STUDIES ON THE PENTOSE METABOLISM BY MICROORGANISMS

1. A NEW TYPE-LACTIC ACID FERMENTATION OF PENTOSES BY LACTIC ACID BACTERIA

Abstract

1) Pentose fermentation by various lactic acid bacteria can be classified into the following two types : a) Formula (I) which proceeds according to the Fred-Peterson-Anderson system, and b) formula (III) which supposedly involves a new pathway of pentose metabolism. Almost all of the examined organisms metabolized various pentoses according to either formula (I) or (III) exclusively. But, some exceptional strains fermented different pentoses by different schemes. For example, Leuconostoc mesenteroides B07 fermented various pentoses only according to formula (I) and L. thermophilus T₁ according to formula (III) exclusively. Whereas, L. thermophilus II was able to ferment L-arabinose by formula (I) and D-xylose by formula (III).
2) From comparative study of pentose fermentation in the presence and absence of carbonate and an isotopic experiment for incorporation of carbonate into lactate, it was concluded that carbonate fixation reaction is not involved in lactate formation from pentoses.
3) Anaerobically, the cells of S. faecalis grown in a L-arabinose medium produced lactic acid from L-arabinose in a yield of 95% by weight of consumed sugar, and likewise those of L. thermophilus T₁ grown in D-xylose medium converted 93% of consumed D-xylose to lactic acid. In both cases no formate and CO₂ were formed. As a consequence of these experiments, we proposed a new formula (II) as an alternative scheme of (III).
4) From the analysis of yields of lactate from glucose, pentose and sedoheptulose, no noticeable difference in yield among these fermentations was observed. Consequently, we have concluded that so-called pentose phosphate pathway may have no inconsistency for accounting for the pentose metabolizing system of S. faecalis. This hypothesis, however, can not be applied for such a strain like L. thermophilus T₁ which unable to ferment sedoheptulose.