Carbon dioxide sequestration by chemolithotrophic oleaginous bacteria for production and optimization of polyhydroxyalkanoate

Green alternatives to petroleum-based plastics: production of bioplastic from Pseudomonas neustonica strain NGB15 using waste carbon source

Polyhydroxyalkanoates have attracted great interest as a suitable alternative to petrochemical based plastics due to their outstanding properties such as biodegradability and biocompatibility. However, the biggest problem in the production of microbial polyhydroxyalkanoates is low cost-effectiveness. In this study, polyhydroxyalkanoate production was carried out using waste substrates with local isolates. Culture conditions were optimized to increase the polyhydroxyalkanoate production potential. The produced polyhydroxyalkanoate was characterized by FTIR analyses, and its metabolic pathway was determined by real-time PCR. According to the results, the best polyhydroxyalkanoate producer bacteria was characterized as Pseudomonas neustonica NGB15. The optimal culture conditions were detected as 30 g/L banana peel powder, 25 °C temperature, pH 8, and 4-day incubation time. Under the optimized conditions, 3.34 g/L PHA production was achieved. As a result of FTIR analyses, major peaks were obtained at 1723, 1277, 1261, 1097, 1054, and 993 cm-1. These peaks represent that the type of produced polyhydroxyalkanoate was poly-β-hydroxybutyrate. According to gene expression profile of NGB15, it was determined that Pseudomonas neustonica NGB15 produces PHA using the de novo fatty acid synthesis metabolic pathway. In conclusion, poly-β-hydroxybutyrate production by Pseudomonas neustonica NGB15 using a low-cost fermentation medium has been shown to be biotechnologically promising.

Traditional Chinese medicine residue enzymatic hydrolysates for production of polyhydroxyalkanoate by newly isolated Bacillus altitudinis

Traditional Chinese medicine residue (TCMR) was utilized as an inexpensive carbon source for the production of poly(3-hydroxybutyrate) (PHB) using the newly isolated Bacillus altitudinis HBU-SI7. The results showed that Yu Ping Feng TCMR could be directly hydrolysed by cellulase to obtain a high proportion of glucose (99 % of total sugar) without pretreatment, achieving an enzymatic hydrolysis rate of up to 89.2 %. B. altitudinis could grow and produce PHB when using enzymatically hydrolysed TCMR in a 5-L fermenter. After 20 h of fermentation, the maximum concentration of PHB was 11.2 g/L, and the highest cell dry weight (CDW) was 15.4 g/L, with 72.7 % of the PHB fraction in CDW. Moreover, this strain could utilize enzymatic hydrolysates from various herbal formulas to produce high levels of PHB. This novel approach aims to accumulate PHB from TCMR hydrolysates, offering an effective and environmentally friendly method to reduce production costs and achieve mass production.

Carbon dioxide and methane as carbon source for the production of polyhydroxyalkanoates and concomitant carbon fixation

The currently used plastics are non-biodegradable, and cause greenhouse gases (GHGs) emission as they are petroleum-based. Polyhydroxyalkanoates (PHAs) are biopolymers with excellent biodegradability and biocompatibility, which can be used to replace petroleum-based plastics. A variety of microorganisms have been found to synthesize PHAs by using typical GHGs: carbon dioxide and methane as carbon sources. Converting carbon dioxide (CO2) and methane (CH4) to PHAs is an attractive option for carbon capture and biodegradable plastic production. In this review, the microorganisms capable of using CO2 and CH4 to produce PHAs were summarized. The metabolic mechanism, PHAs production process, and the factors influencing the production process are illustrated. The currently used optimization techniques to improve the yield of PHAs are discussed. The challenges and future prospects for developing economically viable PHAs production using GHGs as carbon source are identified. This work provides an insight for achieving carbon sequestration and bioplastics based circular economy.

The Role of Bacterial Polyhydroalkanoate (PHA) in a Sustainable Future: A Review on the Biological Diversity

Environmental challenges related to the mismanagement of plastic waste became even more evident during the COVID-19 pandemic. The need for new solutions regarding the use of plastics came to the forefront again. Polyhydroxyalkanoates (PHA) have demonstrated their ability to replace conventional plastics, especially in packaging. Its biodegradability and biocompatibility makes this material a sustainable solution. The cost of PHA production and some weak physical properties compared to synthetic polymers remain as the main barriers to its implementation in the industry. The scientific community has been trying to solve these disadvantages associated with PHA. This review seeks to frame the role of PHA and bioplastics as substitutes for conventional plastics for a more sustainable future. It is focused on the bacterial production of PHA, highlighting the current limitations of the production process and, consequently, its implementation in the industry, as well as reviewing the alternatives to turn the production of bioplastics into a sustainable and circular economy.

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.

Can microbes be harnessed to reduce atmospheric loads of greenhouse gases?

