Polyhydroxybutyrate (PHB) biodegradation using bacterial strains with demonstrated and predicted PHB depolymerase activity

Biodegradable biopolymers: Real impact to environment pollution

Biobased biodegradable polymers (BBP) derived from different renewable resources are commonly considered as attractive alternative to petroleum-based polymers, such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), etc. It is because they can address the issues of serious environmental problems resulted from accumulation of plastic wastes. In the review current methods of obtaining of most abundant BBP, polylactic acid (PLA) and polyhydroxybutyrate (PHB), have been studied with an emphasis on the toxicity of compounds used for their production and additives improving consumer characteristics of PLA and PHB based market products. Substantial part of additives was the same used for traditional polymers. Analysis of the data on the response of different organisms and plants on exposure to these materials and their degradation products confirmed the doubts about real safety of BBP. Studies of safer additives are scarce and are of vital importance. Meanwhile, technologies of recycling of traditional petroleum-based polymers were shown to be well-developed, which cannot be said about PLA or PHB based polymers, and their blends with petroleum-based polymers. Therefore, development of more environmentally friendly components and sustainable technologies of production are necessary before following market expansion of biobased biodegradable products.

Characterization of Ralstonia insidiosa C1 isolated from Alpine regions: Capability in polyhydroxyalkanoates degradation and production

This study ventures into the exploration of potential poly-3-hydroxybutyrate (PHB) degradation in alpine environments. PHB-degrading bacteria were identified in both campus soil, representing a residential area, and Mt. Kurodake soil, an alpine region in Hokkaido, Japan. Next-generation sequencing analysis indicated that the campus soil exhibited higher microbial diversity, while Ralstonia insidiosa C1, isolated from Mt. Kurodake soil, displayed the highest proficiency in PHB degradation. R. insidiosa C1 efficiently degraded up to 3% (w/v) of PHB and various films composed of other biopolymers at 14 °C. This bacterium synthesized homopolymers using substrates such as 3-hydroxybutyric acid, sugars, and acetic acid, while also produced copolymers using a mixture of fatty acids. The analysis results confirmed that the biopolymer synthesized by strain C1 using glucose was PHB, with physical properties comparable to commercial products. The unique capabilities of R. insidiosa C1, encompassing both the production and degradation of bioplastics, highlight its potential to establish a novel material circulation model.

Influence of microbial biomass content on biodegradation and mechanical properties of poly(3-hydroxybutyrate) composites

Biodegradation rates and mechanical properties of poly(3-hydroxybutyrate) (PHB) composites with green algae and cyanobacteria were investigated for the first time. To the authors knowledge, the addition of microbial biomass led to the biggest observed effect on biodegradation so far. The composites with microbial biomass showed an acceleration of the biodegradation rate and a higher cumulative biodegradation within 132 days compared to PHB or the biomass alone. In order to determine the causes for the faster biodegradation, the molecular weight, the crystallinity, the water uptake, the microbial biomass composition and scanning electron microscope images were assessed. The molecular weight of the PHB in the composites was lower than that of pure PHB while the crystallinity and microbial biomass composition were the same for all samples. A direct correlation of water uptake and crystallinity with biodegradation rate could not be observed. While the degradation of molecular weight of PHB during sample preparation contributed to the improvement of biodegradation, the main reason was attributed to biostimulation by the added biomass. The resulting enhancement of the biodegradation rate appears to be unique in the field of polymer biodegradation. The tensile strength was lowered, elongation at break remained constant and Young's modulus was increased compared to pure PHB.

Marine biodegradation of tailor-made polyhydroxyalkanoates (PHA) influenced by the chemical structure and associated bacterial communities

Over recent years, biodegradable polymers have been proposed to reduce environmental impacts of plastics for specific applications. The production of polyhydroxyalkanoates (PHA) by using diverse carbon sources provides further benefits for the sustainable development of biodegradable plastics. Here, we present the first study evaluating the impact of physical, chemical and biological factors driving the biodegradability of various tailor-made PHAs in the marine environment. Our multidisciplinary approach demonstrated that the chemical structure of the polymer (i.e. the side chain size for short- vs. medium-chain PHA) which was intrinsically correlated to the physico-chemical properties, together with the specificity of the biofilm growing on plastic films (i.e., the associated 'plastisphere') were the main drivers of the PHA biodegradation in the marine environment.

