Bioconversion of crude glycerol to polyhydroxyalkanoate by Bacillus thuringiensis under non-limiting nitrogen conditions

Production, optimization, scale up and characterization of polyhydoxyalkanoates copolymers utilizing dairy processing waste

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.

Polyhydroxy butyrate biosynthesis by Azotobacter chroococcum MTCC 3858 through groundnut shell as lignocellulosic feedstock using resource surface methodology

This work appraises the prospect of utilising groundnut shell hydrolysate as a feedstock used for PHB biosynthesis by Azotobacter chroococcum MTCC 3853 under SMF conditions. Sugar reduction: untreated and pretreated 20% H₂SO₄ (39.46 g/l and 62.96 g/l, respectively), untreated and enzymatic hydrolysis (142.35 mg/g and 568.94 mg/g). The RSM-CCD optimization method was used to generate augment PHB biosynthesis from groundnut shell hydrolysate (30 g/l), ammonium sulphate (1.5 g/l), ammonium chloride (1.5 g/l), peptone (1.5 g/l), pH 7, 30 °C, and a 48 h incubation time. The most convincing factors (p < 0.0001), coefficient R² values of biomass 0.9110 and PHB yield 0.9261, PHB production, highest biomass (17.23 g/l), PHB Yield(11.46 g/l), and 66.51 (wt% DCW) values were recorded. The control (untreated GN) PHB yield value of 2.86 g/l increased up to fourfold in pretreated GN. TGA results in a melting range in the peak perceived at 270.55 °C and a DSC peak range of 172.17 °C, correspondingly. According to the results, it furnishes an efficient agricultural waste executive approach by diminishing the production expenditure. It reinforces the production of PHB, thereby shrinking our reliance on fossil fuel-based plastics.

Genome-centric polyhydroxyalkanoate reconciliation reveals nutrient enriched growth dependent biosynthesis in Bacillus cereus IBA1

Microbiological polyhydroxyalkanoates (PHAs) are rooted as the most promising bio-replacements of synthetic polymers. Inherent properties of these PHAs further expand their applicability in numerous industrial, environmental, and clinical sectors. To propel these, a new environmental, endotoxin free gram-positive bacterium i.e., Bacillus cereus IBA1 was identified to harbor advantageous PHA producer characteristics through high-throughput omics mining approaches. Unlike traditional fermentations, nutrient enriched strategy was used to enhance PHA granular concentrations by ∼2.3 folds to 2.78 ± 0.19 g/L. Additionally, this study is the first to confirm an underlying growth dependent PHA biogenesis through exploring PHA granule associated operons which harbour constitutively expressing PHA synthase (phaC) coupled with differentially expressing PHA synthase subunit (phaR) and regulatory protein (phaP, phaQ) amid different growth phases. Moreover, the feasibility of this promising microbial phenomenon could propel next-generation biopolymers, and increase industrial applicability of PHAs, thereby significantly contributing to the sustainable development.

Exploiting Polyhydroxyalkanoates for Biomedical Applications

Polyhydroxyalkanoates (PHA) are biodegradable plastic. Numerous bacteria produce PHAs under environmental stress conditions, such as excess carbon-rich organic matter and limitations of other nutritional elements such as potassium, magnesium, oxygen, phosphorus, and nitrogen. In addition to having physicochemical properties similar to fossil-fuel-based plastics, PHAs have unique features that make them ideal for medical devices, such as easy sterilization without damaging the material itself and easy dissolution following use. PHAs can replace traditional plastic materials used in the biomedical sector. PHAs can be used in a variety of biomedical applications, including medical devices, implants, drug delivery devices, wound dressings, artificial ligaments and tendons, and bone grafts. Unlike plastics, PHAs are not manufactured from petroleum products or fossil fuels and are, therefore, environment-friendly. In this review, a recent overview of applications of PHAs with special emphasis on biomedical sectors, including drug delivery, wound healing, tissue engineering, and biocontrols, are discussed.

Cascading Beta-oxidation Intermediates for the Polyhydroxyalkanoate Copolymer Biosynthesis by Metabolic Flux using Co-substrates and Inhibitors

Polyhydroxyalkanoates (PHAs) are biopolymers that are produced within the microbial cells in the presence of excess carbon and nutrient limitation. Different strategies have been studied to increase the quality and quantity of this biopolymer which in turn can be utilized as biodegradable polymers replacing conventional petrochemical plastics. In the present study, Bacillus endophyticus, a gram-positive PHA-producing bacterium, was cultivated in the presence of fatty acids along with beta-oxidation inhibitor acrylic acid. A novel approach for incorporating different hydroxyacyl groups provided using fatty acids as co-substrate and beta-oxidation inhibitors to direct the intermediates to co-polymer synthesis was experimented. It was observed that higher fatty acids and inhibitors had a greater influence on PHA production. The addition of acrylic acid along with propionic acid had a positive impact, giving 56.49% of PHA along with sucrose which was 1.2-fold more than the control devoid of fatty acids and inhibitors. Along with the copolymer production, the possible PHA pathway functional leading to the copolymer biosynthesis was hypothetically interpreted in this study. The obtained PHA was analyzed by FTIR and ¹H NMR to confirm the copolymer production, which indicated the presence of poly3hydroxybutyrate-co-hydroxyvalerate (PHB-co-PHV), poly3hydroxybutyrate-co-hydroxyhexanoate (PHB-co-PHx).

