Finding a Benign Plasticizer to Enhance the Microbial Degradation of Polyhydroxybutyrate (PHB) Evaluated by PHB Degrader Microbulbifer sp. SOL66

Synthesis and characterization of self-healing bio-based polyurethane from microbial poly(3-hydroxybutyrate) produced in methanotrophs

Poly(3-hydroxybutyrate) (PHB) is an important class of renewable and biodegradable polymers that have recently attracted significant interest. However, the limitations of the physical properties of PHB, owing to its brittle nature, hinder its application in versatile polymers. In this study, we propose an efficient conversion of microbial PHB produced and recovered from methanotrophs to produce the oligomer PHB-diol. The PHB transesterification was conducted using different alcohols and the reaction conditions were optimized to obtain a liquid-like PHB-diol product, a low-molar-mass polyol with a molecular weight of 1000-1400 g/mol for polyurethane (PU) synthesis. A comprehensive characterization of PU samples made from PHB-derived polyol suggested that it could be a viable substitute for 50 wt% traditional petroleum-derived polyol in PU synthesis. In contrast to petroleum-based PU, the synthetic PU film made from microbiologically generated PHB-diol showed noteworthy self-healing ability with a healing efficiency of up to 91.08 % at moderate temperatures after a simple drying process. Self-healing ability is highly desirable and significant for the sustainable manufacturing of advanced materials from bioresources for a wide range of practical applications in electronic devices, coatings, biomedicine, and aerospace.

Polymer degrading marine Microbulbifer bacteria: an un(der)utilized source of chemical and biocatalytic novelty

Microbulbifer is a genus of halophilic bacteria that are commonly detected in the commensal marine microbiomes. These bacteria have been recognized for their ability to degrade polysaccharides and other polymeric materials. Increasingly, Microbulbifer genomes indicate these bacteria to be an untapped reservoir for novel natural product discovery and biosynthetic novelty. In this review, we summarize the distribution of Microbulbifer bacteria, activities of the various polymer degrading enzymes that these bacteria produce, and an up-to-date summary of the natural products that have been isolated from Microbulbifer strains. We argue that these bacteria have been hiding in plain sight, and contemporary efforts into their genome and metabolome mining are going to lead to a proliferation of Microbulbifer-derived natural products in the future. We also describe, where possible, the ecological interactions of these bacteria in marine microbiomes.

Exploring the hidden environmental pollution of microplastics derived from bioplastics: A review

Bioplastics might be an ecofriendly alternative to traditional plastics. However, recent studies have emphasized that even bioplastics can end up becoming micro- and nano-plastics due to their degradation under ambient environmental conditions. Hence, there is an urgent need to assess the hidden environmental pollution caused by bioplastics. However, little is known about the evolutionary trends of bibliographic data, degradation pathways, formation, and toxicity of micro- and nano-scaled bioplastics originating from biodegradable polymers such as polylactic acid, polyhydroxyalkanoates, and starch-based plastics. Therefore, the prime objective of the current review was to investigate evolutionary trends and the latest advancements in the field of micro-bioplastic pollution. Additionally, it aims to confront the limitations of existing research on microplastic pollution derived from the degradation of bioplastic wastes, and to understand what is needed in future research. The literature survey revealed that research focusing on micro- and nano-bioplastics has begun since 2012. This review identifies novel insights into microbioplastics formation through diverse degradation pathways, including photo-oxidation, ozone-induced degradation, mechanochemical degradation, biodegradation, thermal, and catalytic degradation. Critical research gaps are identified, including defining optimal environmental conditions for complete degradation of diverse bioplastics, exploring micro- and nano-bioplastics formation in natural environments, investigating the global occurrence and distribution of these particles in diverse ecosystems, assessing toxic substances released during bioplastics degradation, and bridging the disparity between laboratory studies and real-world applications. By identifying new trends and knowledge gaps, this study lays the groundwork for future investigations and sustainable solutions in the realm of sustainable management of bioplastic wastes.

