Degradation of aliphatic-aromatic copolyesters by bacteria that can degrade aliphatic polyesters

The degradation activities of bacteria that can degrade aliphatic polyesters on various aliphatic-aromatic copolyesters (PBSTIL, PBST, and Ecoflex™) were investigated. Among the bacteria examined, strain TB-71 showed the best degradation activity. An HPLC analysis of the degradation products revealed that PBST55 and Ecoflex™ are degraded into monomers by strain TB-71. In the case of PBSTIL, an unknown peak was detected by the HPLC analysis and was considered to be derived from water-soluble oligomers containing isophthalic acid segments. This finding seemed to be attributed to the chemical structure of the aromatic segments of the copolymers.     

PPDO/OMMT纳米复合材料在微生物环境下的降解行为

采用微生物水性培养液降解实验法对聚对二氧环己酮/有机蒙脱土(PPDO/OMMT)纳米复合材料的生物降解性能进行了研究.通过质量、特性黏数、pH、热分析和电子扫描显微镜(SEM)研究了试样的降解过程.结果表明,在本实验条件下,PPDO/OMMT纳米复合材料降解性随着OMMT含量的增加而增加.降解90天,在微生物水性培养液...     

Characterization of a mesophilic aliphatic-aromatic copolyester-degrading fungus

We isolated 5 mesophilic microorganisms that form clear zones around the colony on an opaque medium containing the aliphatic-aromatic copolyester poly(60 mol% butylene adipate-co-40 mol% butylene terephthalate) (PBAT). Among all strains, the fungal strain NKCM1712 degraded PBAT at the fastest rate (3.5 ± 0.3 μg cm⁻² h⁻¹). Genetic and morphological analyses revealed that this strain was closely related to Isaria fumosorosea (phylum Ascomycota). Mass spectroscopic analysis revealed that the degradation products were T, AB, TB, BAB, and ABT (T, terephthalic acid unit; A, adipic acid unit; B, 1,4-butanediol unit)] in the culture of the strain that used PBAT as the sole carbon source. Furthermore, the PBAT degradation ability of this strain in terms of BOD suggested that it could utilize the PBAT degradation products as growth substrates. This is the first report of a mesophilic strain that can mineralize an aliphatic-aromatic polyester into carbon dioxide on its own.     

The mechanism of biodegradation of polyethylene

LDPE films have been exposed to abiotic and biotic environments. The films were UV irradiated for periods of 0, 7, 14, 26 and 42 days before being mixed with water and soil.Degraded LDPE films were examined by infra-red spectroscopy. The carbonyl peak increased with time in the abiotic environment and the oxidative degradation reported in our earlier works was confirmed.In the presence of a biotic atmosphere, however, this peak decreased. At the same time there was an increase in double bonds which was related to weight loss. An explanation of this behavior is presented as a proposed mechanism for the biodegradation of polyethylene.This mechanism is compared, on the one hand, with abiotic photooxidation, Norrish type I and II degradation, and, on the other, with the biotic paraffin degradation. Abiotic, as well as biotic, ester formation mechanisms are also presented.An ESR spectrum confirms the presence of radicals on the polyethylene samples.At the beginning of the degradation the main agents seem to be UV light and/or oxidizing agents. When carbonyl groups have been produced, these are attacked by microorganisms which degrade the shorter segments of polyethylene chains and form carbon dioxide and water as end products.There is a synergistic effect between photooxidative degradation and biodegradation. The biodegradation of polyethylene can be compared with the biodegradation of paraffin.     

Biotransformation of butyltin compounds using pure strains of microorganisms

The debutylation of tributyltin chloride by several strains of fungi, yeasts and bacteria is described. Under standard conditions and with low initial concentration of substrate, significant biotic degradation of tributyltin (6–32%) was detected after five days at 28°C. Dibutyltin and monobutyltin were formed in all cases, with higher yields of the latter. Two microorganisms catalysed the transformation of monobutyltin to dimethyltin and trimethytin whereas all microorganisms were able to methylate inorganic tin(IV) to trimethyltin. Our results suggest that tributyltin biodegradation by microorganisms is generally possible, provided sufficiently low concentrations of substrate are used.     

