Search

Polyhydroxyalkanoates (PHA) are a promising bio-based alternative to traditional plastics derived from petroleum. Cyanobacteria are photosynthetic organisms that produce PHA from CO2 and sunlight, which can potentially reduce production costs and environmental footprint in comparison to heterotrophic bacteria cultures because (1) they utilize inorganic carbon sources for growth and (2) they do not require intensive aeration for oxygenation. Moreover, supplementing precursors such as propionate, acetate, valerate, etc., can be used to obtain various copolymers with plastic customizable properties in comparison to the classical homopolymers, such as polyhydroxybutyrate, PHB. This critical review covers the latest advances in PHA production, including recent discoveries in the metabolism interplay between PHA and glycogen production, and new insights into cultivation strategies that enhance PHA accumulation, and purification processes. This review also addresses the challenges and suggests potential solutions for a viable industrial PHAs production process. [ABSTRACT FROM AUTHOR]

Polyhydroxybutyrate (PHB) is known for wide applications, biocompatibility, and degradability; however, it cannot be commercialized due to conventional recovery using solvents. The present study employed mechanical cell-disruption methods, such as Pestle and mortar, sonication, and glass bead vortexing, for solvent-free extraction of PHA from Bacillus sp. Different time intervals were set for grinding (5, 10, 15 min), sonicating (1, 3 and 5 min), and vortexing (2, 5 and 8 g glass beads with 5, 10 and 15 min each) hence studying their effect on cell lysis to release PHA. Tris buffer containing phenylmethyl sulfonyl fluoride (PMSF) (20 mM Tris–HCl, pH 8.0, 1 mM PMSF) was employed as a lysis buffer to study its action over Bacillus cells. Its presence was checked with the above methods in cell lysis. Sonicating cells for 5 min in the presence of lysis buffer achieved a maximum PHA yield of 45%. Cell lysis using lysis buffer yielded 35% PHA when vortexing with 5 g glass beads for 15 min. Grinding cells for 15 min showed a maximum yield of 34% but lacked a lysis buffer. The overall results indicated that the action of lysis buffer and physical extraction methods improved PHA yield by %. Therefore, the study sought to evaluate the feasibility of applying laboratory methods for cell disruption. These methods can showcase possible opportunities in large-scale applications. The polymer yield results were compared with standard sodium hypochlorite extraction. Confirmation of obtained polymers as polyhydroxy butyrate (PHB) was made through FTIR and 1HNMR characterization. [ABSTRACT FROM AUTHOR]

The microbial biotransformation using low-cost feedstock to produce biopolymers (degradable), an alternative to petrochemical-based synthesis plastics (non-degradable), can be a beneficial approach towards sustainable development. In this study, the dairy industry processes waste (whey) is used in polyhydroxyalkanoate (PHA) copolymer production. Initial screening suggested that Ralstonia eutropha produced higher PHA as compared to Bacillus megaterium. A central composite rotatable design-based optimization using two process variables (amino acid and tween-80) concentration remarkably influenced PHA co-polymer production under physiological conditions of pH (7), temperature (37 °C), and agitation rate of 150 rpm. High polyhydroxybutyrate (PHB) mass fraction yield of 69.3% was observed as compared to predicted yield of 62.8% from deproteinized whey as feed. The combination of tryptophan (50 mg L−1) and tween-80 (3 mL−1) enhanced R. eutropha mass gain to 6.80 g L−1 with PHB contents of 4.71 g L−1. Further, characterization of PHA and its copolymers was done by ESI–MS, FTIR, and TEM. On upscaling up to 3.0 L, the PHA contents and yields were noted as quite similar by R. eutropha. This study demonstrates that dairy waste processing waste can be potentially utilized as inexpensive feed for producing high content of biopolymers to develop a sustainable system of waste management. [ABSTRACT FROM AUTHOR]

Poly-β-hydroxybutyrate (PHB) is a potential source of biodegradable plastics that are environmentally friendly due to their complete degradation to water and carbon dioxide. This study aimed to investigate PHB production in the cyanobacterium Synechocystis sp. PCC6714 MT_a24 in an outdoor bioreactor using urban wastewater as a sole nutrient source. The culture was grown in a thin-layer raceway pond with a working volume of 100 L, reaching a biomass density of up to 3.5 g L−1 of cell dry weight (CDW). The maximum PHB content was found under nutrient-limiting conditions in the late stationary phase, reaching 23.7 ± 2.2% PHB per CDW. These data are one of the highest reported for photosynthetic production of PHB by cyanobacteria, moreover using urban wastewater in pilot-scale cultivation which multiplies the potential of sustainable cultivation approaches. Contamination by grazers (Poterioochromonas malhamensis) was managed by culturing Synechocystis in a highly alkaline environment (pH about 10.5) which did not significantly affect the culture growth. Furthermore, the strain MT_a24 showed significant wastewater nutrient remediation removing about 72% of nitrogen and 67% of phosphorus. These trials demonstrate that the photosynthetic production of PHB by Synechocystis sp. PCC6714 MT_a24 in the outdoor thin-layer bioreactor using urban wastewater and ambient carbon dioxide. It shows a promising approach for the cost-effective and sustainable production of biodegradable carbon-negative plastics. Key points: • High PHB production by cyanobacteria in outdoor raceway pond • Urban wastewater used as a sole source of nutrients for phototrophic growth • Potential for cost-effective and sustainable production of biodegradable plastics [ABSTRACT FROM AUTHOR]

Polyhydroxybutyrate (PHB), a sustainable biodegradable polymer with various industrial and medical applications, produced by microorganisms is a good replacement of conventional plastics, a major environmental contaminant. The aim of this study is to isolate and evaluate the PHB producing ability of the microorganisms isolated from various soil sources. By employing different staining methods such as Sudan black B, Nile red and Nile blue A, the primary screening of PHB producers was performed. Among the 104 soil isolates, four strains (SNA1, SNA2, SNA3 and SNA4) exhibited positive results for all the staining tests. On further studies, among these the strain SNA2 produced highest level of PHB (64%) from its whole cell dry weight, while glucose (20 g/L) and urea (2 g/L) were used as the carbon and nitrogen sources respectively at pH 7, 30 °C after 48 h of incubation. The Fourier transform infrared spectroscopy (FTIR) and Proton Nuclear Magnetic Resonance (1H NMR) results confirmed that the polymer produced was PHB. The 16S rRNA sequencing revealed results that the strain SNA2 was Klebsiella pneumonia. The production ability of the novel Klebsiella pneumonia SNA2 was further enhanced by optimizing various process parameters such as carbon and nitrogen sources, pH, temperature and incubation period. The process optimization resulted in enhanced PHB synthesis (up to 75%) with Xylose as carbon source and urea as the nitrogen source with pH 7.5 at 35 °C after 36 h. In addition, an attempt to produce a biofilm from the extracted polymer was also successful. Thus, the novel bacterial isolate Klebsiella pneumonia SNA2 was proved to be a challenging host for the synthesis of PHB and the scale up studies are under progress. Whole genome sequencing, identification of pathway genes and metabolic engineering strategies were believed to enhance the PHB synthesis further to the industrial scale. [ABSTRACT FROM AUTHOR]