Electrospinning of biomimetic materials with fibrinogen for effective early-stage wound healing

Electrospun biomimetic materials based on polyester of natural origin poly-3-hudroxybutyrate (PHB) modified with hemin (Hmi) and fibrinogen (Fbg) represent a great interest and are potentially applicable in various fields. Here, we describe formulation of the new fibrous PHB-Fbg and PHB-Hmi-Fbg materials with complex structure for biomedical application. The average diameter of the fibers was 3.5 μm and 1.8 μm respectively. Hmi presence increased porosity from 80 % to 94 %, significantly reduced the number of defects, ensured the formation of a larger number of open pores, and improved mechanical properties. Hmi presence significantly improved the molding properties of the material. Hmi facilitated effective Fbg adsorption on the of the PHB wound-healing material, ensuring uniform localization of the protein on the surface of the fibers. Next, we evaluated cytocompatibility, cell behavior, and open wound healing in mice. The results demonstrated that PHB-Fbg and PHB-Hmi-Fbg electrospun materials had pronounced properties and may be promising for early-stage wound healing - the PHB-Hmi-Fbg sample accelerated wound closure by 35 % on the 3rd day, and PHB-Hmi showed 45 % more effective wound closure on the 15th day.

Microbulbifer litoralis sp. nov., Isolated from Seashore of Weizhou Island

A bacterium designated GXH0434T was isolated from sea shore samples collected from Weizhou Island, Beihai, Guangxi, China. The organism is motile, strictly aerobic, and possesses a rod-coccus cell cycle in association with the growth phase. It can grow at 15-45 °C (optimum 37 °C), at pH 6.0-11.0 (optimum 6.0), and at 0-20% (w/v) NaCl (optimum 5.0-8.0%). The strain is positive for peroxidase and oxidase activity, negative for Voges-Proskauer test, can hydrolyze Tween 20, Tween 60, Tween 80, casein, and is able to produce siderophore and has the function of nitrogen fixation. Molecular phylogenetic analysis based on 16S rRNA gene sequences indicated that GXH0434T was most closely related to Microbulbifer halophilus KCTC 12848T with the similarity of 97.2%, followed by Microbulbifer chitinilyticus JCM 16148T (97.1%) and Microbulbifer taiwanensis LMG 26125T (96.5%). The digital DNA-DNA hybridization and the average nucleotide identity values between GXH0434T and Microbulbifer halophilus KCTC 12848T were 28.90% and 83.38%, respectively, which were below thresholds of species delineation. The genomic DNA G+C content of the strain was 61.9%. The major fatty acids were iso-C15:0, C16:0, iso-C11:0 3-OH, iso-C11:0 and Summed features 8 (C18:0 ω7c and/or C18:0 ω6c). The major polar lipids detected in GXH0434T were diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidylcholine (PC). The major respiratory quinone was ubiquinone Q-8. Based on the above polyphasic classification indicated strain GXH0434T represents a novel species of the genus Microbulbifer, for which the name Microbulbifer litoralis sp. nov. is proposed. The type strain is GXH0434T (= MCCC 1K07158T = KCTC 92169T).

An efficient and eco-friendly approach for the sustainable recovery and properties characterization of polyhydroxyalkanoates produced by methanotrophs

Synthetic biodegradable and bio-based polymers have emerged as sustainable alternatives to nonrenewable petroleum-derived polymers which cause serious environmental issues. In particular, polyhydroxyalkanoates (PHA) are promising biopolymers owing to their outstanding biodegradability and biocompatibility. The production of the homopolymer poly(3-hydroxybutyrate) (PHB) and copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) from type II methanotrophs via microbial fermentation was presented. For the efficient extraction and recovery of intracellular PHA from methanotrophs, different extraction approaches were investigated including solvent extraction using 1,3-dioxolane as a green solvent, integrated cell lysis and solvent extraction, and cell digestion without the use of organic solvents. Among various extraction approaches, the integrated method exhibited the highest extraction performance, with PHA recovery and purity exceeding 91 % and 93 %, respectively, even when the PHA content of the cells was low. Furthermore, the molecular weight, thermal stability, and mechanical properties of the recovered PHA were comprehensively analyzed to suggest its suitable practical applications. The obtained properties were comparable to that of the commercial PHA products and PHA produced from other microbial species, indicating an efficient recovery of high-quality PHA produced from methanotrophs.

