Reduction of cell lysate viscosity during processing of poly(3-hydroxyalkanoates) by chromosomal integration of the staphylococcal nuclease gene in Pseudomonas putida

Poly(3-hydroxyalkanoates) (PHAs) are biodegradable thermoplastics which are accumulated by many bacterial species in the form of intracellular granules and which are thought to serve as reserves of carbon and energy. Pseudomonas putida accumulates a polyester, composed of medium-side-chain 3-hydroxyalkanoic acids, which has excellent film-forming properties. Industrial processing of PHA involves purification of the PHA granules from high-cell-density cultures. After the fermentation process, cells are lysed by homogenization and PHA granules are purified by chemical treatment and repeated washings to yield a PHA latex. Unfortunately, the liberation of chromosomal DNA during lysis causes a dramatic increase in viscosity, which is problematic in the subsequent purification steps. Reduction of the viscosity is generally achieved by the supplementation of commercially available nuclease preparations or by heat treatment; however, both procedures add substantial costs to the process. As a solution to this problem, a nuclease-encoding gene from Staphylococcus aureus was integrated into the genomes of several PHA producers. Staphylococcal nuclease is readily expressed in PHA-producing Pseudomonas strains and is directed to the periplasm, and occasionally to the culture medium, without affecting PHA production or strain stability. During downstream processing, the viscosity of the lysate from a nuclease-integrated Pseudomonas strain was reduced to a level similar to that observed for the wild-type strain after treatment with commercial nuclease. The nuclease gene was also functionally integrated into the chromosomes of other PHA producers, including Ralstonia eutropha.     

Reduction of Cell Lysate Viscosity during Processing of Poly(3-Hydroxyalkanoates) by Chromosomal Integration of the Staphylococcal Nuclease Gene in Pseudomonas putida

Poly(3-hydroxyalkanoates) (PHAs) are biodegradable thermoplastics which are accumulated by many bacterial species in the form of intracellular granules and which are thought to serve as reserves of carbon and energy. Pseudomonas putida accumulates a polyester, composed of medium-side-chain 3-hydroxyalkanoic acids, which has excellent film-forming properties. Industrial processing of PHA involves purification of the PHA granules from high-cell-density cultures. After the fermentation process, cells are lysed by homogenization and PHA granules are purified by chemical treatment and repeated washings to yield a PHA latex. Unfortunately, the liberation of chromosomal DNA during lysis causes a dramatic increase in viscosity, which is problematic in the subsequent purification steps. Reduction of the viscosity is generally achieved by the supplementation of commercially available nuclease preparations or by heat treatment; however, both procedures add substantial costs to the process. As a solution to this problem, a nuclease-encoding gene from Staphylococcus aureus was integrated into the genomes of several PHA producers. Staphylococcal nuclease is readily expressed in PHA-producing Pseudomonas strains and is directed to the periplasm, and occasionally to the culture medium, without affecting PHA production or strain stability. During downstream processing, the viscosity of the lysate from a nuclease-integrated Pseudomonas strain was reduced to a level similar to that observed for the wild-type strain after treatment with commercial nuclease. The nuclease gene was also functionally integrated into the chromosomes of other PHA producers, including Ralstonia eutropha.     

Surface modification of polyhydroxyalkanoate films and their interaction with human fibroblasts

A poly(3-hydroxybutylate-co-hydroxyvalerate) (PHA) film containing 34 mol.% 3-hydroxyvalerate (Biopol D600P) was prepared by the solvent cast method using a 10 wt.% chloroform solution of PHA. The PHA film was exposed to an oxygen plasma glow discharge to produce peroxides on its surfaces. These peroxides were then used as catalysts for the polymerization of acrylic acid (AA) in order to prepare carboxyl group-introduced PHA (PHA-C). Insulin-immobilized PHA was prepared using the coupling reaction of PU-C with insulin. The surface-modified PHAs were then characterized by attenuated total reflection Fourier transform infrared spectroscopy, electron spectroscopy for chemical analysis, and a contact angle goniometer. The amounts of insulin directly coupled to the carboxyl groups on PHA-C and coupled to the terminus amino groups of the grafted polyethylene oxide were 2.9 and 0.8 microg cm(-2), respectively. The PHA water contact angle (75 degrees ) decreased with AA grafting (33 degrees ) and insulin immobilization (31 degrees ), thereby exhibiting the increased hydrophilicity of the modified PHAs. When compared with PHA and PHA-C, the proliferation of human fibroblasts in the presence of serum was significantly accelerated on the insulin-immobilized PHAs.     

