Metabolomic insights into polyhydroxyalkanoates production by halophilic bacteria with acetic acid as carbon source

Efficient polyhydroxybutyrate production using acetate by engineered Halomonas sp. JJY01 harboring acetyl-CoA acetyltransferase

Polyhydroxybutyrate (PHB) is a well-known biodegradable bioplastic synthesized by microorganisms and can be produced from volatile fatty acids (VFAs). Among VFAs acetate can be utilized by Halomonas sp. YLGW01 for growth and PHB production. In this study, Halomonas sp. JJY01 was developed through introducing acetyl-CoA acetyltransferase (atoAD) with LacIq-Ptrc promoter into Halomonas sp. YLGW01. The effect of expression of atoAD on acetate was investigated by comparison with acetate consumption and PHB production. Shake-flask study showed that Halomonas sp. JJY01 increased acetate consumption rate, PHB yield and PHB production (0.27 g/L/h, 0.075 g/g, 0.72 g/L) compared to the wild type strain (0.17 g/L/h, 0.016 g/g, 0.11 g/L). In 10 L fermenter scale fed-batch fermentation, the growth of Halomonas sp. JJY01 resulted in higher acetate consumption rate, PHB yield and PHB titer (0.55 g/L/h, 0.091 g/g, 4.6 g/L) than wild type strain (0.35 g/L/h, 0.067 h/h, 2.9 g/L). These findings demonstrate enhanced acetate utilization and PHB production through the introduction of atoAD in Halomonas strains.

Development of biopolymers from microbes and their environmental applications

Inventions begin with the invasion of humans and furnish a better livelihood. In some cases, it turns out to be imperative. The environmental issues of using synthetic polymers, including bio-incompatibility, toxicity, high cost, poor hydrophilicity, and pro-inflammatory degradation of byproducts, are increasing the need for and application of eco-friendly, alternative polymeric substances from medicine to biotechnology, which includes the industries of medicine, cosmetics, confectionery, wastewater treatment, etc., as tissue scaffolds, wound dressings, drug packaging material, dermal fillers, moisturising cream, carriers, sun protectants, antiperspirants, and deodorants; gelling agents; stabilisers, emulsifiers, photographic films, etc. Biopolymers are available in different compounds, produced by microbes, plants, and animals, where microbes, for example, Pseudomonas aeruginosa and Kamagataeibacter sucrofermetans, retain these compounds at an exorbitant level, helping them to sustain adverse conditions. Moreover, compared to plant and animal biopolymers, microbial biopolymers are preferred due to their ease of production, design, and processing at an industrial levels. In this regard, polyhydroxyalkanoates (PHA) and poly-3-hydroxybutyrate (PHB) have together attained assiduity for their biodegradable properties and possess similar features as petrochemical-based polymers, commonly synthetic polymers like polyethylene, polypropylene, etc. This attributes to its non-toxic nature, i.e., it behaves eco-friendly by degrading the components through a carbon-neutral energy cycle to carbon dioxide and water, which lessens the dependence on petroleum-based polymers. This chapter contemplates the methods to develop biopolymers from microbes and their environmental applications, focusing on the confiscation of heavy metals, organic dyes or oils, etc.

Untargeted metabolomics elucidated biosynthesis of polyhydroxyalkanoate by mixed microbial cultures from waste activated sludge under different pH values

Waste activated sludge has been frequently used as mixed substrate to produce polyhydroxyalkanoate (PHA). However, insufficient research on microbial metabolism has led to difficulties in regulating PHA accumulation in mixed microbial cultures (MMCs). To explore the variation of functional genes during domestication and the effect of different pH conditions on metabolic pathways during PHA accumulation, MMCs were domesticated by adding acetate and propionate with aerobic dynamic feeding strategy for 60 days. As the domestication progressed, the microbial community diversity declined and PHA-producing bacteria, Brevundimonas, Dechloromonas and Hyphomonas, were enriched. Through bacterial function prediction by PICRUSt the gene rpoE involved in starvation resistance of bacteria was enriched after the domestication. The pH value of 8.5 was the best condition for PHA accumulation in MMCs, under which a maximum PHA content reached 23.50% and hydroxybutyric (HB)/hydroxyvaleric (HV) reached 2.22. Untargeted metabolomics analysis exhibited that pH conditions of 7 and 8.5 could promote the up-regulation of significant differential metabolites, while higher alkaline conditions caused the inhibition of metabolic activity. Functional annotation showed that pH condition of 8.5 significantly affected Pyrimidine metabolism, resulting in an increase in PHA production. Regarding the pathways of PHA biosynthesis, acetoacetate was found to be significant in the metabolism of hydroxybutyric, and the alkaline condition could restrain the conversion from hydroxybutyric (HB) to the acetoacetate to protect PHB accumulation in MMCs compared with neutral condition. Taken together, the present results can advance the fundamental understanding of metabolic function in PHA accumulation under different pH conditions.