Accelerating the Biodegradation of Poly(lactic acid) through the Inclusion of Plant Fibers: A Review of Recent Advances

As the global demand for plastics continues to grow, plastic waste is accumulating at an alarming rate with negative effects on the natural environment. The industrially compostable biopolymer poly(lactic acid) (PLA) is therefore being adopted for use in many applications, but the degradation of this material is slow under many end-of-life conditions. This Perspective explores the feasibility of accelerating the degradation of PLA through the formation of PLA-plant fiber composites. Topics include: (a) key properties of PLA, plant-based fibers, and biocomposites; (b) mechanisms of both hydrolytic degradation and biodegradation of PLA-fiber composites; (c) end-of-life degradation of PLA and PLA-plant fiber composites in aerobic and anaerobic conditions, relevant to compost, soil and seawater (aerobic), and landfills (anaerobic); and (d) sustainability and environmental impact of PLA and PLA-plant fiber composites, as evaluated using life cycle assessment. Additional degradation modes, including thermal and photodegradation, which are relevant during processing and use, have been omitted for clarity, as have other types of PLA biocomposites. Multiple studies have shown that the addition of some types of plant fibers to PLA (to form PLA biocomposites) accelerates both water transport in the material and hydrolysis, presenting a possible avenue for improving the end-of-life degradation of these materials. To facilitate the continued development of materials with enhanced biodegradability, we identify a need to implement testing protocols that can distinguish between different degradation mechanisms.

Poly(3-hydroxybutyrate) Degradation by Bacillus infantis sp. Isolated from Soil and Identification of phaZ and bdhA Expressing PHB Depolymerase

Poly(3-hydroxybutyrate) (PHB) is a biodegradable and biocompatible bioplastic. Effective PHB degradation in nutrient-poor environments is required for industrial and practical applications of PHB. To screen for PHB-degrading strains, PHB double-layer plates were prepared and three new Bacillus infantis species with PHB-degrading ability were isolated from the soil. In addition, phaZ and bdhA of all isolated B. infantis were confirmed using a Bacillus sp. universal primer set and established polymerase chain reaction conditions. To evaluate the effective PHB degradation ability under nutrient-deficient conditions, PHB film degradation was performed in mineral medium, resulting in a PHB degradation rate of 98.71% for B. infantis PD3, which was confirmed in 5 d. Physical changes in the degraded PHB films were analyzed. The decrease in molecular weight due to biodegradation was confirmed using gel permeation chromatography and surface erosion of the PHB film was observed using scanning electron microscopy. To the best of our knowledge, this is the first study on B. infantis showing its excellent PHB degradation ability and is expected to contribute to PHB commercialization and industrial composting.

Bioprospecting for polyesterase activity relevant for PET degradation in marine Enterobacterales isolates

Plastics have quickly become an integral part of modern life. Due to excessive production and improper waste disposal, they are recognized as contaminants present in practically all habitat types. Although there are several polymers, polyethylene terephthalate (PET) is of particular concern due to its abundance in the environment. There is a need for a solution that is both cost-effective and ecologically friendly to address this pollutant. The use of microbial depolymerizing enzymes could offer a biological avenue for plastic degradation, though the full potential of these enzymes is yet to be uncovered. The purpose of this study was to use (1) plate-based screening methods to investigate the plastic degradation potential of marine bacteria from the order Enterobacterales collected from various organismal and environmental sources, and (2) perform genome-based analysis to identify polyesterases potentially related to PET degradation. 126 bacterial isolates were obtained from the strain collection of RD3, Research Unit Marine Symbioses-GEOMAR-and sequentially tested for esterase and polyesterase activity, in combination here referred to as PETase-like activity. The results show that members of the microbial families Alteromonadaceae, Shewanellaceae, and Vibrionaceae, derived from marine sponges and bryozoans, are the most promising candidates within the order Enterobacterales. Furthermore, 389 putative hydrolases from the α/β superfamily were identified in 23 analyzed genomes, of which 22 were sequenced for this study. Several candidates showed similarities with known PETases, indicating underlying enzymatic potential within the order Enterobacterales for PET degradation.