Bacterial synthesis of polyhydroxyalkanoates containing aromatic and aliphatic monomers by Pseudomonas putida CA-3

Pseudomonas putida CA-3 has the ability to accumulate to high levels unique polyhydroxyalkanoate (PHA) heteropolymers composed of aromatic and aliphatic monomers. The majority of monomers are aromatic making up 98% of the polymer. (R)-3-hydroxyphenylvalerate and (R)-3-hydroxyphenylhexanoate are the most abundant monomers found in polymers accumulated from phenylalkanoic acids with an uneven and even number of carbons on the acyl side chain respectively. PHAs accumulated from phenylvaleric and phenylhexanoic acid were partially crystalline while all other PHAs were amorphous. Significant differences in the yield and PHA content of the cells occurred when different phenylalkanoic acids were supplied as growth substrates. Increasing the initial concentration of the growth substrate increased both the PHA content of the cells and the overall yield (g PHA/g carbon supplied) of PHA accumulated by P. putida CA-3 cells. The highest PHA content (% cell dry wt.) from an aromatic carbon source was 59% when 15mM phenylvaleric acid was supplied as the sole source of carbon and energy. This corresponded to a maximum PHA yield of 0.42 g PHA/g carbon supplied. In and attempt to increase the level of PHA accumulated from related growth substrates acrylic acid was added to the growth medium. However, the addition of various concentrations of acrylic acid to the growth medium had either no effect or decreased the PHA content of the cell accumulated from phenylalkanoic acids by P. putida CA-3.     

Synthesis of <Emphasis Type="Italic">scl</Emphasis>-poly (3-hydroxyalkanoates) by <Emphasis Type="Italic">Bacillus cereus</Emphasis> found in freshwater,from monosaccharides and disaccharides

Background

Polyhydroxyalkanoates are a good substitute for synthetic plastic because they are highly biocompatible, ecofriendly, and biodegradable. Bacteria in freshwater bodies such as rivers, tube wells, and canals are exposed to alternating high and low concentrations of substrates that induce PHA production.

Methods

Fresh water samples were collected for isolation of bacterial strains. Screening of PHA in bacterial cells was performed with Sudan and Nile Red staining. Extracted PHA was characterized by FTIR.

Results

In this study, nine bacterial isolates were selected for PHA production on the basis of phenotypic screening. Their ability to accumulate PHAs was determined using different monosaccharides and disaccharides. Two bacterial isolates Bacillus cereus T1 (KY746353) and Bacillus cereus R3 (KY746354) produced PHAs. Optimal growth of the bacterial strain (T1) was observed in the presence of glucose, followed by maximum production of PHAs (63% PHAs) during the logarithmic phase of growth. B. cereus R3 (KY746354) accumulated 60% PHAs by dry cell weight.

Conclusion

PHA accumulation was relatively less with fructose, but both strains showed increased production (up to 50%) with sucrose. The polymer produced was characterized by Fourier-transform infrared spectroscopy (FTIR), which showed that the compound contains short-chain PHAs.

     

Production of functionalized polyhydroxyalkanoates by genetically modified <Emphasis Type="Italic">Methylobacterium extorquens</Emphasis> strains

Background  

Methylotrophic (methanol-utilizing) bacteria offer great potential as cell factories in the production of numerous products from biomass-derived methanol. Bio-methanol is essentially a non-food substrate, an advantage over sugar-utilizing cell factories. Low-value products as well as fine chemicals and advanced materials are envisageable from methanol. For example, several methylotrophic bacteria, including Methylobacterium extorquens, can produce large quantities of the biodegradable polyester polyhydroxybutyric acid (PHB), the best known polyhydroxyalkanoate (PHA). With the purpose of producing second-generation PHAs with increased value, we have explored the feasibility of using M. extorquens for producing functionalized PHAs containing C-C double bonds, thus, making them amenable to future chemical/biochemical modifications for high value applications.     