Recent trends of biotechnological production of polyhydroxyalkanoates from C1 carbon sources

Growing concerns over the use of limited fossil fuels and their negative impacts on the ecological niches have facilitated the exploration of alternative routes. The use of conventional plastic material also negatively impacts the environment. One such green alternative is polyhydroxyalkanoates, which are biodegradable, biocompatible, and environmentally friendly. Recently, researchers have focused on the utilization of waste gases particularly those belonging to C1 sources derived directly from industries and anthropogenic activities, such as carbon dioxide, methane, and methanol as the substrate for polyhydroxyalkanoates production. Consequently, several microorganisms have been exploited to utilize waste gases for their growth and biopolymer accumulation. Methylotrophs such as Methylobacterium organophilum produced highest amount of PHA up to 88% using CH₄ as the sole carbon source and 52-56% with CH₃OH. On the other hand Cupriavidus necator, produced 71-81% of PHA by utilizing CO and CO₂ as a substrate. The present review shows the potential of waste gas valorization as a promising solution for the sustainable production of polyhydroxyalkanoates. Key bottlenecks towards the usage of gaseous substrates obstructing their realization on a large scale and the possible technological solutions were also highlighted. Several strategies for PHA production using C1 gases through fermentation and metabolic engineering approaches are discussed. Microbes such as autotrophs, acetogens, and methanotrophs can produce PHA from CO₂, CO, and CH₄. Therefore, this article presents a vision of C1 gas into bioplastics are prospective strategies with promising potential application, and aspects related to the sustainability of the system.

Production of polyhydroxyalkanoates containing monomers conferring amorphous and elastomeric properties from renewable resources: Current status and future perspectives

Petrochemical-based plastics cause environmental pollution and threaten humans and ecosystems. Polyhydroxyalkanoate (PHA) is considered a promising alternative to nondegradable plastics since it is eco-friendly and biodegradable polymer having similar properties to conventional plastics. PHA's material properties are generally determined by composition and type of monomers in PHA. PHA can be designed in tailor-made manner for their suitable application areas. Among many monomers in PHAs, ω-hydroxalkanoates such as 3-hydroxypropionate (3HP), 4-hydroxybutyrate (4HB), 5-hydroxyvalerate (5HV), and 6-hydroxyhexanoate (6HHx) and medium-chain-length 3-hydroxyalkanoate such as 3-hydroxyhexanoate (3HHx) and 4-hydroxyvalerate (4HV), have been examined as potential monomers able to confer amorphous and elastomer properties when these are incorporated as comonomer in poly(3-hydroxybutyrate) copolymer that has 3HB as main monomer along with comonomers in different monomer fraction. Herein, recent advances in production of PHAs designed to have amorphous and elastomeric properties from renewable sources such as lignocellulose, levulinic acid, crude glycerol, and waste oil are discussed.

Novel Production Methods of Polyhydroxyalkanoates and Their Innovative Uses in Biomedicine and Industry

Polyhydroxyalkanoate (PHA), a biodegradable polymer obtained from microorganisms and plants, have been widely used in biomedical applications and devices, such as sutures, cardiac valves, bone scaffold, and drug delivery of compounds with pharmaceutical interests, as well as in food packaging. This review focuses on the use of polyhydroxyalkanoates beyond the most common uses, aiming to inform about the potential uses of the biopolymer as a biosensor, cosmetics, drug delivery, flame retardancy, and electrospinning, among other interesting uses. The novel applications are based on the production and composition of the polymer, which can be modified by genetic engineering, a semi-synthetic approach, by changing feeding carbon sources and/or supplement addition, among others. The future of PHA is promising, and despite its production costs being higher than petroleum-based plastics, tools given by synthetic biology, bioinformatics, and machine learning, among others, have allowed for great production yields, monomer and polymer functionalization, stability, and versatility, a key feature to increase the uses of this interesting family of polymers.

Revealing the Phenotypic and Genomic Background for PHA Production from Rapeseed-Biodiesel Crude Glycerol Using Photobacterium ganghwense C2.2

Polyhydroxyalkanoates (PHA) are promising biodegradable and biocompatible bioplastics, and extensive knowledge of the employed bacterial strain's metabolic capabilities is necessary in choosing economically feasible production conditions. This study aimed to create an in-depth view of the utilization of Photobacterium ganghwense C2.2 for PHA production by linking a wide array of characterization methods: metabolic pathway annotation from the strain's complete genome, high-throughput phenotypic tests, and biomass analyses through plate-based assays and flask and bioreactor cultivations. We confirmed, in PHA production conditions, urea catabolization, fatty acid degradation and synthesis, and high pH variation and osmotic stress tolerance. With urea as a nitrogen source, pure and rapeseed-biodiesel crude glycerol were analyzed comparatively as carbon sources for fermentation at 20 °C. Flask cultivations yielded 2.2 g/L and 2 g/L PHA at 120 h, respectively, with molecular weights of 428,629 g/mol and 81,515 g/mol. Bioreactor batch cultivation doubled biomass accumulation (10 g/L and 13.2 g/L) in 48 h, with a PHA productivity of 0.133 g/(L·h) and 0.05 g/(L·h). Thus, phenotypic and genomic analyses determined the successful use of Photobacterium ganghwense C2.2 for PHA production using urea and crude glycerol and 20 g/L NaCl, without pH adjustment, providing the basis for a viable fermentation process.