Untargeted metabolomics elucidated biosynthesis of polyhydroxyalkanoate by mixed microbial cultures from waste activated sludge under different pH values

Waste activated sludge has been frequently used as mixed substrate to produce polyhydroxyalkanoate (PHA). However, insufficient research on microbial metabolism has led to difficulties in regulating PHA accumulation in mixed microbial cultures (MMCs). To explore the variation of functional genes during domestication and the effect of different pH conditions on metabolic pathways during PHA accumulation, MMCs were domesticated by adding acetate and propionate with aerobic dynamic feeding strategy for 60 days. As the domestication progressed, the microbial community diversity declined and PHA-producing bacteria, Brevundimonas, Dechloromonas and Hyphomonas, were enriched. Through bacterial function prediction by PICRUSt the gene rpoE involved in starvation resistance of bacteria was enriched after the domestication. The pH value of 8.5 was the best condition for PHA accumulation in MMCs, under which a maximum PHA content reached 23.50% and hydroxybutyric (HB)/hydroxyvaleric (HV) reached 2.22. Untargeted metabolomics analysis exhibited that pH conditions of 7 and 8.5 could promote the up-regulation of significant differential metabolites, while higher alkaline conditions caused the inhibition of metabolic activity. Functional annotation showed that pH condition of 8.5 significantly affected Pyrimidine metabolism, resulting in an increase in PHA production. Regarding the pathways of PHA biosynthesis, acetoacetate was found to be significant in the metabolism of hydroxybutyric, and the alkaline condition could restrain the conversion from hydroxybutyric (HB) to the acetoacetate to protect PHB accumulation in MMCs compared with neutral condition. Taken together, the present results can advance the fundamental understanding of metabolic function in PHA accumulation under different pH conditions.

Polyhydroxybutyrate production from crude glycerol using a highly robust bacterial strain Halomonas sp. YLGW01

Petrochemical-based plastics are hardly biodegradable and a major cause of environmental pollution, and polyhydroxybutyrate (PHB) is attracting attention as an alternative due to its similar properties. However, the cost of PHB production is high and is considered the greatest challenge for its industrialization. Here, crude glycerol was used as a carbon source for more efficient PHB production. Among the 18 strains investigated, Halomonas taeanenisis YLGW01 was selected for PHB production due to its salt tolerance and high glycerol consumption rate. Furthermore, this strain can produce poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3 HV)) with 17 % 3 HV mol fraction when a precursor is added. PHB production was maximized through medium optimization and activated carbon treatment of crude glycerol, resulting in 10.5 g/L of PHB with 60 % PHB content in fed-batch fermentation. Physical properties of the produced PHB were analyzed, i.e., weight average molecular weight (6.8 × 10⁵), number average molecular weight (4.4 × 10⁵), and the polydispersity index (1.53). In the universal testing machine analysis, the extracted intracellular PHB showed a decrease in Young's modulus, an increase in Elongation at break, greater flexibility than authentic film, and decreased brittleness. This study confirmed that YLGW01 is a promising strain for industrial PHB production using crude glycerol.

Microbial Biopolymers: Trends in Synthesis, Modification, and Applications

Microbes can act as a factory for the conversion of a variety of carbon and nitrogen sources into diverse kinds of intracellular and extracellular biopolymers, including polyhydroxyalkanoates (PHA) and exopolysaccharides (EPS), under different stress conditions [...].