The survey demonstrated that recombinant Escherichia coli JM109 harboring the polyhydroxyalkanoate biogenesis cistron of Comamonas sp. EB172 had the possible to use both sugar- and acid-based C beginnings for the biogenesis of both poly ( 3-hydroxybutyrate ) and poly ( 3-hydroxybutyrate-co-3-hydroxyvalerate ) copolymers. In shake flask experiments, the strain was capable of bring forthing P ( 3HB-co-3HV ) copolymer from assorted organic acids, and higher productivenesss were obtained utilizing glucose compared to assorted acids. However, PHA accretion was found to be similar regardless of the C beginning used. Nitrogen supplementation was found to better the cell dry weight but negatively affected the 3HV formation. Maximal 3HV monomer ( 3 mol % ) was obtained with C/N 42.1 utilizing assorted acids as substrate. In 2 L bioreactor, the productiveness and output based on substrate use coefficient were found to be 0.16 g PHA/ ( L.h ) and 0.41 g PHA/g substrate under C/N around 75, utilizing 20 g/L glucose and 0.5 g/L ammonium sulfate, severally. The polymer produced by the recombinant strain had molecular weight in the scope of 8.5 x 105 to 1.4 tens 106 Da. Overall, the ability of the recombinant E. coli JM109 to use assorted C beginnings has widened its substrate choice for agitation including the chance to utilize renewable biomass.
Keywords: Recombinant, phaCABco, Mixed acids, Polyhydroxyalkanoate, Comamonas sp. EB172
Polyhydroxyalkanoates ( PHAs ) are energy storage, hydrophobic granules that can be accumulated by many micro-organisms ( Kim et al. 2009 ; Sim et Al. 2001 ; Steinb & A ; uuml ; chel, 2003 ; Sudesh et Al. 2011 ) . PHAs are biodegradable, biocompatible thermoplastics, and therefore, these biopolyesters are non merely the possible alternate campaigners for fractious man-made plastics, but besides present long-run benefits for environmental pollution issues. However, the high cost for PHA production compared to the handiness of low-priced petroleum-based plastic is the major obstruction to commercialize these biosynthesized PHAs ( Naik et al. 2008 ; Sudesh et Al. 2000 ) . The most important factor for the high production cost of PHAs is the agitation procedure, which is chiefly due to the cost of natural stuff every bit good as the recovery procedure ( Khanna and Srivastava, 2005 ) . A great trade of attempt has been made to cut down the production cost by using brilliant microbic strains every bit good as developing agitation and recovery procedure with inexpensive C beginnings and non-halogenated dissolvers, severally ( Khanna and Srivastava, 2005 ; Li et Al. 2007 ; Verlinden et Al. 2007 ) .
Economic biotechnological PHA formation mostly depends on the pick of productive micro-organisms and their civilization status. Recently, in our uninterrupted attempt of using assorted organic acids derived from palm oil factory wastewater ( POME ) for PHA production, we have produced several studies on the isolation, biogenesis and word picture of both P ( 3HB ) and P ( 3HB-co-3HV ) by a local, acerb tolerant strain of Comamonas sp. designated as Comamonas sp. EB172 ( Mumtaz et al. 2010a ; Mumtaz et Al. 2010b ; Zakaria et Al. 2008 ; Zakaria et Al. 2010a ; Zakaria et Al. 2010b ) . While developing a suited agitation scheme to feed assorted acids in its original signifier ( maintaining indistinguishable ratio as obtained ) , our focal point was besides to develop a non-halogenated PHA recovery system at the terminal of fed-batch agitation ( Mumtaz et al. 2010a ; Mohammadi et Al. 2012a ; Mohammadi et Al. 2012b ) . However, Comamonas sp. EB172 is known to use merely fatty acids but non glucose or fructose ( Zakaria et al. 2010a ) . Therefore, the three cistrons involved in the biogenesis of PHAs by Comamonas sp. EB172 were cloned and characterized ( Yee et al. 2012 ) . Meanwhile, the PHA biogenesis cistrons of Comamonas sp. EB172 had besides been cloned and heterologously expressed for its functionality to show the ability of the stray biogenesis cistron on PHA production in E. coli JM109 host.
