Bacterial diversity in thermophilic aerobic sewage sludge

Abstract

Over a 2-year period thermophilic microorganisms were isolated from an aerobic thermophilic, continuously operated sewage sludge treatment process (Altenrhein SG, CH). A representative set of isolates was characterized for microbiological and biochemical properties and compared with thermophilic reference strains. At least 95% of the isolates were characterized as extremely thermophilic Bacilli with a maximal growth temperature>70°C. The other 5% were not finally designated as Bacilli only because sporulation could never be demonstrated. The thermophilic microflora did not produce antimicrobial substances in detectable amounts. All isolates grew rapidly (μ max ranging from 0.7 to 2.2 h −1 ) on sucrose medium in shake flasks with generally low yields (Y ranging from 0.2 to 0.3 g.g −1 ). More than 90% of the isolates could degrade casein and starch and grew on gummi arabicum as sole carbon source. Amylases and proteases were formed in cheap, complex compounds containing media but not in significant amounts in growth media containing simple carbon sources Isolement de microorganismes thermophiles dans un installation de digestion anaerobie thermophile de boues residuaires. Caracterisation des proprietes microbiologiques et biochimiques d'une serie representative des microorganismes isoles et comparaison avec des souches thermophiles de reference