Extremophilic Bacterium Halomonas desertis G11 as a Cell Factory for Poly-3-Hydroxybutyrate-co-3-Hydroxyvalerate Copolymer’s Production

Microbial polyhydroxyalkanoates (PHA) are biodegradable and biocompatible bio-based polyesters, which are used in various applications including packaging, medical and coating materials. In this study, an extremophilic hydrocarbonoclastic bacterium, previously isolated from saline sediment in the Tunisian desert, has been investigated for PHA production. The accumulation of intracellular PHA granules in Halomonas desertis G11 was detected by Nile blue A staining of the colonies. To achieve maximum PHA yield by the strain G11, the culture conditions were optimized through response surface methodology (RSM) employing a Box-Behnken Design (BBD) with three independent variables, namely, substrate concentration (1–5%), inoculum size (1–5%) and incubation time (5–15 days). Under optimized conditions, G11 strain produced 1.5 g/L (68% of DCW) of PHA using glycerol as a substrate. Application of NMR (1H and 13C) and FTIR spectroscopies showed that H. desertis accumulated PHA is a poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV). The genome analysis revealed the presence of typical structural genes involved in PHBV metabolism including phaA, phaB, phaC, phaP, phaZ, and phaR, coding for acetyl-CoA acetyltransferase, acetoacetyl-CoA reductase, class I polyhydroxyalkanoates synthases, phasin, polyhydroxyalkanoates depolymerase and polyhydroxyalkanoates synthesis repressor, respectively. Glycerol can be metabolized to 1) acetyl-CoA through the glycolysis pathway and subsequently converted to the 3HB monomer, and 2) to propionyl-CoA via the threonine biosynthetic pathway and subsequently converted to the 3HV monomer. In silico analysis of PhaC1 from H. desertis G11 indicated that this enzyme belongs to Class I PHA synthase family with a “lipase box”-like sequence (SYCVG). All these characteristics make the extremophilic bacterium H. desertis G11 a promising cell factory for the conversion of bio-renewable glycerol to high-value PHBV.

Biomolecules Production from Greenhouse Gases by Methanotrophs

Harmful effects on living organisms and the environment are on the rise due to a significant increase in greenhouse gas (GHG) emissions through human activities. Therefore, various research initiatives have been carried out in several directions in relation to the utilization of GHGs via physicochemical or biological routes. An environmentally friendly approach to reduce the burden of significant emissions and their harmful effects is the bioconversion of GHGs, including methane (CH4) and carbon dioxide (CO2), into value-added products. Methanotrophs have enormous potential for the efficient biotransformation of CH4 to various bioactive molecules, including biofuels, polyhydroxyalkanoates, and fatty acids. This review highlights the recent developments in methanotroph-based systems for methanol production from GHGs and proposes future perspectives to improve process sustainability via biorefinery approaches.

Anaerobic Digestion of Agri-Food Wastes for Generating Biofuels

Presently, fossil fuels are extensively employed as major sources of energy, and their uses are considered unsustainable due to emissions of obnoxious gases on the burning of fossil fuels, which can lead to severe environmental complications, including human health. To tackle these issues, various processes are developing to waste as a feed to generate eco-friendly fuels. The biological production of fuels is considered to be more beneficial than physicochemical methods due to their environmentally friendly nature, high rate of conversion at ambient physiological conditions, and less energy-intensive. Among various biofuels, hydrogen (H₂) is considered as a wonderful due to high calorific value and generate water molecule as end product on the burning. The H₂ production from biowaste is demonstrated, and agri-food waste can be potentially used as a feedstock due to their high biodegradability over lignocellulosic-based biomass. Still, the H₂ production is uneconomical from biowaste in fuel competing market because of low yields and increased capital and operational expenses. Anaerobic digestion is widely used for waste management and the generation of value-added products. This article is highlighting the valorization of agri-food waste to biofuels in single (H₂) and two-stage bioprocesses of H₂ and CH₄ production.

Efficient Production of Polyhydroxyalkanoate Through Halophilic Bacteria Utilizing Algal Biodiesel Waste Residue

The objective of the current work was to investigate the potential of halophilic bacterial isolates for efficient utilization of crude glycerol from algal biodiesel waste into polyhydroxyalkanoates (PHAs) a green plastic. Screening of the isolates was directly done in algal biodiesel waste residue containing solid agar plates supplemented with Nile red. Crude glycerol is a biodiesel waste whose bioconversion into value-added products provides an alternative for efficient management with dual benefit. For the scale-up studies of PHAs, Halomonas spp. especially H. daqingensis was observed as a potential candidate growing well in 3% Algal biodiesel waste residue (ABWR), 5% NaCl supplementation at 35°C within 48 h of incubation. Maximum Cell dry weight (CDW) of 0.362 ± 0.001 g and 0.236 ± 0.003 g PHA was obtained with H. daqingensis when grown in the fermentor with 0.5 vvm air flow rate and 200 rpm containing 3% ABWR supplemented with 5% NaCl at 35°C incubation temperature for 48 h. ABWR can serve as a sole substrate for PHA production at an industrial scale serving two approaches: getting rid of the biodiesel industrial waste containing high amount of glycerol besides using waste replacing commercial substrate thereby reducing the cost of the product.