Reducing atmospheric loads of greenhouse gases (GHGs), especially CO₂ and CH₄ , has been considered the key to alleviating global crises we are facing, such as climate change, sea level elevation and ocean acidification. To this end, development of strategies and technologies for carbon capture, sequestration and utilization (CCSU) is urgently needed. Although physicochemical methods have been the most actively studied in the early stages of developing CCSU technologies, there have recently been growing interests in developing microbe-based CCSU processes. In this article, we discuss advantages of microbe-based CCSU technologies over physicochemical approaches and even plant-based approaches. Next, various parts of the global carbon cycle where microorganisms can contribute, such as sequestering atmospheric GHGs, facilitating the carbon cycle, and slowing down the depletion of carbon reservoirs are described, emphasizing the impacts of microbes on the carbon cycle. Strategies to upgrade microbes and increase their performance in assimilating GHGs or converting GHGs to value-added chemicals are also provided. Moreover, several examples of exploiting microbes to address environmental crises are discussed. Finally, we discuss things to overcome in microbe-based CCSU technologies and provide future perspectives.

Leads and hurdles to sustainable microbial bioplastic production

Indiscriminate usage, disposal and recalcitrance of petroleum-based plastics have led to its accumulation leaving a negative impact on the environment. Bioplastics, particularly microbial bioplastics serve as an ecologically sustainable solution to nullify the negative impacts of plastics. Microbial production of biopolymers like Polyhydroxyalkanoates, Polyhydroxybutyrates and Polylactic acid using renewable feedstocks as well as industrial wastes have gained momentum in the recent years. The current study outlays types of bioplastics, their microbial sources and applications in various fields. Scientific evidence on bioplastics has suggested a unique range of applications such as industrial, agricultural and medical applications. Though diverse microorganisms such as Alcaligenes latus, Burkholderia sacchari, Micrococcus species, Lactobacillus pentosus, Bacillus sp., Pseudomonas sp., Klebsiella sp., Rhizobium sp., Enterobacter sp., Escherichia sp., Azototobacter sp., Protomonas sp., Cupriavidus sp., Halomonas sp., Saccharomyces sp., Kluyveromyces sp., and Ralstonia sp. are known to produce bioplastics, the industrial production of bioplastics is still challenging. Thus this paper also provides deep insights on the advancements made to maximise production of bioplastics using different approaches such as metabolic engineering, rDNA technologies and multitude of cultivation strategies. Finally, the constraints to microbial bioplastic production and the future directions of research are briefed. Hence the present review emphasizes on the importance of using bioplastics as a sustainable alternative to petroleum based plastic products to diminish environmental pollution.

Optimization of Growth Conditions to Enhance PHA Production by Cupriavidus necator

The accumulation of polyhydroxyalkanoates (PHAs) by microorganisms usually occurs in response to environmental stress conditions. Therefore, it is advantageous to choose two-step cultivation. The first phase is aimed at maximizing biomass production, and only in the second phase, after setting the suitable conditions, PHA production starts. The aim of this work was to optimize the composition of the minimal propagation medium used for biomass production of Cupriavidus necator DSM 545 using the response surface methodology (RSM). Based on the results from the search for optimization limits, the glucose concentration, the ammonium sulfate concentration and the phosphate buffer molarity were chosen as independent variables. The optimal values were found as follows: the glucose concentration 10.8 g/L; the ammonium sulfate concentration 0.95 g/L; and the phosphate buffer molarity 60.2 mmol/L. The predicted biomass concentration was 4.54 g/L, and the verified value was at 4.84 g/L. Although this work was primarily focused on determining the optimal composition of the propagation medium, we also evaluated the optimal composition of the production medium and found that the optimal glucose concentration was 6.7 g/L; the ammonium sulfate concentration 0.60 g/L; and the phosphate buffer molarity 20 mmol/L. The predicted PHB yield was 54.7% (w/w) of dry biomass, and the verified value was 49.1%.

A comprehensive review on recent advancements in biodegradation and sustainable management of biopolymers

Recent years have seen upsurge in plastic manufacturing and its utilization in various fields, such as, packaging, household goods, medical applications, and beauty products. Due to various adverse impacts imposed by synthetic plastics on the health of living well-being and the environment, the biopolymers have been emerged out an alternative. Although, the biopolymers such as polyhydroxyalkanoates (PHA) are entirely degradable. However, the other polymers, such as poly (lactic acid) (PLA) are only partially degradable and often not biosynthesized. Biodegradation of the polymers using microorganisms is considered an effective bioremediation approach. Biodegradation can be performed in aerobic and anaerobic environments. In this context, the present review discusses the biopolymer production, their persistence in the environment, aerobic biodegradation, anaerobic biodegradation, challenges associated with biodegradation and future perspectives. In addition, this review discusses the advancement in the technologies associated with biopolymer production, biodegradation, and their biodegradation standard in different environmental settings. Furthermore, differences in the degradation condition in the laboratory as well as on-site are discussed.