Biomass formation and organic carbon migration potential of microplastics from a PET recycling plant: Implication of biostability

The growth of the polyethylene terephthalate (PET) mechanical recycling industry has resulted in the challenge of generating microplastics (MPs). However, little attention has been given to investigating the release of organic carbon from these MPs and their roles in promoting bacterial growth in aquatic environments. In this study, a comprehensive method is proposed to access the potential of organic carbon migration and biomass formation of MPs generated from a PET recycling plant, and to understand its impact on the biological systems of freshwater habitats. Various MPs sizes from a PET recycling plant were selected to conduct a series of tests, including the organic carbon migration test, biomass formation potential test, and microbial community analysis. The MPs smaller than 100 µm, which are difficult to remove from the wastewater, exhibited greater biomass in the observed samples (1.05 × 10¹¹ bacteria per gram MPs). Moreover, PET MPs altered the microbial diversity, with Burkholderiaceae becoming the most abundant, while Rhodobacteraceae was eliminated after being incubated with MPs. This study partly revealed that organic matter adsorbed on the surface of MPs was a significant nutrient source that increased biomass formation. PET MPs acted not only as carriers for microorganisms but also for organic matter. As a result, it is crucial to develop and refine recycling methods in order to decrease the production of PET MPs and minimize their adverse effects on the environment.

Highly efficient polyhydroxyalkanoate production from lignin using genetically engineered Halomonas sp. Y3

Lignin degradation represents a significant challenge in biological valorization, but it is suffering from insufficiency, putting barriers to efficient lignin conversion. Herein, the study first develops a highly efficient laccase secretion apparatus, enabling high enzyme activity of 184 U/mL, complementing the biochemical limits on lignin depolymerization well in Halomonas sp. Y3. Further engineering of PHA biosynthesis produces a significantly high PHA titer of 286, 742, and 868 mg/L from alkaline lignin, catechol, and protocatechuate, respectively. The integration of laccase-secretion and PHA production modules enables a record titer of 693 and 1209 mg/L in converting lignin and lignin-containing stream to PHA, respectively. The titer is improved furtherly to 740 and 1314 mg/L by developing a non-sterilized fermentation. This study advances a cheaper and greener production of valuable chemicals from lignin by constructing a biosynthetic platform for PHA production and provides novel insight into the lignin conversion by extremophilic microbes.

A comprehensive review on recent advancements in biodegradation and sustainable management of biopolymers

Recent years have seen upsurge in plastic manufacturing and its utilization in various fields, such as, packaging, household goods, medical applications, and beauty products. Due to various adverse impacts imposed by synthetic plastics on the health of living well-being and the environment, the biopolymers have been emerged out an alternative. Although, the biopolymers such as polyhydroxyalkanoates (PHA) are entirely degradable. However, the other polymers, such as poly (lactic acid) (PLA) are only partially degradable and often not biosynthesized. Biodegradation of the polymers using microorganisms is considered an effective bioremediation approach. Biodegradation can be performed in aerobic and anaerobic environments. In this context, the present review discusses the biopolymer production, their persistence in the environment, aerobic biodegradation, anaerobic biodegradation, challenges associated with biodegradation and future perspectives. In addition, this review discusses the advancement in the technologies associated with biopolymer production, biodegradation, and their biodegradation standard in different environmental settings. Furthermore, differences in the degradation condition in the laboratory as well as on-site are discussed.

Isolation and optimization of extracellular PHB depolymerase producer Aeromonas caviae Kuk1-(34) for sustainable solid waste management of biodegradable polymers