Adaptive Laboratory Evolution of Halomonas bluephagenesis Enhances Acetate Tolerance and Utilization to Produce Poly(3-hydroxybutyrate)

Acetate is a promising economical and sustainable carbon source for bioproduction, but it is also a known cell-growth inhibitor. In this study, adaptive laboratory evolution (ALE) with acetate as selective pressure was applied to Halomonas bluephagenesis TD1.0, a fast-growing and contamination-resistant halophilic bacterium that naturally accumulates poly(3-hydroxybutyrate) (PHB). After 71 transfers, the evolved strain, B71, was isolated, which not only showed better fitness (in terms of tolerance and utilization rate) to high concentrations of acetate but also produced a higher PHB titer compared with the parental strain TD1.0. Subsequently, overexpression of acetyl-CoA synthetase (ACS) in B71 resulted in a further increase in acetate utilization but a decrease in PHB production. Through whole-genome resequencing, it was speculated that genetic mutations (single-nucleotide variation (SNV) in phaB, mdh, and the upstream of OmpA, and insertion of TolA) in B71 might contribute to its improved acetate adaptability and PHB production. Finally, in a 5 L bioreactor with intermittent feeding of acetic acid, B71 was able to produce 49.79 g/L PHB and 70.01 g/L dry cell mass, which were 147.2% and 82.32% higher than those of TD1.0, respectively. These results highlight that ALE provides a reliable method to harness H. bluephagenesis to metabolize acetate for the production of PHB or other high-value chemicals more efficiently.

Polyhydroxyalkanoates synthesis using acidogenic fermentative effluents

Polyhydroxyalkanoates (PHA) are natural polyesters synthesized by microbes which consume excess amount of carbon and less amount of nutrients. It is biodegradable in nature, and it synthesized from renewable resources. It is considered as a future polymer, which act as an attractive replacement to petrochemical based polymers. The main hindrance to the commercial application of PHA is the high manufacturing cost. This article provides an overview of different cost-effective substrates, their characteristics and composition, major strains involved in economical production of PHA and biosynthetic pathways leading to accumulation of PHA. This review also covers the operational parameters, various fermentative modes including batch, fed-batch, repeated fed-batch and continuous fed-batch systems, along with advanced feeding strategies such as single pulse carbon feeding, feed forward control, intermittent carbon feeding, feast famine conditions to observe their effects for improving PHA synthesis and associated challenges. In addition, it also presents the economic analysis and future perspectives for the commercialization of PHA production process thereby making the process sustainable and lucrative with the possibility of commercial biomanufacturing.

An Overview of Recent Advancements in Microbial Polyhydroxyalkanoates (PHA) Production from Dark Fermentation Acidogenic Effluents: A Path to an Integrated Bio-Refinery

Global energy consumption has been increasing in tandem with economic growth motivating researchers to focus on renewable energy sources. Dark fermentative hydrogen synthesis utilizing various biomass resources is a promising, less costly, and less energy-intensive bioprocess relative to other biohydrogen production routes. The generated acidogenic dark fermentative effluent [e.g., volatile fatty acids (VFAs)] has potential as a reliable and sustainable carbon substrate for polyhydroxyalkanoate (PHA) synthesis. PHA, an important alternative to petrochemical based polymers has attracted interest recently, owing to its biodegradability and biocompatibility. This review illustrates methods for the conversion of acidogenic effluents (VFAs), such as acetate, butyrate, propionate, lactate, valerate, and mixtures of VFAs, into the value-added compound PHA. In addition, the review provides a comprehensive update on research progress of VFAs to PHA conversion and related enhancement techniques including optimization of operational parameters, fermentation strategies, and genetic engineering approaches. Finally, potential bottlenecks and future directions for the conversion of VFAs to PHA are outlined. This review offers insights to researchers on an integrated biorefinery route for sustainable and cost-effective bioplastics production.