Recovery of medium-chain-length polyhydroxyalkanoates (PHAs) through enzymatic digestion treatments and ultrafiltration

Medium-chain-length (mcl) polyhydroxyalkanoates (PHAs) are biodegradable polyesters accumulated intracellularly as energy resources by bacterial species such as Pseudomonas putida. The most popular method for PHA recovery in the downstream processing is solvent extraction using chloroform and methanol. An alternate method is bioseparation using enzymatic digestion process which eliminates the need for hazardous solvents. This research focuses on an attempt to optimize the recovery of PHAs by solubilisation of non-PHA granules through enzymatic treatments such as; Alcalase (to digest the denatured proteins), sodium dodecyl sulfate (SDS) to assist solubilisation, ethylene diamine tetra acetic acid (EDTA) to complex divalent cations and lysozyme to digest the peptidoglycan wall enveloping the cell. The experiment was designed through Taguchi's design of experiment (DOE) using Qualitek-4 software. The results show that Alcalase enzyme used had the most significant effect on the treatment process and contributed to about 71.5% in terms of process factor importance among the different factors on treatment performance for PHA recovery. It is desired to recover the PHA granules in water suspension after the enzymatic treatment by removing the solubilised non-PHA cell material through crossflow ultrafiltration system and purified through continuous diafiltration process. Final purity of PHA in water suspension obtained using GC analysis is 92.6%, with a nearly 90% recovery, thus concluding that this method is indeed a suitable alternative.     

Characterization of medium-chain-length polyhydroxyalkanoate biosynthesis by Pseudomonas mosselii TO7 using crude glycerol

Polyhydroxyalkanoates (PHAs) are biopolyesters produced by microorganisms that are environmentally friendly. PHAs can be used to replace traditional plastic to reduce environmental pollution in various fields. PHA production costs are high because PHA must be produced from a carbon substrate. The purpose of this study was to find the strain that can used the BDF by-product as the sole carbon source to produce high amounts of medium-chain-length PHA. Three isolates were evaluated for potential PHA production by using biodiesel-derived crude glycerol as the sole carbon source. Among them, Pseudomonas mosselii TO7 yielded high PHA content. The PHA produced from P. mosselii TO7 were medium-chain-length-PHAs. The PHA content of 48% cell dry weight in 48 h with a maximum PHA productivity of 13.16 mg PHAs L^?1 h^?1. The narrow polydispersity index value of 1.3 reflected the homogeneity of the polymer chain, which was conducive to industrial applications.     

The Autotrophic Synthesis of Polyhydroxyalkanoate by Alcaligenes eutrophusin the Presence of Carbon Monoxide

The CO-resistant strain B5786 of the hydrogen-oxidizing bacterium Alcaligenes eutrophuswas found to be able to synthesize polyhydroxyalkanoates (PHAs) under the conditions of growth limitation by nitrogen deficiency (the factor that promotes PHA synthesis) and growth inhibition by carbon monoxide. The gas mixtures that contained from 5 to 20 vol % CO did not inhibit the key enzymes of PHA synthesis–-ketothiolase, acetoacetyl-CoA reductase, hydroxybutyrate dehydrogenase, and PHA synthase. In the presence of CO, cells accumulated up to 70–75 wt % PHA (with respect to the dry biomass) without any noticeable increase in the consumption of the gas substrate. Chromatographic–mass spectrometric analysis showed that the PHA synthesized by A. eutrophusis a copolymer containing more than 99 mol % -hydroxybutyrate and trace amounts of -hydroxyvalerate. The PHA synthesized under the conditions described did not differ from that synthesized by A. eutrophuscells from electrolytic hydrogen.     

Production and characterization of polyhydroxyalkanoates in Pseudomonas aeruginosa ATCC 9027 from glucose, an unrelated carbon source

The production and characterization of polyhydroxyalkanoic acids (PHAs) from glucose in Pseudomonas aeruginosa ATCC 9027 is described. We determined that the synthesis of PHAs was not due to a complete lack of nitrogen source, as previously reported for other microorganisms. The synthesis of PHAs was observed during exponential growth and it depended on the carbon/nitrogen ratio in the culture. More significantly, the specific PHA accumulation rate in this phase was higher than that observed in the storage phase. This phenomenon was a consequence of higher extracellular production rates of gluconate and 2-ketogluconate detected during the storage phase. Therefore, the production of those acids decreased the synthesis of PHAs in P. aeruginosa. The maximum percentage of PHA accumulation obtained was 10.8% of the cell dry matter when all the glucose was consumed. The monomer composition of this PHA consisted only of saturated 3-hydroxy fatty acids (octanoic, decanoic, and dodecanoic acids) as shown by gas chromatography - mass spectroscopy and nuclear magnetic resonance analyses, where 3-hydroxydecanoic acid was the main component because of the high affinity of its PhaC synthase for this monomer. The physical properties of this PHA were determined by differential scanning calorimetry and gel permeation chromatography.     