Bioplastics, synthesized by several microbes, accumulates inside cells under stress conditions as a storage material. Several microbial enzymes play a crucial role in their degradation. This research was carried to test the biodegradability of poly-β-hydroxybutyrate (PHB) utilizing PHB depolymerase, produced by bacteria isolated from sewage waste soil samples. Potent PHB degrader was screened based on the highest zone of hydrolysis followed by PHB depolymerase activity. Soil burial method was employed to check their degradation ability at different incubation periods of 15, 30, and 45 days at 37±2°C, pH 7.0 at 60% moisture with 1% microbial inoculum of Aeromonas caviae Kuk1-(34) (MN414252). Without optimized conditions, 85.76% of the total weight of the PHB film was degraded after 45 days. This degradation was confirmed with Fourier-transform infrared spectroscopy (FTIR) and Scanning electron microscope (SEM) analysis. The presence of bacterial colonies on the surface of the degraded film, along with crest, holes, surface erosion, and roughness, were visible. Media optimization was carried out in statistical mode using Plackett Burman (PB) and Central Composite Design (CCD) of Response Surface Methodology (RSM) by considering ten different factors. Analysis of Variance (ANOVA), Pareto chart, response surface plots, and F-value of 3.82 implies that the above statistical model was significant. The best production of PHB depolymerase enzyme (14.98 U/mL) was observed when strain Kuk1-(34) was grown in a media containing 0.1% PHB, K₂HPO₄ (1.6 gm/L) at 27 ℃ for seven days. Exploiting these statistically optimized conditions, the culture was found to be a suitable candidate for the management of solid waste, where 94.4% of the total weight of the PHB film was degraded after 45 days of incubation.

Phytotoxicity assessment of biodegradable and non-biodegradable plastics using seed germination and early growth tests

Global production of plastics remains at the high level despite the SARS-Cov-2 pandemic. These are primarily petroleum-derived plastics but the contribution of bio-based plastics estimated at the level of 1% in the plastic market in 2019 is expected to be increasing. Simultaneously, the significant part of plastic waste is still disposed improperly and pollutes the environment making a threat to all living organisms. In this work three plastic materials, two bio-based biodegradable: polylactide (PLA) and polyhydroxybutyrate (PHB), and one petroleum-derived non-biodegradable polypropylene (PP) were studied towards their effects on seed germination and early growth of higher plants. The following plants were used as bioindicators: monocotyledonous plant - Sorghum saccharatum and two dicotyledonous plants: Sinapsis alba and Lepidium sativum. Plastics did not affect seed germination of higher plants even at the highest concentration tested (11.9% w/w) but their presence in soil acted in various ways on growth of the plants. Either no or inhibitive or stimulation effects on growth of roots or stems were noticed. It depended on the concentration and chemical composition of the plastic tested, and plant species. PHB and PLA more often caused to the inhibition of root growth than PP did. This phenomenon was observed in particular with regard to the dicotyledonous plants. Moreover, in the tests with the dicotyledonous plants (S. alba and L. sativum) the dose-response relations were usually determined as statistically relevant. Among these plants cress (L. sativum) occurred to be more sensitive and allowed for obtaining the dose-response dependence for both root and stem length, and, what is important, it took place in the case of each of materials tested. Therefore, cress is recommended to be used as a bioindicator in the assessment of the effect of plastics (petroleum-derived and bio-based plastics) on the early stages of growth of higher plants.

A review on polyhydroxyalkanoate production from agricultural waste Biomass: Development, Advances, circular Approach, and challenges

Polyhydroxyalkanoates are biopolymers produced by microbial fermentation. They have excellent biodegradability and biocompatibility, which are regarded as promising substitutes for traditional plastics in various production and application fields. This review details the research progress in PHA production from lignocellulosic crop residues, lipid-type agricultural wastes, and other agro-industrial wastes such as molasses and whey. The effective use of agricultural waste can further reduce the cost of PHA production while avoiding competition between industrial production and food. The latest information on fermentation parameter optimization, fermentation strategies, kinetic studies, and circular approach has also been discussed. This review aims to analyze the crucial process of the PHA production from agricultural wastes to provide support and reference for further scale-up and industrial production.

Polyhydroxyalkanoates (PHAs) degradation by the newly isolated marine Bacillus sp. JY14