Challenges & Opportunities on Catalytic Conversion of Glycerol to Value Added Chemicals

With the rapid expansion of biodiesel industry, its main by-product, crude glycerol, is anticipated to reach a global production of 6 million tons in 2025. It is actually a worrying phenomenon as glycerol could potentially emerge as an excessive product with little value. Glycerol, an alcohol and oxygenated chemical from biodiesel production, has essentially enormous potential to be converted into higher value-added chemicals. Using glycerol as a starting material for value-added chemical production will create a new demand on the glycerol market such as lactic acid, propylene glycol, alkyl lactatehydrogen, olefins and others. This paper briefly reviews the recent development on value-added chemicals derived from glycerol through catalytic conversion of refined and crude glycerol that have been proven to be promising in research stage with commercialization potential, or have been put in a corporate marketable production. Despite of the huge potential of products that can be transformed from glycerol, there are still numerous challenges to be addressed and discussed that include catalyst design and robustness; focus on crude or refined glycerol; reactor technology, reaction mechanism and thermodynamic analysis; and overall process commercial viability. The discussion will hopefully provide new insights on justified direction to focus on for glycerol transformation technology. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Biotin and Zn2+ Increase Xylitol Production by Candida tropicalis

In this study, the medium requirements to increase the production of xylitol by using Candida tropicalis (CT) have been investigated. The technique of single addition or omission of medium components was applied to determine the nutritional requirements. The addition of amino acids such as Asp, Glu, Gln, Asn, Thr, and Gly had no significant effect on CT growth. However, in the absence of other metal ions, there was a higher concentration of cell growth and xylitol production when only Zn2+ was present in the medium. The analysis of various vitamins unveiled that biotin and thiamine were the only vitamins required for the growth of CT. Surprisingly, when only biotin was present in the medium as a vitamin, there was less growth of CT than when the medium was complete, but the amount of xylitol released was significantly higher. Overall, this study will increase the xylitol production using the single omission or addtion technique.

Glycerol waste to value added products and its potential applications

The rapid industrial and economic development runs on fossil fuel and other energy sources. Limited oil reserves, environmental issues, and high transportation costs lead towards carbon unbiased renewable and sustainable fuel. Compared to other carbon-based fuels, biodiesel is attracted worldwide as a biofuel for the reduction of global dependence on fossil fuels and the greenhouse effect. During biodiesel production, approximately 10% of glycerol is formed in the transesterification process in a biodiesel plant. The ditching of crude glycerol is important as it contains salt, free fatty acids, and methanol that cause contamination of soil and creates environmental challenges for researchers. However, the excessive cost of crude glycerol refining and market capacity encourage the biodiesel industries for developing a new idea for utilising and produced extra sources of income and treat biodiesel waste. This review focuses on the significance of crude glycerol in the value-added utilisation and conversion to bioethanol by a fermentation process and describes the opportunities of glycerol in various applications.

Graphic abstract

What Is New in the Field of Industrial Wastes Conversion into Polyhydroxyalkanoates by Bacteria?

The rising global consumption and industrialization has resulted in increased food processing demand. Food industry generates a tremendous amount of waste which causes serious environmental issues. These problems have forced us to create strategies that will help to reduce the volume of waste and the contamination to the environment. Waste from food industries has great potential as substrates for value-added bioproducts. Among them, polyhydroxyalkanaotes (PHAs) have received considerable attention in recent years due to their comparable characteristics to common plastics. These biodegradable polyesters are produced by microorganisms during fermentation processes utilizing various carbon sources. Scale-up of PHA production is limited due to the cost of the carbon source metabolized by the microorganisms. Therefore, there is a growing need for the development of novel microbial processes using inexpensive carbon sources. Such substrates could be waste generated by the food industry and food service. The use of industrial waste streams for PHAs biosynthesis could transform PHA production into cheaper and more environmentally friendly bioprocess. This review collates in detail recent developments in the biosynthesis of various types of PHAs produced using waste derived from agrofood industries. Challenges associated with this production bioprocess were described, and new ways to overcome them were proposed.

Polyhydroxyalkanoates: Trends and advances toward biotechnological applications

Plastics are an integral part of most of the daily requirements. Indiscriminate usage and disposal have led to the accumulation of massive quantities of waste. Their non-biodegradable nature makes it increasingly difficult to manage and dispose them. To counter this impending disaster, biodegradable polymers, especially polyhydroxy-alkanoates (PHAs), have been envisaged as potential alternatives. Owing to their unique physicochemical characteristics, PHAs are gaining importance for versatile applications in the agricultural and medical sectors. Applications in the medical sector are more promising because of their commercial viability and sustainability. Despite such potential, their production and commercialization are significant challenges. The major limitations are their poor mechanical strength, production in small quantities, costly feed, and lack of facilities for industrial production. This article provides an overview of the contemporary progress in the field, to attract researchers and stakeholders to further exploit these renewable resources to produce biodegradable plastics on a commercial scale.

