THE HUNT FOR THE G-BACTERIA IN ACTIVATED-SLUDGE BIOMASS

Routine microscopic examination of biomass samples from many activated sludge plants around the world reveals the presence of large numbers of both Gram positive and Gram negative coccoid cells often arranged i n distinctive tetrads or sheets of tetrads. Three Gram negative tetrad cocci were successfully isolated into pure culture using micromanipul ation from samples of biomass from plants in Tamworth, N.S.W., Austral ia, Verona, Italy and Macau. After extensive phenotypic characterisati on and 16S rDNA sequence analysis, all isolates showed high overall si milarity to each other, but were phylogenetically quite different to a ny previously sequenced bacterium. They have therefore been classified as three species of a new genus, the genus Amaricoccus in the a Prote obacteria in the domain Bacteria. None could accumulate polyphosphate granules, and production of intracellular poly-beta-hydroxybutyrate (P HB) granules depended on the carbon source used in the medium. A simil ar characterisation of the original isolate of the G-bacteria describe d by Cech and Hartman showed this organism also belonged to the same g enus as the other three isolates, but as a distinct species. The pract ical implications of these observations are discussed. (C) 1998 IAWQ. Published by Elsevier Science Ltd.