Acetic acid from microorganisms

Whole-cell based biocatalysis utilizes an entire microorganism for the production of the desired product. One of the oldest examples for industrial applications of whole-cell biocatalysis is the production of acetic acid from ethanol with an immobilized Acetobacter strain, which was developed nearly 200 yr ago. The key advantage of whole-cell biocatalysis is the ability to use cheap and abundant raw materials and catalyze multistep reactions. Recent advances in metabolic engineering have brought a renaissance to whole-cell biocatalysis. In the following sections, two novel industrial processes that utilize whole-cell biocatalysis are discussed with emphasis on the important role played by metabolic engineering. 

Many anaerobic microorganisms can use CO or CO2 as a sole source of carbon and CO and/or H2 for the generation of energy [1]. Thus, acetogens generate acetyl coenzyme A, an activated acetic acid that serves as a universal precursor for the generation of biomass (see below), and acetic acid from... 

Llangwell A process for making acetic acid by fermenting the cellulose in com cobs. Xylose is a co-product. The microorganism was isolated from the gut of the goat. Piloted on a large scale by the Commercial Solvents Company, Terre Haute, IN, from 1928 to 1930. 

The waste products of a home include paper, containers, tin cans, aluminum cans, and food scraps, as well as sewage. The waste products of industry and commerce include paper, wood, and metal scraps, as well as agricultural waste products. Biodegradable wastes, such as paper fines and industrial biosludge, into mixed alcohol fuels (e g., isopropanol, isobutanol, isopentanol). The wastes are first treated with lime to enhance reactivity. Then, they are converted to volatile fatly acids (VFAs) such as acetic acid, propionic acid, and butyric acid, using a mixed culture of microorganisms derived from cattle rumen or anaerobic waste treatment facihties. 

These short-chain fatty acids are acetic, butyric, lactic and propionic acids, also known as volatile fatty acids, VFA. They are produced from fermentation of carbohydrate by microorganisms in the colon and oxidised by colonocytes or hepatocytes (see above and Chapter 4). Butyric acid is activated to produce butyryl-CoA, which is then degraded to acetyl-CoA by P-oxidation acetic acid is converted to acetyl-CoA for complete oxidation. Propionic acid is activated to form propionyl-CoA, which is then converted to succinate (Chapter 8). The fate of the latter is either oxidation or, conversion to glucose, via glu-coneogenesis in the liver. 

The largest number of indole derivatives which have been structurally characterized are the indole alkaloids these mainly arise from plant sources. Not unexpectedly, in view of tryptophan s status as one of the essential amino acids, there are also diverse derivatives found in microorganisms. Indole-3-acetic acid plays a major role in plant metabolism, being a growth regulator (74MI30600). 

There is a substantial literature on the transformation of simple phenolic acids by microorganisms.2,7,11,16,18,20,22,25,29,44 For example, ferulic acid is transformed by fungi to either caffeic acid or vanillic acid, and these are transformed to protocatechuic acid. Next the ring structure of protocatechuic acid is broken to produce 3-carboxy-c/s,c/s-muconic acid, which is then converted to (3-oxoadipic acid (Fig. 3.1), which in turn is broken down to acetic acid and succinic acid, and these ultimately are broken down to C02 and water.11,18,29 Flowever, distribution of residual 14C-activity after growth of Hendersonula toruloidea, a fungus, in the presence of specifically 14C-labeled ferulic acid ranged from 32 to 45% in C02, 34 to 45% in cells, 9 to 20% in humic acid and 4 to 10% in fulvic acid.29 Thus, a considerable portion of the ferulic-acid carbon was bound/fixed over a 12-week period, and the initial ferulic acid transformation products (e.g., caffeic acid, vanillic acid and protocatechuic acid) were clearly of a transitory nature. Similar observations have also been made for other simple phenolic acids 22,23 however, the proportions metabolized to C02 and fixed into cells and the soil... 

Various microorganisms under certain conditions are able to excrete intermediate products (organic acids) from or closely related to the tricarboxylic acid cycle (Fig. 3, Table 4). For example, Clostridium produces acetic acid and butyric acid, Lactobacillus and Streptococcus species produce lactic acid, Acetobacter species acetic, gluconic, and ketogluconic acids, and Pseudomonas species 2-ketogluconic and a-ketoglutaric acids. 

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