A Novel Nucleic Lateral Flow Assay for Screening phaR-Containing Bacillus spp

Polyhydroxyalkanoate (PHA) synthase is a key enzyme for PHA production in microorganisms. The class IV PHA synthase is composed of two subunits: PhaC and PhaR. The PhaR subunit, which encodes the phaR gene, is only present in class IV PHA synthases. Therefore, the phaR gene is used as a biomarker for bacteria that contain a class IV PHA synthase, such as some Bacillus spp. The phaR gene was developed to screen phaR-containing Bacillus spp. The phaR screening method involved two steps: phaR gene amplification by PCR and phaR amplicon detection using a DNA lateral flow assay. The screening method has a high specificity for phaR-containing Bacillus spp. The lowest amount of genomic DNA of B. thuringiensis ATCC 10792 that the phaR screening method could detect was 10 pg. This novel screening method improves the specificity and sensitivity of phaR gene screening and reduces the time and cost of the screening process, which could enhance the opportunity to discover good candidate PHA producers. Nevertheless, the screening method can certainly be used as a tool to screen phaR-containing Bacillus spp. from environmental samples.

Direct production of polyhydroxybutyrate from waste starch by newly-isolated Bacillus aryabhattai T34-N4

Polyhydroxybutyrate (PHB) is a natural microbial polyester produced by a variety of bacteria and archaea from renewable resources. PHB resembles some petrochemical plastics but is completely biodegradable. It is desirable to identify suitable microbial strains and develop processes that can directly use starch from agricultural wastes without commercial amylase treatment. Here, PHB production using starch from agricultural waste was developed using a newly isolated strain, Bacillus aryabhattai T34-N4. This strain hydrolyzed cassava pulp and oil palm trunk starch and accumulated up to 17 wt% PHB of the cell dry weight. The α-amylase of this strain, AmyA, showed high activity in the presence of cassava pulp starch (69.72 U) and oil palm trunk starch (70.53 U). High expression of amyA was recorded in the presence of cassava pulp starch, whereas low expression was detected in the presence of glucose. These data suggest that starch saccharification by amyA allows strain T34-N4 to grow and directly produce PHB from waste starch materials such as cassava pulp and oil palm trunk starch, which may be used as low-cost substrates.

Polyhydroxyalkanoates: Next generation natural biomolecules and a solution for the world's future economy

Petrochemical plastics have become a cause of pollution for decades and finding alternative plastics that are environmental friendly. Polyhydroxyalkanoate (PHA), a biopolyester produced by microbial cells, has characteristics (biocompatible, biodegradable, non-toxic) that make it appropriate as a biodegradable plastic substance. The different forms of PHA make it suitable to a wide choice of products, from packaging materials to biomedical applications. The major challenge in commercialization of PHA is the cost of manufacturing. There are a lot of factors that could affect the efficiency of a development method. The development of new strategic parameters for better synthesis, including consumption of low cost carbon substrates, genetic modification of PHA-producing strains, and fermentational strategies are discussed. Recently, many efforts have been made to develop a method for the cost-effective production of PHAs. The isolation, analysis as well as characterization of PHAs are significant factors for any developmental process. Due to the biodegradable and biocompatible properties of PHAs, they are majorly used in biomedical applications such as vascular grafting, heart tissue engineering, skin tissue repairing, liver tissue engineering, nerve tissue engineering, bone tissue engineering, cartilage tissue engineering and therapeutic carrier. The emerging and interesting area of research is the development of self-healing biopolymer that could significantly broaden the operational life and protection of the polymeric materials for a broad range of uses. Biodegradable and biocompatible polymers are considered as the green materials in place of petroleum-based plastics in the future.

Introducing the Newly Isolated Bacterium Aneurinibacillus sp. H1 as an Auspicious Thermophilic Producer of Various Polyhydroxyalkanoates (PHA) Copolymers-1. Isolation and Characterization of the Bacterium

Extremophilic microorganisms are considered being very promising candidates for biotechnological production of various products including polyhydroxyalkanoates (PHA). The aim of this work was to evaluate the PHA production potential of a novel PHA-producing thermophilic Gram-positive isolate Aneurinibacillus sp. H1. This organism was capable of efficient conversion of glycerol into poly(3-hydroxybutyrate) (P3HB), the homopolyester of 3-hydroxybutyrate (3HB). In flasks experiment, under optimal cultivation temperature of 45 °C, the P3HB content in biomass and P3HB titers reached 55.31% of cell dry mass and 2.03 g/L, respectively. Further, the isolate was capable of biosynthesis of PHA copolymers and terpolymers containing high molar fractions of 3-hydroxyvalerate (3HV) and 4-hydroxybutyrate (4HB). Especially 4HB contents in PHA were very high (up to 91 mol %) when 1,4-butanediol was used as a substrate. Based on these results, it can be stated that Aneurinibacillus sp. H1 is a very promising candidate for production of PHA with tailored material properties.

Promotion of compound K production in Saccharomyces cerevisiae by glycerol

BACKGROUND

Ginsenoside compound K (CK), one of the primary active metabolites of protopanaxadiol-type ginsenosides, is produced by the intestinal flora that degrade ginseng saponins and exhibits diverse biological properties such as anticancer, anti-inflammatory, and anti-allergic properties. However, it is less abundant in plants. Therefore, enabling its commercialization by construction of a Saccharomyces cerevisiae cell factory is of considerable significance.

