Production and characterization of poly‐3‐hydroxybutyrate from biodiesel‐glycerol by Burkholderia cepacia ATCC 17759

Glycerol, a byproduct of the biodiesel industry, can be used by bacteria as an inexpensive carbon source for the production of value‐added biodegradable polyhydroxyalkanoates (PHAs). Burkholderia cepacia ATCC 17759 synthesized poly‐3‐hydroxybutyrate (PHB) from glycerol concentrations ranging from 3% to 9% (v/v). Increasing the glycerol concentration results in a gradual reduction of biomass, PHA yield, and molecular mass (M_n and M_w) of PHB. The molecular mass of PHB produced utilizing xylose as a carbon source is also decreased by the addition of glycerol as a secondary carbon source dependent on the time and concentration of the addition. ¹H‐NMR revealed that molecular masses decreased due to the esterification of glycerol with PHB resulting in chain termination (end‐capping). However, melting temperature and glass transition temperature of the end‐capped polymers showed no significant difference when compared to the xylose‐based PHB. The fermentation was successfully scaled up to 200 L for PHB production and the yield of dry biomass and PHB were 23.6 g/L and 7.4 g/L, respectively. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

Comparative study on the production of poly(3-hydroxybutyrate) by thermophilic Chelatococcus daeguensis TAD1: a good candidate for large-scale production

In spite of numerous advantages on operating fermentation at elevated temperatures, very few thermophilic bacteria with polyhydroxyalkanoates (PHAs)-accumulating ability have yet been found in contrast to the tremendous mesophiles with the same ability. In this study, a thermophilic poly(3-hydroxybutyrate) (PHB)-accumulating bacteria (Chelatococcus daeguensis TAD1), isolated from the biofilm of a biotrickling filter used for NOx removal, was extensively investigated and compared to other PHB-accumulating bacteria. The results demonstrate that C. daeguensis TAD1 is a growth-associated PHB-accumulating bacterium without obvious nutrient limitation, which was capable of accumulating PHB up to 83.6 % of cell dry weight (CDW, w/w) within just 24 h at 45 °C from glucose. Surprisingly, the PHB production of C. daeguensis TAD1 exhibited strong tolerance to high heat stress as well as nitrogen loads compared to that of other PHB-accumulating bacterium, while the optimal PHB amount (3.44?±?0.3 g l^?1) occurred at 50 °C and C/N?=?30 (molar) with glucose as the sole carbon source. In addition, C. daeguensis TAD1 could effectively utilize various cheap substrates (starch or glycerol) for PHB production without pre-hydrolyzed, particularly the glycerol, exhibiting the highest product yield (Y _P/S, 0.26 g PHB per gram substrate used) as well as PHB content (80.4 % of CDW, w/w) compared to other carbon sources. Consequently, C. daeguensis TAD1 is a viable candidate for large-scale production of PHB via utilizing starch or glycerol as the raw materials.     

Polyhydroxyalkanoates production from carbohydrates by a genetic recombinant Aeromonas sp.

Aims: To develop an Aeromonas strain able to utilize inexpensive carbon sources such as starch for the synthesis of polyhydroxyalkanoates (PHA). Methods and Results: A recombinant Aeromonas sp. (strain KC007‐1) was constructed by introducing the PHB synthesis genes (phaCAB) into the bacterium. Strain KC001‐R1 can not only use carbohydrate (including starch) for growth but also accumulate significant amounts of polyhydroxybutyrate (PHB) in the cells. Conclusions: One of the present focuses on PHA production has been on lowering the production costs. Starch is an example of an inexpensive carbohydrate for use in industrial production of PHA. We have demonstrated that by introducing the phaCAB operon into Aeromonas sp. allowed the bacterium able to accumulated PHB using this substrate. Significance and Impact of the Study: Aeromonas spp. are able to synthesize PHA using fatty acids as carbon source. Although good robust growth results with use of starch as sole carbon source for Aeromonas, PHA synthesis does not occur. Strain KC007‐R1 showed the ability to accumulate PHA in relative high amount with both carbohydrates and fatty acids as carbon source, and can be cultivated to a significant amount of cell mass and hence is a potential strain for further development for industrial applications.     

