Halomonas uses short-chain fatty acids to synthesize polyhydroxyalkanoates / 生物工程学报

Halomonas can grow on diverse carbon sources. As it can be used for unsterile fermentation under high-salt conditions, it has been applied as a chassis for next-generation industrial biotechnology. Short-chain volatile fatty acids, including acetate, propionate, and butyrate, can be prepared from biomass and are expected to be novel carbon sources for microbial fermentation. Halomonas sp. TD01 and TD08 were subjected to shaking culture with 10-50 g/L butyrate, and they were found to effectively synthesize poly-3-hydroxybutyrate with butyrate as the carbon source. The highest yield of poly-3-hydroxybutyrate was achieved at butyrate concentration of 20 g/L (9.12 g/L and 7.37 g/L, respectively). Butyrate at the concentration > 20 g/L inhibited cell growth, and the yield of poly-3-hydroxybutyrate decreased to < 4 g/L when butyrate concentration was 50 g/L. Moreover, Halomonas sp. TD08 can accumulate the copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate by using propionate and butyrate as carbon sources. However, propionate was toxic to cells. To be specific, when 2 g/L propionate and 20 g/L butyrate were simultaneously provided, cell dry weight and polymer titer were 0.83 g/L and 0.15 g/L, respectively. The addition of glycerol significantly improved cell growth and boosted the copolymer titer to 3.95 g/L, with 3-hydroxyvalerate monomer content of 8.76 mol%. Short-chain volatile fatty acids would be promising carbon sources for the production of polyhydroxyalkanoates by Halomonas.

Improvement of polyhydroxybutyrate production by deletion of csrA in Escherichia coli

BACKGROUND: Poly-3-hydroxybutyrate (PHB) can be efficiently produced in recombinant Escherichia coli by the overexpression of an operon (NphaCAB) encoding PHB synthetase. Strain improvement is considered to be one of critical factors to lower the production cost of PHB in recombinant system. In this study, one of key regulators that affect the cell growth and PHB content was confirmed and analyzed. RESULT: S17-3, a mutant E. coli strain derived from S17-1, was found to be able to achieve high cell density when expressing NphaCAB with the plasmid pBhya-CAB. Whole genome sequencing of S17-3 revealed genetic alternations on the upstream regions of csrA, encoding a global regulator cross-talking between stress response, catabolite repression and other metabolic activities. Deletion of csrA or expression of mutant csrA resulted in improved cell density and PHB content. CONCLUSION: The impact of gene deletion of csrA was determined, dysfunction of the regulators improved the cell density of recombinant E. coli and PHB production, however, the detail mechanism needs to be further clarified.

Analysis of the genome sequencing data of the Marinobacterium genus / 生物工程学报

The marine genus Marinobacterium was first identified in 1997, and a total of 18 species have been characterized so far, 10 of which have published whole-genome sequencing data. This article summarizes the characteristics of Marinobacterium genus and analyzes the genome sequencing data related to the carbon source utilization, polyhydroxyalkanoate metabolism, and aromatic compounds degradation. The Marinobacterium species possess the complete glycolysis pathway and tricarboxylic acid cycle, yet lack genes involved in xylose utilization. All strains of the Marinobacterium genus contain the genes encoding for the typeⅠand type Ⅲ polyhydroxyalkanoate synthases, suggesting that the genus may have ability of polyhydroxyalkanoate accumulation. The Marinobacterium species contain the degradation pathways of aromatic compounds. Benzene, phenol and benzoic acid can be degraded into catechol via different enzymes, subsequently catechol is converted to 3-ketoadipate through the ortho-cleavage pathway. Alternatively, catechol can be degraded into pyruvate and acetyl-CoA. The analysis of genome sequencing data of the Marinobacterium genus provides in-depth understanding of the metabolic characteristics, indicating that the genus may have certain applications in the synthesis of polyhydroxyalkanoate and the removal of marine aromatic compounds.

