Pathogens are known to survive in compost and to regrow under the influence of certain factors, such as moisture content, temperature and nutrient availability. Dead biomass, by providing available nutrients, is a factor that may affect pathogen regrowth. However, the indigenous microorganisms, including pathogens, that grown on the dead biomass of compost have not yet been identified. Here, the regrowth potential of the pathogenic indicator bacterium Escherichia coli in the presence of dead bacterial biomass was determined, and the biomass metabolizers that grew competitively with E. coli were identified by high-sensitivity stable isotope probing of rRNA. Culture-dependent analysis indicated that the addition of dead bacterial biomass did not stimulate E. coli growth. High-throughput analysis of density-resolved 16S rRNA molecules from compost samples amended with carbon-13-labeled dead bacterial biomass revealed dead bacterial-assimilating bacteria, including Sphingobium sp., myxobacterial lineages and Bacillales. These bacteria are potentially competitive with pathogens due to their preferential assimilation of dead biomass in compost.