Polyhydroxybutyrate production in halophilic marine bacteria Vibrio proteolyticus isolated from the Korean peninsula

Polyhydroxybutyrates (PHB) are biodegradable polymers that are produced by various microbes, including Ralstonia, Pseudomonas, and Bacillus species. In this study, a Vibrio proteolyticus strain, which produces a high level of polyhydroxyalkanoate (PHA), was isolated from the Korean marine environment. To determine optimal growth and production conditions, environments with different salinity, carbon sources, and nitrogen sources were evaluated. We found that the use of a medium containing 2% (w/v) fructose, 0.3% (w/v) yeast extract, and 5% (w/v) sodium chloride (NaCl) in M9 minimal medium resulted in high PHA content (54.7%) and biomass (4.94 g/L) over 48 h. Addition of propionate resulted in the production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(HB-co-HV)) copolymer as propionate acts as a precursor for the HV unit. In these conditions, the bacteria produced poly(3-hydroxybutyrate-co-3-hydroxyvalerate) containing a 15.8% 3HV fraction with 0.3% propionate added as the substrate. To examine the possibility of using unsterilized media with high NaCl content for PHB production, V. proteolyticus was cultured in sterilized and unsterilized conditions. Our results indicated a higher growth, leading to a dominant population in unsterilized conditions and higher PHB production. This study showed the conditions for halophilic PHA producers to be later implemented at a larger scale.

     

Polyhydroxybutyrate production by Saccharophagus degradans using raw starch as carbon source

Biosynthesis of poly(3‐hydroxybutyrate) (PHB) from raw starch as the carbon source by the polysaccharide‐digesting bacteria Saccharophagus degradans was investigated in a fed‐batch culture. The production and properties of the PHB synthesized from starch were compared to those obtained using glucose as carbon source. In fed‐batch cultures, S. degradans accumulated 21.35 and 17.46% of PHB, using glucose or starch as carbon source, respectively. The physical properties of the biopolymer produced from each carbon source were similar between them. Molecular mass, melting temperature and heat of fusion were 54.23 kDa, 165.61°C and 59.59 J/g, respectively, using glucose; and 57.07 kDa, 174.31°C and 67.66 J/g, respectively, using starch. This is the first work describing the capability of S. degradans to utilize raw starch as the sole carbon source for the production of PHB.     

Thermophilic bacterium Caldimonas taiwanensis produces poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from starch and valerate as carbon sources

Caldimonas taiwanensis accumulated polyhydroxybutyrate (PHB) at 55 °C from gluconate, fructose, maltose, and glycerol under nitrogen-limited condition. The PHB content peaked at 14 h after inoculation from gluconate. C. taiwanensis did not grow or accumulate PHA from fatty acids as the sole carbon source; however, it incorporated 3-hydroxyvalerate (3-HV) into PHB polymer from gluconate and valerate as a mixed carbon source. By adjusting the valerate concentration, the molar fraction of 3-HV could be modulated from 10 mol% to 95 mol%. Fatty acid valerate substantially inhibited cell growth and PHA accumulation with the addition of as little as 5 mM to the medium. Supplementing the medium with yeast extract overcame the inhibition, which enhanced not only the yield of biomass but also PHA productivity. The in vivo substrate specificity of PHA synthase ranged from C₄ to C₆. In addition, C. taiwanensis also incorporated a wide range of 3-HV into PHA from soluble starch and valerate as a mixed carbon source. Food-grade starches made from cassava, corn, potato, sweet potato and wheat respectively mixed with valerate were studied for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] production. In this study, C. taiwanensis exhibited high promise for reducing the production cost of P(3HB-co-3HV).     

