Non-symbiotic nitrogen-fixing bacteria in soil. I. Studies on Clostridium butyricum.

Abstract

The use of nitrogen-free selective media in the counting of Clostridium has been examined. The results indicate that, owing to lack of necessary growth factors, the counts given by this method are very much lower than the number of viable cells actually present. Toxicity of some agar media towards Clostridium has been demonstrated, and it is suggested that this factor may greatly reduce the numbers shown by plate counts. Exceptionally high values for efficiency of nitrogen fixation have been obtained with a strain of Clostridium butyricum. The role of Clostridium in the nitrogen economy of arable soil is discussed in the light of these findings.