Polyhydroxyalkanoates (PHAs) are bioplastic substitutes for petroleum-derived plastics that may help to reduce the increasing environmental impact of plastic pollution. Among them, polyhydroxybutyrate (PHB) is a promising biopolymer, incentivizing many researchers to search for PHB-producing and PHB-degrading bacteria for improved PHB utilization. Many novel PHB-producing microorganisms have been discovered; however, relatively few PHB-degrading bacteria have been identified. Six PHB-degrading bacteria were found in marine soil and investigated their PHB-degrading abilities under various temperature and salinity conditions using solid-media based culture. Finally, thermotolerant and halotolerant PHB-degrader Bacillus sp. JY14 was selected. PHB degradation was confirmed by monitoring changes in the physical and chemical properties of PHB films incubated with Bacillus sp. JY14 using scanning electron microscopy, Fourier-transform infrared spectroscopy, and gel permeation chromatography. Further, PHB degradation ability of Bacillus sp. JY14 was measured in liquid culture by gas chromatography. After 14 days of cultivation with PHB film, Bacillus sp. JY14 achieved approximately 98% PHB degradation. Applying various bioplastics to assess the bacteria's biodegradation capabilities, the result showed that Bacillus sp. JY14 could also degrade P(3HB-co-4HB) and P(3HB-co-3HV). Overall, this study identified a thermotolerant and halotolerant bacteria capable of PHB degradation under solid and liquid conditions. These results suggest that this bacteria could be utilized to degrade various PHAs.

Microbial degradation of polyhydroxybutyrate with embedded polyhexamethylene guanidine derivatives

The aim of this study was to isolate biofilm-forming bacteria that are capable of degrading polyhydroxybutyrate (PHB) with polyhexamethylene guanidine (PHMG) derivatives. The three types of derivatives incorporated in PHB and their concentration affected the biodegradability of the tested films in both water and compost. The PHMG derivative granular polyethylene wax at the highest concentration significantly inhibited BOD in both environments. At the same time, in water, PHB with PHMG stearate at 1% concentration was also found to inhibit biodegradation but to a lesser extent than PHMG polyethylene wax granulate. Analyzing the values of biofilm abundance and their hydrolytic activity in water, low concentrations of PHMG derivatives (0.2 and 0.6%) slightly inhibited biofilm abundance on the surface of the tested composites. Only granular polyethylene wax PHMG (at 1% concentration) significantly reduced biofilm formation and hydrolase activity in the compost to the greatest extent. Bacteria from biofilm were isolated and identified. Based on the 16S rRNA gene sequence, the strains belong to Bacillus toyonensis HW1 and Variovorax boronicumulans HK3. Introduction of the tested isolates to the environment can enhance composites degradation. However, this requires further research.

Landfill microbiome harbour plastic degrading genes: A metagenomic study of solid waste dumping site of Gujarat, India

Globally, environmental pollution by plastic waste has become a severe ecological and social problem worldwide. The present study aimed to analyse the bacterial community structure and functional potential of the landfill site using high throughput shotgun metagenomic approach to understand plastic degrading capabilities present in the municipal solid waste (MSW) dumping site. In this study, soil, leachate and compost samples were collected from various locations (height and depth) of the Pirana landfill site in Ahmedabad city Gujarat, India. In total 30 phyla, 58 class, 125 order, 278 families, 793 genera, and 2468 species were predicted. The most dominant phyla detected were Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria in the soil and compost samples. Whereas, in leachate samples, the predominant phyla belonged to Firmicutes (54.24%) followed by Actinobacteria (43.67%) and Proteobacteria (1.02%). The functional profiling revealed the presence of enzymatic groups and pathways involved in biodegradation of xenobiotics. The results also demonstrated the presence of potential genes that is associated with the biodegradation of different types of plastics such as polyethylene (PE), polyethylene terephthalate (PET), and polystyrene (PS). Present study extablishes the relationship between microbial community structure and rich sources of gene pool, which are actively involved in biodegradation of plastic waste in landfill sites.

Recent approaches for enhanced production of microbial polyhydroxybutyrate: Preparation of biocomposites and applications

In modern decades, an increase in environmental awareness has attracted the keen interest of researchers to investigate eco-sustainable, recyclable materials to minimize reliance on petroleum-based polymeric compounds. Poly (3-hydroxybutyrate) is amorphous, linear, and biodegradable bacterial polyesters that belong to the polyhydroxyalkanoates family with enormous applications in many fields. The present review provides comprehensive information on polyhydroxybutyrate production from different biomass feedstock. Various studies on PHB production by genetically engineered bacterial cells and optimization of parameters have been discussed. Recent technological innovation in processing polyhydroxybutyrate-based biocomposite through the different process has also been examined. Besides this, the potential applications of the derived competent biocomposites in the other fields have been depicted.