A chemiluminescence study on degradation of gelatine: Biodegradation by bacteria and fungi isolated from cinematographic films

Chemiluminescence (CL) has become a sensitive tool for the study of polymer degradation, induced by exposure to various factors, such us heat, UV-light and oxygen. In this paper, the results obtained with this technique in the study of gelatine samples hydrolytically degraded under sterilisation conditions are presented. Also, photographic gelatine exposed to bacterial and fungal degradations, in water solution and under controlled conditions, have been study by the chemiluminescence emission of their corresponding films and the biodegradation extent was determined by viscosity. The bacteria and fungi employed in this work have been isolated from cinematographic films in a previous work.The high intensities of chemiluminescence emission obtained for gelatines biodegraded by bacteria and fungi, in aqueous solution at 37 and 25 °C, respectively, are different to those obtained in the thermal degradation. The hydrolytic degradation mechanism is through a cleavage of the peptide bond of the protein without significant oxidation of the material. In contrast, biodegradation by bacteria and fungi at low temperatures decreases the molecular weight of the gelatine (viscosity) by the enzymatic activity but, also, produces an important oxidation in the material due to the reactive oxygen species (ROS) generated in the microbial metabolism.     

Accelerated Microbial Degradation of Poly(L-lactide)

Acceleration of the biodegradation of poly(L -lactide) (PLA) was studied. We found that the degradation rate of high molecular weight (1.3×10⁵) PLA film was greatly increased by the addition of gelatin into the culture medium of the microorganisms. 100 mg of PLA film was almost completely degraded by the fungus, Tritirachium album (eukaryotic microorganisms), and by an actinomycete, Saccharothrix waywayandensis (prokaryotic microorganisms). In addition to gelatin, various insoluble proteins, peptides and amino acids also accelerate the biodegradation of PLA. Silk fibroin was the best inducer for the production of PLA-degrading enzymes of an actinomycete, Amycolatopsis orientalis.     

Biodegradation of poly(lactic acid) and its nanocomposites

PLA nanocomposites based on organically modified montmorillonites at 5% w/w loading were prepared by melt blending using an internal mixer and then degraded in a commercial compost. The addition of nanoclays was found to increase the PLA degradation rate, especially for the highest dispersed clay in the polymer matrix. Biodegradation by microorganisms isolated from the compost showed the bacterium Bacillus licheniformis as one of the responsible for PLA biodegradation in compost. It was also found that clays can influence the polymer bacterial degradation depending on their chemical structure and affinity of the bacterium towards the clay.     

Aerobic and anaerobic microbial degradation of poly-beta-hydroxybutyrate produced by Azotobacter chroococcum

Food industry wastewater served as a carbon source for the synthesis of poly-β-hydroxybutyrate (PHB) by Azotobacter chroococcum. The content of polymer in bacterial cells grown on the raw materials reached 75%. PHB films were degraded under aerobic, microaerobic, and anaerobic conditions in the presence and absence of nitrate by microbial populations of soil, sludges from anaerobic and nitrifying/denitrifying reactors, and sediment from a sludge deposit site. Changes in molecular mass, crystallinity, and mechanical properties of PHB were studied. Anaerobic degradation was accompanied by acetate formation, which was the main intermediate utilized by denitrifying bacteria or methanogenic archaea. On a decrease in temperature from 20 to 5° C in the presence of nitrate, the rate of PHB degradation was 7.3 times lower. Under anaerobic conditions and in the absence of nitrate, no PHB degradation was observed, even at 11°C. The enrichment cultures of denitrifying bacteria obtained from soil and anaerobic sludge degraded PHB films for a short time (3–7 d). The dominant species in the enrichment culture from soil were Pseudomonas fluorescens and Pseudomonas stutzeri. The rate of PHB degradation by the enrichment cultures depended on the polymer molecular weight, which reduced with time during biodegradation.     

