THE TRICARBOXYLIC ACID CYCLE IN PSEUDOMONAS NIGRIFACIENS

All the enzymes of the tricarboxylic acid cycle, with the exception of oxalosuccinic acid decarboxylase, were detected in sonic extracts of the moderately halophilic bacterium Pseudomonas nigrifaciens. Several of the component enzymes of the cycle exhibited a slight salt requirement; activity of the others was reduced in the presence of added salt. These results are in contrast to the optimal salt requirement of the organism for growth (1.5 to 3.0% NaCl).Apart from the effects of salt on their activities, the component enzymes of the tricarboxylic acid cycle in P. nigrifaciens appear to be similar to those described from other sources.

THE EFFECT OF SALTS ON THE GROWTH OF MICROCOCCUS HALODENITRIFICANS N. SP

A halophilic coccus, Micrococcus halodenitrificans n. sp., isolated from meat curing brines is described. This organism grows optimally in media containing between 4.4 and 8.8% sodium chloride as determined by viable counts and manometric methods. The viable count decreases in media containing 2.2% or less sodium chloride. As salt concentrations increase above 8.8%, the length of the lag phase increases and the rate of growth decreases. The organism exhibits a specific sodium chloride requirement for growth. However, it continues to respire in the presence of sodium bromide.

THE EFFECTS OF SALTS ON THE NITRITASE AND LACTIC ACID DEHYDROGENASE ACTIVITY OFMICROCOCCUS HALODENITRIFICANS

With Micrococcus halodenitrificans, maximum production of nitritase occurs just after nitrite has been reduced completely to nitrogen. Maximum denitrifying activity takes place at pH 7.6 in the presence of 0.38 to 0.75 molar sodium chloride or sodium bromide. The activity is slightly less in the presence of lithium chloride but reaches a peak at 0.19 to 0.38 molar concentration. The reduction of nitrate to nitrite is inhibited by azide whereas reduction of nitrite to nitrogen is not, suggesting the possibility that at least two separate enzymes may be involved in these reactions. The lactic acid dehydrogenase of this organism shows maximum activity in the presence of 0.75 molar sodium chloride.