SUMMARY: Two hundred and ninety-six strains of mesophilic species of the genus were isolated from soil and examined for the characters described principally by Smith, Gordon & Clark (1946) as well as for some additional characters. Two hundred and forty-six belonged clearly to named species in the classification of Smith , thirty-two strains were clearly intermediate between two species and eight strains remained unallocated. In addition, eleven other strains appeared to represent a previously undescribed species (Proom & Knight, 1950).

Ability to grow under strictly anaerobic conditions, to give the Gibson & Abdel-Malek (1945) test and to produce typical (lecithinase-like) or ‘restricted’ reactions with egg-yolk emulsion were valuable diagnostic characters in this genus.

A survey was made of the nutritional requirements of some 200 strains which included many of the newly isolated ones and representative laboratory strains. Typical nutritional patterns characterizing the species were found, with an unexpected degree of uniformity with the groups of strains examined; the number of nutritionally aberrant strains in each species was very small.

The characteristic nutritional patterns were:

and grew with ammonia as nitrogen source and in the absence of added growth factors.

and grew in absence of added growth factors but required mixtures of amino-acids instead of ammonia only.

and both grew with ammonia + biotin, and grew with ammonia + biotin + aneurin.

required amino-acids + aneurin; and required amino-acids and usually both aneurin and biotin; some strains of

Some strains of required amino-acids + aneurin, others required biotin as well, and all of the strains of var. required amino-acids + aneurin + biotin.

The strains of were the most heterogeneous in their nutritional requirements, the components ammonium ion, amino-acids, aneurin, biotin and nicotinic acid being involved. All strains required amino-acids and aneurin; in addition, biotin or nicotinic acid and sometimes ammonium ion were required, depending on the particular strain.


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