Lignin biodegradation by the ascomyceteChrysonilia sitophila

The lignin biodegradation process has an important role in the carbon cycle of the biosphere. The study of this natural process has developed mainly with the use of basidiomycetes in laboratory investigations. This has been a logical approach since most of the microorganisms involved in lignocellulosic degradation belong to this class of fungi. However, other microorganisms such as ascomycetes and also some bacteria, are involved in the lignin decaying process. This work focuses on lignin biodegradation by a microorganism belonging to the ascomycete class,Chrysonilia sitophila. Lignin peroxidase production and characterization, mechanisms of lignin degradation (lignin model compounds and lignin in wood matrix) and biosynthesis of veratryl alcohol are outstanding. Applications of C.sitophila for effluent treatment, wood biodegradation and single-cell protein production are also discussed.     

Biodegradation of poly(lactic acid)/starch/coir biocomposites under controlled composting conditions

The aim of this work was to investigate the aerobic biodegradation of a composite under controlled composting conditions using standard test methods. Composite was formed by poly(lactic acid) (PLA), with and without the addition of maleic anhydride (MA), acting as coupling agent, thermoplastic starch (TPS) and short natural fibre (coir). For comparison its starting materials, such as TPS and matrix (containing 75 wt% of PLA and 25 wt% of TPS), were also tested.At the end of the incubation period, TPS appeared to be the most bio-susceptible material being totally biodegraded and the matrix showed a higher level of biodegradation (higher amounts of evolved CO₂) than PLA, probably due to the TPS domains preferentially attacked by microorganisms and increasing the percentage of carbon dioxide produced. Fibres seemed to play a secondary role in the process as confirmed by the slight differences in carbon dioxide produced. The compatibilised composite revealed a lower percentage of evolved CO₂ than the uncompatibilised one. Finally, the degradation results were confirmed by thermal properties' changes of tested materials at different incubation times, as monitored by thermal analysis, and by the scanning electron microscopy (SEM) analyses of the compost aged samples. SEM micrographs showed the formation of patterns and cracks on the surface of the materials aged in the compost evidencing a profound loss of structure. Moreover, an extended biofilm (evident also with optical microscopy observation) was detected on the biodegraded materials, thus indicating the growth of a large number of bacteria and fungi on their surfaces.     

Random UV Mutagenesis Approach for Enhanced Biodegradation of Sulfonated Azo Dye, Green HE4B

The objective of the study was to execute mutant bacteria for efficient biodegradation of sulfonated azo dye, Green HE4B (GHE4B). UV irradiation was used to introduce random mutations in Pseudomonas sp. LBC1. Genetic alterations induced by UV irradiation in selected mutant bacteria were confirmed by random amplification of polymorphic DNA technique. The mutant bacteria named as Pseudomonas sp. 1 F reduced the time required for complete degradation of recalcitrant dye GHE4B by 25 % when compared with the wild one. The biodegradation was monitored by UV–Vis spectrophotometric analysis. Activities of enzymes like laccase, lignin peroxidase, veratryl alcohol oxidase, and NADH dichlorophenol indophenol reductase were found to be boosted in mutant bacteria as a consequence of UV-induced mutation. Matrix-assisted laser desorption/ionization-time of flight analysis of differentially expressed proteins of mutant bacteria suggested active role of antioxidant enzymes in the degradation of the dye. The degradation product was analyzed by Fourier transform infrared spectroscopy, high-performance thin-layer chromatography, and gas chromatography–mass spectrometry. Results revealed few variations in the degradation end products of wild-type and mutant bacteria. Phytotoxicity study underlined the safer biodegradation of GHE4B by mutant Pseudomonas sp. 1 F.     