Role of carbon-dioxide sequestering bacteria for clean air environment and prospective production of biomaterials: a sustainable approach

The increase in demand of fossil fuel uses for developmental activity and manufacturing of goods have resulted a huge emission of global warming gases (GWGs) in the atmosphere. Among all GWGs, CO₂ is the major contributor that inevitably causes global warming and climate change. Mitigation strategies like biological CO₂ capture through sequestration and their storage into biological organic form are used to minimize the concentration of atmospheric CO₂ with the goal to control climate change. Since increasing atmospheric CO₂ level supports microbial growth and productivity thus microbial-based CO₂ sequestration has remarkable advantages as compared to plant-based sequestration. This review focuses on CO₂ sequestration mechanism in bacteria through different carbon fixation pathways, involved enzymes, their role in calcite, and other environmentally friendly biomaterials such as biofuel, bioplastic, and biosurfactant.

The impact of carbon to nitrogen ratios and pH on the microbial prevalence and polyhydroxybutyrate production levels using a mixed microbial starter culture

Growth conditions have been frequently studied in optimizing polyhydroxybutyrate (PHB) production, while few studies were performed to unravel the dynamic mixed microbial consortia (MMCs) in the process. In this study, the relationship between growth conditions (C/N ratios and pH) and the corresponding key-microbes were identified and monitored during PHB accumulation. The highest PHB level (70 wt% of dry cell mass) was obtained at pH 9, C/N 40, and acetic acid 10 g/L. Linking the dominant genera with the highest point of PHB accumulation, Thauera was the most prevalent species in all MMCs of pH 9, except when a C/N ratio of 1 was applied. Notably, dominant bacteria shifted at pH 7 (C/N 10) from Thauera (0 h) to Paracoccus, and subsequently to Alcaligenes following the process of PHB accumulation and consumption. Further understanding of the relationship between the structure of the microbial community and the performance will be beneficial for regulating and obtaining high PHB accumulation within an MMC. Our study illustrates the impact of C/N ratios and pH on microbial prevalence and PHB production levels using a mixed microbial starter culture. This knowledge will broaden industrial perspectives for regulating high PHB production and timely harvesting.

Integrated analysis of Whole genome sequencing and life cycle assessment for polyhydroxyalkanoates production by Cupriavidus sp. ISTL7

The current study demonstrates the enhanced production capability of strain Cupriavidus sp. ISTL7 for polyhydroxyalkanoates (PHA) using acetate and glucose (4.93 ± 0.4571 g L^-1) which was characterised analytically by GC-MS, FTIR and NMR analysis. Whole genome sequencing of strain ISTL7 unveiled an array of PHA metabolism genes which included phaA, phaB and phaC. Life cycle assessment of the protocol established that the production was most sustainable with the carbon source acetate. + Glucose as compared to acetate/glucose alone. It also concluded that solvent extraction of PHA and energy consumption during the process requires optimization to sustain the production on ecological fronts. Additionally, acetoacetyl-CoA reductase (phaB) gene was molecularly cloned, expressed and purified (27 KDa, 2.63 mg/ml). Conclusively, Cupriavidus sp. ISTL7 is a potential strain for PHA production with a scope of improvement on energy fronts which would transform the production environmentally and economically appealing.

Bio-conversion of CO2 into biofuels and other value-added chemicals via metabolic engineering

Carbon dioxide (CO₂) occurs naturally in the atmosphere as a trace gas, which is produced naturally as well as by anthropogenic activities. CO₂ is a readily available source of carbon that in principle can be used as a raw material for the synthesis of valuable products. The autotrophic organisms are naturally equipped to convert CO₂ into biomass by obtaining energy from sunlight or inorganic electron donors. This autotrophic CO₂ fixation has been exploited in biotechnology, and microbial cell factories have been metabolically engineered to convert CO₂ into biofuels and other value-added bio-based chemicals. A variety of metabolic engineering efforts for CO₂ fixation ranging from basic copy, paste, and fine-tuning approaches to engineering and testing of novel synthetic CO₂ fixing pathways have been demonstrated. In this paper, we review the current advances and innovations in metabolic engineering for bio-conversion of CO₂ into bio biofuels and other value-added bio-based chemicals.

