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Plastics derived from fossil fuels are used ubiquitously owing to their exceptional physicochemical characteristics. However, the extensive and short-term use of plastics has caused environmental challenges. The biotechnological plastic conversion can help address the challenges related to plastic pollution, offering sustainable alternatives that can operate using bioeconomic concepts and promote socioeconomic benefits. In this context, using soil from a plastic-contaminated landfill, two consortia were established (ConsPlastic-A and -B) displaying versatility in developing and consuming polyethylene or polyethylene terephthalate as the carbon source of nutrition. The ConsPlastic-A and -B metagenomic sequencing, taxonomic profiling, and the reconstruction of 79 draft bacterial genomes significantly expanded the knowledge of plastic-degrading microorganisms and enzymes, disclosing novel taxonomic groups associated with polymer degradation. The microbial consortium was utilized to obtain a novel Pseudomonas putida strain (BR4), presenting a striking metabolic arsenal for aromatic compound degradation and assimilation, confirmed by genomic analyses. The BR4 displays the inherent capacity to degrade polyethylene terephthalate (PET) and produce polyhydroxybutyrate (PHB) containing hydroxyvalerate (HV) units that contribute to enhanced copolymer properties, such as increased flexibility and resistance to breakage, compared with pure PHB. Therefore, BR4 is a promising strain for developing a bioconsolidated plastic depolymerization and upcycling process. Collectively, our study provides insights that may extend beyond the artificial ecosystems established during our experiments and supports future strategies for effectively decomposing and valorizing plastic waste. Furthermore, the functional genomic analysis described herein serves as a valuable guide for elucidating the genetic potential of microbial communities and microorganisms in plastic deconstruction and upcycling.

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Environmental pollution caused by petroleum-derived plastics continues to increase annually. Consequently, current research is interested in the search for eco-friendly bacterial polymers. The importance of Bacillus bacteria as producers of polyhydroxyalkanoates (PHAs) has been recognized because of their physiological and genetic qualities. In this study, twenty strains of Bacillus genus PHA producers were isolated. Production was initially evaluated qualitatively to screen the strains, and subsequently, the strain B12 or Bacillus sp. 12GS, with the highest production, was selected through liquid fermentation. Biochemical and molecular identification revealed it as a novel isolate of Bacillus cereus. Production optimization was carried out using the Taguchi methodology, determining the optimal parameters as 30 °C, pH 8, 150 rpm, and 4% inoculum, resulting in 87% and 1.91 g/L of polyhydroxybutyrate (PHB). Kinetic studies demonstrated a higher production within 48 h. The produced biopolymer was analyzed using Fourier-transform infrared spectroscopy (FTIR), confirming the production of short-chain-length (scl) polyhydroxyalkanoate, named PHB, and differential scanning calorimetry (DSC) analysis revealed thermal properties, making it a promising material for various applications. The novel B. cereus isolate exhibited a high %PHB, emphasizing the importance of bioprospecting, study, and characterization for strains with biotechnological potential.

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Inulin is a fructose-based polysaccharide that can be found in several plant species, from grass and onions to chicory roots; thus, it has the potential to be an excellent renewable source of fructose for several industrial applications. Among them, inulin hydrolysis can be coupled to a fermentation operation to produce polyhydroxybutyrate (PHB) using Cupriavidus necator H16. This work reports the PHB production process involving chicory root inulin hydrolysis using inulinase Novozym 960 followed by a C. necator fermentation. It was found that the maximum saccharification (95% wt.) was reached at 269 U/ginulin after 90 min. The hydrolysates obtained were then inoculated with C. necator, leading to a biomass concentration of 4 g/L with 30% (w/w) polymer accumulation. Although PHB production was low, during the first hours, the cell growth and polymer accumulation detected did not coincide with a fructose concentration decrease, suggesting a simultaneous saccharification and fermentation process, potentially alleviating the product inhibition inherent to the inulinase-fructose system. The characterization of the obtained PHB showed a polymer with more homogeneous values of Mw, and better thermal stability than PHB produced using pure fructose as a fermentation substrate. The results obtained demonstrate a viable alternative carbon substrate for PHB production, opening the possibility for inulin-rich renewable feedstock valorization.