Thermal degradation of MDI-based segmented polyurethanes

Thermal degradations of 4,4′-diphenylmethane diisocyanate-based thermoplastic polyurethane elastomers were conducted and investigated as functions of heating conditions by using thermogravimetric analysis, ultraviolet-visible (UV-vis) spectroscopy, gel permeation chromatography (GPC), and Fourier transform infrared (FTIR) spectroscopy. The extent of degradation increased with increasing temperatures and times. The degradation was accompanied by crosslinking and was more significant under air than under nitrogen, indicating that a free-radical mechanism was involved. The degradation mainly was due to unstable hard segments and gave a red shift in the UV-vis spectra. The degradation, leading to considerable discoloration, was demonstrated by UV-vis spectroscopy, starting from 240 °C in air for 10 min. Heated in nitrogen for the same period of time, the samples did not show considerable discoloration until 280 °C. The UV-vis data suggested that the degradation occurred through cleavages of N H bonds and C H bonds on the hard segments. Chain scission of polymer main chains, as demonstrated by GPC data, occurred at a temperature as low as 200 °C in nitrogen, although cleavage of N H bonds was not detectable by UV-vis and FTIR spectroscopy at these conditions. FTIR spectroscopy also provided evidence of cleavage of N H bonds and depolymerization of urethane linkages. Irganox 1010 was found to be an efficient antioxidant. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4126–4134, 1999     

Biodegradation of PVA-based formulations

Investigation of the biodegradability of water soluble poly(vinyl alcohol) (PVA) based blown films was carried out under different lab-scale environmental conditions. In particular respirometric tests were utilized in order to evaluate the biodegradability of PVA films in composting, in modified Sturm test and in soil burial simulation tests. Several microbial inocula present in river water, mature compost, forest and farm soils as well as sewage sludge from municipal and paper mill wastewater treatments plants were utilized for the relevant tests. A mixed PVA-degrading microbial culture was obtained by a common enrichment procedure by using sewage sludge from paper mill as inoculum; this culture was tentatively utilized for the isolation of single PVA-degrading microorganisms. As a first result we can stress that significant biodegradation extent in fairly low incubation time can be obtained only in the presence of acclimated microbial populations such as those deriving from paper mill sewage sludge, in liquid cultures. Nevertheless separation of single degrading microbial species was impossible most likely due to the establishment of symbiotic or commensal interactions between the single components of the PVA-degrading mixed cultures. On the other hand, limited mineralization rates were recorded in solid cultures in the presence of soil or compost. Finally, a mechanism of degradation of polymer chains unlike random or unzipping was suggested in the presence of either PVA-degrading mixed culture and its filtrate by means of viscometric determinations of molecular weight within the time.     

Methyl methacrylate-methyl isopropenyl ketone copolymers: Degradation under environmental conditions

Reactivity ratios for the radical copolymerisation of the methylmethacrylate (MMA) (1)/methyl isopropenyl ketone (MIK) (2) system have been evaluated at 60°C as r₁=0·97; r₂=1·09. Copolymers with MIK contents from 0 to 15% have been prepared. Films were exposed to sunlight under environmental conditions at ground level and buried under-ground at a depth of 9 cm and their photo-degradation, as measured by chain scissions and mechanical properties, was followed with exposure time. For the specimens at ground level, a clear dependence of degradation on sunlight exposure time and MIK content is observed, similar to that observed under laboratory conditions, whether in film or in solution. Negligible degradation was observed over a 2-year period in the buried specimens. Laboratory biodegradation tests seem to indicate that attack by microorganisms starts at a polymer molecular weight of about 20 000.     

Synthesis and biodegradation of poly(ester amide)s containing amino acid residues: The effect of the stereoisomeric composition of L‐ and D‐phenylalanines on the enzymatic degradation of the polymers

Biodegradable poly(ester amide)s that contained phenylalanine residues in the main chains were synthesized by the polycondensation of di‐p‐nitrophenyl sebacate and phenylalanine 2‐aminoethyl ester. The stereoisomeric composition (L /D ratio) of the phenylalanine residue in the monomer did not affect the yield and molecular weight of the polymer much. From the optical rotations of the polymers, it was found that the L /D ratio of the phenylalanine residue in the polymer was almost equal to the L /D ratio of the phenylalanine residue in the monomer. The biodegradability of the poly(ester amide)s was studied in aqueous solutions with proteases as catalysts. The polymer with 100% L ‐phenylalanine residue was effectively degraded by α‐chymotrypsin or subtilisins. However, the replacement of 10% L ‐phenylalanine with D ‐isomer resulted in a dramatic decrease in degradability. The polymers with less than 30% L ‐isomer were hardly degraded by the enzymes. Gel permeation chromatography studies suggested that the solubility of the degradation products in water greatly affected the rate and extent of biodegradation. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 385–392, 2002     