Production of PHA from starchy wastewater via organic acids

Polyhydroxyalkanoate (PHA) was produced from a starchy wastewater in a two-step process of microbial acidogenesis and acid polymerization. The starchy organic waste was first digested in a thermophilic upflow anaerobic sludge blanket (UASB) reactor to form acetic (60-80%), propionic (10-30%) and butyric (5-40%) acids. The total volatile fatty acids reached 4000 mg l(-1) at a chemical oxygen demand (COD) loading rate of 25-35 g l(-1) day(-1). A carbon balance indicates that up to 43% of the organic carbon in the starchy waste went to the organic acids and the rest to biogas, volatile suspended solids and residual sludge accumulated in the reactor. The acid composition profile was affected by COD loading rate: a medium rate around 9 g l(-1) day(-1) gave a high propionic acid content (29% wt) and a high rate around 26 g l(-1) day(-1) led to a high butyric acid content (34% wt). The acids in the effluent solution after microfiltration were utilized and polymerized into PHA by bacterium Alcaligenes eutrophus in a second reactor. Fifty grams of PHA was produced from 100 g total organic carbon (TOC) utilized, a yield of 28% based on TOC, which is comparable with 55 g PHA per 100 g TOC of pure butyric and propionic acids used. PHA formation from individual acids was further investigated in a semi-batch reactor with three acid feeding rates. With a limited nitrogen source (80-100 mg NH(3) per liter), the active biomass of A. eutrophus, not including the accumulated PHA in cells, was maintained at a constant level (8-9 g l(-1)) while PHA content in the cell mass increased continuously in 45 h; 48% PHA with butyric acid and 53% PHA with propionic acid, respectively. Polyhydroxybutyrate was formed from butyric acid and poly(hydroxybutyrate-hydroxyvalerate) formed from propionic acid with 38% hydroxyvalerate.     

Screening and identification of polyhydroxyalkanoates producing bacteria and biochemical characterization of their possible application

Polyhydroxyalkanoates (PHAs) accumulating bacteria were isolated under various selective conditions such as pH, salt concentrations and types of heavy metal. Fifty strains of bacterial isolates were found to belong to Bacillus, Proteus, Pseudomonas, Aeromonas, Alcaligenes and Chromobacterium, based on phenotypical features and genotypic investigation. Only twenty five bacterial isolates were selected and observed for the production of PHAs. Interestingly, bacteria belonging to Firmucutes Bacillus sp. produced a high amount of PHAs. The maximum PHAs were accumulated by B. licheniformis PHA 007 at 68.80% of dry cell weight (DCW). Pseudomonas sp., Aeromonas sp., Alcaligenes sp. and Chromobacterium sp. were recorded to produce a moderate amount of PHAs, varying from 10.00-44.32% of DCW. The enzymatic activity was preliminarily analyzed by the ratio of the clear zone diameter to colony diameter. Bacillus gave the highest ratio of hydrolysis zone which corresponds to the highest hydrolytic enzyme activities. Bacillus licheniformis PHA 007 had the highest lipase and protease activity at 2.1 and 5.1, respectively. However, the highest amylase activity was observed in Bacillus sp. PHA 023 at 1.4. Determination of metabolic characteristics was also investigated to check for their ability to consume a wide range of substrates. Bacillus, Aeromonas sp. and Alcaligenes sp. had great ability to utilize a variety of substrates. To decrease high PHA cost, different sources of cheap substrates were tested for the production of PHAs. Bacillus cereus PHA 008 gave the maximal yield of PHA production (64.09% of DCW) when cultivated in anaerobically treated POME. In addition, the accumulation of PHA copolymers such as 3-hydroxyvalerate and 3-hydroxyhexanoate was also observed in Bacillus and Pseudomomas sp. strain 012 and 045, respectively. Eight of the nine isolates accumulated a significant amount of PHAs when inexpensive carbon sources were used as substrates. Here it varied from 1.69% of DCW by B. licheniformis PHA 007 to 64.09% of DCW by B. cereus PHA 008.     

