Strategies for the isolation of cellulolytic fungi for composting of wheat straw

It was shown that inoculation of straw with cellulolytic fungi offers potential for manipulating and improving the composting of cellulose waste, where the C:N ratio is not optimal for composting. In this paper we report on a screening strategy used to isolate novel cellulolytic fungi from field samples. The screen comprised of two phases. In phase I, 300 cellulolytic fungi were isolated to pure culture from field samples collected from Hawaii, China and the UK. Isolates were selected on the basis of high cellulolytic activities and growth rates on cellulose agar. A total of 137 lead isolates progressed to an unreplicated phase II screen to rapidly identify strains that improved quality of the resulting compost over and above that of the uninoculated control. Compost quality was assessed by measuring C:N ratio, water holding capacity, water content and potential and polysaccharide content of the resulting compost. Effect on the aggregate stability of soil and the growth of wheat seedlings was assessed when compost was added to a sandy loam soil. Performance of each isolate was quantified by allocating a utility score for each compost analysed. Utility scores were based on the sum of the logged ranked score in each assay. The 10 highest scoring isolates were subsequently processed through a replicated phase II screen and the best performing isolates identified by calculating utility scores as before. Significantly lower C:N ratios, higher water-holding capacities and improved aggregate stabilities were obtained with some inoculated treatments compared to the uninoculated control, whilst the results obtained for polysaccharide content and plant growth showed no significant differences. Isolate 304, isolated from decomposing vegetation obtained from Egham, Surrey, UK, and identifed as a Trichurus sp., appeared the most effective inoculant, significantly decreasing the C:N ratio by 36% and increasing the aggregate stability of soil by 54% compared to the uninoculated control. As a result of adopting this screening strategy, it has been possible to identify cellulolytic fungi that can, under non-sterile (laboratory) conditions, significantly improve the quality of compost. This screening approach therefore offers real possibilities for selecting microbial inoculants in low-tech agricultural practices.