Biodegradation of Alprazolam in Pharmaceutical Wastewater Using Mesoporous Nanoparticles-Adhered Pseudomonas stutzeri

The release of pharmaceutical wastewaters in the environment is of great concern due to the presence of persistent organic pollutants with toxic effects on environment and human health. Treatment of these wastewaters with microorganisms has gained increasing attention, as they can efficiently biodegrade and remove contaminants from the aqueous environments. In this respect, bacterial immobilization with inorganic nanoparticles provides a number of advantages, in terms of ease of processing, increased concentration of the pollutant in proximity of the cell surface, and long-term reusability. In the present study, MCM-41 mesoporous silica nanoparticles (MSN) were immobilized on a selected bacterial strain to remove alprazolam, a persistent pharmaceutical compound, from contaminated water. First, biodegrading microorganisms were collected from pharmaceutical wastewater, and Pseudomonas stutzeri was isolated as a bacterial strain showing high ability to tolerate and consume alprazolam as the only source for carbon and energy. Then, the ability of MSN-adhered Pseudomonas stutzeri bacteria was assessed to biodegrade alprazolam using quantitative HPLC analysis. The results indicated that after 20 days in optimum conditions, MSN-adhered bacterial cells achieved 96% biodegradation efficiency in comparison to the 87% biodegradation ability of Pseudomonas stutzeri freely suspended cells. Kinetic study showed that the degradation process obeys a first order reaction. In addition, the kinetic constants for the MSN-adhered bacteria were higher than those of the bacteria alone.     

Cellulose fiber biodegradation in natural waters: river water,brackish water,and seawater

Cellulose, the main component of plant cell walls, is degradable in nature. However, to the best of our knowledge, this is the first report that compares the biodegradability of cellulose fibers with different structures in natural waters. River water, brackish water, and seawater were collected from the Kamo River and Osaka Bay, Japan. Biodegradation of cellulose fibers with different structures and crystallinities, ramie, mercerized ramie, and regenerated cellulose fibers in the collected natural water was investigated in the dark at 20 °C for 30 days. The primary and aerobic ultimate biodegradability were evaluated by weight loss and biochemical oxygen demand (BOD) tests, respectively. In the weight-loss test, cellulose fibers were found to be degraded by more than 50% in any natural water within 30 days. However, in the BOD test, biodegradation was diminished, with values of 40%, 20–30%, and 2–10% in river water, brackish water, and seawater, respectively. These results indicate that cellulose fibers are easily degraded into fine fragments, but it is difficult to cause their ultimate decomposition into water and carbon dioxide. Existence of such a tendency in the degree of biodegradation among the cellulose fibers remains unclear. The molecular weight of cellulose fibers in natural water was also measured during their degradation. The degradation behavior in river water and seawater was observed to be different from that in brackish water. The results thus obtained indicate that the microorganisms and enzymes that degrade cellulose fibers differ depending on the natural water, which influences the degree and mechanism of biodegradation.

     

Degradation of the blends of natural and synthetic copolyesters in different natural environments

The paper presents results of the biodegradation of the blends of natural and synthetic copolyesters in two different natural environments. Environmental degradation took place in compost with activated sludge at sewage farm and - for comparison - in the Baltic Sea in Gdynia Harbour. Degradation of these blends was monitored for 16 weeks in compost and for 6 weeks in sea water. The changes in macroscopic features of surface and the weight loss of the samples were measured during the performed experiment. The characteristic parameters of compost and sea water were also controlled during all incubation time and their influence on the rate of biodegradation is discussed. The results of this study revealed that the natural aliphatic copolyester i.e. 3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) and its blends with the synthetic aliphatic-aromatic copolyester of 1,4-butandiol with adipic and terephthalic acids degrade faster in compost than in sea water. The rate of the biodegradation process depends on the composition of blends and different abiotic parameters of compost and sea water.