Recombinant E. coli has normally been employed for PHA production due to its convenience for familial use, fast growing, high cell denseness cultivation and ability to use cheap C beginnings. The strain has been reported to bring forth short-chain-length ( scl ) polyesters incorporating C4 or C5 monomers, such as P ( 3HB ) , poly ( 3-hydroxyvalerate ) P ( 3HV ) , poly ( 4-hydroxybutyrate ) P ( 4HB ) homopolymer, or the P ( 3HB-co-3HV ) copolymer ( Song et al. 1999 ) and P ( 3HB-co-4HB ) ( Valentin and Dennis, 1997 ) . Nevertheless, recombinant E. coli, incorporating the phaC1 cistron from Pseudomonas aeruginosa, was able to bring forth medium-chain- length ( mcl ) PHAs holding C6 to C14 monomers including homopolymers of 3-hydroxyhexanoate ( 3HHx ) , 3-hydroxydodecanoate ( 3HDD ) and terpolymer poly ( 3-hydroxybutyrate-co-3-hydroxyvalerate-co-hydroxyhexanoate ) , P ( 3HB-co-3HV-co-3HHx ) ( Langenbach et al. 1997 ; Park et Al. 2001 ) , when beta-oxidation cistron fadB was deleted ( Langenbach et al. 1997 ) . Meanwhile, intercrossed polymers incorporating both scl- and mcl-monomer units such as poly ( 3-hydroxybutyrate-co-hydroxyhexanoate ) , P ( 3HB-co-3HHx ) , produced of course by Aeromonas caviae, can besides be synthesized in recombinant E. coli through familial use ( Fukui and Doi, 1997 ; Fukui et Al. 1998 ) . For commercial PHA production, recombinant E. coli has besides been employed by Metabolix, USA and Jiang Su Nan Tian Co. Ltd, China ( Chen 2009 ) . Metabolically engineered E. coli can easy show the enzyme involved in PHA biogenesis with assorted monomer composings. Therefore, E. coli JM109 was chosen to show the PHA biogenesis cistrons from Comamonas sp. EB172. The potency of this recombinant strain was examined in the shingle flasks and bioreactor surveies utilizing both refined and non-refined C beginnings.
In this survey, the public presentation of recombinant E. coli JM109 was examined for P ( 3HB-co-3HV ) copolymer production and better cell growing utilizing glucose and assorted organic acids as the C beginnings. The polymer produced was further characterized for its chemical construction and molecular weight. The information reported herewith may be utile for future work utilizing recombinant strain with local renewable substrates such as POME and oil thenar fronds ( OPF ) ( Zahari et al. 2012 ) .
Materials and methods
Bacterial strains, plasmids and civilization conditions
Recombinant E. coli JM109 that harboured plasmid pGEM’-phaCABCo incorporating PHA biogenesis cistron phaCABCo of Comamonas sp. EB172 was used in this survey ( Yee et al. 2012 ) . E. coli JM109 is a general host for cloning. Through this survey, we can detect the substrate or enzyme ability of the cloned cistrons for the PHA accretion under assorted conditions. Hence, simple E. coli bacteriums strain is necessary instead than the look host such as E. coli DH5? . The E. coli DH5? can be the strain for future familial alteration and procedure optimisation. Recombinant E. coli JM109 was cultivated at 37 & A ; deg ; C and 200 revolutions per minute in the Luria-Bertani medium, consisting the undermentioned constituents: 10 g casein peptone, 10 g Na chloride and 5 g barm infusion in 1 L of distilled H2O. The antibiotic Principen ( 50 µg/mL ) was added to the civilization medium to keep the stableness of the plasmids.
PHA accretion in shingle flask
The recombinant E. coli JM109 was pre-cultured in the Luria-Bertani medium at 37 & A ; deg ; C and 200 revolutions per minute for 14 H, and 10 % ( v/v ) of the civilization ( OD600nm? 3.0 ) was inoculated into a 250-mL shingle flask incorporating 50 milliliter of nitrogen-limited mineral salts ( MS ) medium ( pH 7.0 ) . The MS medium consisted of ( in g/L ) 5g KH2PO4, 2g K2HPO4, 1g ( NH4 ) 2SO4, 0.4g MgSO4a?™7H2O and 1mL of hint element solution ( Yee et al. 2012 ) . Ampicillin ( 50 µg/mL ) was added when it was necessary for plasmid care. Glucose was sterilized individually and was added to the remainder of the medium before vaccination to avoid caramelization consequence. The mixtures of three acids ( acetic: propionic: n-butyric acid ) in a ratio of 3:1:1 were sterilized along with other salts in the MS medium to give a concluding concentration of 10 g/L. The mass ratio of 3:1:1 for the assorted organic acids was to imitate anaerobically the fermented POME as the C beginning ( Yee et al. 2003 ) . The civilizations were cultivated at 37 & A ; deg ; C and 200 revolutions per minute for 48 H in the brooder shaker. The cell growing, cell concentration and concluding pH were monitored during the agitation.