Process optimization, metabolic engineering interventions and commercialization of microbial polyhydroxyalkanoates production - A state-of-the art review

Microbial polyhydroxyalkanoates (PHAs) produced using renewable resources could be the best alternative for conventional plastics. Despite their incredible potential, commercial production of PHAs remains very low. Nevertheless, sincere attempts have been made by researchers to improve the yield and economic viability of PHA production by utilizing low-cost agricultural or industrial wastes. In this context, the use of efficient microbial culture or consortia, adoption of experimental design to trace ideal growth conditions, nutritional requirements, and intervention of metabolic engineering tools have gained significant attention. This review has been structured to highlight the important microbial sources for PHA production, use of conventional and non-conventional substrates, product optimization using experimental design, metabolic engineering strategies, and global players in the commercialization of PHA in the past two decades. The challenges about PHA recovery and analysis have also been discussed which possess indirect hurdle while expanding the horizon of PHA-based bioplastics. Selection of appropriate microorganism and substrate plays a vital role in improving the productivity and characteristics of PHAs. Experimental design-based bioprocess, use of metabolic engineering tools, and optimal product recovery techniques are invaluable in this dimension. Optimization strategies, which are being explored in isolation, need to be logically integrated for the successful commercialization of microbial PHAs.

Biopolymer production using volatile fatty acids as resource: Effect of feast-famine strategy and lignin reinforcement

The present study aimed to investigate the biopolymer production using VFA's as carbon source through feast and famine strategy in a sequencing batch reactor. Famine condition with nutrients and oxygen limitation resulted in high polyhydroxybutyrate yield (PHB: 2.65 ± 0.012 g/L; 0.36 ± 0.015 gPHB/gVFA) than feast mode (0.26 ± 0.02 g/L; 0.034 ± 0.013 gPHB/gVFA). Repeated batch operations induced substrate consumption, wherein acetate utilization was high in both the conditions (feast: 83%, famine 74%) followed by butyrate (feast: 74%, famine 72%). Besides, high biomass concentration was also observed in feast condition (3.45 ± 0.14 g/L VSS), while oxygen and nutrients limitation in famine mode regulated the carbon use for biomass growth (2.46 ± 0.15 g/L VSS). Further, PHB grafting with lignin (3% and 5%) exhibited increased thermal stability than pristine PHB. Biopolymer production using VFA's as carbon source and utilization of lignin as functional filler for strengthening PHB offer lignin valorization also wider its applications specifically in the biomedical field.

Poly(3-hydroxypropionate): Biosynthesis Pathways and Malonyl-CoA Biosensor Material Properties

Many single-use non-degradable plastics are a threat to life today, and several polyhydroxyalkanoates (PHAs) biopolymers have been developed in the bioplastic industry to place petrochemical-based plastics. One of such is the novel biomaterial poly(3-hydroxypropionate) [poly(3HP)] because of its biocompatibility, biodegradability, and high yield synthesis using engineered strains. To date, many bio-polymer-based functional composites have been developed to increase the value of raw microbial-biopolymers obtained from cheap sources. This review article broadly covers poly(3HP), a comprehensive summary of critical biosynthetic production pathways comparing the yields and titers achieved in different Microbial cell Factories. This article also provides extensive knowledge and highlights recent progress on biosensors' use to optimize poly(3HP) production, some bacteria host adopted for production, chemical and physical properties, life cycle assessment for poly(3HP) production using corn oil as carbon source, and some essential medical applications of poly(3HP).

Genomic insights into waste valorized extracellular polymeric substances (EPS) produced by Bacillus sp. ISTL8

The present study discusses the genomic analysis of Bacillus sp. ISTL8 along with the production of EPS (Extracellular polymeric substances) using carbofuran, a toxic carbamate pesticide. Bacillus strain was isolated from landfill soil and evaluated for high growth rates and EPS production. One strain, renamed ISTL8 grew on a broad range of carbon sources, including toxic carbofuran, while producing copious EPS. Growth assays verified the strain to be thermophilic, low salt tolerant, and with a preference for neutral pH. SEM (Scanning Electron Microscopy) was used for morphological characterization of the EPS while the monomeric composition, bonding patterns and functional groups were deduced by GC-MS (Gas Chromatography-Mass Spectrometry), ¹H and ¹³C NMR (Nuclear Magnetic Resonance) and FTIR (Fourier Transform Infrared Spectroscopy). The production of EPS using carbofuran (carbamate pesticide) as a carbon source was found to be 6.20 ± 0.29 g L^-1 containing 61.17% w/w carbohydrates, 29.72% w/w proteins and 6.11% w/w lipids (of dry EPS). The potential cytotoxicity of EPS was evaluated with 3- (4,5-dimethyl thiazol-2-Yl) -2,5-diphenyl tetrazolium bromide (MTT) assay and found non-toxic (2.25%). WGS (Whole genome sequencing) was performed for the strain Bacillus sp. ISTL8 producing EPS; an array of genes putatively involved in the EPS production were identified in several different genomic locations, guiding potential genetic manipulation studies in the future. The results highlight the potency of a bacterial isolate Bacillus sp. ISTL8 to produce non-cytotoxic EPS using carbofuran that can be further harnessed for environmental and commercial applications. Additionally, WGS revealed an array of EPS specific genes which can be effectively engineered for much enhanced production.