RESULTS

We induced overexpression of PGM2, UGP1, and UGT1 genes in WLT-MVA5, and obtained a strain that produces ginsenoside CK. The production of CK at 96 h was 263.94 ± 2.36 mg/L, and the conversion rate from protopanaxadiol (PPD) to ginsenoside CK was 64.23 ± 0.41%. Additionally, it was observed that the addition of glycerol was beneficial to the synthesis of CK. When 20% glucose (C mol) in the YPD medium was replaced by the same C mol glycerol, CK production increased to 384.52 ± 15.23 mg/L, which was 45.68% higher than that in YPD medium, and the PPD conversion rate increased to 77.37 ± 3.37% as well. As we previously observed that ethanol is beneficial to the production of PPD, ethanol and glycerol were fed simultaneously in the 5-L bioreactor fed fermentation, and the CK levels reached 1.70 ± 0.16 g/L.

CONCLUSIONS

In this study, we constructed an S. cerevisiae cell factory that efficiently produced ginsenoside CK. Glycerol effectively increased the glycosylation efficiency of PPD to ginsenoside CK, guiding higher carbon flow to the synthesis of ginsenosides and effectively improving CK production. CK production attained in a 5-L bioreactor was 1.7 g/L after simultaneous feeding of glycerol and ethanol.

Insights into the effect of different levels of crude oil on hydrolyzed polyacrylamide biotransformation in aerobic and anoxic biosystems: Bioresource production, enzymatic activity, and microbial function

The differences of crude oil recovery ratio resulted in different levels of crude oil in actual hydrolyzed polyacrylamide (HPAM)-containing wastewater. The effect of crude oil on HPAM biotransformation was explored from bioresource production, enzymatic activity and microbial function. In aerobic biosystems, the highest polyhydroxyalkanoate (PHA) yield (19.6%-40.2%) and dehydrogenase (DH) activity (4.06-8.32 mg·g^-1 VSS) occurred in the 48th hour, and increased with crude oil concentration (0-400 mg·L^-1). In anoxic biosystems, the highest PHA yield (24.5%-50.5%) and DH activity (3.24-6.69 mg·g^-1 VSS) occurred in the 72nd hour, and increased with crude oil concentration. The higher substrate removal (38.5%-65.7%) occurred in aerobic biosystems, while the higher PHA accumulation occurred in anoxic biosystems. PHA yield, DH activity and HPAM removal were related. Microbial function related to HPAM biodegradation and PHA synthesis was discussed. The main function of Pseudomonas and Bacillus in aerobic biosystems was to degrade HPAM, and in anoxic biosystems was to synthesize PHA.

Aligning Microbial Biodiversity for Valorization of Biowastes: Conception to Perception

Generation of biowastes is increasing rapidly and its uncontrolled, slow and persistent fermentation leads to the release of Green-house gases (GHGs) into the environment. Exploration and exploitation of microbial diversity for degrading biowastes can result in producing diverse range of bioactive molecules, which can act as a source of bioenergy, biopolymers, nutraceuticals and antimicrobials. The whole process is envisaged to manage biowastes, and reduce their pollution causing capacity, and lead to a sustainable society. A strategy has been proposed for: (1) producing bioactive molecules, and (2) achieving a zero-pollution emission by recycling of the GHGs through biological routes.

Scale Up Studies for Polyhydroxyalkanoate Production by a Bacillus flexus Strain with Industrial Potential

Polyhydroxyalkanoates (PHA) are synthesized by bacteria under unfavourable growth conditions like excess of carbon over nitrogen, coupled with oxygen limitation. The PHA polymers of microbial origin are diverse in chemical composition and material properties. A bioprocess for PHA production by indigenously isolated Bacillus flexus MTCC 12841 was devised and optimized at a laboratory fermentor scale. Fermentation strategies that involved modifications in some parameters like aeration, agitation, temperature, nutrient feeding or changes in C:N ratio led to substantial improvement of 59% in PHA production reaching highest concentration of 9.73 g/L. Biomass too was enhanced to 15.70 g/L equivalent to 126% increase over the optimized shake flask runs. PHA (Yp/s) and biomass (Yx/s) yields were found to be 0.32 and 0.51 g/g respectively, indicating good carbon utilization efficiency. The characterization of polymer by GC-MS revealed that the culture produced poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) as a co-polymer. The novelty of the research findings lies in the demonstration of increased production of PHA at lab fermentor level coupled with the identification of the natural ability of the strain to also produce PHBV without any need for exogenous addition of precursors. The fermentation process as well as the strain may be subjected to further optimization to increase the PHA production as well as to increase the % of HV content in the co-polymer.

Cloning, Expression and Characterization of a Highly Active Alcohol Dehydrogenase for Production of Ethyl (S)-4-Chloro-3-Hydroxybutyrate

A novel alcohol dehydrogenase from Bartonella apis (BaADH) was heterologous expressed in Escherichia coli. Its biochemical properties were investigated and used to catalyze the synthesis of ethyl (S)-4-chloro-3-hydroxybutanoate ((S)-CHBE), which is a chiral intermediate of the cholesterol-lowering drug atorvastatin. The purified recombinant BaADH displayed 182.4 U/mg of the specific activity using ethyl 4-chloroacetoacetate as substrate under the conditions of 50 °C in pH 7.0 Tris-HCl buffer. It was stable in storage buffers of pH 7 to 9 and retains up to 96.7% of the initial activity after 24 h. The K _m and V _max values of BaADH were 0.11 mM and 190.4 μmol min^-1 mg^-1, respectively. Synthesis of (S)-CHBE catalyzed by BaADH was performed with a cofactor regeneration system using a glucose dehydrogenase, and a conversion of 94.9% can be achieved after 1 h reaction. Homology modeling and substrate docking revealed that a typical catalytic triad is in contact with local water molecules to form a catalytic system. The results indicated this ADH could contribute to the further enzymatic synthesis of (S)-CHBE.