High cell density culture of Paracoccus sp. LL1 in membrane bioreactor for enhanced co-production of polyhydroxyalkanoates and astaxanthin

A cell retention culture of Paracoccus sp. LL1 was performed in a membrane bioreactor equipped with an internal ceramic filter module to reach high cell density and thus enhance the co-production of polyhydroxyalkanoates (PHA) and astaxanthin as growth-associated products. Cell retention culture results showed that PHA accumulation increased with increasing dry cell weight (DCW), giving rise to a maximum of 113 ± 0.92 g/L of DCW with 43.9 ± 0.91 g/L of PHA (38.8% of DCW) at 48 h. A significant increase in both intracellular and extracellular astaxanthin concentrations was also recorded during fermentation process achieving a maximum of 8.51 ± 0.20 and 10.2 ± 0.24 mg/L, respectively. Amounts of PHA and total astaxanthin produced by cell retention culture were 6.29 and 19.7-folds higher, respectively, than those recorded under batch cultivation. PHA and total astaxanthin productivities by cell retention culture also increased up to 0.914 g/L/h and 0.781 mg/L/h, respectively, which were 3.54 and 11.1-folds higher than those of batch culture. Based on gas chromatography, Fourier transform infrared spectroscopy, and ¹H nuclear magnetic resonance spectroscopy, the extracted PHA was identified as a copolymer of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a 3-hydroxyvalerate content of 3.78 mol%.

Effects of different sodium salts and nitrogen sources on the production of 3-hydroxybutyrate and polyhydroxybutyrate by Burkholderia cepacia

The effects of NaCl, Na2SO4, Na2HPO4, and Na3C6H5O7 on the production of 3-hydroxybutyrate, polyhydroxybutyrate, and by-products by Burkholderia cepacia. Proper addition of Na3C6H5O7 can significantly promote the production of 3-hydroxybutyric acid and polyhydroxybutyrate. The concentration, productivity, and yield of 3-hydroxybutyrate were increased by 48.2%, 55.6%, and 48.3% at 16 mM Na3C6H5O7. The increases of 80.1%, 47.1%, and 80.0% in the concentration, productivity, and yield of polyhydroxybutyrate were observed at 12 mM Na3C6H5O7. Na2SO4 and Na2HPO4 also have positive effects on the production capacity of 3-hydroxybutyrate and polyhydroxybutyrate within a certain range of concentration. NaCl is not conducive to the improvement of fermentation efficiency. Compared with a single nitrogen source, a mixed nitrogen source is more conducive to enhancing the production of 3-hydroxybutyrate and polyhydroxybutyrate.

MicroRNAs play an essential role in autophagy regulation in various disease phenotypes

Autophagy is a highly conserved catabolic process and fundamental biological process in eukaryotic cells. It recycles intracellular components to provide nutrients during starvation and maintains quality control of organelles and proteins. In addition, autophagy is a well-organized homeostatic cellular process that is responsible for the removal of damaged organelles and intracellular pathogens. Moreover, it also modulates the innate and adaptive immune systems. Micro ribonucleic acids (microRNAs) are a mature class of post-transcriptional modulators that are widely expressed in tissues and organs. And, it can suppress gene expression by targeting messenger RNAs for translational repression or, at a lesser extent, degradation. Research indicates that microRNAs regulate autophagy through different pathways, playing an essential role in the treatment of various diseases. It is an important regulator of fundamental cellular processes such as proliferation, autophagy, and cell apoptosis. In this review article, we first review the current knowledge of autophagy and the function of microRNAs. Then, we summarize the mechanism of autophagy and the signaling pathways related to autophagy by citing at least the main proteins involved in the different phases of the process. Second, we introduce other members of RNA and report some examples in various pathologies. Finally, we review the current literature regarding microRNA-based therapies for cancer, atherosclerosis, cardiac disease, tuberculosis, and viral diseases. MicroRNAs can cause autophagy upregulation or downregulation by targeting genes or affecting autophagy-related signaling pathways. Therefore, the microRNAs have a huge potential in autophagy regulation, and it is the function as diagnostic and prognostic markers.