PHA accretion in 2 L bioreactor
The pre-cultured recombinant E. coli JM109 in a 100-mL Luria-Bertani medium in a 500-mL shingle flask was used as the seed civilization. The seed civilization was incubated at 37 & A ; deg ; C and agitated at 200 revolutions per minute for 14 h. One hundred milliliters ( 10 % v/v ) of the seed civilization ( OD600nm? 3.0 ) was inoculated into a 2L bioreactor with a 900-mL MS medium supplemented with 10 g/L, 20 g/L glucose or 10 g/L assorted acids as the C beginning. Three different concentrations of ammonium sulfate ( without N add-on, 0.5 g/L and 1.0 g/L ) were supplemented in the MS medium. The cells were grown at 37 & A ; deg ; C and pH 7 ( controlled utilizing 1 M NaOH ) throughout the experiment. The dissolved O tenseness ( DOT ) degree was maintained above 30 % of air impregnation by automatically raising the agitation velocity from 150 to 600 revolutions per minute. The air flow rate was kept at 1 vvm throughout the agitation. The batch agitation was cultivated for 24 H depending on the exhaustion of the C beginnings in the MS stock. The cell growing, cell concentration and PHA accretion were monitored during the class of the agitation.
Gas chromatography analysis
Grown cells were harvested by centrifugation ( 6000 x g, 10 proceedingss, 4 & A ; deg ; C ) , washed with distilled H2O and lyophilised. The lyophilised cells after methanolysis at 100 & A ; deg ; C for 140 proceedingss in the presence of sulfuric acid and methyl alcohol ( 15:85 v/v ) ( Braunegg et al. 1978 ) were subjected for cellular PHA content and polymer composing by gas chromatography ( Shimadzu, GC2014 ) analysis.
Extraction and purification of polymer from cell
Polymers were extracted from the lyophilised cells utilizing the modified method of Amirul et Al. ( 2008 ) . One gm of lyophilised cells was stirred overnight in 250 milliliter of trichloromethane at room temperature. The mixture of cell dust and polymers was separated through Whatman No. 1 membrane filter paper with the pore size of 11 µm. PHA dissolved in trichloromethane and was recovered by precipitating utilizing cold methyl alcohol in the ratio of 1:5. The precipitated polymer was filtered utilizing 0.45 µm PTFE membrane filter and dried overnight at room temperature. The extracted pure polymer was so characterized for its chemical construction and molecular weight by proton atomic magnetic resonance ( 1HNMR, 500 MHz JEOL JNM-ECP500 FT NMR ) and size-exclusion chromatography ( SEC, TOSOH HLC-8120 ) , severally ( Ariffin et al. 2008 ) .
Word picture of polymer
1H NMR spectra were recorded on a 500 MHz JEOL JNM-ECP500 FT NMR. Chloroform-d ( CDCl3 ) was used as a dissolver. Chemical displacements were reported as ? values ( ppm ) relation to internal tetramethylsilane ( TMS ) in CDCl3 unless otherwise stated. The molecular weights of the polymers were measured on a TOSOH HLC-8120 SEC system with refractile index ( RI ) and UV ( UV, ? = 254 nanometer ) sensors under the undermentioned conditions: TSKgel Super HM-H additive column ( one-dimensionality scope, 1×103 – 8 x106 ; molecular weight exclusion bound, 4 x108 ) , chloroform eluent at a flow rate of 0.6 mL min-1, and column temperature of 40 & A ; deg ; C. The standardization curves for SEC analysis were obtained utilizing polystyrene criterions with a low polydispersity ( 5.0×102, 1.05 x103, 2.5 x103, 5.87 ten 103, 9.49 x103, 1.71×104, 3.72 x104, 9.89×104, 1.89×105, 3.97×105, 7.07 x105, 1.11×106, TOSOH Corp. ) .