Cloning, Sequencing and In Silico Analysis of phbC Gene from Pseudomonas spp

We report here isolation and analysis of PCR amplified phbC gene from Pseudomonas spp. strain phbmbb15-B3. This strain was previously developed from mutations of landfill isolates and found to be an efficient Poly Hydroxy butyrate (PHB) producer. The fragment was cloned into pTZ57R/T cloning vector and then the gene has been sequenced and submitted to GenBank (Accession Number KT933807). The sequence results confirmed the clone to be phbC homologue and the ORF was 910 base pairs long and coded for 303 amino acids, which shared 92-99% amino acid sequence identity with the available bacterial sequences in Gene Bank. We could also predict the primary and secondary structural features of the expected phbC protein. Phylogenetic analysis also revealed its similarity with several pseudomonads. The results of the present study shall provide a stable foundation for further research on modeling studies of PHB synthase and developing PHB a commercial technology.

Valorization of polyhydroxyalkanoates production process by co-synthesis of value-added products

Polyhydroxyalkanoates (PHAs) are the only polyesters that are completely synthesized biologically and possess features equivalent to petroleum-based plastics besides being biodegradable. PHA based materials may certainly prove helpful in addressing the concerns caused due to the indiscriminate use of synthetic plastics. However, the cost of producing these polymers on a large scale is still uneconomical. Various approaches have been developed to tackle this issue through usage of agro-industrial wastes, co-production of high market value products, polymer extraction using green solvents, etc. The advent of recombineering and CRISPR technologies has broadened the scope of constructing a microbe capable of synthesizing multiple products with economic feasibility. Quite a few high-market value chemicals are possible to synthesize along with the favorable accumulation of PHA. The present article attempts to review all PHA polymer co-production processes with other chemicals reported till date and discusses the opportunities for their large-scale operation in future.

Biotic and Abiotic Synthesis of Renewable Aliphatic Polyesters from Short Building Blocks Obtained from Biotechnology

Biobased polymers have seen their attractiveness increase in recent decades thanks to the significant development of biorefineries to allow access to a wide variety of biobased building blocks. Polyesters are one of the best examples of the development of biobased polymers because most of them now have their monomers produced from renewable resources and are biodegradable. Currently, these polyesters are mainly produced by using traditional chemical catalysts and harsh conditions, but recently greener pathways with nontoxic enzymes as biocatalysts and mild conditions have shown great potential. Bacterial polyesters, such as poly(hydroxyalkanoate)s (PHA), are the best example of the biotic production of high molar mass polymers. PHAs display a wide variety of macromolecular architectures, which allow a large range of applications. The present contribution aims to provide an overview of recent progress in studies on biobased polyesters, especially those made from short building blocks, synthesized through step-growth polymerization. In addition, some important technical aspects of their syntheses through biotic or abiotic pathways have been detailed.

Enhanced thermostability of halo-tolerant glutaminase from Bacillus licheniformis ATCC 14580 by immobilization onto nano magnetic cellulose sheet and its application in production of glutamic acid

A halo-tolerant glutaminase gene (BlglsA) was isolated from Bacillus licheniformis. Heterologous expression of BlglsA revealed that it encodes for a 36 kDa protein containing 327 amino acid residues. The purified enzyme showed optimal activity at a pH of 9.5 while 35 °C was found to be the optimum temperature. The enzyme retained about 92 and 97% stability at pH 12 and temperature (40 °C) respectively. Subsequent immobilization of BlglsA on nano magnetic cellulose sheet (NMCS) led to an enhanced tolerance to higher temperature. NMCS-BlglsA showed optimum activity at 45 °C, although it was stable even at 60 °C. NaCl tolerance (≥90% in 0.3 M) was almost similar to BlglsA and NMCS-BlglsA. The metal ions Fe²⁺ (5 mM) and Mn²⁺ (2.5 mM) improved the BlglsA relative activity by 61 and 48%, respectively. In contrast, 5 mM Mn²⁺ was found suitable to enhance the activity of NMCS-BlglsA up to 72%. The production of glutamic acid by NMCS-BlglsA was 1.61 g/l in 48 h. Reusability test of NMCS-BlglsA showed 76 and 35% retention of the actual activity after 4th and 7th cycle, respectively. Such remarkable biochemical properties of NMCS-BlglsA make it an attractive enzyme for food industries.

Bio-hydrogen production by co-digestion of domestic wastewater and biodiesel industry effluent

The increasing water crisis makes fresh water a valuable resource, which must be used wisely. However, with growing population and inefficient waste treatment systems, the amount of wastewater dispelled in rivers is increasing abominably. Utilizing this freely available waste-water along with biodiesel industry waste- crude glycerol for bio-hydrogen production is being reported here. The bacterial cultures of Bacillus thuringiensis strain EGU45 and Bacillus amyloliquefaciens strain CD16 produced2.4-3.0 L H2/day/L feed during a 60 days continuous culture system at hydraulic retention time of 2 days. An average H2 yield of 100-120 L/L CG was reported by the two strains. Recycling of the effluent by up to 25% resulted in up to 94% H2 production compared to control.