Microbial production of poly (glycolate-co-lactate-co-3-hydroxybutyrate) from glucose and xylose by Escherichia coli / 生物工程学报

Escherichia coli was metabolically engineered to produce poly(glycolate-co-lactate-co-3-hydroxybutyrate) using glucose and xylose as carbon sources. The combinatorial biosynthetic route was constructed by the overexpression of a series of enzymes including D-tagatose 3-epimerase, L-fuculokinase, L-fuculose-phosphate aldolase, aldehyde dehydrogenase, propionyl-CoA transferase, β-ketothiolase, acetoacetyl-CoA reductase, and polyhydroxyalkanoate synthase. Overexpression of polyhydroxyalkanoate granule associated protein significantly improved biopolymer synthesis, and the recombinant strain reached 3.73 g/L cell dry weight with 38.72% (W/W) biopolymer content. A co-culture engineering strategy was developed to produce biopolymer from a mixture of glucose and xylose, achieving 4.01 g/L cell dry weight containing 21.54% (W/W) biopolymer. The results of this work offer an approach for simultaneously utilizing glucose and xylose and indicate the potential for future biopolymer production from lignocellulosic biomass.

Optimization of polyhydroxyalkanoate (PHA) production by Burkholderia cepacia BPT1213 utilizing waste glycerol as the sole carbon source

@#Aims:This study was carried out to optimize the fermentation conditions using statistical approach for polyhydroxyalkanoate(PHA) production by a local isolate, Burkholderia cepaciaBPT1213, in the shake flask system.Methodology and results:Throughout this study, B. cepaciaBPT1213 was grown in minimal salt medium (MSM) supplemented with 2% of waste glycerol (86.70% purity).The strain can produce up to 1.33 g/L cell dry weight (CDW) with 22.21% of PHA content, thus giving a total PHA concentration 0.30 g/L before optimization. A factorial design experiment that was carried out showed all parameters KH2PO4, Na2HPO4·2H2O, carbon-to-nitrogen ratio (C/N), initial pH of medium, and temperature significantly affected the growth (cell dry weight, CDW) and PHA content. Response surface methodology (RSM) using central composite design (CCD) was then applied to optimize these parameters. The optimum conditions suggested were at 2.5 g/L KH2PO4, 4.5 g/L Na2HPO4·2H2O, 30 (g/g) C/N ratio, initial medium pH of 8.5 and 37 °C cultivation temperature, with a predicted CDW of 3.43 g/L and PHA content of 45.71% contributing to 1.57 g/L total PHA concentration. The verification experiment resulted in 3.60 g/L of CDW with 48.08% of PHA content contributing to 1.73 g/L total PHA concentration.Conclusion, significance and impact of study:The statistical approach using factorial design and RSM have succeeded in increasing the production of PHA by B. cepaciaBPT1213 using waste glycerol as the sole carbon source which is a promising renewable and cheaper feedsto

Efficient biosynthesis and recovery of polyhydroxyalkanoate

Petrochemical-derived plastics have become a source of pollution for decades, and finding alternative plastics that are environmentally friendly has become a matter of urgency. Polyhydroxyalkanoate (PHA), a biopolyester synthesized by microbial cells, has properties that make it suitable as a biodegradable plastic material. The diversity of PHA makes it applicable to a wide range of products, from packaging to biomedical devices. The main challenge in commercialization of PHA is the cost of production. Although many studies have been focused on obtaining high yields of PHA, up until now, there is no absolute definition of efficient production of PHA, as there are many factors that could contribute to the efficiency of a process. Efficiency in PHA recovery also contributes to the commercial viability of PHA production. This review focuses on the efficiency of PHA biosynthesis from several aspects relating to the criteria for efficient production. The development of new strategies for improved production, including utilization of low cost carbon sources, genetic modification of PHA-producing microbes, and fermentation strategies are discussed here. Advances in recovery of PHA, as well as the potential of biological recovery techniques, are also highlighted in this review.