Production of poly-beta-hydroxyalkanoates from soy molasses oligosaccharides by new, rapidly growing Bacillus species

AIMS: To isolate and characterize bacteria from nature capable of producing poly-beta-hydroxyalkanoates in high yields from soy molasses oligosaccharides. METHODS AND RESULTS: Several strains of bacteria were obtained from enrichment cultures employing raffinose as major carbon source and inoculated with soybean field soil, lake sediment, or lake water. Many of the isolates were Bacillus species and produced polyhydroxyalkanoates (PHAs) to high yield. The raffinose-degrading isolates produced endospores, were highly saccharolytic, and both respired and fermented a variety of mono-, di-, tri- and tetrasaccharides. Strain CL1 produced 90% of cell dry mass as PHA from various sugars, including raffinose, and did so without requiring a nutrient limitation. CONCLUSIONS: Strain CL1 could be the catalyst for an industrial fermentation converting soy molasses and other waste carbohydrates to PHAs. The properties of this organism that make it ideally suited for such a fermentation include (i) its ability to use a wide variety of plant-associated carbohydrates as PHA feedstocks; (ii) its rapid growth; (iii) its ability to grow under anoxic conditions; and (iv) its ability to produce spores. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report of bacteria capable of making biodegradable plastics to high yield from soy molasses oligosaccharides.     

An alternative approach to the fermentation of sweet sorghum juice into biopolymer of poly-β-hydroxyalkanoates (PHAs) by newly isolated, Bacillus aryabhattai PKV01

This work revealed for the first time the possible use of a newly isolated Bacillus aryabhattai PKV01 for poly-β-hydroxyalkanoates (PHAs) production from fermentative sweet sorghum juice. Its growth and PHA production were investigated under different pH and nitrogen sources. Medium composition was optimized using statistical tools. The highest biomass and PHA content were reached at pH 6.5 with the use of urea. Plackett-Burman design was then applied to test the relative importance of medium components and process variables on cell growth and PHA production. Cell growth and PHAs production were affected by total sugar and urea and were subjected to optimize the sorghum juice medium using response surface methodology (RSM) via central composite design (CCD). The predicted optimal culture composition was achieved. Maximum dry cell weight and PHAs were obtained using a flask and almost double the amount was achieved using a bioreactor. After PHA recovery, the structure and thermal properties were characterised and revealed to be similar to the standard of poly-β-hydroxybutyrate (PHB).     

Rapid flow cytometry – Nile red assessment of PHA cellular content and heterogeneity in cultures of Pseudomonas aeruginosa 47T2 (NCIB 40044) grown in waste frying oil

The accumulation of cytoplasmic polyhydroxyalkanoates (PHAs) and the heterogeneity of bacterial populations were analysed by flow cytometry and SYTO-13 and Nile red staining in rhamnolipid-producing Pseudomonas aeruginosa cultures grown in waste frying oil as carbon source. A combination of SYTO-13 and Nile red fluorescence with cytometric forward and side scatter values may allow increases in the final production of polyhydroxyalkanoates (PHA) by two basic mechanisms: (i) rapid assessment of polyhydroxyalkanoate content and (ii) definition of flow cytometric cell sorting protocols to select high polyhydroxyalkanoate (PHA)-producing strains. We report a rapid (less than 30 min) flow cytometric assessment of PHAs in Pseudomonas aeruginosa 47T2 following Nile red staining: (i) to estimate cellular PHAs content; (ii) to study heterogeneity of the batch cultures producing PHAs and (iii) to establish the basis for sorting sub-populations with a high capacity to accumulate PHAs.     

Bacillus subtilis as potential producer for polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are biodegradable polymers produced by microbes to overcome environmental stress. Commercial production of PHAs is limited by the high cost of production compared to conventional plastics. Another hindrance is the brittle nature and low strength of polyhydroxybutyrate (PHB), the most widely studied PHA. The needs are to produce PHAs, which have better elastomeric properties suitable for biomedical applications, preferably from inexpensive renewable sources to reduce cost. Certain unique properties of Bacillus subtilis such as lack of the toxic lipo-polysaccharides, expression of self-lysing genes on completion of PHA biosynthetic process – for easy and timely recovery, usage of biowastes as feed enable it to compete as potential candidate for commercial production of PHA.     

Bioproduction of polyhydroxyalkanoates from bacteria: a metabolic approach

The advent of molecular biological techniques and a developing environmental awareness initiated a renewed scientific interest in Polyhydroxyalkanoates (PHAs) and the biosynthetic machinery for PHA metabolism has been the area of research over the last two decades. PHAs are polyesters of hydroxyalkanoates synthesized by numerous bacterial species with atleast five different PHA biosynthetic pathways. These are accumulated as an intracellular carbon and energy storage material. This diversity, in combination with genetic and molecular engineering has opened up this area for development of optimum PHA producing organisms. Even though PHAs have been recognized as a good candidate for biodegradable plastics, their industrial application is limited owing to high production cost. The classical microbiology and modern molecular biology have been brought together to decipher the intricacies of PHA metabolism both for production purposes and for the unraveling of the natural role of PHA. This review provides an overview of the different PHA biosynthetic systems, the enzymes involved in PHA biosynthesis and there genetic background followed by a detailed summation of how this natural diversity is being used to develop commercially attractive recombinant process for large scale production of PHAs.     

