The Influence of Process Management and Microbial Community Structure on the Cultivation of a Biological Control Agent in Compost

摘要

Utilization of compost as a substrate and carrier for biological control agents offers opportunities for recycling of organic wastes and reduction in pesticide applications. Understanding the growth of biological control agents and their detection incompost is critical to the success of this application. Controlled inoculation studies were carried out in a model system using the biological control agent Trichoderma harzianum ATCC 52444 to determine the influence of degree of substrate decomposition,microbial competition and composting process management after inoculation on colonization. Compost was produced from grape pomace and rice straw in aerated, one-liter reactors and inoculations were performed after 3, 7 and 13 days of composting. Temperature after inoculation was maintained at 26 deg C, 30 deg C and 35 deg C. Compost samples were analyzed for microbial community structure, biomass and T. harzianum population by phospholipid fatty acid analysis and by denaturing gradient gel electrophoresis profiling of small subunit ribosomal RNA genes amplified from DNA extracted directly from compost samples. T. harzianum colonization was also measured by plating serial dilutions of compost samples on a selective medium. T. harzianum colonized all autoclaved compost samples when temperature was maintained at 26 deg C or 30 deg C. T. harzianum colonization of non-sterile compost samples was poor when both available substrate and microbial biomass levels were high. Poor colonization of non-sterile compost samples was also observed when the pH was high or when the temperature was maintained at 35 deg C. In conclusion, the potential for microbial competition, temperature and pH played significant roles in colonization of compost samples by T. harzianum. Finally, colonization of sterile compost was a poor indicator of the potential for colonization of nonsterile compost.