Statistical analysis of the experimental consequences was carried out utilizing MSTAT-C package. Duncan ‘s Multiple Range Test at 5 % ( p & A ; lt ; 0.05 ) alpha degree was used for average experimental information comparings.
Consequence of C and N beginning on PHA biogenesis in shingle flask
Table 1 shows the cell growing and PHA production of the recombinant E. coli JM109 utilizing different C beginnings ( i.e. glucose and assorted acids ) . It was observed that the recombinant E. coli JM109 preferred glucose compared to assorted acids as its C beginning for growing. The cell titer showed a important difference ( p & A ; lt ; 0.05 ) depending on the initial concentration of C beginning. It can be observed that the cell growing was affected by the initial concentration of glucose, in which higher glucose concentration reduced the CDW formation. However, there was no important difference on PHA accretion when a different type of C beginning was used. There was merely a little addition in PHA accretion one time glucose was used ( Table 1 ) . This may be due to the substrate concentration inhibitory of the initial sum of glucose used. However, the recombinant still can use for PHA biogenesis. Therefore, the usage of higher concentration of glucose ( 40 g/L ) non merely decreased the cell growing and but besides P ( 3HB ) accretion ( informations non shown ) .
Glucose was utilized for better cell formation and PHA accretion compared with assorted organic acids, whereby they merely affected accretion of PHA. Nevertheless, declined growing of recombinant E. coli JM109 was observed in medium incorporating 10 g/L assorted acids supplemented with nitrogen beginning. The assorted organic acids were consumed more efficaciously by recombinant without N addendum compared to the cultivation under same status with 1 g/L nitrogen beginning.
Table 1 and Table 2 show the consequence of N on the CDW and PHA accretion of the recombinant E. coli JM109. When the recombinant E. coli JM109 was cultivated in the MS medium incorporating N beginning [ 1 g/L of ( NH4 ) 2SO4 ] and 10 g/L glucose, CDW increased from 1.5 g/L ( Table 1, experiment 1 ) to 2.3 g/L ( Table 2, experiment 1 ) and PHA content increased from 34 % to 46 % , severally. Once once more, the CDW and PHA contents of increased sum of glucose ( 20 g/L ) did non demo any important difference to 10 g/L glucose as the C beginning ( Table 2, experiment 2 ) .
On the other manus, declined growing of the recombinant E. coli JM109 was observed in the medium incorporating assorted acids supplemented with nitrogen beginning. This may be due to the repressive consequence of assorted organic acids in the ratio of 3:1:1 ( acetic acid: propionic acid: n-butyric acid ) . Even with the theoretical account being, C. necator, the maximal CDW and PHA contents utilizing 3 g/L assorted acids in the ratio of 3:1:1 ( acetic acid: propionic acid: n-butyric acid ) were shown to be 1.1 g/L and 58.2 wt % , severally, after 41 H of cultivation ( Yang et al. 2010 ) . However, it has to be noted that the tolerance degree of assorted acids differs among bacterial species and PHA accretion in native manufacturers, such as in C. necator, which require nitrogen restriction.
As shown in Table 2, the PHA accretion was somewhat better when the MS medium incorporating assorted organic acids was supplemented with ( NH4 ) 2SO4. It was observed that with the presence of N in the civilization medium, PHA accretion was somewhat increased from 32 % to 37 % , but the 3HV monomer content was decreased ( Table 2, experiment 3 ) . Similar observations were reported by Kim et Al. ( 1992 ) in Alcaligenes sp. SH-69, in which N beginning was found to impact the chemical composing of polymer. Chien et Al. ( 2012 ) reported that the addition in concentration of yeast infusion in cultivation medium had decreased the 3HV formation in P ( 3HB-co-3HV ) copolymer produced.
