Glucose acetic acid bacteria

Acetic acid bacteria (AAB) are known for their ability to oxidize different substrates containing ethanol into various types of vinegar (Trcek, 2005). Substrates used as energy sources include glucose, ethanol, lactate, or glycerol. Most of these compounds are not completely oxidized into COz and HzO and many metabolites, such as acetic acid, may be accumulated in the growth medium. AAB are commonly found in nature and acetic... 

Various strains of the AAB are ethanol-tolerant, and the majority of strains have been found to be able to grow at 5% v/v ethanol, and some even at 10%. Glucose tolerance has often been described in various AAB, and is frequently found in strains isolated from traditional balsamic vinegar. One of the inhibiting substances for acetic acid bacteria is high... 

Williamson s deep-liver medium Contains yeast extract, liver extract, casein hydrolysate, glucose and pot. monohydrogen phosphate. Encourages some acetic acid bacteria and Hafnia. 

Fig. 12.2 Classical two-step fermentation process. The D-glucose was hydrogenated to form D-sorbitol. The D-sorbitol was converted into L-sorbose by acetic acid bacteria. The L-sorbose was further oxidized with a mixture culture system with B. megaterium and K. vulgare to form 2-KLG. The 2-KLG was then esterified and lactonized to form vitamin C. The only difference between the classical two-step process and the Reichstein process is the replacement of low efficient protective oxidation with a fermentation process. The G. oxydans here was further identified to be K. vulgare...

The direct incomplete oxidation of sugars without phosphorylation leads to the formation of the corresponding ketones. The aldoses are oxidized into aldonic acids. The aldehydic function of this sugar is transformed into a carboxylic acid function. Glucose is oxidized into gluconic acid in this manner. The glucose oxidase catalyzes the reaction, which is coupled with the reduction of FAD. In acetic acid bacteria, electrons and protons are transported by the cytochrome chain to oxygen, which is the final acceptor. 

Fig. 7.2. Degradation of glucose by acetic acid bacteria (hexose monophosphate pathway)...

Asai (1935) divided the acetic acid bacteria into two genera one genus included the species that oxidized ethanol more intensely than o-glucose and had the... 

When the composition, especially the carbon sources, of the medium in the enrichment procedure is changed, the selective isolation of acetic acid bacteria can be expected. In fact, strains of Asaia bogorensis and Asaia siamensis were first isolated by the use of o-sorbitol or dulcitol instead of o-glucose (Yamada et al. 2000 Katsura et al. 2001). Several kinds of media employed for the enrichment procedure result in the effective isolation of acetic acid bacteria (Lisdiyanti et al. 2003b Suzuki et al. 2010). Instead of the pH 3.5 medium, the pH 4.5 medium containing 0.03 % acetic acid (v/v) can be used (Yamada et al. 1976). 

To select acetic acid bacteria from a number of the strains isolated, it is suitable to test the strains for growth on a pH 3.5 medium, which contains, for example, 1.0 % D-glucose (w/v), 0.5 % ethanol (99.8 %) (v/v), 0.3 % peptone (w/v), and 0.2 % yeast extract (w/v) the pH is adjusted to 3.5 with hydrochloric acid (Yamada et al. 1999). A pH 4.0 medium can be used for the growth test. If a certain strain is an acetic acid bacterium, appropriate growth can be seen. If the pH of the medium is adjusted to 4.5, bacteria other than acetic acid bacteria sometimes can grow. 

The biosynthetic pathway that produces bacterial cellulose from glucose and fructose is shown in Fig. 14.2. Glucose is phosphorylated by glucose hexokinase and not by the phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS). The resulting glucose-6-phosphate (G6P) is metabolized through the pentose pathway, because the activity of fructose-6-phosphate (F6P) kinase, which phos-phorylates F6P to fructose-1,6-diphosphate (FDP), is absent in acetic acid bacteria. 

Fig. 14.2 Cellulose biosynthetic pathway in cellulose-producing acetic acid bacteria. FIP firuc-tose-1-phosphate, F6P fructose-6-phosphate, FDP fructose diphosphate, PGA phosphogluconate GHK glucose hexokinase, FHK fructose hexokinase, IPFK fructose-1-phosphate kinase, FBP fructose blsphosphatase, PGI phosphoglucose isomerase, PGM phosphoglucomutase, UGP UDP-glucose pyrophosphorylase, G6PD glucose-6-phosphate dehydrogenase, PTS phosphotransferase system EMP Embden-Myerhoff pathway...

Various strains of acetic acid bacteria have been selected and studied for the vitamin C production processes since the 1960s. The strains used for the processes from three substrates ([la L-sorbose], [lb D-sorbitol], [2 D-glucose]) in the initial series of experiments are briefly summarized here. 

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