Utilization of agricultural residues for poly(3-hydroxybutyrate) production by Halomonas boliviensis LC1

Aims: Utilization of cheap and readily available agricultural residues as cheap carbon sources for poly(3‐hydroxybutyrate) (PHB) production by Halomonas boliviensis. Methods and Results: Wheat bran was hydrolysed by a crude enzyme preparation from Aspergillus oryzae NM1 to provide a mixture of reducing sugars composed mainly of glucose, mannose, xylose and arabinose. Growth of H. boliviensis using a mixture of glucose (0·75% w/v) and xylose (0·25% w/v) in the medium led to a PHB content and concentration of 45 wt% and 1 g l^?1, respectively, after 30 h. A similar PHB concentration was attained when H. boliviensis was grown on wheat bran hydrolysate but with a lower PHB content, 34 wt%. In a batch cultivation mode in a fermentor, using 1·8% (w/v) reducing sugars, the maximum PHB accumulation by H. boliviensis was attained in 20 h, but was reduced to about 30 wt%. By adding butyric acid (0·8% v/v), sodium acetate (0·8% w/v) and decreasing the reducing sugars concentration to 1·0% w/v in the medium, PHB accumulation and concentration were increased to 50 wt% and 4 g l^?1, respectively, after 20 h. Butyric acid and sodium acetate for PHB production could also be provided by anaerobic digestion of solid potato waste. Conclusions: Cheap and readily available agricultural residues can be used as substrates to produce PHB. The production of PHB by H. boliviensis using wheat bran hydrolysate as source of carbon is expected to reduce the production cost and motivates further studies. Significance and Impact of the Study: Large‐scale commercial utilization of PHB is mainly hampered by its high production cost. Carbon source for PHB production accounts up to 50% of the total production costs. Thus, the use of waste agricultural residues can substantially reduce the substrate cost (and in turn even provide value to the waste), and can downsize the production costs. This improves the market competitiveness. Studies on PHB production by moderate halophiles were recently initiated with H. boliviensis and findings show that it has potential for commercial exploitation. PHB production by H. boliviensis using wheat bran and potato waste is hence interesting.     

Starch industry wastewater as a substrate for antagonist, Trichoderma viride production

Starch industry wastewater was investigated to assess and improve its potential as a raw material for the conidia production of biocontrol fungi, Trichoderma viride. The wastewater was tested with and without supplements of glucose, soluble starch, meat peptone and probable conidiation inducer chemicals in shake flask culture. Addition of complex carbon source (soluble starch, 1% and 2% w/v) produced maximum conidia ( approximately 3.02 and 4.2 x 10(10)CFU/mL, respectively). On the other hand, glucose addition as a simpler carbon source was either ineffective or, reduced conidia production (from 1.6 x 10(8) in control to 3.0 x 10(7)CFU/mL in 5% w/v glucose supplement). Supplement of nitrogen source showed a small increase of conidia concentration. Propionic, maleic and humic acids, EDTA, pyridine, glycerol and CaCO(3) were examined as probable conidiation inducers and showed effect only on initial rate of conidiation with no increase in final conidia concentration. Intra and extracellular ATP correlation with spore production showed dependence on growth media used and conidia concentration at the end of fermentation. Addition of carbon and nitrogen sources showed an increase in protease activity (from 0.4985 to 2.43 IU/mL) and entomotoxicity (from 10448 to 12335 spruce budworm unit (SBU)/microL). Entomotoxicity was improved by 11% in fermenter over shake flask when starch industry wastewater was supplemented with meat peptone.     

