Ecological Studies on the Microbial Upgrading of Straw

Abstract

The work reported here was part of a larger research programme designed to obtain a method of increasing the digestibility of waste straw using a selected microorganism. The experiments which are the subject of the thesis were carried out to investigate the ecology of the environmental niche thus created and to examine the possibilities of controlling this environment to allow a selected fungus to become the dominant coloniser. Coprinus cinereus (Schaeff ex Fr.) S F Gray sensu Konr., an edible, endemic coloniser of straw was the selected microorganism and it was found to be widespread on material from the bale and the field and also in soils which had been under cereals, A technique was developed to isolate this fungus using aqueous ammonia and this being so, it was suggested that this species may warrant being placed in the 'chemoecological' grouping of ‘ammonia fungi'. It was shown that the presence of free ammonia can produce a unique selective pressure in favour of C cinereus which was not observed using other nitrogen sources at an elevated pH. The optimum levels of ammonia and temperature required to bring this about were investigated, together with the nature of this selective pressure. The qualitative and quantitative effects of ammonia on the microbial populations of straw over a two week period were studied and the implications of the results for the proposed upgrading technique were considered. The utilisation of lignin and cellulose by a number of isolates of C cinereus were compared under conditions of varying pH and temperature and capabilities were found to differ with the isolates. The feasibility of the straw upgrading process was then discussed taking into consideration the results and conclusions obtained from this research programme.