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The placement of a polymeric electrospun scaffold is among the most promising strategies to improve nerve regeneration after critical neurotmesis. It is of great interest to investigate the effect of these structures on Schwann cells (SCs), as these cells lead nerve regeneration and functional recovery. The aim of this study was to assess SC viability and morphology when cultured on polyhydroxybutyrate (PHB) electrospun scaffolds with varied microfiber thicknesses and pore sizes. Six electrospun scaffolds were obtained using different PHB solutions and electrospinning parameters. All the scaffolds were morphologically characterized in terms of fiber thickness, pore size, and overall appearance by analyzing their SEM images. SCs seeded onto the scaffolds were analyzed in terms of viability and morphology throughout the culture period through MTT assay and SEM imaging. The SCs were cultured on three scaffolds with homogeneous smooth fibers (fiber thicknesses: 2.4 µm, 3.1 µm, and 4.3 µm; pore sizes: 16.7 µm, 22.4 µm, and 27.8 µm). SC infiltration and adhesion resulted in the formation of a three-dimensional network composed of intertwined fibers and cells. The SCs attached to the scaffolds maintained their characteristic shape and size throughout the culture period. Bigger pores and thicker fibers resulted in higher SC viability.

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In this work, polyhydroxybutyrate (PHB) was maleic anhydride (MA)-grafted in the molten state, using dicumyl peroxide (DCP) as a reaction initiator. Tin(II) 2-ethylhexanoate (Sn(Oct)2) and styrene monomer (St.) were used to maximize the maleic anhydride grafting degree. When PHB was modified with MA/DCP and MA/DCP/Sn(Oct)2, viscosity was reduced, suggesting chain scission in relation to pure PHB. However, when the styrene monomer was added, the viscosity increased due to multiple grafts of MA and styrene into the PHB chain. In addition, the FTIR showed the formation of a new band at 1780 cm-1 and 704 cm-1, suggesting a multiphase copolymer PHB-g-(St-co-MA). The PHB (MA/DCP) system showed a grafting degree of 0.23%; however, the value increased to 0.39% with incorporating Sn(Oct)2. The highest grafting efficiency was for the PHB (MA/DCP/St.) system with a value of 0.91%, while the PHB (MA/DCP/St./Sn(Oct)2) hybrid mixture was reduced to 0.73%. The chemical modification process of PHB with maleic anhydride increased the thermal stability by about 20 °C compared with pure PHB. The incorporation of 0.5 phr of the Sn(Oct)2 catalyst increased the efficiency of the grafting degree in the PHB. However, the St./Sn(Oct)2 hybrid mixture caused a deleterious effect on the maleic anhydride grafting degree.

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In this work, scaffolds based on poly(hydroxybutyrate) (PHB) and micronized bacterial cellulose (BC) were produced through 3D printing. Filaments for the printing were obtained by varying the percentage of micronized BC (0.25, 0.50, 1.00, and 2.00%) inserted in relation to the PHB matrix. Despite the varying concentrations of BC, the biocomposite filaments predominantly contained PHB functional groups, as Fourier transform infrared spectroscopy (FTIR) demonstrated. Thermogravimetric analyses (i.e., TG and DTG) of the filaments showed that the peak temperature (Tpeak) of PHB degradation decreased as the concentration of BC increased, with the lowest being 248 °C, referring to the biocomposite filament PHB/2.0% BC, which has the highest concentration of BC. Although there was a variation in the thermal behavior of the filaments, it was not significant enough to make printing impossible, considering that the PHB melting temperature was 170 °C. Biological assays indicated the non-cytotoxicity of scaffolds and the provision of cell anchorage sites. The results obtained in this research open up new paths for the application of this innovation in tissue engineering.