Polyhydroxyalkanoate synthesis and characterization: A proteogenomic and process optimization study for biovalorization of industrial lignin

The strain Burkholderia sp. ISTR5 (R5) was studied for polyhydroxyalkanoate (PHA) production on Kraft lignin (KL) and lignosulfonate (LS) as substrates. During the initial screening, the maximum PHA mass fraction in biomass produced on KL and LS was 23% and 18%, respectively, at 96 h. PHA production on KL was further optimized using the Box-Behnken Design (BBD) model of Response Surface Methodology (RSM). After optimization, a 42.5% increase in PHA production and a 32.2% increase in the total cell biomass was observed. PHA was characterized by GC-MS, TEM, FTIR, NMR, and fluorescence microscopy. It was found to be a small chain length PHA with a copolymer of poly (hydroxybutyrate-co-hydroxyvalerate) (PHBV). The degradation of PHBV was also studied using this strain; it was observed that R5 completely degraded PHBV in 120 h. Genomic and proteomic analysis of R5 revealed numerous enzymes for the metabolism of lignin degradation and PHA production.

Lignin valorization by bacterial genus Pseudomonas: State-of-the-art review and prospects

The most prominent aromatic feedstock on Earth is lignin, however, lignin valorization is still an underrated subject. The principal preparatory strategies for lignin valorization are fragmentation and depolymerization which help in the production of fuels and chemicals. Owing to lignin's structural heterogeneity, these strategies result in product generation which requires tedious separation and purification to extract target products. The bacterial genus Pseudomonas has been dominant for its lignin valorization potency, owing to a robust enzymatic machinery that is used to funnel variable lignin derivatives into certain target products such as polyhydroxyalkanotes (PHAs) and cis, cis-muconic acid (MA). In this review, the potential of genus Pseudomonas in lignin valorization is critically reviewed along with the advanced genetic techniques and tools to ease the use of lignin/lignin-model compounds for the synthesis of bioproducts. This review also highlights the research gaps in lignin biovalorization and discuss the challenges and possibilities for future research.

Bacteria from industrial waste: potential producers of polyhydroxyalkanoates (PHAs) in Manizales, Colombia

Polymers are currently used in the industry as raw material, yet they are rapidly eliminated and largely contaminate the environment. To address this issue, there is a special interest in biodegradable polymers, namely, polyhydroxyalkanoates (PHAs), produced by microorganisms. This study identifies PHA-producing bacteria from two industrial wastewaters of Manizales, Colombia. The samples were cultured in mineral salt medium with glucose as the carbon source in the presence of Nile red stain. The fluorescent colonies were independently transferred to another medium and assessed through fluorescence microscopy with Nile blue stain. The fluorescent strains under Nile blue staining were purified in Nutrient Agar, and their morphological and microbiological characteristics were determined. The bacteria positive for red-orange fluorescence were purified in Nutrient Agar medium, and molecular analyses were performed by PCR amplification of a 650-bp fragment of the 16S ribosomal DNA gene. The bacteria were also assessed in terms of PHA production. We confirmed the identity of 12 out of 14 PHA-positive strains, which belonged to the following genera: Bacillus, Lactococcus, Citrobacter, Enterobacter, and Acinetobacter. Five of the isolates (Enterobacter cloacae, Enterobacter sp., Enterobacter ludwigii, Bacillus thuringiensis, and Bacillus safensis) are promising strains for PHA production, with production values ranging from 0.360 to 0.9960 g/L. Bacteria that produce more than 0.3 g/L are considered useful for the industrial manufacture of bioplastic. We recommend performing large-scale studies on these strains to assess their use for the industrial production of biopolymers, allowing to generate high-impact bioconversion processes of industrial interest.

Biodiesel production from transesterification of Serratia sp. ISTD04 lipids using immobilised lipase on biocomposite materials of biomineralized products of carbon dioxide sequestrating bacterium

Production of biodiesel from lipids of Serratia sp. ISTD04 by lipase of Pseudomonas sp. ISTPL3 immobilised on biocomposite materials to increase the enzyme stability and reusability was studied. Lipase extracted, partially purifiedand immobilized onto activated biochar, impregnated with calcite obtained from biomineralization-based conversion of CO₂ from ISTD04, and bioactive ceramics materials, Na₂Ca₂Si₃O₉ prepared by chemical process. The composition, structure and texture of biocomposite materials determined by SEM and EDS methods. The composition of synthesized biodiesel was determined by GC-MS. The results imply that the immobilized lipase on activated biochar impregnated with calcite gave the maximum yield of fatty acid methyl esters (FAME:97.41%) followed by immobilized lipase on biochar (FAME:94.91), immobilized lipase on glass-ceramic (FAME:91.50%) and NaOH (FAME:85.63%). The reusability of lipase immobilized on activated biochar impregnated with calcite retained 75.11%and 50% catalytic activity after 5 and 10 cycles of transesterification reaction, respectively.

