Simultaneous Biosynthesis of Polyhydroxyalkanoates and Extracellular Polymeric Substance (EPS) from Crude Glycerol from Biodiesel Production by Different Bacterial Strains

A Review of Current Achievements and Recent Challenges in Bacterial Medium-Chain-Length Polyhydroxyalkanoates: Production and Potential Applications

Using petroleum-derived plastics has contributed significantly to environmental issues, such as greenhouse gas emissions and the accumulation of plastic waste in ecosystems. Researchers have focused on developing ecofriendly polymers as alternatives to traditional plastics to address these concerns. This review provides a comprehensive overview of medium-chain-length polyhydroxyalkanoates (mcl-PHAs), biodegradable biopolymers produced by microorganisms that show promise in replacing conventional plastics. The review discusses the classification, properties, and potential substrates of less studied mcl-PHAs, highlighting their greater ductility and flexibility compared to poly(3-hydroxybutyrate), a well-known but brittle PHA. The authors summarize existing research to emphasize the potential applications of mcl-PHAs in biomedicine, packaging, biocomposites, water treatment, and energy. Future research should focus on improving production techniques, ensuring economic viability, and addressing challenges associated with industrial implementation. Investigating the biodegradability, stability, mechanical properties, durability, and cost-effectiveness of mcl-PHA-based products compared to petroleum-based counterparts is crucial. The future of mcl-PHAs looks promising, with continued research expected to optimize production techniques, enhance material properties, and expand applications. Interdisciplinary collaborations among microbiologists, engineers, chemists, and materials scientists will drive progress in this field. In conclusion, this review serves as a valuable resource to understand mcl-PHAs as sustainable alternatives to conventional plastics. However, further research is needed to optimize production methods, evaluate long-term ecological impacts, and assess the feasibility and viability in various industries.

Membrane Fouling Mitigation in MBR via the Feast–Famine Strategy to Enhance PHA Production by Activated Sludge

Fouling is considered one of the main drawbacks of membrane bioreactor (MBR) technology. Among the main fouling agents, extracellular polymeric substances (EPS) are considered one of the most impactful since they cause the decrease of sludge filterability and decline of membrane flux in the long term. The present study investigated a biological strategy to reduce the membrane-fouling tendency in MBR systems. This consisted of seeding the reactor with activated sludge enriched in microorganisms with polyhydroxyalkanoate (PHA) storage ability and by imposing proper operating conditions to drive the carbon toward intracellular (PHA) rather than extracellular (EPS) accumulation. For that purpose, an MBR lab-scale plant was operated for 175 days, divided into four periods (1–4) according to different food to microorganisms’ ratios (F/M) (0.80 kg COD kg TSS⁻¹ d⁻¹ (Period 1), 0.13 kg COD kg TSS⁻¹ d⁻¹ (Period 2), 0.28 kg COD kg TSS⁻¹ d⁻¹ (Period 3), and 0.38 kg COD kg TSS⁻¹ d⁻¹ (Period 4)). The application of the feast/famine strategy favored the accumulation of intracellular polymers by bacteria. The increase of the PHA accumulation inside the cells corresponded to the decrease of EPS and an F/M of 0.40–0.50 kg COD kg TSS⁻¹ d⁻¹ was found as optimum to maximize the PHA production, while minimizing EPS. The lowest EPS content in the sludge (18% of total suspended solids) that corresponded to the maximum content of PHA (9.3%) was found in Period 4 and determined significant mitigation of the fouling rate, whose value was close to 0.10 × 10¹¹ m⁻¹ h⁻¹. Thus, by imposing proper operating conditions, it was possible to drive the organic matter toward PHA accumulation. Moreover, a lower EPS content corresponded to a decrease in the irreversible fouling mechanism, which would imply a lower frequency of the extraordinary cleaning operations. This study highlighted the possibility of obtaining a double benefit by applying an MBR system in the frame of wastewater valorization: minimizing the fouling tendency of the membrane and recovery precursors of bioplastics from wastewater in line with the circular economy model.

Concomitant production of value-added products with polyhydroxyalkanoate (PHA) synthesis: A review

The concern over the damaging effects of petrochemical plastics has inspired innumerable researchers to synthesize green plastics. Polyhydroxyalkanoates (PHAs) are promising candidates as they are biodegradable and possess characteristics similar to conventional plastics. However, their large-scale production and market application still have a long way to go due to the high production cost associated. Approaches like using industrial wastes as substrates and developing green strategies for PHA extraction during downstream processing have been investigated to make the process more economical. Recently, PHA production cost was minimized by concomitant synthesis of other valuable bioproducts with PHA. Investigating these co-products and recovering them can also make the process circular bioeconomic. Therefore, the paper attempts to review the recent strategies for the simultaneous synthesis of value-added bioproducts with PHA together with the challenges and opportunities for their large-scale production and applications.