Production and Characterization of Polyhydroxyalkanoate from Lignin Derivatives by Pandoraea sp. ISTKB

The present study investigates polyhydroxyalkanoate (PHA) production from lignin and its derivatives by a previously reported lignin-degrading bacterial strain Pandoraea sp. ISTKB. PHA production was screened by fluorescence microscopy and flow cytometry using a Nile red stain. PHA and biomass accumulation, while screening, was found to be maximum on 4-hydroxybenzoic acid followed by p-coumaric acid, vanillic acid, 2,6-dimethoxyphenol, and kraft lignin after 96 h. Monomer composition was analyzed by gas chromatography-mass spectrometry (GC-MS) and was followed by Fourier transform infrared and ¹H NMR analysis, indicating PHA to be a copolymer of P(hydroxybutyrate-co-hydroxyvalerate). Genomic analysis of Pandoraea sp. ISTKB also complemented the results of GC-MS and NMR, and the relevant genes responsible for the synthesis of small chain length PHA were discovered in the genome. Process parameters were optimized by response surface methodology for enhanced production of PHA and biomass on 4-hydroxybenzoate. Optimization results showed 30 and 66% increase in the biomass and PHA production, respectively. The results obtained were promising and indicated that if lignin is depolymerized into low-molecular-weight intermediates, then it can easily be utilized and converted into value-added products like PHA by microbes.

Co-utilization of Crude Glycerol and Biowastes for Producing Polyhydroxyalkanoates

Polyhydroxyalkanoate (PHA) production by Bacillus thuringiensis EGU45 and defined mixed culture of Bacillus spp. were studied by using crude glycerol (CG) and hydrolyzed biowastes as feed material. Hydrolysates from onion peels (OP), potato peels, pea-shells (PS), apple pomace 2% total solids obtained with defined mixed hydrolytic cultures (MHC2) were inoculated with B. thuringiensis EGU45 and defined mixed bacterial cultures (5MC1), which produced PHA at the rate of 40-350 and 65-450 mg/L, respectively. Addition of CG (1%, v/v) to these hydrolysates resulted in 1.8-fold and 4.5-fold enhancement in PHA production from OP by B. thuringiensis EGU45 and 5MC1, respectively. Co-utilization of OP and PS (in 2:1 ratio) supplemented with CG (1%, v/v) by B. thuringiensis EGU45 resulted in 2-fold increase in PHA production in comparison to OP + CG. This co-metabolism of OP and PS also enabled PHA co-polymer production (1300 mg/L), having an enhanced HV content of 21.2% (w/w).

Bacillus and biopolymer: Prospects and challenges

The microbially derived polyhydroxyalkanoates biopolymers could impact the global climate scenario by replacing the conventional non-degradable, petrochemical-based polymer. The biogenesis, characterization and properties of PHAs by Bacillus species using renewable substrates have been elaborated by many for their wide applications. On the other hand Bacillus species are advantageous over other bacteria due to their abundance even in extreme ecological conditions, higher growth rates even on cheap substrates, higher PHAs production ability, and the ease of extracting the PHAs. Bacillus species possess hydrolytic enzymes that can be exploited for economical PHAs production. This review summarizes the recent trends in both non-growth and growth associated PHAs production by Bacillus species which may provide direction leading to future research towards this growing quest for biodegradable plastics, one more critical step ahead towards sustainable development.

Bioconversion of fish solid waste into PHB using Bacillus subtilis based submerged fermentation process

Currently, one of the major problem affecting the world is solid waste management, predominantly petroleum-based plastic and fish solid waste (FSW). However, it is very difficult to reduce the consumption of plastic as well as fish products, but it is promising to convert FSW to biopolymer to reduce eco-pollution. On account of that, the bioconversion of FSW extract to polyhydroxybutyrate (PHB) was undertaken by using Bacillus subtilis (KP172548). Under optimized conditions, 1.62 g/L of PHB has been produced by the bacterium. The purified compound was further characterized by advanced analytical technologies to elucidate its chemical structure. Results indicated that the biopolymer was found to be PHB, the most common homopolymer of polyhydroxyalkanoates (PHAs). This is the first report demonstrating the efficacy of B. subtilis to utilize FSW extract to produce biopolymer. The biocompatibility of the PHB against murine macrophage cell line RAW264.7 demonstrated that, it was comparatively less toxic, favourable for surface attachment and proliferation in comparison with poly-lactic acid (PLA) and commercially available PHB. Thus, further exploration is highly indispensable to use FSW extract as a substrate for production of PHB at pilot scale.

Bioprocessing of Biodiesel Industry Effluent by Immobilized Bacteria to Produce Value-Added Products

Biodiesel industrial effluent rich in crude glycerol (CG) was processed to produce value-added product. Under continuous culture system, Bacillus amyloliquefaciens strain CD16 immobilized within its biofilm, produced 3.2 L H₂/day/L feed, over a period of 60 days at a hydraulic retention time of 2 days. The effective H₂ yield by B. amyloliquefaciens strain CD16 was 165 L/L CG. This H₂ yield was 1.18-fold higher than that observed with non-biofilm forming Bacillus thuringiensis strain EGU45. Bioprocessing of the effluent released after this stage, by recycling it up to 25% did not have any adverse effect on H₂ production by strain EGU45; however, a 25% reduction in yield was recorded with strain CD16. Biofilm forming H₂ producers thus proved effective as self-immobilizing system leading to enhanced process efficiency.