Recent advances in polyhydroxyalkanoate production: Feedstocks, strains and process developments

Polyhydroxyalkanoates (PHAs) have been actively studied in academia and industry for their properties comparable to petroleum-derived plastics and high biocompatibility. However, the major limitation for commercialization is their high cost. Feedstock costs, especially carbon costs, account for the majority of the final cost. Finding cheap feedstocks for PHA production and associated process development are critical for a cost-effective PHA production. In this study, waste materials from different sources, particularly lignocellulosic biomass, were proposed as suitable feedstocks for PHA production. Strains involved in the conversion of these feedstocks into PHA were reviewed. Newly isolated strains were emphasized. Related process development, including the factors that affect PHA production, fermentation modes and downstream processing, was elaborated upon.

Thauera aminoaromatica MZ1T Identified as a Polyhydroxyalkanoate-Producing Bacterium within a Mixed Microbial Consortium

Polyhydroxyalkanoates (PHAs) form a highly promising class of bioplastics for the transition from fossil fuel-based plastics to bio-renewable and biodegradable plastics. Mixed microbial consortia (MMC) are known to be able to produce PHAs from organic waste streams. Knowledge of key-microbes and their characteristics in PHA-producing consortia is necessary for further process optimization and direction towards synthesis of specific types of PHAs. In this study, a PHA-producing mixed microbial consortium (MMC) from an industrial pilot plant was characterized and further enriched on acetate in a laboratory-scale selector with a working volume of 5 L, and 16S-rDNA microbiological population analysis of both the industrial pilot plant and the 5 L selector revealed that the most dominant species within the population is Thauera aminoaromatica MZ1T, a Gram-negative beta-proteobacterium belonging to the order of the Rhodocyclales. The relative abundance of this Thauera species increased from 24 to 40% after two months of enrichment in the selector-system, indicating a competitive advantage, possibly due to the storage of a reserve material such as PHA. First experiments with T. aminoaromatica MZ1T showed multiple intracellular granules when grown in pure culture on a growth medium with a C:N ratio of 10:1 and acetate as a carbon source. Nuclear magnetic resonance (NMR) analyses upon extraction of PHA from the pure culture confirmed polyhydroxybutyrate production by T. aminoaromatica MZ1T.

Nitrification and denitrification processes for mitigation of nitrous oxide from waste water treatment plants for biovalorization: Challenges and opportunities

Nitrous oxide (N₂O) is a potent greenhouse gas. Even though its emissions is much lesser than CO₂ but its global warming potential (GWP) is 298 times more than CO₂. N₂O emissions from wastewater treatment plants was caused due to incomplete nitrification or incomplete denitrification catalyzed by ammonia-oxidizing bacteria and heterotrophic denitrifiers. Low dissolved oxygen, high nitrite accumulation, change in optimal pH or temperature, fluctuation in C/N ratio, short solid retention time and non-availability of Cu ions were responsible for higher N₂O leakage. Regulation of enzyme metabolic pathways involved in N₂O production and reduction has also been reviewed. Sequential bioreactors, bioscrubbers, membrane biofilters usage have helped microbial nitrification-denitrification processes in succumbing N₂O production in wastewater treatment plants. Reduction of N₂O negativity has been studied through its valorization for the formation of value added products such as biopolymers has led to biorefinery approaches as an upcoming mitigation strategy.

Genomic analysis of carbon dioxide sequestering bacterium for exopolysaccharides production

In the present study, genomic analysis of a previously reported carbon dioxide (CO2) sequestering bacterium Serratia sp. ISTD04 was performed along with exopolysaccharide (EPS) production. Genomic analysis identified key and accessory enzymes responsible for CO2 sequestration. EPS synthesis genes were discovered in the genome and identified 8 putative clusters responsible for lipopolysaccharide, stewartan, emulsan, polysaccharide B, capsular polysaccharide and fatty acid-saccharide production. The production of EPS was found to be 0.88 ± 0.08, 1.25 ± 0.13 and 1.44 ± 0.10 g L-1 on glucose, bicarbonate (NaHCO3) and NaHCO3 plus glucose respectively at pH 7.8. After optimizing process parameters, the EPS production increased more than 3 folds. The morphology of strain and elemental composition of EPS was characterized by SEM-EDX. The functional groups, monomer composition, linkage analysis and structure of purified EPS was characterized by FTIR, GC-MS and 1H and 13C NMR. Glucose, galactose, mannose and glucosamine are the monomers detected in the EPS. EPS was further applied for bioflocculation (kaolin test) and dye removal. The EPS showed 68% ± 0.9 flocculating activity and decolorized cationic dye acridine orange (80%) and crystal violet (95%). The results highlight CO2 sequestration and EPS production potential of Serratia sp. ISTD04 that can be harnessed in future.