Microalgae as Contributors to Produce Biopolymers

Biopolymers are very favorable materials produced by living organisms, with interesting properties such as biodegradability, renewability, and biocompatibility. Biopolymers have been recently considered to compete with fossil-based polymeric materials, which rase several environmental concerns. Biobased plastics are receiving growing interest for many applications including electronics, medical devices, food packaging, and energy. Biopolymers can be produced from biological sources such as plants, animals, agricultural wastes, and microbes. Studies suggest that microalgae and cyanobacteria are two of the promising sources of polyhydroxyalkanoates (PHAs), cellulose, carbohydrates (particularly starch), and proteins, as the major components of microalgae (and of certain cyanobacteria) for producing bioplastics. This review aims to summarize the potential of microalgal PHAs, polysaccharides, and proteins for bioplastic production. The findings of this review give insight into current knowledge and future direction in microalgal-based bioplastic production considering a circular economy approach. The current review is divided into three main topics, namely (i) the analysis of the main types and properties of bioplastic monomers, blends, and composites; (ii) the cultivation process to optimize the microalgae growth and accumulation of important biobased compounds to produce bioplastics; and (iii) a critical analysis of the future perspectives on the field.

The "beauty in the beast"-the multiple uses of Priestia megaterium in biotechnology

Abstract

Over 30 years, the Gram-positive bacterium Priestia megaterium (previously known as Bacillus megaterium) was systematically developed for biotechnological applications ranging from the production of small molecules like vitamin B₁₂, over polymers like polyhydroxybutyrate (PHB) up to the in vivo and in vitro synthesis of multiple proteins and finally whole-cell applications. Here we describe the use of the natural vitamin B₁₂ (cobalamin) producer P. megaterium for the elucidation of the biosynthetic pathway and the subsequent systematic knowledge-based development for production purposes. The formation of PHB, a natural product of P. megaterium and potential petro-plastic substitute, is covered and discussed. Further important biotechnological characteristics of P. megaterium for recombinant protein production including high protein secretion capacity and simple cultivation on value-added carbon sources are outlined. This includes the advanced system with almost 30 commercially available expression vectors for the intracellular and extracellular production of recombinant proteins at the g/L scale. We also revealed a novel P. megaterium transcription-translation system as a complementary and versatile biotechnological tool kit. As an impressive biotechnology application, the formation of various cytochrome P450 is also critically highlighted. Finally, whole cellular applications in plant protection are completing the overall picture of P. megaterium as a versatile giant cell factory.

Key points

• The use of Priestia megaterium for the biosynthesis of small molecules and recombinant proteins through to whole-cell applications is reviewed.

• P. megaterium can act as a promising alternative host in biotechnological production processes.

Characterization and Biotechnological Potential of Intracellular Polyhydroxybutyrate by Stigeoclonium sp. B23 Using Cassava Peel as Carbon Source

The possibility of utilizing lignocellulosic agro-industrial waste products such as cassava peel hydrolysate (CPH) as carbon sources for polyhydroxybutyrate (PHB) biosynthesis and characterization by Amazonian microalga Stigeoclonium sp. B23. was investigated. Cassava peel was hydrolyzed to reducing sugars to obtain increased glucose content with 2.56 ± 0.07 mmol/L. Prior to obtaining PHB, Stigeoclonium sp. B23 was grown in BG-11 for characterization and Z8 media for evaluation of PHB nanoparticles' cytotoxicity in zebrafish embryos. As results, microalga produced the highest amount of dry weight of PHB with 12.16 ± 1.28 (%) in modified Z8 medium, and PHB nanoparticles exerted some toxicity on zebrafish embryos at concentrations of 6.25-100 µg/mL, increased mortality (<35%) and lethality indicators as lack of somite formation (<25%), non-detachment of tail, and lack of heartbeat (both <15%). Characterization of PHB by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimeter (DSC), and thermogravimetry (TGA) analysis revealed the polymer obtained from CPH cultivation to be morphologically, thermally, physically, and biologically acceptable and promising for its use as a biomaterial and confirmed the structure of the polymer as PHB. The findings revealed that microalgal PHB from Stigeoclonium sp. B23 was a promising and biologically feasible new option with high commercial value, potential for biomaterial applications, and also suggested the use of cassava peel as an alternative renewable resource of carbon for PHB biosynthesis and the non-use of agro-industrial waste and dumping concerns.