Preparation and characterization of polyhydroxyalkanoate bioplastics with antibacterial activity / 生物工程学报

Polyhydroxyalkanoates (PHAs), as a novel class of biopolymer, are attracting more attention due to their diverse material properties and environment-independent biodegradability. Here we report the preparation of PHA exhibiting efficient antibacterial activity by embedding Nisin, a food additive generally recognized as safe, into poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx), a type of PHA with high biocompatibility. We first prepared Nisin-containing PHBHHx films using solvent casting method. Confocal laser scanning microscopy analysis showed that a well-mixed integrated structure of the films with an even distribution of the Nisin particles in the PHBHHx matrices. Then the antimicrobial activity of PHBHHx/Nisin films against Micrococcus luteus was quantified on agar plate by measuring the size of inhibition zone. Cultivation in liquid media further confirmed the releasing of Nisin from the films and the long-time antibacterial activity. Results showed that the threshold of Nisin concentration for long-time and effective inhibition against bacteria growth is 25 μg/g. These results altogether establish a technological foundation for the application of PHA in biomedicine and food industry.

Production of Polyhydroxybutyrate by Bacillus axaraqunsis BIPC01 using Petrochemical Wastewater as Carbon Source

The aim of this study was to use petrochemical wastewater as the source of carbon for the production of polyhydroxyalkanoates (PHA) in an effort to decrease its cost of production. For this purpose, PHA producing bacteria were isolated from the petrochemical wastewater of Bandar Imam, Iran. The purified colonies were screened for PHA by Sudan Black B and Nile Blue A staining. Among positively stained bacteria, the best PHA producer was selected on the basis of cell growth, PHA content and the monomer composition of PHA. The phenotypic and genotypic identification this isolate showed it to be Bacillus axaraqunsis. The PHA was produced at a cell density of about 9.46 g/l of maximum concentration of 6.33g/l l, corresponding to 66% of cell dry weight. These results showed that B. axaraqunsis BIPC01 could be a potent PHA producer using wastewater for industrial purpose and simultaneously reducing the environmental pollution.

Agro-industrial residues and starch for growth and co-production of Polyhydroxyalkanoate copolymer and alfa-amylase by Bacillus. SP CFR67îen

Polyhydroxyalkanoates (PHA) and α-amylase (α-1,4 glucan-4-glucanohydrolase, E.C. 3.2.1.1) were co-produced by Bacillus sp. CFR-67 using unhydrolysed corn starch as a substrate. Bacterial growth and polymer production were enhanced with the supplementation of hydrolysates of wheat bran (WBH) or rice bran (RBH) individually or in combination (5-20 g L-1, based on weight of soluble substrates-SS). In batch cultivation, a mixture of WBH and RBH (1:1, 10 g L-1 of SS) along with ammonium acetate (1.75 g L-1) and corn starch (30 g L-1) produced maximum quantity of biomass (10 g L-1) and PHA (5.9 g L-1). The polymer thus produced was a copolymer of polyhydroxybutyrate-co-hydroxyvalerate of 95:5 to 90:10 mol%. Presence of WBH and corn starch (10-50 g L-1) in the medium enhanced fermentative yield of α-amylase (2-40 U mL-1 min-1). The enzyme was active in a wide range of pH (4-9) and temperature (40-60ºC). This is the first report on simultaneous production of copolymer of bacterial PHA and α-amylase from unhydrolysed corn starch and agro-industrial residues as substrates.

