Fungal bioremediation of polyethylene: Challenges and perspectives

Plastics have become ubiquitous in both their adoption as materials and as environmental contaminants. Widespread pollution of these versatile, man-made and largely petroleum-derived polymers has resulted from their long-term mass production, inappropriate disposal and inadequate end of life management. Polyethylene (PE) is at the forefront of this problem, accounting for one-third of plastic demand in Europe in part due to its extensive use in packaging. Current recycling and incineration processes do not represent sustainable solutions to tackle plastic waste, especially once it becomes littered, and the development of new waste-management and remediation technologies are needed. Mycoremediation (fungal-based biodegradation) of PE has been the topic of several studies over the last two decades. The utility of these studies is limited by an inconclusive definition of biodegradation and a lack of knowledge regarding the biological systems responsible. This review highlights relevant features of fungi as potential bioremediation agents, before discussing the evidence for fungal biodegradation of both high- and low-density PE. An up-to-date perspective on mycoremediation as a future solution to PE waste is provided.     

De novo phenol bioproduction from glucose using biosensor-assisted microbial coculture engineering

Microbial biosynthesis has been extensively adapted for the production of commodity chemicals using renewable feedstocks. This study integrated metabolite biosensors into rationally designed microbial cocultures to achieve high-efficiency bioproduction of phenol from simple carbon substrate glucose. Specifically, two sets of E. coli–E. coli cocultures were first constructed for accommodation of two independent phenol biosynthesis pathways via 4-hydroxybenzoate (4HB) and tyrosine (TYR), respectively. Biosensor-assisted microbial cell selection mechanisms were subsequently incorporated into the coculture systems to address the insufficient pathway intermediate provision that limited the overall bioproduction. For the 4HB- and TYR-dependent pathways, this approach improved the phenol production by 2.3- and 3.9-fold, respectively, compared to the monoculture controls. Notably, the use of biosensor-assisted cell selection strategy in monocultures resulted in reduced phenol production, highlighting the advantage of coculture engineering for coupling with biosensing. After stepwise optimization, the phenol bioproduction yield of the engineered coculture's reached 0.057 g/g glucose. Furthermore, the coculture biosynthesis was successfully scaled up at both shake flask and bioreactor levels. Overall, the findings of this study demonstrate the outstanding potential of coupling biosensing and modular coculture engineering for advancing microbial biosynthesis of valuable molecules from renewable carbon substrates.     

高温胁迫对新菠萝灰粉蚧不同地理种群保护酶活性的影响

为分析高温胁迫下新菠萝灰粉蚧Dysmicoccus neobrevipes Beardsley不同地理种群保护酶活性的差异,阐明该粉蚧对高温适应性的生理响应。本研究以室内26℃处理为对照测定了高温胁迫下(35℃、38℃、41℃、44℃)新菠萝灰粉蚧4个不同地理(广西、广东、海南和云南)种群雌成虫过氧化物酶(POD)、酚氧化酶(PO)及谷胱甘肽-S-转移酶(GST)的活性。结果表明,在35～44℃高温胁迫下,新菠萝灰粉蚧不同地理种群雌成虫POD和GST活性均高于常温对照的,PO活性均低于常温对照的(除云南种群38℃处理外);在35～44℃高温胁迫下该粉蚧3种酶活性变化均具有随着处理温度的升高呈先升高后降低趋势。在常温26℃下,该粉蚧除了广西、广东种群POD活性显著高于海南、云南种群外,4个种群的PO、GST间的活性无显著差异。在38℃、41℃和44℃高温处理下广西、广东、云南种群间的POD活性无显著差异。在相同高温处理下,除广东种群38℃处理的GST活性显著低于其它种群的外,其它相同温度处理的不同种群间的GST活性无显著差异。说明新菠萝灰粉蚧广西、广东、云南种群的POD对38℃、41℃、...     

Extracellular enzyme activities during humic acid degradation by the white rot fungi Phanerochaete chrysosporium and Trametes versicolor

Abstract The relationship between humic acid biodegradation and extracellular lignin peroxidase and Mn-dependent peroxidase activities of two white rot fungi, Phanerochaete chrysosporium and Tranetes versicolor , reported to be lignin degraders, was examined. In experimental conditions promoting culture aeration, particularly with T. versicolor no extracellular peroxidase activity could be detected unless humic acids were included in the culture medium. In the presence of humic acids, appreciable enzymatic activities were determined in the culture filtrate of the two fungi. However, T. versicolor was a more effective degrader than P. chrysosporium , and mineralization assays on synthetic humic acids with culture filtrates showed the important role played by Mn²⁺. The surfactant properties of humic acids are suggested to be responsible for the increase of enzymatic activities.     

