated, that despite several limitations lactose-containing substrates can be successfully used for both—the production of microalgal biomass and removal of high amounts of excess nutrients from the cultivation media. Moreover, co-cultivation of microalgae and other microorganisms can further increase the removal of nutrients and the production of biomass. Further investigations on lactose metabolism by microalgae, selection of suitable strains and optimisation of the cultivation process is required in order to enable large-scale microalgae production on these substrates.

The degradation of the prevalent environmental contaminants benzene, toluene, ethylbenzene, and xylenes (BTEX) along with a common co-contaminant methyl tert-butyl ether (MTBE) by Rhodococcus rhodochrous ATCC Strain 21198 was investigated. The ability of 21198 to degrade these contaminants individually and in mixtures was evaluated with resting cells grown on isobutane, 1-butanol, and 2-butanol. Growth of 21198 in the presence of BTEX and MTBE was also studied to determine the growth substrate that best supports simultaneous microbial growth and contaminants degradation. Cells grown on isobutane, 1-butanol, and 2-butanol were all capable of degrading the contaminants, with isobutane grown cells exhibiting the most rapid degradation rates and 1-butanol grown cells exhibiting the slowest. However, in conditions where BTEX and MTBE were present during microbial growth, 1-butanol was determined to be an effective substrate for supporting concurrent growth and contaminant degradation. Contaminant degradation was found to be a combination of metabolic and cometabolic processes. Evidence for growth of 21198 on benzene and toluene is presented along with a possible transformation pathway. MTBE was cometabolically transformed to tertiary butyl alcohol, which was also observed to be transformed by 21198. This work demonstrates the possible utility of primary and secondary alcohols to support biodegradation of monoaromatic hydrocarbons and MTBE. Furthermore, the utility of 21198 for bioremediation applications has been expanded to include BTEX and MTBE.

Pyritic minerals generally occur in nature together with other trace metals as impurities, that can be released during the ore oxidation. To investigate the role of such impurities, the presence of copper (Cu(II)), arsenic (As(III)) and nickel (Ni(II)) during pyrite mediated autotrophic denitrification has been explored in this study at 30 °C with a specialized microbial community of denitrifiers as inoculum. The three metal(loid)s were supplemented at an initial concentration of 2, 5, and 7.5 ppm and only Cu(II) had an inhibitory effect on the autotrophic denitrification. The presence of As(III) and Ni(II) enhanced the nitrate removal efficiency with autotrophic denitrification rates between 3.3 [7.5 ppm As(III)] and 1.6 [7.5 ppm Ni(II)] times faster than the experiment without any metal(loid) supplementation. The Cu(II) batches, instead, decreased the denitrification kinetics with 16, 40 and 28% compared to the no-metal(loid) control for the 2, 5 and 7.5 ppm incubations, respectively. The kinetic study revealed that autotrophic denitrification with pyrite as electron donor, also with Cu(II) and Ni(II) additions, fits better a zero-order model, while the As(III) incubation followed first-order kinetic. The investigation of the extracellular polymeric substances content and composition showed more abundance of proteins, fulvic and humic acids in the metal(loid) exposed biomass.

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Plastic accumulation has become a serious environmental threat. Mitigation of plastic is important to save the ecosystem of our planet. With current research being focused on microbial degradation of plastics, microbes with the potential to degrade polyethylene were isolated in this study. In vitro studies were performed to define the correlation between the degrading capability of the isolates and laccase, a common oxidase enzyme. Instrumental analyses were used to evaluate morphological and chemical modifications in polyethylene, which demonstrated a steady onset of the degradation process in case of both isolates, Pseudomonas aeruginosa O1-P and Bacillus cereus O2-B. To understand the efficiency of laccase in degrading other common polymers, in silico approach was employed, for which 3D structures of laccase in both the isolates were constructed via homology modeling and molecular docking was performed, revealing that the enzyme laccase can be exploited to degrade a wide range of polymers.

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This study presents the effect of ultra-violet (UV) light radiation on the process kinetics, metabolic performance, and biodegradation capability of Scenedesmus vacuolatus. The impact of the UV radiation on S. vacuolatus morphology, chlorophyll, carotenoid, carbohydrates, proteins, lipid accumulation, growth rate, substrate affinity and substrate versatility were evaluated. Thereafter, a preliminary biodegradative potential of UV-exposed S. vacuolatus on spent coolant waste (SCW) was carried out based on dehydrogenase activity (DHA) and total petroleum hydrocarbon degradation (TPH). Pronounced structural changes were observed in S. vacuolatus exposed to UV radiation for 24 h compared to the 2, 4, 6, 12 and 48 h UV exposure. Exposure of S. vacuolatus to UV radiation improved cellular chlorophyll (chla = 1.89-fold, chlb = 2.02-fold), carotenoid (1.24-fold), carbohydrates (4.62-fold), proteins (1.44-fold) and lipid accumulations (1.40-fold). In addition, the 24 h UV exposed S. vacuolatus showed a significant increase in substrate affinity (1/Ks) (0.959), specific growth rate (µ) (0.024 h⁻¹) and biomass accumulation (0.513 g/L) by 1.50, 2 and 1.9-fold respectively. Moreover, enhanced DHA (55%) and TPH (100%) degradation efficiency were observed in UV-exposed S. vacuolatus. These findings provided major insights into the use of UV radiation to enhance S. vacuolatus biodegradative performance towards sustainable green environment negating the use of expensive chemicals and other unfriendly environmental practices.

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Six cadmium (Cd)-resistant microbial strains were isolated and their ability to immobilise Cd²⁺ in soil investigated. Cd-1, Cd-2, Cd-5, and Cd-6 were identified as Stenotrophomonas sp., Cd-3 as Achromobacter sp., and Cd-7 as Staphylococcus sp. The six strains showed a wide adaptation range for salinity and a strong tolerance to Cd²⁺. The effects of the initial Cd²⁺ concentration (1–100 mg/L), duration (18–72 h), temperature (10–40 °C), and pH (5.0–9.0) on the efficiency of Cd²⁺ removal were analysed. The results revealed that the Cd²⁺ removal rate was higher at an initial Cd²⁺ concentration of 5–100 mg/L than at 1 mg/L. The maximum Cd²⁺ removal effect was at a culture duration of 36 h, temperature of 10–35 °C, and pH of 5.0–7.0. X-ray diffraction (XRD) analysis revealed that the Cd²⁺ was immobilised by Stenotrophomonas sp. Cd-2 and Staphylococcus sp. Cd-7 through bio-precipitation. X-ray photoelectron spectroscopy (XPS) revealed that the Cd²⁺ was adsorbed by Stenotrophomonas sp. Cd-2, Achromobacter sp. Cd-3, and Staphylococcus sp. Cd-7. Fourier transform infrared spectroscopy (FTIR) analysis revealed that the isolates reacted with the Cd²⁺ mainly through the O–H, protein N–H, C–N, lipid C–H, fatty acid COO, polysaccharide C–O, P–O, and other functional groups, as well as with lipid molecules on the cell wall surfaces. Scanning electron microscopy (SEM) analysis revealed that there was little difference in the cells after Cd²⁺ treatment. The results of the soil remediation experiments indicated that the toxicity of Cd in soil could be effectively reduced using certain strains of microbe.

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