Effects of oxygen tension on growth,respiration, and types of bacteria isolated from soil suspensions

Fifty-seven bacteria were isolated from soil suspensions incubated under pO₂ of 1.5 or 159 mm Hg and their growth and generic characteristics were elucidated.The isolates were cultured under both high (159 mm Hg) and low (3 mm Hg) pO₂. On the basis of their growth responses to the different pO₂, the isolates were classified into two types; (A-type) the lag time, specific growth rate, and/or maximum growth depended on pO₂, and (B-type) these three growth characteristics did not depend on pO₂. B-types were found only among isolates from soil suspensions incubated under the low pO₂. The respiration of some B-type isolates was inhibited by higher pO₂. No A-type isolates were inhibited by high pO₂.The isolates were classified into eight generic groups: Under 159 mm Hg O₂, Groups I(Bacillus spp) and IV(Pseudomonas spp etc.) dominated the others; under 1.5 mm Hg O₂, Group I, III(coryneform bacteria) and V(Alcaligenes spp etc.) dominated. Microaerophilic isolates (isolated only from the soil suspension incubated under 1.5 mm Hg O₂) were classified into Group V. Isolates belonging to the B-type were classified into the coryneform and Group V bacteria.