In order to analyze the consequence of N and 3HV molar fraction of P ( 3HB-co-3HV ) copolymer, the recombinant E. coli JM109 was grown in a different concentration of ( NH4 ) 2SO4 with equal sum of assorted acids at 10 g/L in the shingle flask. As shown in Table 3, more 3HV can be produced with lower supplementation of the N beginning. The highest 3HV fraction of 2.65 mol % was observed with an add-on of 0.5 g/L ( NH4 ) 2SO4 ( C/N ratio at 42.1 ) and with low CDW. A C/N ratio of more than 21 mol/mol enhanced the cell growing and PHA accretion, whereas at lower C/N ratio, both the 3HV and CDW were decreased ( Table 3 ) . On the other manus, PHA content was the highest at 21 mol/mol C/N ratio utilizing assorted organic acids. Obviously, the CDW and fraction of 3HV monomer of the recombinant E. coli were decreased by 1 g/L ( NH4 ) 2SO4 add-on compared to lower concentration of nitrogen add-on. Hence, extra C beginnings and restricting nitrogen supplementation status were needed for synthesising the copolymer and impacting the growing of the constructed recombinant E. coli JM109.
Batch agitation of recombinant E. coli JM109 in 2 L bioreactor
Batch agitation was performed in a 2 L bioreactor to acquire higher cell and PHA concentrations under controlled status compared to the shingle flask agitation. As shown in Table 1 and Table 2, the handiness of propionic acids in the assorted organic acids in the medium could take to the biogenesis of 3HV monomer for the accrued polymer while the use of glucose in the medium could better the cell growing. Furthermore, the add-on of N was able to increase the CDW and PHA accretion utilizing glucose in the medium as substrate. Table 4 illustrates the kinetic parametric quantity values for batch agitation utilizing 10 and 20g/L glucose as substrate with 0.5g/L ( NH4 ) 2SO4 ( 37.7 and 75.5 C/N, severally ) . The recombinant E. coli JM109 was cultivated in 10g/L and 20g/L glucose supplemented with 0.5g/L, 1g/L and without ( NH4 ) 2SO4. However, higher productiveness was observed in the medium supplemented with 0.5g/L ( NH4 ) 2SO4. Although the PHA output based on PHA biogenesis per cell ( g PHA/g cell ) in the agitation utilizing 10 and 20 g/L of glucose was similar, the substrate use coefficient, Yp/s ( g PHA/g substrate ) , and productiveness were higher when 20 g/L glucose was used as the exclusive C beginning. Bioreactor agitation performed at controlled pH and DO can surely better the biomass and PHA production as compared to agitate flask agitation with merely controlled initial pH. The lower degree of PHA biogenesis utilizing 10 g/L glucose could be due to rapid exhaustion of glucose concentration ( less than 1 g/L ) after 18 h cultivation. Slightly higher PHA biogenesis per cell ( g PHA/g cell ) of the recombinant E. coli JM109 was obtained in the agitation utilizing 10 g/L glucose. However, the best productiveness, 0.16 g PHA/ ( L.h ) , was observed in medium with 20 g/L glucose supplemented with 0.5 g/L ( NH4 ) 2SO4.
Figure 1 and 2 shows the profile for the OD, CDW and PHA content for the batch reaction utilizing 10 g/L and 20 g/L glucose with 0.5g/L ( NH4 ) 2SO4. Higher concentration of glucose, the cell growing was slower than the PHA accretion compared to the lower glucose concentration where the cell growing about relative to the PHA accretion. The recombinant bacteriums preferred to bring forth C compound intracellularly and subsequently cell metamorphosis with lower concentration of C beginning.
On the other manus, batch agitation was performed by feeding 10 g/L assorted organic acids with 1 g/L ( NH4 ) 2SO4 to detect the ability of a recombinant cells that can use assorted organic acids derived from POME instead than glucose as substrate. However, the experiment farther proved that the assorted organic acids were non an ideal exclusive C substrate for PHA accretion in batch agitation. On the contrary, when assorted organic acids were used as the C beginning, lower productiveness and output [ 0.003g PHA/ ( L.h-1 ) and 0.03g PHA/g substrate, severally ] were achieved. During batch agitation with assorted organic acids, 1.9 mol % of 3HV monomer fraction was observed at 30 h cultivation clip. The 3HV monomer was decreased to 1.1 mol % at 33 H at the terminal of the agitation with the increasing of PHA content from 22.5 to 32.2 wt % , severally ( informations non shown ) . Table 6 shows some recombinant E. coli which use for production of P ( 3HB-co-3HV ) . The assorted organic acids were chiefly fed for accretion of copolymer and the entire PHA accumulated comparable with old survey. Therefore, assorted organic acids derived from POME can be used as an alternate C beginning as the recombinant E. coli JM109 can still use this less favorable substrate for PHA accretion. For this intent, a proper agitation scheme utilizing 2 L bioreactor necessary established to bring forth co-polymers utilizing assorted organic acids by the designed recombinant.