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Bacteria frequently store excess carbon in hydrophobic granules of polyhydroxybutyrate (PHB) that in some growth conditions can occupy most of the cytoplasmic space. Different types of proteins associate to the surface of the granules, mainly enzymes involved in the synthesis and utilization of the reserve polymer and a diverse group of proteins known as phasins. Phasins have different functions, among which are regulating the size and number of the granules, modulating the activity of the granule-associated enzymes and helping in the distribution of the granules inside the cell. Caulobacter crescentus is an oligotrophic bacterium that shows several morphological and regulatory traits that allow it to grow in very nutrient-diluted environments. Under these conditions, storage compounds should be particularly relevant for survival. In this work, we show an initial proteomic characterization of the PHB granules and describe a new type of phasin (PhaH) characterized by the presence of an N-terminal hydrophobic helix followed by a helix-hairpin-helix (HhH) domain. The hydrophobic helix is required for maximal PHB accumulation and maintenance during the stationary phase while the HhH domain is involved in determining the size of the PHB granules and their distribution in the cell.

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Poly(3-hydroxybutyrate), PHB, is a hydrophobic biopolymer with good mechanical and barrier properties. However, neat PHB is a semicrystalline polymer with a relative high degree of crystallinity and poor film properties. In this work, this biopolymer was plasticized with glycerol tributyrate and functionalized with copper (II) sulfate, allowing us to obtain biodegradable antimicrobial flexible films. Films with the minimum inhibitory concentration (MIC) of copper (II) sulfate presented a higher roughness than neat PHB films. The presence of plasticizer significantly improved the copper sulfate diffusion process, which was evidenced by a greater inhibition halo for plasticized materials compared to unplasticized ones, at the same salt concentration. Plasticized PHB with 2.5% copper (II) sulfate inhibited both Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomona aeruginosa) bacteria, as determined by the bacterial inhibition halo. In addition, neat PHB films and PHB containing copper (II) sulfate did not show in vitro cytotoxicity in the L-929 cell line. Thus, plasticized PHB functionalized with copper (II) sulfate can be used as biodegradable antimicrobial flexible films for different applications.

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Gram-negative Azospirillum brasilense accumulates approximately 80% of polyhydroxybutyrate (PHB) as dry cell weight. For this reason, this bacterium has been characterized as one of the main microorganisms that produce PHB. PHB is synthesized inside bacteria by the polymerization of 3-hydroxybutyrate monomers. In this review, we are focusing on the analysis of the PHB production by A. brasilense in order to understand the metabolism during PHB accumulation. First, the carbon and nitrogen sources used to improve PHB accumulation are discussed. A. brasilense accumulates more PHB when it is grown on a minimal medium containing a high C/N ratio, mainly from malate and ammonia chloride, respectively. The metabolic pathways to accumulate and mobilize PHB in A. brasilense are mentioned and compared with those of other microorganisms. Next, we summarize the available information to understand the role of the genes involved in the regulation of PHB metabolism as well as the role of PHB in the physiology of Azospirillum. Finally, we made a comparison between the properties of PHB and polypropylene, and we discussed some applications of PHB in biomedical and commercial areas.

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The aim of this study was to investigate the influence of exogenous carbon supplementation and nitrogen source reduction on Chlorella fusca LEB 111 growth, biomass composition, and polyhydroxybutyrate accumulation. First, assays were performed with 50 % and 25 % reduced nitrogen source concentrations (NaNO3). In the second stage, the influence of culture supplementation with 10, 20, and 30 mg L-1 D-xylose, associated with 50 and 25 % reductions in NaNO3, was evaluated. The experiments conducted with a 25 % reduction in NaNO3 and supplementation with 10 mg L-1 D-xylose resulted in a positive effect on the biomass productivity of C. fusca LEB 111, with production as high as 354.4 mg L-1 d-1. The maximum concentration of PHB extracted from C. fusca LEB 111 was 3.7 % (w w-1) and was obtained when the microalgae were cultivated with a 25 % of reduction in NaNO3 and supplementation of D-xylose at 20 mg L-1. Therefore, this study brings new perspectives regarding reducing the use of nutritional sources and using exogenous carbon sources in using microalgae to produce molecules of high biotechnological potential.

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