Polydisulfides of substituted phenols as effective protectors of peroxidase against inactivation by ultrasonic cavitation

Kinetics of inactivation of horseradish peroxidase (HP) induced by low-frequency ultrasonic (US) treatment (27 kHz) with the specific power of 60 W/cm² were studied in phosphate (pH 7.4) and acetate (pH 5.2) buffers within the temperature range of 36.0 to 50.0°C and characterized by effective first-order rate constants of US inactivation k _in (us) in min^–1. Values of k _in (us) depend on the specific ultrasonic power within the range of 20-60 W/cm², on the concentration of HP, and on pH and temperature of the solutions. The activation energy of US inactivation of HP is 9.4 kcal/mole. Scavengers of HO^· radicals, mannitol and dimethylformamide, significantly inhibit the US inactivation of HP at 36.0°C, whereas micromolar concentrations of polydisulfide of gallic acid (poly(DSG)) and of poly(2-aminodisulfide-4-nitrophenol) (poly(ADSNP)) virtually completely suppress the US inactivation of peroxidase at the ultrasonic power of 60 W/cm² on the sonication of the enzyme solutions for more than 1 h at pH 5.2. Various complexes of poly(DSG) with human serum albumin effectively protect HP against the US inactivation in phosphate buffer (pH 7.4). The findings unambiguously confirm a free radical mechanism of the US inactivation of HP in aqueous solutions. Polydisulfides of substituted phenols are very effective protectors of peroxidase against inactivation caused by US cavitation.     

Potential application of catalase-peroxidase from Comamonas terrigena N3H in the biodegradation of phenolic compounds

Comamonas terrigena N3H is a gram-negative rod-shaped bacterium that was isolated from contaminated soil in Slovakia. This bacterium showed remarkable biodegradation properties. We investigated the expression and functioning of two catalase isozymes in this bacterium. The typical catalase could be induced by cadmium ions, whereas the catalase-peroxidase enzyme was constitutively expressed. Since C. terrigena lacks the key enzyme for complete degradation of phenols (phenolhydroxylase), we analysed the possible removal of phenol by the two catalases of this bacterium. Addition of phenol to the culture medium led to increased expression of the catalase-peroxidase. Applying oxidative stress prior to phenol administration markedly induced the expression of the typical catalase, irrespective of the nature of the added agent. Thus, the rate of phenol degradation is rather reduced under these conditions, while growth of the cells is not impaired. We concluded that phenol peroxidation in C. terrigena can be largely attributed to the action of a catalase-peroxidase. The potential application of this enzyme in the removal of phenol from the environment is discussed.     

A comparison of the ability of forest and agricultural soils to mineralize chlorinated aromatic compounds

Soils were sampled from two agricultural fields, two relatively pristine forests, and one suburban forest in Ontario, Canada. The ability of these soils to mineralize 2,4-dichlorophenoxyacetate, 3-chlorobenzoate, 4-chlorophenol, 2,4-dichlorophenol, pentachlorophenol, and atrazine was determined using ¹⁴C-labeled substrates. Direct preexposure was necessary before atrazine mineralization could be detected; however, it was not necessary for degradation of any of the other chemicals. 2,4-dichlorophenoxyacetate and pentachlorophenol mineralization was much higher in the agricultural soils relative to the pristine forest soils, but 3-chlorobenzoate and 2,4-dichlorophenol mineralization rates showed the opposite trend. Mineralization of 4-chlorophenol was about equivalent in all soils. Suburban forests soils were indistinguishable from agricultural soils with respect to their degradation of 2,4-dichlorophenoxyacetate and chlorobenzoate. Additionally, they were better able than any of the soils to withstand the toxic effects of pentachlorophenol. Pentachlorophenol mineralization was highly variable in the pristine forest soils, ranging from about 6 to 50%. Abiotic factors such as pH, soil type, and organic and moisture content did not account for these significant site differences. The selective forces responsible for these differences, and the possible differences in microbial populations are discussed.