Production of green biodegradable plastics of poly(3-hydroxybutyrate) from renewable resources of agricultural residues

This work describes potential opportunities for utilization of agro-industrial residues to produce green biodegradable plastics of poly(3-hydroxybutyrate) (PHB). Wheat straws were examined with good efficacy of carbon substrates using Cupriavidus necator. Production was examined in separate hydrolysis and fermentation (SHF) in the presence and absence of WS hydrolysis enzymes, and in simultaneous saccharification and fermentation (SSF) with enzymes. Results showed that production of PHB in SSF was more efficient in terms of viable cell count, cell dry weight, and PHB production and yield compared to those of SHF and glucose-control cultures. While glucose control experiment produced 4.6 g/L PHB; SSF produced 10.0 g/L compared to 7.1 g/L in SHF when utilizing enzymes during WS hydrolysis. Results showed that most of sugars produced during the hydrolysis were consumed in SHF (~98 %) compared to 89.2 % in SSF. Results also demonstrated that a combination of glucose and xylose can compensate for the excess carbon required for enhancing PHB production by C. necator. However, higher concentration of sugars at the beginning of fermentation in SHF can lead to cell inhibition and consequently catabolite repressions. Accordingly, results demonstrated that the gradual release of sugars in SSF enhanced PHB production. Moreover, the presence of sugars other than glucose and xylose can eliminate PHB degradation in medium of low carbon substrate concentrations in SSF.     

Improving culture conditions for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) production by Bacillus sp. ND153, a bacterium isolated from a mangrove forest in Vietnam

The production of polyhydroxyalkanoate (PHA) by Bacillus sp. ND153, a bacterium strain isolated from a mangrove forest in Vietnam, was studied. Bacillus sp. ND153 was grown on HM-1 medium with different carbon sources (e.g. glucose, sucrose, maltose, dextrin, and starch). Glucose was found to be the most suitable carbon source for PHA accumulation, whereas starch and dextrin favored cell growth over PHA accumulation. Optimization of the culture medium for PHA production was investigated by applying factorial design, and a maximum PHA content of 79 % (w/w) was obtained with low concentrations of NH₄Cl and MgSO₄ and a high concentration of KH₂PO₄ in the medium. Propionate was used as the precursor for the production of copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and the amount of 3-hydroxyvalerate (3HV) in the polymer showed an increasing linear trend with the increase in propionate concentration from 0.2 g l^?1 to 1.0 g l^?1. Thus, the production of PHBV by Bacillus sp. ND153, with 3HV fraction ranging from 1 mol% to 30 mol%, was noted to be high, and the characteristics of fast cell growth and accumulation of PHA exhibited by Bacillus sp. ND153 make it a promising choice for biopolyester production.     

The accumulation of poly(3-hydroxyalkanoates) in Rhodobacter sphaeroides

In recent years industrial interest has been focussed on the evaluation of poly(3-hydroxyalkanoates) (PHA) as potentially biodegradable plastics for a wide range of technical applications. Studies have been carried out in order to optimize growth and culture conditions for the intracellular formation of PHA in the phototrophic, purple, non-sulfur bacterium Rhodobacter sphaeroides. Its potential to produce polyesters other than poly(3-hydroxybutyrate) (PHB) was investigated. On an industrial scale, the use of photosynthetic bacteria could harness sunlight as an energy source for the production of these materials. R. sphaeroides was grown anaerobically in the light on different carbon sources. Under nitrogenlimiting conditions a PHA content of up to 60 to 70% of the cellular dry weight was detected. In all of the cases studied, the storage polymer contained approximately 98 mol% of 3-hydroxybutyrate (HB) and 2 mol% 3-hydroxyvalerate (HV) monomer units. Decreasing light intensities did not stimulate PHA formation. Compared to Rhodospirillum rubrum (another member of the family of Rhodospirillaceae), R. sphaeroides showed a limited flexibility in its ability to form PHA with varying monomer unit compositions.     

