Isolation of strains degrading poly(Vinyl alcohol) at high temperatures and their biodegradation ability

Isolation and screening of low-density polyethylene (LDPE) bags degrading bacteria from Addis Ababa municipal solid waste disposal site “Koshe”

Purpose

This study aims to screen bacterial isolates from the Addis Ababa municipal solid waste dumping site (Koshe) for the biodegradation of low-density polyethylene bags and analyzes their efficiency in degrading plastic bags.

Methods

In this study, low-density polyethylene bag-degrading bacteria were isolated from the Koshe municipal solid waste disposal area in Addis Ababa, Ethiopia. Screening of isolates for low-density polyethylene bag biodegradation was carried out using a clear zone method. Additionally, the efficiency of the isolates for low-density polyethylene biodegradation was evaluated using the weight loss method, scanning electron microscopy analysis, and Fourier transform infrared analysis. Finally, molecular identification of potential low-density polyethylene degrader bacterial isolates was done by 16S rDNA sequencing.

Results

Isolates KS35, KS14, and KS119 resulted in significant weight loss of low-density polyethylene film (42.87 ± 1.91%, 37.2 ± 3.06%, and 23.87 ± 0.11% weight loss, respectively). These isolates were selected for further biodegradation study using scanning electron microscopy and Fourier transform infrared analysis. Scanning electron microscopy analysis shows the formation of pores, pits, and distortion of the plastic surface. Fourier transform infrared analysis indicates the appearance of new peaks at the surface of low-density polyethylene films. Phylogenetic analysis of the three potential bacterial isolates was also carried out, and the result indicates that the sequence of isolate KS35 had 99% similarity with sequences of Methylobacterium radiotolerans MN525302. Isolate KS119 had 100% similarity with Methylobacterium fujisawaense KT720189, and the sequence of isolate KS14 had 99% similarity with species of Lysinibacillus fusiformis.

Conclusions

Weight loss, scanning electron microscopy analysis, and Fourier transform infrared analysis results show that isolates KS35, KS14, and KS119 have high potential in degrading low-density polyethylene bags.

Biodegradation of poly (vinyl alcohol) by an orychophragmus rhizosphere-associated fungus Penicillium brevicompactum OVR-5, and its proposed PVA biodegradation pathway

In recent years, the utilisation of endophytes has emerged as a promising biological treatment technology for the degradation of plastic wastes such as biodegradation of synthetic plastics. This study, therefore, aimed to explore and extensively screen endophytic fungi (from selected plants) for efficient in vitro polyvinyl alcohol (PVA) biodegradation. In total, 76 endophytic fungi were isolated and cultivated on a PVA screening agar medium. Among these fungi, 10 isolates showed potential and were subsequently identified based on phenotypical characteristics, ITS ribosomal gene sequences, and phylogenetic analyses. Four strains exhibited a maximum level of PVA-degradation in the liquid medium when cultivated for 10 days at 28 °C and 150 rpm. These strains showed varied PVA removal rates of 81% (Penicillium brevicompactum OVR-5), 67% (Talaromyces verruculosus PRL-2), 52% (P. polonicum BJL-9), and 41% (Aspergillus tubingensis BJR-6) respectively. The most promising PVA biodegradation isolate 'OVR-5', with an optimal pH at 7.0 and optimal temperature at 30 °C, produced lipase, manganese peroxidase, and laccase enzymes. Based on analyses of its metabolic intermediates, as identified with GC-MS, we proposed the potential PVA degradation pathway of OVR-5. Biodegradation results were confirmed through scanning electron microscopy and Fourier transform infrared spectroscopy. This study provides the first report on an endophytic P. brevicompactum strain (associated with Orychophragmus violaceus) that has a great ability for PVA degradation providing more insight on potential fungus-based applications in plastic waste degradation.

A novel Poly(vinyl alcohol) / carboxymethyl cellulose / yeast double degradable hydrogel with yeast foaming and double degradable property

A novel polyvinyl alcohol/carboxymethyl cellulose/yeast double degradable hydrogel was prepared with yeast as a foaming agent. The chemical structure of the hydrogel was characterized by FTIR and XPS. The micro-structure of the hydrogel was observed by SEM. The specific surface area and pore size of hydrogel were measured by BET. Methylene blue adsorption capacity of the hydrogels were investigated and the adsorption mechanism was explored. The biodegradability of double degradable hydrogel was investigated. The results showed that yeast was encapsulated in hydrogel by electrostatic action. With the addition of yeast, not only the specific surface area and average pore size of the hydrogel increased but also methylene blue maximum adsorption capacity of the double degradable hydrogel (110 ± 3.5 mg/g) was significantly higher than that of the hydrogel without yeast (57 ± 1.9 mg/g). The adsorption mechanism was dominated by chemical adsorption and was accompanied by biodegradable and electrostatic adsorption. The kinetic data were fitted to the pseudo-second-order kinetic model reasonably well. The introduction of yeast promoted the biodegradable of hydrogel and increased the degradation rate of polyvinyl alcohol in the material with a maximum degradation rate of 45 ± 2.8%.

