Biotechnological Stratagems for the Production of Microbial Bioplastics and Its Commercial Applications

Harnessing yeast for polyhydroxyalkanoates (PHAs) production: Challenges, engineering strategies, and future prospects.

This review provides the current state of PHAs production from wild yeast strains and the various approaches that have been used to improve yield, and discusses the performance, challenges, and limitations of various synthetic biology and metabolic engineering strategies in yeast strains for PHAs production.

Standardising Cellulose Production From Acetobacter diazotrophicus

Optimization of Bioethanol Produced from Chlorella vulgaris

Increasing global energy demand, together with the ecological impacts of fossil fuels, has renewed interest in biofuels. Microalgae such as Chlorella vulgaris have attracted significant interest because of their high carbohydrate content and rapid growth, as well as because their cultivation does not require arable land to the same extent as traditional crops. This positions C. vulgaris as a promising feedstock for third-generation bioethanol. In this study, dried C. vulgaris biomass was pretreated with α-amylase, followed by enzymatic hydrolysis to release fermentable sugars. A Box–Behnken design within response surface methodology was employed to investigate the effects of pH, inoculum size, and retention time on sugar release and ethanol production. The overall model was highly significant (F = 186.28, P < 0.001). Retention time exerted the greatest influence on hydrolysis and yield (F = 1551.39, P < 0.001), followed by pH (F = 48.50, P < 0.001); inoculum size had no significant effect (F = 2.49, P = 0.130). Quadratic terms contributed significantly to the model (F = 23.44, P < 0.001), whereas two-variable interactions were not significant (F = 1.28, P = 0.309). Peak yields exceeding 73% were obtained at pH 5.0–6.0 with a retention time of 72 h, and the validation trials closely matched the model predictions. ANOVA indicated a significant lack of fit (F = 26.64, P < 0.001), suggesting that the quadratic model did not adequately represent the response surface and that the actual relationship among the variables may be more complex than can be captured by a second-order equation. Despite this limitation, the close agreement between predicted and observed yields indicates that the model retained practical value for forecasting bioethanol production under the investigated fermentation conditions.

Polyhydroxybutyrate (PHB) production from halophiles: a comprehensive review

The growing environmental impact of petroleum-based plastics has intensified the search for sustainable and biodegradable alternatives. Polyhydroxybutyrate (PHB), a microbial polyester from the polyhydroxyalkanoate (PHA) family, has emerged as a promising biopolymer due to its biodegradability, biocompatibility, and thermoplastic qualities that rival those of conventional polymers. Halophilic bacteria have attracted considerable attention among PHB-producing microorganisms because they thrive in hypersaline environments, enabling non-sterile cultivation, reducing contamination risks, and facilitating cost-effective downstream recovery by osmotic cell lysis. This review provides a comprehensive overview of recent improvements in PHB production by halophilic bacteria, covering physiological adaptations, metabolic pathways, substrate usage, fermentation techniques, and bioreactor optimisation. Particular emphasis is placed on the use of agro-industrial residues and waste-derived feedstocks as sustainable carbon sources to reduce production costs and increase circular bioeconomy results. Recent advances in downstream processing, such as green extraction technologies, metabolic engineering, CRISPR-based gene editing, and synthetic biology approaches to increasing PHB productivity, are critically reviewed. Additionally, developments in polymer modification, life cycle assessment, industrial scalability, regulatory frameworks, and potential applications in packaging, agriculture, and biomedical engineering are discussed. Despite significant progress, issues such as process economics, saline wastewater control, polymer brittleness, and large-scale commercialisation remain. Integrating halophilic biotechnology with waste valorisation, green recovery technologies, sophisticated metabolic engineering, and circular biorefinery concepts offers a promising strategy for developing economically and environmentally sustainable PHB production systems.

Process intensification for the protein production from microalgae: a comprehensive review

Microalgae (predominantly unicellular photosynthetic eukaryotes) has been recognized as a “protein bio-factory” because they may produce up to 70% of protein (dry basis). Advantageous aspects of proteins from microalgae compared to conventional animal- and plant-based proteins were proven. Numerous review articles have addressed the effects of composition of cultivation medium and operational parameters to obtain high protein yield from microalgae. Nevertheless, several critical limitations remain for the industrial expansions of the production of proteins from microalgae. Presently, process intensification is considered a strategic approach for the scalable production of proteins from microalgae, achieved by implementing mutagenic and recombinant strains, increasing productivity through high-cell-density cultivation strategies, using cold-adapted microalgae and minimizing equipment footprint via integrating multiple unit operations into a more efficient and compact system. Different strategies of random mutagenesis (chemical: ethyl methane sulfonate-mediated, physical: heavy-ion irradiation-mediated and ultraviolet-mediated) have been employed to get the desired phenotype of microalgae for higher protein yield. Emerging genetic engineering approaches, including the design of expression vectors, identification of genetic regulatory elements, and genetic transformation methods, along with bioinformatics algorithms, have been employed to develop recombinant strains of microalgae with higher protein yield. Combined cultivation systems, such as sequential heterotrophic-autotrophic system, switching of nitrogen-rich cultivation medium from nitrogen-deficient medium and mixotrophic system have come to the forefront. In this review article, process intensification strategies for the production of proteins from microalgae are comprehensively discussed, with special emphasis on the development of mutant and recombinant strains, strategies of cultivation and decisive operational parameters of bioreactor operation.

Bioremediation of PET Pollution Using Microorganisms Active at Moderate Temperatures

Plastics such as polyethylene terephthalate (PET) are widely used worldwide because they are inexpensive, versatile, and suitable for numerous applications. However, most products made of PET are designed for single use, and the resulting waste is chemically inert and highly resistant to microbial degradation. Consequently, PET accumulation has become a major source of environmental pollution and poses serious threats to ecosystems. Biorecycling and bioupcycling have emerged as some of the most promising strategies for reducing PET pollution. For macro-scale PET waste, industrial approaches are being developed, including those pursued by the French company Carbios, although significant technical and economic challenges remain. In contrast, for micro- and nanosized PET particles, commonly referred to as microplastics, no large-scale remediation systems have been implemented yet. Here we highlight the potential applications of microorganisms and their enzymes for remediation of microplastic pollution, especially because these systems can function at moderate temperatures, in contrast to high-temperature industrial processes. In particular, we highlight the potential of utilizing the Ideonella sakaiensis system that was discovered a decade ago. PET-degrading enzymes encoded by this bacterium, such as IsPETase and IsMHEtase, are able to operate at moderate temperatures, unlike most other enzymes being developed to provide bioremediation of PET pollution.