Poly-β-hydroxybutyrate Productivity Research Articles

Light excess stimulates Poly-beta-hydroxybutyrate yield in a mangrove-isolated strain of Synechocystis sp.

Poly-β-hydroxybutyrate (PHB) is a biodegradable biopolymer that may replace fossil-based plastics reducing its negative environmental impact. One highly sustainable strategy to produce these biopolymers is the exploitation of photosynthetic microorganisms that use sunlight and CO2 to produce biomass and subsequently, PHB. Exploring environmental biological diversity is a powerful tool to find resilient microorganisms potentially exploitable to produce bioproducts. In this work, a cyanobacterium (Synechocystis sp.) isolated from a contaminated area close to an important industrial complex was shown to produce PHB under different culture conditions. Carbon, nutrients supply and light intensity impact on biomass and PHB productivity were assessed, showing that the highest yield of PHB achieved was 241 mg L−1 (31%dcw) under high light intensity. Remarkably this condition not only stimulated PHB accumulation by 70% compared to other conditions tested but also high cellular duplication rate, maximizing the potential of this strain for PHB production.

Photofermentative production of hydrogen and poly-β-hydroxybutyrate from dark fermentation products

The aim of this work is to investigate the hydrogen and poly-β-hydroxybutyrate (PHB) production during the photofermentative treatment of the effluent from a dark fermentation reactor fed with the organic fraction of municipal solid waste. Two different inocula, an adapted culture of Rhodobacter sphaeroides AV1b and a mixed consortium of purple non sulphur bacteria have been investigated under the same operational conditions. Different hydrogen productivities of 364 and 559NmL H2 L−1 were observed for the Rhodobacter sphaeroides and the mixed culture consortium tests, respectively: the consortium of PNSB resulted 1.5-fold more productive than the pure culture. On the other hand, Rhodobacter sphaeroides culture showed a higher PHB productivity (155mg PHB g COD−1) than the mixed culture (55mg PHB g COD−1). In all the tests, the concomitant H2 and PHB production was associated to a dissolved COD removal higher than 80%.

Microbial biopolymer production by Microbacterium WA81 in batch fermentation

Microbial Poly-β-hydroxybutyrate (PHB) was the first and the most widespread polymer to be used in the biodegradable polymer industry. The optimization of the Egyptian local bacterial strain Microbacterium sp. WA81 productivity was performed using statistical design of experiment tools. A Plackett–Burman design was carried out to screen the effect of different carbon and different nitrogen sources, each in a separate experiment. Moreover, a subsequent Response Surface Methodology was applied to achieve the maximum PHB productivity at shake flask level. Upon scaling up to a bench top bioreactor run scale (5 L), using the generated medium, the amount of the polymer significantly increased (1.42 g/L), which represented a 78-fold increase of that prior optimization. During the bioreactor run, the preliminary effect of Dissolved Oxygen (DO) was explored, and the levels of carbon and nitrogen uptakes were monitored. In conclusion, the statistical design of experiment tools enabled us to optimize and engineer a growth medium and conditions to enhance PHB productivity by the Egyptian isolate Microbacterium sp. WA81.

COST-EFFECTIVE PRODUCTION OF THE BIO-PLASTIC POLY-β-HYDROXYBUTYRATE USING ACINETOBACTER BAUMANNII ISOLATE P39

Being biodegradable and biocompatible natural polymer, poly-β-hydroxybutyrate (PHB) drew the attention of scientists to substitute synthetic plastics in our daily lives. However, its industrial production is hampered by its high cost. In this study, an extensive screening program was done to isolate bacteria with high PHB productivity from agricultural fields and develop a cost-effective PHB production. A promising bacterial isolate Acinetobacter baumannii P39 was recovered and identified using 16S ribosomal gene sequencing. It produced 24% PHB per dry weight after 48 h. Several experiments were conducted to optimize the composition of the culture medium and environmental factors for the selected isolate. Results revealed that 60% aeration, 28°C incubation temperature and initial pH 7.5 showed the highest productivity. Besides, 0.7% corn oil and 0.1 g/L peptone were the best carbon and nitrogen sources, respectively. Substituting glucose with corn oil led to a 23% reduction in total input cost and an estimate price for 1kg PHB is 20.5 L.E. Strain improvement by UV mutation succeeded in improving PHB production by two fold in the selected mutant P39M2. Finally, this study valorizes usage of Acinetobacter isolate in PHB production in addition to solving the critical problem of high cost of production.