Microbial Polyhydroxyalkanoates Granules: An Approach Targeting Biopolymer for Medical Applications and Developing Bone Scaffolds

Microbial polyhydroxyalkanoates (PHA) are proteinaceous storage granules ranging from 100 nm to 500 nm. Bacillus sp. serve as unique bioplastic sources of short-chain length and medium-chain length PHA showcasing properties such as biodegradability, thermostability, and appreciable mechanical strength. The PHA can be enhanced by adding functional groups to make it a more industrially useful biomaterial. PHA blends with hydroxyapatite to form nanocomposites with desirable features of compressibility. The reinforced matrices result in nanocomposites that possess significantly improved mechanical and thermal properties both in solid and melt states along with enhanced gas barrier properties compared to conventional filler composites. These superior qualities extend the polymeric composites' applications to aggressive environments where the neat polymers are likely to fail. This nanocomposite can be used in different industries as nanofillers, drug carriers for packaging essential hormones and microcapsules, etc. For fabricating a bone scaffold, electrospun nanofibrils made from biocomposite of hydroxyapatite and polyhydroxy butyrate, a form of PHA, can be incorporated with the targeted tissue. The other methods for making a polymer scaffold, includes gas foaming, lyophilization, sol-gel, and solvent casting method. In this review, PHA as a sustainable eco-friendly NextGen biomaterial from bacterial sources especially Bacillus cereus, and its application for fabricating bone scaffold using different strategies for bone regeneration have been discussed.

Metabolic activity of cryogenic soils in the subarctic zone of Siberia towards "green" bioplastics

The present study investigates, for the first time, the structure of the microbial community of cryogenic soils in the subarctic region of Siberia and the ability of the soil microbial community to metabolize degradable microbial bioplastic - poly-3-hydroxybutyrate [P(3HB)]. When the soil thawed, with the soil temperature between 5-7 and 9-11 °C, the total biomass of microorganisms at a 10-20-cm depth was 226-234 mg g^-1 soil and CO₂ production was 20-46 mg g^-1 day^-1. The total abundance of microscopic fungi varied between (7.4 ± 2.3) × 10³ and (18.3 ± 2.2) × 10³ CFU/g soil depending on temperature; the abundance of bacteria was several orders of magnitude greater: (1.6 ± 0.1) × 10⁶ CFU g^-1 soil. The microbial community in the biofilm formed on the surface of P(3HB) films differed from the background soil in concentrations and composition of microorganisms. The activity of microorganisms caused changes in the surface microstructure of polymer films, a decrease in molecular weight, and an increase in the degree of crystallinity of P(3HB), indicating polymer biodegradation due to metabolic activity of microorganisms. The clear-zone technique - plating of isolates on the mineral agar with polymer as sole carbon source - was used to identify P(3HB)-degrading microorganisms inhabiting cryogenic soil in Evenkia. Analysis of nucleotide sequences of rRNA genes was performed to identify the following P(3HB)-degrading species: Bacillus pumilus, Paraburkholderia sp., Pseudomonas sp., Rhodococcus sp., Stenotrophomonas rhizophila, Streptomyces prunicolor, and Variovorax paradoxus bacteria and the Penicillium thomii, P. arenicola, P. lanosum, Aspergillus fumigatus, and A. niger fungi.

Flexible and Stretchable Temperature Sensors Fabricated Using Solution-Processable Conductive Polymer Composites

Accurate monitoring of physiological temperatures is important for the diagnosis and tracking of various medical conditions. This work presents the design, fabrication, and characterization of temperature sensors using conductive polymer composites (CPCs) patterned on both flexible and stretchable substrates through both drop coating and direct ink writing (DIW). These composites were formed using a high melting point biopolymer polyhydroxybutyrate (PHB) as the matrix and the graphenic nanomaterial reduced graphene oxide (rGO) as the nanofiller (from 3 to 12 wt%), resulting in a material that exhibits a temperature-dependent resistivity. At room temperature the composites exhibited electrical percolation behavior. Around the percolation threshold, both the carrier concentration and mobility were found to increase sharply. Sensors were fabricated by drop-coating PHB-rGO composites onto ink-jet printed silver electrodes. The temperature coefficient of resistance was determined to be 0.018 /°C for pressed rGO powders and 0.008 /°C for the 3 wt% samples (the highest responsivity of all composites). Composites were found to have good selectivity to temperature with respect to pressure and moisture. Thermal mapping was demonstrated using 6 × 7 arrays of sensing elements. Stretchable devices with a meandering pattern were fabricated using DIW, demonstrating the potential for these materials in healthcare monitoring devices.