Isolation of a novel poly-γ-glutamic acid-producing Bacillus licheniformis A14 strain and optimization of fermentation conditions for high-level production

In the present study, bacteria producing poly-γ-glutamic acid were isolated from marine sands, and an efficient producer identified. γ-PGA was rapidly screened by thin-layer chromatography and UV spectrophotometer assay. Media optimization was carried out, and for the cost-effective production of γ-PGA, monosodium glutamate was used as the substrate for the synthesis of γ-PGA instead of glutamic acid. Lastly, Plackett-Buman design (PB) and Response surface methodology (RSM) were used to determine significant media components and their interaction effect to achieve maximum γ-PGA production. With this integrated method, a bacterial strain with a high yield of γ-PGA was obtained rapidly, and the production was increased up to 37.8 g/L after optimization.

Microalgae as source of polyhydroxyalkanoates (PHAs) - A review

Polyhydroxyalkanoates (PHA) are biopolymers synthesized by different microorganisms and considered substitute powers for petroleum-based plastics because they have similar mechanical properties as synthetic polymers, can be processed in a similar way and are fully biodegradable. Currently commercial PHAs are produced in fermenters using bacteria and large amounts of organic carbon sources and salts in the culture media, accounting for approximately 50% of the total production costs. A greater commercial application of the PHA is limited to a decrease in the cost of production. Several studies suggest that microalgae are a type of microorganisms that can be used to obtain PHAs at a lower cost because they have minimum nutrient requirements for growth and are photoautotrophic in nature, i.e. they use light and CO₂ as their main sources of energy. Thus, this work aims to provide a review on the production of PHAs of different microalgae, focusing on the properties and composition of biopolymers, verifying the potential of using these bioplastics instead of petroleum based plastics. Studies of stimulation PHA synthesis by microalgae are still considered incipient. Still, it is clear that microalgae have the potential to produce biopolymers with lower cost and can play a vital role in the environment.

Valorization of crude glycerol based on biological processes for accumulation of lipophilic compounds

Bacteria that are capable of accumulating lipids in their cells as storage compounds can also produce polyhydroxyalkanoates of high technological value, depending on the specific culture conditions. The objective of this study was to utilize crude glycerol from biodiesel (CGB) as a substrate, which is a major byproduct from biodiesel production, to produce lipophilic compounds. Bacillus megaterium INCQS 425 was cultivated and evaluated for the production of lipophilic compounds and the properties of these compounds were investigated. Cultivation of the bacteria in a medium with a C:N ratio of 0.60:1 favored the accumulation of lipids by (17.5%) comprising mainly palmitic acid (13.08%), palmitoleic (39.48%), and especially oleic acid (37.02%), which imparts good characteristics to biodiesel. Meanwhile, cultivation of the bacteria in a medium with a C:N ratio of 4:1 favored the accumulation of polyhydroxyalkanoates (PHA) (3.31gL^-1) mainly comprising medium and long chain PHA. Low crystallinity (<30%) and excellent thermal properties make them suitable for processes that demand high temperatures, such as extrusion. The lipids produced in the present study had satisfactory oxidative stability for the production of quality biodiesel. The polyhydroxyalkanoates produced in the study are of low cost and have promising thermal properties that justify its technological potential, thereby configuring highly competitive bioproducts.

Pilot-scale isolation and characterization of extracellular polymeric substances (EPS) from cell-free medium of Spirulina sp. LEB-18 cultures under outdoor conditions

This objective of this work was to monitor the EPS production during the growth of Spirulina sp. LEB-18, evaluate the productivity and to characterize the exopolymers obtained on pilot-scale under outdoor conditions. The production of crude EPS occurred in all phases of biomass growth and was approximately ten folds higher than that biomass concentration of Spirulina sp. LEB-18 at the end cultivation, demonstrating the importance of the use of supernatant after harvesting of Spirulina to obtain high value bioproducts. The EPS extracted by Spirulina sp. LEB-18 are typically heteropolymers with one high molecular weight fraction (polysaccharides) with potential to be utilized as an alternative bioflocculant and another fraction of lower molecular mass (proteins). The presence of uronic acids, pyruvates and acyl groups of carbohydrates or carboxylic groups of amino acids in protein moiety is the main responsible for overall negative charge of EPS, which is also of biotechnological importance. Moreover, due to the pseudoplastic behavior of the solutions and high thermal stability, the obtained EPS can be widely applied in several industrial sectors, thus determining its technological and market potentiality.