Fermentation of cellulose

Gulf A process for making ethanol by the simultaneous hydrolysis and fermentation of cellulose. 

The usual diet of ruminants consists of fresh and preserved herbage and cereals. As a result of microbial activity in the rumen, esterified dietary fatty acids are hydrolyzed, short chain fatty acids are produced by fermentation of cellulose and other polysaccharides, unsaturated fatty acids are hydrogenated and/or converted to geometric (trans) and positional isomers, and microbial lipids are synthesized. These activities account in part for the enormous diversity of fatty acids in milk and the unique features short-chain and a high proportion of long chain saturated fatty acids. (Patton and Jensen, 1976 Christie, 1979B). 

Peitersen, N. and E. W. Ross, "Mathematical Model for Enzymatic Hydrolysis and Fermentation of Cellulose by Trichoderma" Biotechnol. Bioeng. 21 (1979) 997-1017. 

Ghose TK, Tyagi RD (1979), Rapid ethanol fermentation of cellulose hydrolysate. II. Product and substrate inhibition and optimization of fermentor design, Biotech-nol. Bioeng. 21 1401-1420. 

Teunissen MJ, Smits AA, Op den Camp HJ, Huis in t Veld JH, Vogels GD (1991) Fermentation of cellulose and production of cellulolytic and xylanolytic enzymes by anaerobic fungi from ruminant and non-ruminant herbivores. Arch Microbiol 156 290-296 Tielens AG, Rotte C, van Hellemond JJ, Martin W (2002) Mitochondria as we don t know them. Trends Biochem Sci 27 564-572... 

The de novo synthesis of fatty acids in the mammary gland utilizes mainly acetate and some (3-hydroxybutyrate. These precursors arise from the microbial fermentation of cellulose and related materials in the rumen. Once in the mammary gland, acetate is activated to acetyl-CoA. The mechanism of fatty acid synthesis essentially involves the carboxylation of acetyl-CoA to malonyl-CoA, which is then used in a step-wise chain elongation process. This leads to a series of short-chain and medium-chain length fatty acids, which differ by two CH2 groups (e.g., 4 0, 6 0, 8 0, etc.) (Hawke and Taylor, 1995). These are straight-chain, even-numbered carbon fatty acids. However, if a precursor such as propionate, valerate or isobutyrate, rather than acetate, is used, branched-chain or odd-numbered carbon fatty acids are synthesised (Jenkins, 1993 see Chapter 2). 

Venkatesh, K.V. 1997. Simultaneous saccharification and fermentation of cellulose to lactic acid. Bioresource Technology 62 91-98. 

An interesting alternative, however, is batch culture using cellulose as the feedstock. Because cellulose will only be consumed gradually, the effective value of S is much lower than the actual cellulose concentration, which decreases the rate of cell growth u and, according to Fig. 4, increases. In this system, the substrate uptake rate will depend on the amount of cellulase present. Because of its complexity, the kinetics of fermentation of cellulose will not be developed further here. However, batch culture has been used for cellulase production and is an option to consider in a fermentation design, as the feedstock is inexpensive. Handling and sterilization of the insoluble solid is a concern. 

The following are the advantages of SSF over the separate saccharification and fermentation of cellulose ... 

Costs might be lowered by combining steps and by starting with cheaper raw materials, such as wastes. Simultaneous saccharification and fermentation of cellulose (a polymer of glucose) has been accomplished by combining a... 

This disintegration of the albuminoid substance, which converts almost the whole of the organic nitrogen into ammonia, results from the combined action of numerous micro-organisms, of different species and nature. The products elaborated by one class of bacteria often serve as the point of attack for another. Thus the volatile acids and oxyacids furni.shed in the course of ammoniacal fermentation constitute a nutritive rruitcrial for the ferments of cellulose, bacteria abundantly represented in the soil Calcium acetate, as well as its homologues, react under these conditions in the following manner ... 

Fermentability using human fecal inoculum ranges from a high of 91% (cabbage) to a low of 0% (Maillard product) demonstrating the sensitivity of human microflora to different fiber sources. Fermentability of cellulose by human fecal microflora (23Z) is substantially less than rumen microflora (94%). The microflora in the human intestine may be more affected by fiber composition than rumen microflora. Work by Bryant (19) and Jeraci (11) leads to speculation that variation among inoculum sources in humans on a particular substrate could be greater than in other species. 

The principal features of a mathematical model described for the enzymatic hydrolysis and fermentation of cellulose by Trichoderma reesei are the assumption of two forms of cellulose (crystalline and amorphous), two sugars (cellobiose and D-glucose), and two enzymes (cellulase and j3-D-glucosidase). An inducer-repressor-messenger RNA mechanism is used to predict enzyme formation, and pH effects are included. The model consists of 12 ordinary differential equations for 12 state variables and contains 38 parameters. The parameters were estimated from four sets of experimental data by optimization. The results appear satisfactory, and the computer programs permit simulation of a variety of system changes. 

The principal features of a mathematical model described for the enzymatic hydrolysis and fermentation of cellulose by Trichoderma reesei are the assumption of two forms of cellulose (crystalline and amorphous), two sugars... 

Carboxylic lonophores and Efficiency of Feed Conversion by Livestock. A strong note of relevance to studies of the chemical and pharmacological properties of carboxylic lonophores derives from the large scale use of monensin as a livestock feed additive. The rationale is that carboxylic lonophores control endemic coccidiosis in the poultry gut (30) and promote a more favorable fermentation of cellulose in the bovine rumen (31). In either case, the net result is the economically important Increased efficiency of conversion of feed into meat. 

Weimer, RJ. and Zeikus, J.G. (1977) Fermentation of cellulose and cel-lobiose by Clostridium thermocellum in the absence of Methanobacterium thermoautotrophicum. Appl Environ. Microbiol, 33 (2), 289-297. 

Figure 6 Biocatalytic conversion and concomitant fermentation of cellulose to 1, 3-Propanediol...

The process of fermentation of cellulose materials differs from that of starch or sugar materials (1) the hydrolysate of the lignocellulosic material is toxic to the fermentative microorganisms (2) there is more xylose in the hydrolysate. So, the utilization of pentose is one of the most important decisive factors for the process economics (Zaldivar et al. 2001). 

The methods for fermentation of cellulose ethanol include direct and indirect fermentation, mixed strain fermentation, SSF, simultaneous saccharification and cofermentation (SSCF), nonisothermal SSF, and immobilized cell fermentation. 

The direct fermentation method is based on the direct fermentation of cellulose by cellulolytic bacteria, without acidic or alkali pretreatment. It has the features of simple equipment and low cost, but with low ethanol yield and production of organic acid and other by-products. The problems can be solved partly by mixed strain fermentation. 

Ghosh P, Pamment NB, Martin WRB. (1982). Simultaneous saccharification and fermentation of cellulose—effect of beta-d-glucosidase activity and ethanol inhibition of ceUulases. Enzyme Microb Technol, 4(6), 425 30. 

Szczodrak J, Targotiski Z. (1988). Selection of theimotolerant yeast strains for simultaneous saccharification and fermentation of cellulose. Biotechnol Bioeng, 31, 300-303. 

Wen F, Sun J, Zhao H. (2010). Yeast surface display of trifunctional minicellulosomes for simultaneous saccharification and fermentation of cellulose to ethanol. Appl Environ Microbiol, 76, 1251-1260. 

Yoon HH. (1997). Simultaneous saccharification and fermentation of cellulose for lactic acid production. Biotechnol Bioprocess Eng, 2, 101-104. 

---