Beyond oil degradation: enzymatic potential of Alcanivorax to degrade natural and synthetic polyesters

Pristine marine environments are highly oligotrophic ecosystems populated by well‐established specialized microbial communities. Nevertheless, during oil spills, low‐abundant hydrocarbonoclastic bacteria bloom and rapidly prevail over the marine microbiota. The genus Alcanivorax is one of the most abundant and well‐studied organisms for oil degradation. While highly successful under polluted conditions due to its specialized oil‐degrading metabolism, it is unknown how they persist in these environments during pristine conditions. Here, we show that part of the Alcanivorax genus, as well as oils, has an enormous potential for biodegrading aliphatic polyesters thanks to a unique and abundantly secreted alpha/beta hydrolase. The heterologous overexpression of this esterase proved a remarkable ability to hydrolyse both natural and synthetic polyesters. Our findings contribute to (i) better understand the ecology of Alcanivorax in its natural environment, where natural polyesters such as polyhydroxyalkanoates (PHA) are produced by a large fraction of the community and, hence, an accessible source of carbon and energy used by the organism in order to persist, (ii) highlight the potential of Alcanivorax to clear marine environments from polyester materials of anthropogenic origin as well as oils, and (iii) the discovery of a new versatile esterase with a high biotechnological potential.

Streamlined production, purification, and characterization of recombinant extracellular polyhydroxybutyrate depolymerases

Heterologous production of extracellular polyhydroxybutyrate (PHB) depolymerases (PhaZs) has been of interest for over 30 years, but implementation is sometimes difficult and can limit the scope of research. With the constant development of tools to improve recombinant protein production in Escherichia coli, we propose a method that takes characteristics of PhaZs from different bacterial strains into account. Recombinant His‐tagged versions of PhaZs (rPhaZ) from Comamonas testosteroni 31A, Cupriavidus sp. T1, Marinobacter algicola DG893, Pseudomonas stutzeri, and Ralstonia sp. were successfully produced with varying expression, solubility, and purity levels. PhaZs from C. testosteroni and P. stutzeri were more amenable to heterologous expression in all aspects; however, using the E. coli Rosetta‐gami B(DE3) expression strain and establishing optimal conditions for expression and purification (variation of IPTG concentration and use of size exclusion columns) helped circumvent low expression and purity for the other PhaZs. Degradation activity of the rPhaZs was compared using a simple PHB plate‐based method, adapted to test for various pH and temperatures. rPhaZ from M. algicola presented the highest activity at 15°C, and rPhaZs from Cupriavidus sp. T1 and Ralstonia sp. had the highest activity at pH 5.4. The methods proposed herein can be used to test the production of soluble recombinant PhaZs and to perform preliminary evaluation for applications that require PHB degradation.

Biodegradation of polyhydroxybutyrate by Pseudomonas sp. DSDY0501 and purification and characterization of polyhydroxybutyrate depolymerase

Strain DSDY0501 with polyhydroxybutyrate (PHB)-degrading ability was isolated from activated sludge. The morphological, physiological, and biochemical properties of the strain and phylogenetic analysis indicated that the strain belongs to Pseudomonas sp. The strain used PHB as the sole carbon source and degraded PHB films completely in 21 h in liquid culture. An extracellular PHB depolymerase was purified from the supernatant of the culture by ultrafiltration and Sephacryl S-200 gel filtration. The specific activity of the purified enzyme increased 24.2-fold, and the recovery yield was 16.61%. Extracellular PHB depolymerase, a monomeric enzyme with a molecular weight of approximately 57.9 kDa, showed optimum activity at 60 °C and pH 9.0, and was stable in the temperature range of 10-60 °C and a pH range of 6.0-10.0. The secondary structure of the enzyme contained approximately 60% α-helix and 40% β-pleated sheet according to the circular dichroism spectrum. Mass spectrum analysis showed that the main degradation product of the enzyme was PHB monomer, indicating the exo-type action of this PHB depolymerase.