Polymer word picture
The methyl esters of the component hydroxyalkanoic acids were analyzed utilizing GC. The GC consequence showed that PHA synthesized from the recombinant E. coli JM109 contained 3HV monomer fraction. Hence, 1H NMR analysis was carried out to find the chemical construction of the polymer. Figure 3 shows the 1H NMR spectrum of polymer produced by the recombinant E. coli JM109 from the 2 L bioreactor. The spectrum confirmed that the PHA synthesized by the recombinant E. coli JM109 in batch agitation utilizing 10 g/L assorted organic acids with 1 g/L nitrogen supplementation was a P ( 3HB-co-3HV ) copolymer. The present signals for 3HB molar fraction were identified at 1.27 ppm, 2.4-2.6 ppm and 5.27 ppm, which represent methyl ( CH3 ) , methylene ( CH2 ) and methine ( CH ) groups, severally. The signals of 3HV monomer were attributed by the methyl signal shown by a three at 0.9 ppm. Other characteristic signals of 3HV unit can non be seen, which could either due to low strength or overlapping with 3HB characteristic signal, such as methylene signals at 2.4-2.6 ppm. Thus, based on the GC and 1H NMR analyses, it was confirmed that the polymer was P ( 3HB-co-3HV ) copolymer produced from assorted organic acids as the exclusive C beginning.
Table 5 shows the molecular weight and polydispersity index ( PDI ) of chloroform-extracted polymers produced by the recombinant E. coli JM109 from the 2 L bioreactor with glucose or assorted organic acids as the C beginning. In this survey, the weight norm of molecular weight ( Mw ) of the polymer accumulated by the recombinant E. coli JM109 was in the scope of 8.5 x 105 to 1.4 tens 106 Da. The Mw of the polymer was non affected by the difference in PHA content of the cells. However, the type of C beginning and the different concentration of substrate could impact the Mw of the polymers. Under the same cultivation status, the PHA produced from 10 g/L glucose represented the highest Mw compared to 20 g/L glucose and 10 g/L assorted organic acids. These molecular weights were found to be higher than the PHA polymer synthesized by the recombinant E. coli showing a different PHA synthase ( Agus et al. 2010 ; Tomizawa et Al. 2011 ) . The highest Manganese was achieved from batch agitation with 10 g/L glucose, whereas the lowest PDI was obtained from the agitation of assorted acids ( Table 5 ) .
E. coli JM109 is known to be a host that can efficaciously show the enzyme and capable to synthesise assorted PHAs with different monomer composings without debasement ( Mahishi et al. 2003 ) . The mechanism for PHA biogenesis in E. coli is different from other bacteriums, where alimentary restricting status is non necessary for PHA production ( Lee et al. 1994 ) . Therefore, nitrogen beginning provides particularly for cell growing. However, Steinb & A ; uuml ; chel and Pieper ( 1992 ) reported that recombinant A. eutrophus is capable for P ( 3HB-co-3HV ) copolymer accretion from assorted unrelated C beginnings when N is limited and C beginnings are supplementing in surplus. In this survey, the consequence of different C beginnings on cell growing and PHA production from the recombinant E. coli JM109 harboring plasmid pGEM’-phaCABCo was carried out in the shingle flask. The agitation in the shingle flasks was carried out with or without nitrogen beginning to analyze the consequence of N beginning on the growing and PHA accretion of E. coli.
From Table 1, it is seen that the recombinant E. coli JM109 was able to use assorted organic acids for P ( 3HB-co-3HV ) copolymer accretion. A similar observation was besides reported late ( Yee et al. 2012 ) . This is in understanding with old determination by Chien and the colleagues ( 2012 ) , whereby it was discussed that the presence of propionic acid in the agitation broth contributed to P ( 3HB-co-3HV ) copolymer biogenesis ( Yee et al. 2012 ; Chien et Al. 2012 ) .