Transgenic plants as a source of polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) make a large class of biodegradable biopolymers that are naturally synthesized by numerous microorganisms. These biopolymers could be an alternative to commonly used plastics based on petroleum. Production of PHAs in bioreactors using microorganisms is not widely applied due to its unprofitability. Using transgenic plants for this purpose may be cheaper and more environmental friendly because the biosynthesis of PHAs in plants is based only on water, mineral salts, CO₂ and light. Additionally, plants are not capable of degrading PHAs as bacteria do, and extraction of PHAs from plant tissues is not always necessary. The main objective of this work is a review of possibilities of PHA biosynthesis in transgenic plants and presentation of general information on properties and potential application possibilities of these biopolymers. The possibility of syntheses and accumulation of PHA in several transgenic plants has been studied for some years. Many experiments were performed on model plant Arabidopsis thaliana, however, the research has also revealed a great potential of transgenic crop plants such as camelina (Camelina sativa), tobacco (Nicotiana tabacum) or sugarcane (Saccharum officinarum) as a good sources of PHAs. The highest level of PHAs accumulation in plants was achieved in transgenic A. thaliana (up to 40% of the dry weight of the leaf), and among crop plants in C. sativa (up to 20% of the dry weight of the seed). Increasing knowledge on PHAs permits expansion of the possibilities of these biopolymers use even at a low level of their accumulation in plant tissues.     

Cloning and molecular organization of the polyhydroxyalkanoic acid synthase gene (phaC) of Ralstonia eutropha strain B5786

Class I polyhydroxyalkanoic acid (PHA) synthase gene (phaC) of Ralstonia eutropha strain B5786 was cloned and characterized. R. eutropha B5786 features the ability to synthesize multicomponent PHAs with short- and medium-chain-length monomers from simple carbohydrate substrate. A correlation was made between the molecular structure of PHA synthase and substrate specificity and the ability of strain-producers to accumulate PHAs of this or that structure. A strong similarity of PHA synthase of R. eutropha strain B5786 with PHA synthase of R. eutropha strain H16, which, as opposed to strain B5786, enables to incorporate medium chain length PHAs if hexanoate is used as carbon source, exhibited 99%. A correlation between the structure of PHA synthase of B5786 strain with synthases of microorganisms which synthesize short and medium chain length PHAs similarly to B5786 strain, showed an identity level from 26 to 41% (homology with synthase of Rhodospirillum rubrum makes 41%, Ectothiorhodospira shaposhnikovii makes 26%, Aeromonas punctata makes 40%, Thiococcus pfennigii makes 28%, Rhodococcus ruber makes 38%, and with PhaCl and PhaC2 synthases of Pseudomonas sp. 61–3 makes 34 and 37%, respectively). This allows for speaking about the absence of a direct connection between the molecular organization of PHA synthases and their functional abilities, namely, the ability to synthesize PHAs of a particular composition.     

Production of polyhydroxyalkanoates from inexpensive extruded rice bran and starch by Haloferax mediterranei

Low-cost raw materials can be used to reduce significantly the production cost of polyhydroxyalkanoates (PHA). In this study, extruded rice bran (ERB) and extruded cornstarch (ECS) were used as carbon sources to produce PHA by an archaea, Haloferax mediterranei, which cannot use native rice bran or cornstarch as a carbon source. By employing pH-stat control strategy to maintain pH at 6.9–7.1 in a 5-liter jar fermentor using ERB:ECS (1:8 g/g) as the major carbon source, we obtained a cell concentration of 140 g/L, PHA concentration of 77.8 g/L and PHA content of 55.6 wt.% in a repeated fed-batch fermentation. In contrast, when ECS was used as the major carbon source, we obtained 62.6 g/L cell concentration, 24.2 g/L PHA concentration and 38.7 wt.% PHA content. Under a hyper-saline condition and with no nitrogen-limitation restriction, the repeated fed-batch process can be sustained a long time for the mass production of PHA.