Methanol‐Assimilation durch ein acidophiles Bacterium der Gattung Acetobacter

Generally, methylotrophic bacteria grow optimally in a pH range between 6 and 7.2. The assimilation of methanol can take place via several pathways. Acetobacter methanolicus preiers an acidic pH range for growth, the pH optimum is about 4, and it uses the FBP variant for methanol assimilation. The latter is interesting from a regulatory point of view because phosphofructokinase disappears during growth on glucose, which is assimilated via the hexosemonophosphate pathway. Since Entner‐Doudoroff enzymes and phosphoketolase are absent in A. `ethanolicus as well as in non‐methylotrophic Acetobacter and Gluconobacter species phosphofructokinase becomes a key enzyme of the assimilation of methanol. Although A. methanolicus uses the hexulosephosphate pathway the growth yield on methanol is smaller than with other “hexulosephosphate pathway bacteria” e. g. with obligate methanol assimilating bacteria. At first sight it may appear that the acidic optimum pH is responsible for the smaller growth yield and the discrepancy between the experimental and predicted values. The relationship between the dependence on and the protection from, high external proton concentration on the one hand and the causes of the low growth yield on the other are discussed. Accordingly, A. methanolicus and another heterotrophic acidophiles seem to be acidoresistant above all, their machinery guaranteeing the protection from the high proton concentration is responsible for the acidophily and the low growth efficiency is caused by a simple respiratory chain.