Development of eco-friendly bioplastic like PHB by distillery effluent microorganisms

During screening for poly-β-hydroxybutyrate (PHB) producing bacteria from distillery effluent sample, six out of 30 isolates comprising of three strains of Alcaligenes sp., two strains of Bacillus sp., and one strain of Pseudomonas sp. were found to accumulate varying levels of intracellular PHB. Amongst the various isolates, Alcaligenes sp. RZS4 was found as the potent PHB-producing organism, accumulating higher amounts of PHB. PHB productivity was further enhanced in the presence of oxygen, nitrogen-limiting conditions, and cloning of PHB synthesizing genes of Alcaligenes sp. RZS 4 into Escherichia coli. A twofold increase in PHB yield was obtained from recombinant E. coli vis-à-vis Alcaligenes sp.; the recombinant E. coli accumulated more PHB in NDMM, produced good amount of PHB in a single-stage cultivation process under both nutrient-rich and nutrient-deficient conditions. Extraction of PHB with acetone-alcohol (1:1) was found as suitable method for optimum extraction of PHB as this mixture selectively extracted PHB without affecting the non-PHB cell mass. PHB extract from recombinant E. coli showed the presence of C-H, =O stretching, =C-H deformation, =C-H, =CH, and =C-O functional groups characteristic of PHB.

Effect of feed composition on PHB production from methanol by HCDC of Methylobacterium extorquens (DSMZ 1340)

AbstractBACKGROUND: Poly‐β‐hydroxybutyrate (PHB), produced by several species of bacteria, has attracted great attention as a biodegradable and biocompatible compound with similar properties to polypropylene. Unfortunately, its use is currently limited due to high production costs. One of the most common methods for overcoming this constraint is the use of inexpensive substrates, like methanol, in high cell density cultivations (HCDC).RESULTS: Fermentation was carried out with optimized feed composition (639 g l−1 methanol, 4 g l−1 MgSO4.7H2O, 41 mL L−1 trace elements, 5.6 g L−1 NaH2PO4.H2O and 24.3 g L−1 K2HPO4) and a feeding strategy based on the detection of substrate limitation by dissolved oxygen (DO). After 35 h, at which dry cell weight (DCW) reached a value of 70 g L−1, PHB production was stimulated, and biomass and PHB productivities of 2.8 and 0.98 g L−1 h−1 were obtained, respectively. These results surpassed those reported in the literature for PHB production from methanol by Methylobacterium species.CONCLUSION: The proposed feed composition and feeding strategy for PHB production from methanol by Methylobacterium extorquens 1340 in fed‐batch cultivation resulted in high biomass and PHB productivity. They can be implemented for recombinant bioproducts (proteins) produced by M. extorquens due to the lack of PHB accumulation in the growth phase. Copyright © 2009 Society of Chemical Industry

Determination of poly-β-hydroxybutyrate production by Bacillus spp. isolated from the intestines of various fishes

In this study, 30 strains of the genus Bacillus were isolated from various fresh fishes obtained from fish markets in Ankara, Turkey. They were identified as Bacillus pasteurii, Bacillus badius, Bacillus circulans, Bacillus licheniformis, Bacillus megaterium, Bacillus thuringiensis, Bacillus brevis, Bacillus cereus, Bacillus sphaericus, Bacillus subtilis, Bacillus coagulans, Bacillus lentus, and Bacillus pumilus. When poly-β-hydroxybutyrate (PHB) production by these strains was determined by spectrophotometry, it was found that PHB production ranged from 0.81–23.38% (w/v). PHB production and productivity were highest for B. pasteurii P2 (20.58% w/v) and B. lentus P18 (23.38% w/v). Furthermore, B. pasteurii P2 and B. lentus P18 were examined for PHB production using different carbon and nitrogen sources and in combined medium containing both carbon and nitrogen sources. The amounts of PHB produced by the strains in these media were more different than the amounts of PHB produced in nutrient broth medium.

