MICROBIAL COMMUNITY DYNAMICS DURING COMPOSTING OF STRAW MATERIAL STUDIED USING PHOSPHOLIPID FATTY-ACID ANALYSIS

Microbial biomass and community structure were investigated in two com posts using the phospholipid fatty acid technique. The composts consis ted of shredded straw of Miscanthus with the addition of pig slurry to give an initial C:N ratio of about 25. Samples were taken following c hanges in the compost temperature (at 5 degrees C intervals) during th e first month of composting and additionally after 2 and 3 months. The total microbial biomass, measured as total amount of phospholipid fat ty acid, peaked after 1 day with about six times the initial values. T he temperature also peaked after 1 day, being above 60 degrees C, and then slowly declined to around 25 degrees C over 3 months. Microbial b iomass was approximately halved during this time. When the total amoun t of phospholipid fatty acid was separated into indicator phospholipid fatty acids for different groups of microorganisms, these groups show ed different patterns during the composting process. Gram-positive bac teria increased rapidly with increasing temperature and decreased with decreasing temperature. Gram-negative bacteria and fungi increased in itially up to a temperature around 50 degrees C, but decreased during the extreme heating phase. When the temperature declined to about 50 d egrees C, the amounts of phospholipid fatty acids indicative of these two groups increased again. The phospholipid fatty acid indicative of actinomycetes, 10Me18:0, was at a low level during the whole experimen t, but increased slightly during the last month of composting. The dev elopment of the microbial community in the two composting systems was similar during the initial thermophilic phase of the composting proces s, but the communities after 3 months differed. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V . All rights reserved.