Fermentation Strategies

PHB production using R. eutropha ATCC 17697 and A. latus ATCC 29712 was evaluated using a bioreactor as batch by Azhar et al. Maximum sugar consumption and sugar utilization efficiency were attained after lOOh ammonia was completely assimilated after 80 h. The cell dry weight after 100 and 80 h were 10.18 and 8.73 g/L, respectively. 

PHB synthesis from a mutant strain A. vinelandii using glucose in a batch reactor was optimized by Dhanasekar et al. The initial medium pH significantly affects the productivity. Incubation temperature does not have a significant role in PHB production. Substrate concentration significantly affects the productivity as well as the PHB yield. It was observed that maximum productivity was observed with short fermentation period and lag phase were also minimized. 

Fed-batch cultivation is one of the best methods to produce high cell density with high PHB content. The important strategy for fed-batch fermentation is to feed the growth limiting substrates at the same rate as the rate of substrate is utilized by the organism.This helps in preventing the formation of by-products that are produced when the substrate is excess and leads to production of product of interest. 

PHB production by Saaharophagus degradans using raw starch as carbon source in a fed-batch culture was evaluated by Gonzalez-Garcia et al. The strain accumulated 21.35% and 17.46% of PHB using glucose and starch as sole carbon source. The physical properties of these polymers were similar. 

Patnaik reported fed-batch optimization of PHB synthesis through mechanistic, cybernetic, and neural approaches. Enhancement of PHB productivity was investigated by applying two artificial neural networks to a bioreactor with finite dispersion and noise in feed streams. One network filtered the noise and other controlled the filtered feed rates of carbon and nitrogen sources. The study revealed that neural optimization doubled the maximum PHB concentration in fed-batch fermentation with R. eutropha by optimizing the time dependent feed rates. 

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The vast majority of these interesting biopolyesters have been studied and produced only on the laboratory scale. However, there have been several attempts to develop pilot scale processes, and these provide some insight into the production economics of poly(3HAMCL)s other than poly(3HB) and poly(3HB-co-3HV). These processes utilize diverse fermentation strategies to control the monomer composition of the polymer, enabling the tailoring of polymer material properties to some extent. The best studied of these is poly(3-hydroxyoctano-ate) (poly(3HO)), which contains about 90% 3-hydroxyoctanoate. This biopolyester has been produced on the pilot scale and is now being used in several experimental applications. 

Strain PHA Fermentation strategy Substrate Time (h) Cell concen- tration (g/D PHA concen- tration (g/D PHA content (%) Produc- tivity (g/l/h) Reference... 

Tang B, Liaoa X et al (2010) Enhanced production of poly(vinyl alcohol)-degrading enzymes by mixed microbial culture using 1,4-butanediol and designed fermentation strategies. Polym Degrad Stab 95 557-563... 

In the present experiment, the yield of copolymer production was optimized on a molecular basis using a fermentation strategy. 

The characteristics of processibility, high crystallinity, and high melting point (Tn, value) of PHB can be modified by the microbial fermentation strategy, which can be adjusted for the production of co- and terpolymers, or by the generation of polymeric blends. 

Kleist S, Miksch G, Hitzmann B, Arndt M, Friehs K, Flaschel E (2003). Optimization of the extracellular production of bacterial phytase with Escherichia coli by using different fed-batch fermentation strategies. Appl. Microbiol. Biotechnol. 61 456-462. 

The common theme in the development of optimum fermentation strategies is "environmental management". The examples described here cover a spectrum of fermentations including cell mass, enzyme and secondary metabolite production, yet it will become apparent that there is a common need for careful environmental management with particular emphasis on carbon source management throughout the fermentation. 

Other compounds have also been produced. For example, hydrogen was produced by a fermentative strategy using hydrogenase (Hyd) and fhl enzymes [199]. 1,2-PDO has also been produced from glycerol in E. coli by a pathway through DHAP and methylglyoxal [200]. Ethanol and other fermentative products have also been produced [201]. Limonene has been produced by an E. coli strain from... 

Fed-batch cultivation is a fermentation strategy whereby one or more nutrients are supplied to the cell culture until the end of the process. The concentration of nutrients that are fed into the bioreactor can be controlled by regulating the feed rate. In fed-batch cultivation the cells are fed continuously as per the required feeding method regime... 

As mentioned above for high cell density fed-batch cultures, the two-step fermentation strategy has often been applied, where the cell division is separated from the PHA accumulation phase. With use of octanoic acid as a substrate, PHA contents of up to 75% (w/w) at a cell concentration of 55 gL" and a volumetric productivity of 0.63 gL h were obtained with P. putida GPol under nitrogen limitation (Kim et al. 2002). With Pseudomonas IPT 046, cell concentrations of up to 50 gL with a PHA content of 63% (w/w) and a volumetric productivity of 0.8 gL" h were reached under phosphate limitation using glucose and fructose as a mixed carbon source (Diniz et al. 2004). When oleic acid was used as a substrate for the cultivation of P. putida KT2442, a cell concentration of 141 gL" with a PHA content of 51% (w/w) and a volumetric productivity of 1.91 gL" h were obtained under phosphate limitation (Lee et al. 2000). 

Poly(hydroxyalkanoate)s have been the focus of attention as a biodegradable and biocompatible substitute for the corresponding conventional non-degradable plastics (3). However, the costs of the large-scale production of these polymers have barred the widespread use. Now, new fermentation strategies have been developed for the efficient production of poly(hydroxyalkanoate)s. 

Taherzadeh MJ. (1999). Ethanol from lignocellulose physiological effects of inhibitors and fermentation strategies. Department of Chemical Reaction Engineering. Goteborg, Sweden, Chalmers University of Technology. 

Oh BR, Seo JW, Heo S Y, Hong WK, Luo LH, Son JH, Park DH, Kim CH. (2012). Fermentation strategies for 1,3-propanediol production from glycerol using a genetically engineered Klebsiella pneumoniae strain to eliminate by-product formation. Bioproc Biosyst Eng, 35, 159-165. 

Roa Engel CA, van Gulik WM, Marang L, van der Widen LAM, Straathof AJJ. (2011). Development of a low pH fermentation strategy for fumaric acid production by Rhizopus... 

Bio-based succinic acid is a very promising compound which can be used in many different application fields and has the potential to substitute several petroleum-based bulk chemicals. Research within the past years led to the development of a number of different production strains, fermentation strategies, and downstream processes suitable for industrial needs. Based on these results, several companies started bio-succinic acid production at industrial scale. The short overview of these companies given above, which is certainly not complete, and... 

A new fermentation strategy using cell recycle membrane system was developed by Ahn et al. for the efficient production of PHB from whey by recombinant E. coli strain CGSC 4401 harboring the A. latus PHA biosynthesis genes. The working volume of fermentation was constandy maintained by cell recycle and by fed-batch cultivation employing an external membrane module. The PHB concentration and PHB content were 168 g/L and 87%, respectively. 

Ramadas NV, Sindhu R, Binod P, Pandey A. Development of a novel solid-state fermentation strategy for the production of poly-3-hydroxybutyrate using polyurethane foams by Bacillus sphaericus Nil 0838. Ann Microbiol 2013 63 1265-74. 

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