Sequestration and utilization of carbon dioxide by chemical and biological methods for biofuels and biomaterials by chemoautotrophs: Opportunities and challenges

To meet the CO₂ emission reduction targets, carbon dioxide capture and utilization (CCU) comes as an evolve technology. CCU concept is turning into a feedstock and technologies have been developed for transformation of CO₂ into useful organic products. At industrial scale, utilization of CO₂ as raw material is not much significant as compare to its abundance. Mechanisms in nature have evolved for carbon concentration, fixation and utilization. Assimilation and subsequent conversion of CO₂ into complex molecules are performed by the photosynthetic and chemolithotrophic organisms. In the last three decades, substantial research is carry out to discover chemical and biological conversion of CO₂ in various synthetic and biological materials, such as carboxylic acids, esters, lactones, polymer biodiesel, bio-plastics, bio-alcohols, exopolysaccharides. This review presents an over view of catalytic transformation of CO₂ into biofuels and biomaterials by chemical and biological methods.

Recovery of polyhydroxyalkanoates from municipal secondary wastewater sludge

In the current study, the feasibility of utilizing municipal secondary wastewater sludge for Polyhydroxyalkanoate (PHA) extraction was improved by optimization of various parameters (temperature, duration and concentration of sludge solids). Optimized process parameters resulted in PHA recovery of 0.605 g, significantly higher than un-optimized conditions. The characterization of PHA was carried out by GC-MS, FT-IR and NMR (¹H and ¹³C) spectroscopy. The PHA profile was found to be dominated by mcl PHA (58%) along with other diverse PHA. The results of the present study show rich diversity of PHA extracted from a raw material which is readily available at minimal cost. In conclusion, exploring the potential of wastes for production of bioplastics not only reduces the cost of bioplastic production, but also provides a sustainable means for waste management.

Biofuel production and phycoremediation by Chlorella sp. ISTLA1 isolated from landfill site

The present study aims to investigate the biofuel production ability and potential of heavy metal remediation of Chlorella sp. ISTLA1 isolated from a landfill site. The strain was cultured in Bold's Basal medium at different concentration of NaHCO₃ and pH. Response surface methodology was employed for the optimization of nutrient sources for higher lipid production. Under the optimized conditions, the yield of lipid and biomass was 365.42 and 833.14 mg L^-1 respectively. GC-MS analysis of lipid indicated the presence of C₈ to C₃₁ organic compounds consisting mainly of palmitic acid (C16:0), stearic acid (C18:0) and oleic acid (C18:1). Additionally, remediation of heavy metals like Zn, Cu, Mn and Fe from waste water was observed by AAS and EDX. The removal efficiency was 82.6% for Zn, 56.5% for Cu, 79.8% for Mn and 40% for Fe. The study revealed simultaneous biodiesel production and waste water treatment by Chlorella sp. ISTLA1.

Production, process optimization and molecular characterization of polyhydroxyalkanoate (PHA) by CO2 sequestering B. cereus SS105

Carbon dioxide sequestering bacterial strains were previously isolated from free air CO₂ enriched (FACE) soil. In the present study, these strains were screened for PHA accumulation and Bacillus cereus SS105 was found to be the most prominent PHA accumulating strain on sodium bicarbonate and molasses as carbon source. This strain was further characterized by Spectrofluorometric method and Confocal microscopy after staining with Nile red. PHA granules in inclusion bodies were visualized by Transmission Electron Microscopy. The PHA and its monomer composition were characterized by GC-MS followed by FTIR and NMR. The genetic basis of PHA production was confirmed by the amplification, cloning and analysis of PHA biosynthesis genes phaR, phaB and phaC from B. cereus with the degenerate primers. The PHA production was further optimized by Response Surface Methodology and the percent increase observed after optimization was 55.16% (w/v).

Carbon dioxide capture, storage and production of biofuel and biomaterials by bacteria: A review

Due to industrialization and urbanization, as humans continue to rely on fossil fuels, carbon dioxide (CO₂) will inevitably be generated and result in an increase of Global Warming Gases (GWGs). However, their prospect is misted up because of the environmental and economic intimidation posed by probable climate shift, generally called it as the "green house effect". Among all GWGs, the major contributor in greenhouse effect is CO₂. Mitigation strategies that include capture and storage of CO₂ by biological means may reduce the impact of CO₂ emissions on environment. The biological CO₂ sequestration has significant advantage, since increasing atmospheric CO₂ level supports productivity and overall storage capacity of the natural system. This paper reviews CO₂ sequestration mechanism in bacteria and their pathways for production of value added products such as, biodiesel, bioplastics, extracellular polymeric substance (EPS), biosurfactants and other related biomaterials.