Microbial production of poly-β-hydroxybutyrate by marine microbes isolated from various marine environments

Considering the industrial interest of Poly-β-hydroxybutyrate (PHB), bacteria isolated from the various marine arenas were screened for their ability to accumulate PHB and were compared with Wausteria eutropha (MTCC-1285). Among the 42 isolates, four strains showed the accumulation of PHB. The maximum PHB producer Vibrio sp. (MK4) was further studied in detail. To increase the productivity, steps were taken to evaluate the effect of carbon sources, nitrogen sources, pH and sodium chloride concentration on PHB productivity by MK4. The optimized conditions were further used for the batch fermentation over a period of 72 h. Significantly higher maximum biomass of 9.1 g/L with a PHB content of 4.223 g/L was obtained in a laboratory-scale bioreactor at 64 h, thus giving a productivity of 0.065 g/L/h. The extracted polymer was compared with the authentic PHB and was confirmed to be PHB using FTIR analysis and 1H NMR analysis. Thus, the study highlights the potential of the use of Vibrio sp (MK4) in the commercial production of PHB.

Continuous production of poly‐β‐hydroxybutyrate by high‐cell‐density cultivation of Wautersia eutropha

AbstractBACKGROUND: Poly‐β‐hydroxybutyrate (PHB) accumulation is triggered by limitation of a nutrient other than carbon. The production cost of PHB is very high. In order to reduce this cost, continuous cultivation for the accumulation of PHB was investigated. The culture was first allowed to grow under fed‐batch conditions to yield a significant increase in biomass and PHB accumulation. Thereafter this high‐cell‐density biomass containing PHB was allowed to grow and maintained under conditions of continuous cultivation so that the overall process could be simplified and economised.RESULTS: For continuous cultivation a medium containing 90 g L−1 fructose and 2.5 g L−1 nitrogen (as urea) was fed continuously at a dilution rate of 0.1 h−1. A steady state biomass of 27.7 g L−1 with a PHB concentration of 5.5 g L−1 was established in the bioreactor. This resulted in a continuous PHB productivity of 0.55 g L−1 h−1.CONCLUSION: The experiments have resulted in the development of a novel production technology involving the integration of batch, fed‐batch and continuous processes. At the same time the production of PHB under continuous cultivation increases the overall industrial importance of the system. Copyright © 2008 Society of Chemical Industry

Determination of poly-β-hydroxybutyrate (PHB) production by some Bacillus spp.

In this study, 29 strains of the genus Bacillus were isolated from different soil samples which were taken from grasslands of Ankara, Turkey and were identified as B. brevis, B. sphaericus, B. cereus, B. megaterium, B. circulans, B. subtilis, B. licheniformis and B. coagulans. Two strains, B. sphaericus ATCC 14577 and B. subtilis ATCC 6633 were also included in this study. Poly-β-hydroxybutyrate (PHB) production by these strains was determined by the spectrophotometric method, and it was found that PHB production ranged from 1.06–41.67% (w/v) depending on the dry cell weight. The highest PHB production and productivity percentage was found in B. brevis M6 (41.67% w/v).

Simulation and optimisation of PHB production in fed-batch culture of Ralstonia eutropha

Fed-batch culture is commonly used to produce partially growth-associated products such as poly-β-hydroxybutyrate (PHB). However, without a proper feeding strategy this culture would not result much higher productivity than bath culture. Therefore, in this study a dynamic optimisation program written in matlab environment was employed to determine optimal feeding rates of carbon and nitrogen sources. A fed-batch mathematical model was developed and validated against experimental data before it was incorporated into the optimisation program. The optimal feeding strategy obtained from the simulation was applied experimentally. The results of this experiment were compared with the results of other fed-batch culture experiments whose feeding strategies were determined based on bioreactor engineering sen se. PHB productivity was increased around 100% using optimal feeding strategy.

Optimization of two-stage continuous culture system for production of poly-β-hydroxybutyrate

The optimization of poly-β-hydroxybutyrate (PHB) fermentation process is essential to obtain a high PHB productivity. An optimization of two-stage continuous culture system by complex method for PHB production is presented. PHB production rate of the system obtained in the present study was chosen as the objective function. The PHB production rate of the system was higher than that of the phasewise optimization method which maximizes the growth rate of residual biomass in the first stage and the PHB production rate in the second stage. When the inlet glucose concentration in the first stage increased, PHB content and yield also increased. When the fermentor volume ratio (V2/V1) was 0.5, maximum PHB productivity in the second stage was 2.86 g/L’ h, which is highest compared with the reported value on PHB.