S U M M A R YMore than IOO Gram-negative, strictly aerobic, methane-utilizing bacteria were isolated. All used only methane and methanol of the substrates tested for growth. The organisms were classified into five groups on the basis of morphology, fine structure, and type of resting stage formed (exospores and different types of cysts) and into subgroups on other properties. Methods of enrichment, isolation and culture are described.

SUMMARYSome lactic acid bacteria formed detectable H202 and some did not, regardless of their preference or requirement for aerobic or anaerobic conditions. Whether or not H202 was formed depended in some instances on the substrate used as energy source. Two H202-splitting activities were encountered though never in the same organism. One, named pseudocatalase activity, was insensitive to 0.01 M-azide or 0.01 M-cyanide and appeared to be the action of an acid-sensitive non-haem-containing enzyme detectable in some leuconostocs and pediococci when grown in media containing a low concentration of glucose. The second, named catalase activity, was detected in a number of lactobacilli, leuconostocs, streptococci and pediococci grown on media containing haematin or heated blood; presumably these organisms are able to synthesize the apoenzyme but not the prosthetic group of catalase. This activity was inhibited by 0.01 M-azide or 0.01 M-cyanide; it was not acid-sensitive. There was little correlation between H202-splitting activity and the preference or requirement of the organisms for aerobic or anaerobic conditions, or between H202-splitting activity and H202 formation. Of a few organisms examined, some appeared capable of forming cytochromes when grown in media containing heated blood. One showed traces of a cytochrome whether grown in the presence or absence of heated blood.

Three varieties of resting stage, an exospore and two types of cyst, were formed by methane-utilizing bacteria. Exospores were budded off by two types of organism, both of which underwent a change in morphology prior to spore formation. Exospores possessed some properties in common with endospores : staining properties, some structural features, mode of germination, desiccation and heat resistance, but contained no detectable dipicolinic acid. Some organisms formed desiccation-resistant cysts similar in morphology, staining properties and fine structure to cysts formed by Azotobacter species. Other strains formed non-desiccation-resistant bodies considered to be similar to immature azotobacter-type cysts. A desiccation-resistant cyst formed by one strain differed in structure and appearance from Azotobactertype cysts and was referred to as a 'lipid' cyst.