Production of poly(3-hydroxybutyrate) by solid-state fermentation with <Emphasis Type="Italic">Ralstonia eutropha</Emphasis>

The use of solid-state fermentation is examined as a low-cost technology for the production of poly(hydroxyalkanoates) (PHAs) by Ralstonia eutropha. Two agroindustrial residues (babassu and soy cake) were evaluated as culture media. The maximum poly(hydroxybutyrate) (PHB) yield was 1.2 mg g^–1 medium on soy cake in 36 h, and 0.7 mg g^–1 medium on babassu cake in 84 h. Addition of 2.5% (w/w) sugar cane molasses to soy cake increased PHB production to 4.9 mg g^–1 medium in 60 h. Under these conditions, the PHB content of the dry biomass was 39% (w/w). The present results indicate that solid-state fermentation could be a promising alternative for producing biodegradable polymers at low cost.Revisions requested 31 August 2004; Revisions received 12 October 2004     

Zobellella denitrificans strain MW1, a newly isolated bacterium suitable for poly(3-hydroxybutyrate) production from glycerol

Aims: To search for new bacteria for efficient production of polyhydroxyalkanoates (PHAs) from glycerol. Methods and Results: Samples were taken from different environments in Germany and Egypt, and bacteria capable of growing in mineral salts medium with glycerol as sole carbon source were enriched. From a wastewater sediment sample in Egypt, a Gram‐negative bacterium (strain MW1) was isolated that exhibited good growth and that accumulated considerable amounts of polyhydroxybutyrate (PHB) from glycerol and also from other carbon sources. The 16S rRNA gene sequence of this isolate exhibited 98·5% and 96·2% similarity to Zobellella denitrificans strain ZD1 and to Zobellella taiwanensis strain ZT1 respectively. The isolate was therefore affiliated as strain MW1 of Z. denitrificans. Strain MW1 grows optimally on glycerol at 41°C and pH 7·3 and accumulated PHB up to 80·4% (w/w) of cell dry weight. PHB accumulation was growth‐associated. Although it was not an absolute requirement, 20 g l^?1 sodium chloride enhanced both growth (5 g cell dry weight per litre) and PHB content (87%, w/w). Zobellella denitrificans strain MW1 is also capable to accumulate the poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) copolymer if sodium propionate was used as cosubstrate in addition to glycerol. Conclusions: A new PHB‐accumulating strain was isolated and identified. This strain is able to utilize glycerol for growth and PHB accumulation to high content especially in the presence of NaCl that will enable the utilization of waste glycerol from biodiesel industry. Significance and Impact of the Study: This study is the first report on accumulation of PHA in a member of the new genus Zobellella. Furthermore, utilization of glycerol as the sole carbon source for fast growth and PHB biosynthesis, growth in the presence of NaCl and high PHB contents of the cells will make this newly isolated bacterium a potent candidate for industrial production of PHB from crude glycerol occurring as byproduct during biodiesel production.     

Biosynthesis of poly(3-hydroxybutyrate) (PHB) by Cupriavidus necator H16 from jatropha oil as carbon source

Poly(3-hydroxybutyrate) (PHB) is a biodegradable polymer that can be synthesized through bacterial fermentation. In this study, Cupriavidus necator H16 is used to synthesize PHB by using Jatropha oil as its sole carbon source. Different variables mainly jatropha oil and urea concentrations, and agitation rate were investigated to determine the optimum condition for microbial fermentation in batch culture. Based on the results, the highest cell dry weight and PHB concentrations of 20.1 and 15.5 g/L, respectively, were obtained when 20 g/L of jatropha oil was used. Ethanol was used as external stress factor and the addition of 1.5 % ethanol at 38 h had a positive effect with a high PHB yield of 0.987 g PHB/g jatropha oil. The kinetic studies for cell growth rate and PHB production were conducted and the data were fitted with Logistic and Leudeking–Piret models. The rate constants were evaluated and the theoretical values were in accordance with the experimental data obtained.     

