Composition of Microbial Communities in Composts A Tool to Assess Process Development and Quality of the Final Product

Steger, K. 2006. Composition of Microbial Communities in Composts A Tool to Assess Process Development and Quality of the Final Product. Doctoral dissertation. ISSN 1652-6880, ISBN 91-576-7080-3 The potential of microbial community fingerprinting methods to provide information about compost maturity in composting facilities was investigated. Studies in a pilot-scale reactor equipped with independent control of oxygen content and temperature showed that low oxygen contents or low temperature had no dramatic effects on overall development of microbial community structure, determined with the PLFA (phospholipid fatty acid) method, although the process was generally delayed. Analyses of PLFAs typical for Actinobacteria, however, revealed that these bacteria were favoured when the maximum temperature was 40oC. Actinobacteria populations constituted almost 50% of the microbial community during later stages of the reactor experiments, when only relatively complex, recalcitrant compounds remained, suggesting that some Actinobacteria may be suitable as indicator organisms for mature compost. Studies in a full-scale composting system showed that Actinobacteria constituted a relatively low, but constant proportion at roughly 10% of the microbial community. Analyses of Actinobacteria species composition using PCRDGGE (denaturing gradient gel electrophoresis) targeting 16S rRNA genes demonstrated that members of Corynebacterium were present at early stages and that thermo-tolerant Actinobacteria, e.g. Thermobifida, Streptosporangium, Saccharomonospora and Saccharopolyspora, were found throughout the long thermophilic phase. During the stage of decreasing temperature, the community included both thermo-tolerant and mesophilic Actinobacteria. The ester-linked fatty acid (EL) method for describing microbial community structure was shown to provide information related to aspects of maturity, and is potentially a relatively simple and fast method of assessing compost maturity. Combination of signature lipid and nucleic acid-based analyses greatly expanded the specificity and scope for assessing microbial community composition in composts.