Formation of 4-keto-D-aldopentoses and 4-pentulosonates with acetic acid bacteria

ADACHI, O.; HOURS, R.A.; AKAKABE, Y.; YAKUSHI, T; MATSUSHITA, K.

Sapporo

Congreso; XIII International Congress of Bacteriology and Applied Microbiology (IUMS 2011); 2011

International Union of Microbiological Societies, IUMS

In contrast with the industrial significance of 2-keto-L-gulonate for L-ascorbate formation from 2,5-diketo-D-gluconate (25DKA), sporadic studies of 25DKA degradation were done but not followed up extensively. Our newly isolated strains of Gluconacetobacter liquefaciens from the Argentine water kefir accumulated 25DKA strongly in the culture medium. 25DKA was in turn converted to an unidentified compound when cultivation was prolonged to the late stationary phase. The isolated compound was identified as 4-keto-D-arabonate (4KAB). The occurrence of 4KAB was assumed by Ameyama and Kondo about 50 years ago in their study on the carbohydrate metabolism of acetic acid bacteria (Bull. Agr. Chem. Soc. Jpn., 22, 271-272, 380-386, 1958). Alternatively, 4KAB was formed directly from D-arabonate by another membrane-bound enzyme, D-aldopentonate 4-dehydrogenase. There has been no report or information about 4KAB formation in oxidative fermentation as well as in other fields of science. This is the first report confirming microbial production of 4KAB. Encouraged with the findings above, formation of novel 4-keto-D-pentoses and their oxidized compounds was examined extensively with acetic acid bacteria. 4-Keto-D-pentoses and their oxidized D-4-pentulosonates were confirmed with Gluconacetobacter and Gluconobacter strains. 25DKA was decarboxylated to 4-keto-D-arabinose and further oxidized to 4KAB. More directly, aldopentoses of D-erythro-configuration were oxidized to form novel sugars. D-Arabinose was oxidized to 4-keto-D-arabinose and further oxidized to 4KAB. Likewise, 4-keto-D-ribose and 4-keto-D-ribonate were formed from D-ribose. This paper may be the first one, because there has been no report on formation of 4-keto-D-aldopentoses and D-4-pentulosonates. Already known ketopentoses, such as D-ribulose or D-xylulose, have a keto group at C-2-position. Growing cells, resting cells, and isolated cytoplasmic membranes were able to catalyze formation of the novel 4-keto-D-aldopentoses and D-4-pentulosonates. In this study, new membrane-bound enzymes such as 2,5-diketo-D-gluconate decarboxylase, aldopentose 4-dehydrogenase, 4-keto-D-aldopentose 1-dehydrogenase, and D-aldopentonate 4-dehydrogenase were found in acetic acid bacteria.