Comparison of two cellulomas strains and their interaction with Azospirillum brasilense in degradation of wheat straw and associated nitrogen fixation

Abstract

A mutant strain of Cellulomonas sp. CS1-17 was compared with Cellulomonas gelida 2480 as the cellulolytic component of a mixed culture whch was responsible for the breakdown of wheat straw to support asymbiotic nitrogen fixation by Azospirillum brasilense Sp7 (ATCC 29145). Cellulomonas sp. strain SC1-17 was more efficient than was C. gelida in cellulose breadown at lower oxygen concentrations and, in mixed culture with A. brasilense, it supported higher nitrogenase activity (C2H2 reduction) and nitrogen fixation with straw as the carbon source. Based on gravimetric determinations of straw breakdown and total N determinations, the efficiency of nitrogen fixation was 72 and 63 mg of N per g of straw utilized for the mixtures containing Cellulomonas sp. and C. gelida, respectively. Both Cellulomonas spp. and Azospirillum spp. exhibited a wide range of pH tolerance. When introduced into sterilized soil, the Cellulomonas sp.-Azospirillum brasilense association was more effective in nitrogen fixation at a pH of 7.0 than at the native soil pH (5.6). This was also true of the indigenous diazotrophic microflora of this soil. The potential implications of this work to the field situation are discussed.