Hyperproduction of poly(4-hydroxybutyrate) from glucose by recombinant Escherichia coli

ABSTRACT: BACKGROUND: Poly(4-hydroxybutyrate) [poly(4HB)] is a strong thermoplastic biomaterial with remarkable mechanical properties, biocompatibility and biodegradability. However, it is generally synthesized when 4-hydroxybutyrate (4HB) structurally related substrates such as gamma-butyrolactone, 4-hydroxybutyrate or 1,4-butanediol (1,4-BD) are provided as precursor which are much more expensive than glucose. At present, high production cost is a big obstacle for large scale production of poly(4HB). RESULTS: Recombinant Escherichia coli strain was constructed to achieve hyperproduction of poly(4-hydroxybutyrate) [poly(4HB)] using glucose as a sole carbon source. An engineering pathway was established in E. coli containing genes encoding succinate degradation of Clostridium kluyveri and PHB synthase of Ralstonia eutropha. Native succinate semialdehyde dehydrogenase genes sad and gabD in E. coli were both inactivated to enhance the carbon flux to poly(4HB) biosynthesis. Four PHA binding proteins (PhaP or phasins) including PhaP1, PhaP2, PhaP3 and PhaP4 from R. eutropha were heterologously expressed in the recombinant E. coli, respectively, leading to different levels of improvement in poly(4HB) production. Among them PhaP1 exhibited the highest capability for enhanced polymer synthesis. The recombinant E. coli produced 5.5 g L-1 cell dry weight containing 35.4% poly(4HB) using glucose as a sole carbon source in a 48 h shake flask growth. In a 6-L fermentor study, 11.5 g L-1 cell dry weight containing 68.2% poly(4HB) was obtained after 52 h of cultivation. This was the highest poly(4HB) yield using glucose as a sole carbon source reported so far. Poly(4HB) was structurally confirmed by gas chromatographic (GC) as well as 1H and 13C NMR studies. CONCLUSIONS: Significant level of poly(4HB) biosynthesis from glucose can be achieved in sad and gabD genes deficient strain of E. coli JM109 harboring an engineering pathway encoding succinate degradation genes and PHB synthase gene, together with expression of four PHA binding proteins PhaP or phasins, respectively. Over 68% poly(4HB) was produced in a fed-batch fermentation process, demonstrating the feasibility for enhanced poly(4HB) production using the recombinant strain for future cost effective commercial development.     

Production of poly-β-hydroxybutyrate on molasses by recombinant Escherichia coli

Beet molasses successfully replaced glucose as sole carbon source to produce poly--hydroxybutyrate by a recombinant Escherichia coli strain (HMS174/pTZ18u-PHB). The fermentation with molasses was cheaper than with glucose. The final dry cell weight, PHB content and PHB productivity were 39.5 g/L, 80% (w/w) and 1 g/Lh, respectively, in a 5 L stirred tank fermenter after 31.5 h fed-batch fermentation with constant pH and dissolved O2 content. © Rapid Science Ltd. 1998     

Biotechnological conversion of agro-industrial wastewaters into biodegradable plastic, poly beta-hydroxybutyrate

Waste activated sludge generated from a combined dairy and food processing industry wastewater treatment plant was evaluated for its potential to produce biodegradable plastic, poly beta-hydroxybutyric acid (PHB). Deproteinized jowar grain-based distillery spentwash yielded 42.3% PHB production (w/w), followed by filtered rice grain-based distillery spentwash (40% PHB) when used as substrates. Addition of di-ammonium hydrogen phosphate (DAHP) resulted in an increase in PHB production to 67% when raw rice grain-based spentwash was used. Same wastewater, after removal of suspended solids by filtration and with DAHP supplementation resulted in lower PHB production (57.9%). However, supplementing other wastes with DAHP led to a substantial decrease in PHB content in comparison to what was observed in the absence of DAHP.     