Agro-industrial residues and starch for growth and co-production of polyhydroxyalkanoate copolymer and -amylase by Bacillus sp. CFR-67

Polyhydroxyalkanoates (PHA) and -amylase (-1,4 glucan-4-glucanohydrolase, E.C. 3.2.1.1) were co-produced by Bacillus sp. CFR-67 using unhydrolysed corn starch as a substrate. Bacterial growth and polymer production were enhanced with the supplementation of hydrolysates of wheat bran (WBH) or rice bran (RBH) individually or in combination (5-20 g L-1, based on weight of soluble substrates-SS). In batch cultivation, a mixture of WBH and RBH (1:1, 10 g L-1 of SS) along with ammonium acetate (1.75 g L-1) and corn starch (30 g L-1) produced maximum quantity of biomass (10 g L-1) and PHA (5.9 g L-1). The polymer thus produced was a copolymer of polyhydroxybutyrate-co-hydroxyvalerate of 95:5 to 90:10 mol%. Presence of WBH and corn starch (10-50 g L-1) in the medium enhanced fermentative yield of -amylase (2-40 U mL-1 min-1). The enzyme was active in a wide range of pH (4-9) and temperature (40-60ºC). This is the first report on simultaneous production of copolymer of bacterial PHA and -amylase from unhydrolysed corn starch and agro-industrial residues as substrates.

Evaluation of Factors Affecting Polyhydroxyalkanoates Production by Comamonas sp. EB172 Using Central Composite Design

Aims: Statistical approach, central composite design (CCD) was used to investigate the complex interaction among temperature (25-37 °C), initial medium pH (5-9), inoculum size (4-10 % (v/v)), concentration of (NH4)2SO4 (0-1 g/L) and concentration of mixed organic acids (5-10 g/L) in the production of polyhydroxyalkanoates by Comamonas sp. EB172. Methodology and Results: Mixed organic acids derived from anaerobically treated palm oil mill effluent (POME) containing acetic:propionic:butyric (ratio of 3:1:1) were used as carbon source in the batch culture of Comamonas sp. EB172 to produce polyhydoxyalkanoates (PHAs). The analysis of variance (ANOVA) showed that all five factors were significantly important in the batch fermentation by shake flask with a P value of less than 0.001. The optimal temperature, initial medium pH, inoculum size, concentration of (NH4)2SO4 and concentration of mixed organic acids were 30 °C, 7.04, 4.0 % (v/v), 0.01 g/L and 5.05 g/L respectively. Conclusion, significance and impact of study: Optimization of the production medium containing mixed organic acids has improved the PHA production for more than 2 folds. Under optimal condition in the shake flask fermentation, the predicted growth is 2.98 g/L of dry cell weight (DCW) with 47.07 wt % of PHA content. The highest yield of PHA was 0.28 g of PHA per g mixed organic acids.

Biosynthesis and Lipase-Catalysed Hydrolysis of 4-Hydroxybutyrate-Containing Polyhydroxyalkanoates from Delftia acidovorans

Aims: Polyhydroxyalkanoates (PHA) having various molar fractions of 4-hydroxybutyrate has been successfully synthesized by Delftia acidovorans. Methodology and results: The monomer compositions of the PHA were varied by cultivating the bacterium in a mixture of 1,4-butanediol and sodium valerate, γ-butyrolactone and sodium valerate as well as 4-hydroxybutyric acid and sodium valerate, which resulted in the production of PHA terpolymers. Although the highest terpolymer content achieved was only 57 wt% of the dry cell weight, the 4HB molar fractions can be regulated from 2-50 mol% when culture conditions such as initial pH, inoculum concentration and aeration were varied. The in vitro degradation of [P(3HB-co-50 % 4HB)]synthesized by D. acidovorans were also studied by monitoring the erosion rate of the copolymer in aqueous solutions of lipases (Lipase A ‘Amano’ 12 and Newlase F). Results have shown that the types of lipases, concentration of lipase solution and pH of the buffer solution influenced the degradation rate of the PHA copolymer. Conclusion, significance and impact of the study: The overall results have shown that D. acidovorans is a very promising strain for the production of 4HB containing PHAs with specific compositions which are very suitable to be tailor made into biodegradable and biocompatible materials for medical applications.