The consequences showed that both CDW and PHA content were improved when the agitation was supplemented with ( NH4 ) 2SO4. This indicates that PHA biogenesis in recombinant E. coli happened during growing and non under alimentary restriction like those phenomenon observed in wild type PHA manufacturer such as C. necator ( Lee et al. 1994 ) . However, the complex medium could cut down the P ( 3HB ) accretion while supplementation of little sum of complex N beginnings ( Lee and Chang, 1994 ) , aminic acids or oleic acids ( Lee et al. 1995 ) could better the P ( 3HB ) synthesised. The add-on of N beginnings will increase the sum of acetyl-CoA and/or NADPH in the PHA metabolic tract for PHA production ( Lee et al. 1995 ; Lee et Al. 1996 ) . Chien and colleagues ( 2012 ) reported that entire CDW of recombinant E. coli was increased as the increase of yeast infusion with glucose as C beginning in medium. The increased concentration of barm infusion besides led to better the PHA content in the recombinant cells. Meanwhile, Lee and Chang ( 1994 ) reported that add-on of complex N beginnings in the agitation medium could significantly heighten the concentration of accrued P ( 3HB ) in both shake flasks and fed-batch agitation of the recombinant E. coli harboring the cistrons from Alcaligenes eutrophus. Hence, the CDW and PHA content in the cells can be improved under regular C and nitrogen addendum in recombinant cells.
From the shingle flask and batch agitation, we know that P ( 3HB ) can be accumulate utilizing glucose and assorted organic acids. However, P ( 3HB-co-3HV ) copolymer merely accrued utilizing assorted organic acids. However, there are two chief issues a ) the low cell growing and B ) production of co-polymer from supplied C beginning. Therefore, development of a agitation scheme that capable to provide the issues is necessary. PHA was accumulated intracellularly hence by increasing the CDW will fundamentally better the PHA content. A proper eating scheme can be suggested for using as suited manner for PHA production with assorted organic acids. Fed-batch cultivation is an industrial preferable manner of operation in order to accomplish high cell denseness and cut down the substrate inhibitory. Therefore, the assorted organic acids concentration can be maintained for biological and metabolic activities at appropriate degree. Fed-batch agitation may better CDW, PHA accretion or 3HV monomer fraction.
Based on the belongingss, co-polymer will be preferred in PHA production since it is more valuable in applications. Molar mass is an of import factor finding physical belongingss of polymers and is known to change with substrate and civilization conditions ( Chen and Page, 1994 ) . The mean Numberss of molecular weight ( Mn ) of the P ( 3HB ) recovered from A. eutrophus and the recombinant E. coli strain by trichloromethane extraction were reported to be 1.2 ten 106 Da and 1.53 tens 106 Da, severally ( Hahn et al. 1995 ) . A high molecular weight with a low polydispersity is normally desired in the production of trade good thermoplastics. A molecular weight of 6 ten 105 Da or above is considered acceptable for thermoplastic applications of scl-P ( 3HB-co-3HV ) ( Braunegg et al. 1998 ) . Therefore, the polymer produced from this survey has desired molecular weight, suited for thermoplastic applications. On the other manus, in coatings, pressure-sensitive adhesives, polymer binding agents in organic-solvent-free pigments and in a scope of medical applications, low molecular weights are preferred ( Reddy et al. 2003 ) . Apparently, the PDI value was found to be similar to the values reported for the PHAs synthesized by other bacteriums.
Unlike the wild type Comamonas sp. EB172, the recombinant E. coli JM109 was able to use both glucose and assorted organic acids to bring forth P ( 3HB-co-3HV ) copolymer. This implies that recombinant E. coli JM109 has possible to use the waste-stream byproducts from oil thenar industry such as assorted acids from POME and/or assorted sugars from oil thenar frond juice for PHA production. On the other manus, familial alteration on threonine tract or protein technology on PHA biogenesis cistrons may better the substrate or enzyme specificity will besides our hereafter focal point.
The writers would wish to admit the fiscal and proficient supports provided by the Ministry of Science, Technology and Innovation ( MOSTI ) , Malaysia, Universiti Putra Malaysia, and Japan Society for Promotion of Science ( JSPS ) , Japan. We are thankful for the aid provided by Mr Kohtaro Watanabe and Mr Wong Yoke Ming during the sample analysis.