Influence of electron acceptor,carbon, nitrogen,and phosphorus on polyhydroxyalkanoate (PHA) production by <Emphasis Type="Italic">Brachymonas</Emphasis> sp. P12

Polyhydroxyalkanoates (PHAs), intracellular carbon and energy reserve compounds in many bacteria, have been used extensively in biodegradable plastics. PHA formation is influenced by nutrient limitations and growth conditions. To characterize the PHA accumulation in a new denitrifying phosphorus-removing bacterium Brachymonas sp. P12, batch experiments were conducted in which the electron acceptor (oxygen or nitrate) was varied and different concentrations of carbon (acetate), nitrogen (NH₄Cl), and phosphorus (KH₂PO₄) were used. Polyhydroxybutyrate (PHB) was the dominant product during PHA formation when acetate was the sole carbon source. The PHB content of aerobically growing cells increased from 431 to 636 mg PHB g⁻¹ biomass, but the PHB concentration of an anoxic culture decreased (−218 mg PHB g⁻¹ biomass), when PHB was utilized simultaneously with acetate as an electron donor for anoxic denitrification. The specific PHB production rate of the carbon-limited batch, 158.2 mg PHB g⁻¹ biomass h⁻¹, was much greater than that of batches with normal or excess carbon. The effects of phosphorus and nitrogen concentrations on PHB accumulation were clearly less than the effect of carbon concentration. According to the correlation between the specific PHB production rate and the specific cell growth rate, PHB accumulation by Brachymonas sp. P12 is enhanced by nutrient limitation, is growth-associated, and provides additional energy for the biosynthesis of non-PHB cell constituents to increase the cell growth rate beyond the usual level.     

Parametric optimization of feruloyl esterase production from Aspergillus terreus strain GA2 isolated from tropical agro-ecosystems cultivating sweet sorghum

A fungal strain, Aspergillus terreus strain GA2, isolated from an agricultural field cultivating sweet sorghum, produced feruloyl esterase using maize bran. In order to obtain maximum yields of feruloyl esterase, the solid state fermentation (SSF) conditions for enzyme production were standardized. Effective feruloyl esterase production was observed with maize bran as substrate followed by wheat bran, coconut husk, and rice husk among the tested agro-waste crop residues. Optimum particle size of 0.71- 0.3 mm and moisture content of 80% favored enzyme production. Moreover, optimum feruloyl esterase production was observed at pH 6.0 and a temperature of 30 degrees C. Supplementation of potato starch (0.6%) as the carbon source and casein (1%) as the nitrogen source favored enzyme production. Furthermore, the culture produced the enzyme after 7 days of incubation when the C:N ratio was 5. Optimization of the SSF conditions revealed that maximum enzyme activity (1,162 U/gds) was observed after 7 days in a production medium of 80% moisture content and pH 6.0 containing 16 g maize bran [25% (w/v)] of particle size of 0.71-0.3 mm, 0.6% potato starch, 3.0% casein, and 64 ml of formulated basal salt solution. Overall, the enzyme production was enhanced by 3.2-fold as compared with un-optimized conditions.     

Exploring two-stage fermentation strategy of polyhydroxyalkanoate production using Aeromonas hydrophila

With consideration of sustainable development, this study explored the fermentation strategy of cost-effective production of biodegradable polymer- polyhydroxyalanoates (PHAs) for feasibility of eco-friendly materials recycling during wastewater treatment. As prior studies showed that Aeromonas hydrophila NIU01 was a promising PHA-producing bacterium, this follow-up study tended to seek for optimal nutrient-supplementation strategy to stimulate maximal PHA accumulation of A. hydrophila NIU01 for cellular production. As maximal PHA production took place at growth-limiting conditions, two-stage fermentation was much more appropriate for practical applications compared to batch mode of operation. Moreover, this optimal two-stage operation strategy maximized cellular PHA production under nitrogen-limiting conditions at C/N molar ratio of 60/1. For materials recycling, this operation strategy could be applicable to simultaneous PHB production and wastewater decolorization using A. hydrophila.