RESPIRATORY CHARACTERISTICS OF TWO OLIGOTROPHIC BACTERIA: AGROMONAS OLIGOTROPHICA JCM 1494 AND AEROMONAS HYDROPHILA 315

We have studied the respiratory characteristics in the growing and the We have studied the respiratory characteristics in the growing and the rWe have studied the respiratory characteristics in the growing and the resting cells in the soil oligotrophic bacterium Agromonas oligotrophica JCM 1494 and the aquatic oligotroph Aeromonas hydrophila 315. The growth of A. oligotrophica on 1% trypticase peptone plus 0.1% yeast extract medium (TY) was biphasic. The molar growth yield on oxygen consumed (YO2, g of cell dry weight/mol O2) in the first phase increased 1.7-fold in the second phase. In the growth of A. hydrophila, YO2 nearly doubled with shifting from TY to 10-fold diluted TY (TY/10). These two cases of significant YO2 increase may indicate the operation of an efficient energetic regulation of the respiratory system apparently in response to changing cell density and medium nutrient levels. The studies of in vitro respiration with resting cells on a single substrate (low organic acids) revealed rather higher Km values for A. oligotrophica and A. hydrophila than for Escherichia coli K12 as a reference strain. But the apparent Km of A. oligotrophica for TY as a complex respiratory substrate was definitely lower than that with E. coli K12. This suggests a unique simultaneous uptake for multiple substrates. In A. oligotrophica cells, a-, b-, and c-type cytochromes and a CO-binding b-type cytochrome (assumed to be cytochrome o) were identified. But the a type was not detected in A. hydrophila cells. These cytochrome patterns in the two strains, described in oligotrophs for the first time, were not detestably changed by medium dilution, and there appears to be a sequence leading to cytochrome o in the aerobic electron transfer in both strains.