Metabolic and proteomic mechanism of benzo[a]pyrene degradation by Brevibacillus brevis

Benzo[a]pyrene (BaP) is a model compound of polycyclic aromatic hydrocarbons. The relationship between its toxicity and some target biomolecules has been investigated. To reveal the interactions of BaP biodegradation and metabolic network, BaP intermediates, proteome, carbon metabolism and ion transport were analyzed. The results show that 76% BaP was degraded by Brevibacillus brevis within 7 d through the cleavage of aromatic rings with the production of 1-naphthol and 2-naphthol. During this process, the expression of xylose isomerase was induced for xylose metabolism, whereas, α-cyclodextrin could no longer be metabolized. Lactic acid, acetic acid and oxalic acid at 0.1-1.2 mg dm^-3 were released stemming from their enhanced biosynthesis in the pathways of pyruvate metabolism and citrate cycle, while 5-7 mg dm^-3 of PO₄^3- were transported for energy metabolism. The relative abundance of 43 proteins was significantly increased for pyruvate metabolism, citrate cycle, amino acid metabolism, purine metabolism, ribosome metabolism and protein synthesis.

Biosorption and degradation of decabromodiphenyl ether by Brevibacillus brevis and the influence of decabromodiphenyl ether on cellular metabolic responses

There is global concern about the effects of decabromodiphenyl ether (BDE209) on environmental and public health. The molecular properties, biosorption, degradation, accumulation, and cellular metabolic effects of BDE209 were investigated in this study to identify the mechanisms involved in the aerobic biodegradation of BDE209. BDE209 is initially absorbed by wall teichoic acid and N-acetylglucosamine side chains in peptidoglycan, and then, BDE209 is transported and debrominated through three pathways, giving tri-, hepta-, octa-, and nona-bromodiphenyl ethers. The C-C bond energies decrease as the number of bromine atoms on the diphenyl decreases. Polybrominated diphenyl ethers (PBDEs) inhibit protein expression or accelerate protein degradation and increase membrane permeability and the release of Cl(-), Na(+), NH4 (+), arabinose, proteins, acetic acid, and oxalic acid. However, PBDEs increase the amounts of K(+), Mg(2+), PO4 (3-), SO4 (2-), and NO3 (-) assimilated. The biosorption, degradation, accumulation, and removal efficiencies when Brevibacillus brevis (1 g L(-1)) was exposed to BDE209 (0.5 mg L(-1)) for 7 days were 7.4, 69.5, 16.3, and 94.6 %, respectively.

A thiostrepton resistance gene and its mutants serve as selectable markers in Geobacillus kaustophilus HTA426

Effective utilization of microbes often requires complex genetic modification using multiple antibiotic resistance markers. Because a few markers have been used in Geobacillus spp., the present study was designed to identify a new marker for these thermophiles. We explored antibiotic resistance genes functional in Geobacillus kaustophilus HTA426 and identified a thiostrepton resistance gene (tsr) effective at 50 °C. The tsr gene was further used to generate the mutant tsr(H258Y) functional at 55 °C. Higher functional temperature of the mutant was attributable to the increase in thermostability of the gene product because recombinant protein produced from tsr(H258Y) was more thermostable than that from tsr. In fact, the tsr(H258Y) gene served as a selectable marker for plasmid transformation of G. kaustophilus. This new marker could facilitate complex genetic modification of G. kaustophilus and potentially other Geobacillus spp.

Polysaccharide-degrading thermophiles generated by heterologous gene expression in Geobacillus kaustophilus HTA426

Thermophiles have important advantages over mesophiles as host organisms for high-temperature bioprocesses, functional production of thermostable enzymes, and efficient expression of enzymatic activities in vivo. To capitalize on these advantages of thermophiles, we describe here a new inducible gene expression system in the thermophile Geobacillus kaustophilus HTA426. Six promoter regions in the HTA426 genome were identified and analyzed for expression profiles using β-galactosidase reporter assay. This analysis identified a promoter region upstream of a putative amylose-metabolizing gene cluster that directed high-level expression of the reporter gene. The expression was >280-fold that without a promoter and was further enhanced 12-fold by maltose addition. In association with a multicopy plasmid, this promoter region was used to express heterologous genes. Several genes, including a gene whose product was insoluble when expressed in Escherichia coli, were successfully expressed as soluble proteins, with yields of 0.16 to 59 mg/liter, and conferred new functions to G. kaustophilus strains. Remarkably, cellulase and α-amylase genes conferred the ability to degrade cellulose paper and insoluble starch at high temperatures, respectively, generating thermophiles with the potential to degrade plant biomass. Our results demonstrate that this novel expression system expands the potential applications of G. kaustophilus.