Influence of Epoxidized Canola Oil (eCO) and Cellulose Nanocrystals (CNCs) on the Mechanical and Thermal Properties of Polyhydroxybutyrate (PHB)-Poly(lactic acid) (PLA) Blends

Two major obstacles to utilizing polyhydroxybutyrate (PHB)-a biodegradable and biocompatible polymer-in commercial applications are its low tensile yield strength (<10 MPa) and elongation at break (~5%). In this work, we investigated the modification of the mechanical properties of PHB through the use of a variety of bio-derived additives. Poly(lactic acid) (PLA) and sugarcane-sourced cellulose nanocrystals (CNCs) were proposed as mechanical reinforcing elements, and epoxidized canola oil (eCO) was utilized as a green plasticizer. Zinc acetate was added to PHB and PLA blends in order to improve blending. Composites were mixed in a micro-extruder, and the resulting filaments were molded into 2-mm sheets utilizing a hot-press prior to characterization. The inclusion of the various additives was found to influence the crystallization process of PHB without affecting thermal stability. In general, the addition of PLA and, to a lesser degree, CNCs, resulted in an increase in the Young's modulus of the material, while the addition of eCO improved the strain at break. Overall, samples containing eCO and PLA (at concentrations of 10 wt %, and 25 wt %, respectively) demonstrated the best mechanical properties in terms of Young's modulus, tensile strength and strain at break.

Microbial Ecotoxicology of Marine Plastic Debris: A Review on Colonization and Biodegradation by the "Plastisphere"

Over the last decades, it has become clear that plastic pollution presents a global societal and environmental challenge given its increasing presence in the oceans. A growing literature has focused on the microbial life growing on the surfaces of these pollutants called the "plastisphere," but the general concepts of microbial ecotoxicology have only rarely been integrated. Microbial ecotoxicology deals with (i) the impact of pollutants on microbial communities and inversely (ii) how much microbes can influence their biodegradation. The goal of this review is to enlighten the growing literature of the last 15 years on microbial ecotoxicology related to plastic pollution in the oceans. First, we focus on the impact of plastic on marine microbial life and on the various functions it ensures in the ecosystems. In this part, we also discuss the driving factors influencing biofilm development on plastic surfaces and the potential role of plastic debris as vector for dispersal of harmful pathogen species. Second, we give a critical view of the extent to which marine microorganisms can participate in the decomposition of plastic in the oceans and of the relevance of current standard tests for plastic biodegradability at sea. We highlight some examples of metabolic pathways of polymer biodegradation. We conclude with several questions regarding gaps in current knowledge of plastic biodegradation by marine microorganisms and the identification of possible directions for future research.

Colonization and degradation of polyhydroxyalkanoates by lipase-producing bacteria

Biodegradation of short-chain-length polyhydroxyalkanoates (scl-PHAs) and medium-chain-length polyhydroxyalkanoates (mcl-PHAs) was studied using 2 bacteria, Pseudomonas chlororaphis and Acinetobacter lwoffii, which secrete an enzyme, or enzymes, with lipase activity. These bacteria produced clear zones of depolymerization on Petri plates containing colloidal solutions of PHA polymers with different monomer compositions. Lipase activity in these bacteria was measured using p-nitrophenyl octanoate as a substrate. In liquid medium, scl-PHA (e.g., PHBV) and mcl-PHA (e.g., PHO) films were used as the sole carbon source for growth, and after 7 days, 5%-18% loss in mass of PHA films was observed. Scanning electron microscopy of these films revealed bacterial colonization of the polymers, with cracks and pitting in the film surfaces. Degradation of polymers released 3-hydroxyhexanoate, 3-hydroxyoctanoate, and 3-hydroxydecanoate monomers into the liquid medium, depending on the starting polymer. Genes encoding secretory lipases, with amino acid consensus sequences for lipase boxes and oxyanion holes, were identified in the genomes of P. chlororaphis and A. lwoffii. Although amino acid consensus sequences for lipase boxes and oxyanion holes are also present in PHA depolymerases identified in the genomes of other PHA-degrading bacteria, the P. chlororaphis and A. lwoffii lipases had low homology with these depolymerases.