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.

Characterization of carbon dioxide concentrating chemolithotrophic bacterium Serratia sp. ISTD04 for production of biodiesel

Proteomics and metabolomics analysis has become a powerful tool for characterization of microbial ability for fixation of Carbon dioxide. Bacterial community of palaeoproterozoic metasediments was enriched in the shake flask culture in the presence of NaHCO₃. One of the isolate showed resistance to NaHCO₃ (100mM) and was identified as Serratia sp. ISTD04 by 16S rRNA sequence analysis. Carbon dioxide fixing ability of the bacterium was established by carbonic anhydrase enzyme assay along with proteomic analysis by LC-MS/MS. In proteomic analysis 96 proteins were identified out of these 6 protein involved in carbon dioxide fixation, 11 in fatty acid metabolism, indicating the carbon dioxide fixing potency of bacterium along with production of biofuel. GC-MS analysis revealed that hydrocarbons and FAMEs produced by bacteria within the range of C₁₃-C₂₄ and C₁₁-C₁₉ respectively. Presence of 59% saturated and 41% unsaturated organic compounds, make it a better fuel composition.

Analysis and optimization of process parameters for production of polyhydroxyalkanoates along with wastewater treatment by Serratia sp. ISTVKR1

A previously reported biodegrading bacterial strain Serratia sp. ISTVKR1 was studied for polyhydroxyalkanoate (PHA) production along with wastewater contaminant removal. Nile red fluorescence, GC-MS, FT-IR, NMR and TEM confirmed the accumulation of homopolymer poly-3-hydroxyvalerate (PHV) within the bacterial cells. Analysis of culture after 72h of bacterial treatment showed maximum COD removal (8.4-fold), non-detection of organic contaminants such as 1H-Cyclopropa [a] naphthalene (R.T.=10.12) using GC-MS and increased proportion of elements like Cr, Mn, Fe, Ni, Cu, Cd and Pb in the bacterial cell pellets by SEM-EDX analysis. Optimization of process parameters for enhanced PHA production along with wastewater treatment done using Response Surface Methodology (RSM) showed 5% and 0.74% increase in the PHA production (0.3368±0.13gL^-1) and % COD reduction (88.93±2.41) of wastewater, respectively. The study, thus established the production of PHA along with wastewater contaminant removal by Serratia sp. ISTVKR1.

Recycling of carbon dioxide by free air CO2 enriched (FACE) Bacillus sp. SS105 for enhanced production and optimization of biosurfactant

Carbon dioxide utilizing bacterium Bacillus sp. SS105 was isolated from FACE (free air CO₂ enriched) sample. The strain was grown in shake flask containing minimal salt medium with 50mM NaHCO₃ as autotrophic carbon source and molasses as a low cost byproduct for mixotrophic growth. Carbon dioxide sequestration property of Bacillus sp. SS105 was determined by enzyme assay of carbonic anhydrase and ribulose-1, 5-bisphosphate carboxylase/oxygenase (RuBisCO). Along with CO₂ sequestration this strain produced biosurfactant and its characterization by FTIR and ¹H NMR indicated lipopeptide nature. Optimization of process parameter along with nutrient sources for higher biosurfactant production was done by Response Surface Methodology (RSM). Under optimized conditions, the yield of biosurfactant and biomass was 2.65 and 2.78gL^-1 respectively. The study revealed simultaneous CO₂ sequestration and biosurfactant production by Bacillus sp. SS105.

Fabrication, characterization, and application of polyester/wood flour composites

The mechanical properties, thermal properties, antibacterial activity, and fabrication of three-dimensional (3D) printing strips of composite materials containing polyhydroxyalkanoate (PHA) and wood flour (WF) were evaluated. Maleic anhydride (MA)-grafted PHA (PHA-g-MA) and WF were used to enhance the desired characteristics of these composites. The PHA-g-MA/WF composites had better mechanical properties than the PHA/WF composites did. This effect was attributed to a greater compatibility between the grafted polyester and WF. Additionally, the PHA-g-MA/WF composites provided higher quality 3D printing strips and were more easily processed because of ester formation. The water resistance of the PHA-g-MA/WF composite was greater than that of PHA/WF. Moreover, WF enhanced the antibacterial activity of the composites. Composites of PHA-g-MA or PHA containing WF had better antibacterial activity.

Genome Sequence of Carbon Dioxide-Sequestering Serratia sp. Strain ISTD04 Isolated from Marble Mining Rocks

The Serratia sp. strain ISTD04 has been identified as a carbon dioxide (CO₂)-sequestering bacterium isolated from marble mining rocks in the Umra area, Rajasthan, India. This strain grows chemolithotrophically on media that contain sodium bicarbonate (NaHCO₃) as the sole carbon source. Here, we report the genome sequence of 5.07 Mb Serratia sp. ISTD04.