NEW FOAM-FORMING NOCARDIOFORMS FOUND IN ACTIVATED-SLUDGE

In a numerical taxonomic survey;of foam-forming actinomycetes, represe ntatives of four groups were selected for further taxonomic study beca use they either did not cluster with known reference strains of nocard ioforms or their relationship to them was uncertain. Phylogenetic stud ies, using 16S rDNA sequencing, showed that one group probably represe nted a previously described species, Rhodococcus erythropolis, but two possibly represented new species of Gordona and Rhodococcus. The four th group represented an independent line of descent, possibly a new ge nus. These, together with strains of foam-formers Gordona amarae and S kermania piniformis, were evaluated for their growth on hydrophobic su bstrates likely to be found in activated sludge plants. All grew well on vegetable oils (olive, safflower and coconut) and on mixtures of hy drocarbons like paraffin oil, but at varying rates. However, growth on kerosene and hexadecane was less consistent. One feature of growth on the hydrophobic substrates was the attachment of most cells to the hy drophobic substrate rather than growth in the aqueous phase. This sugg ests a possible method for competing for nutrients with faster-growing (but not hydrophobic) organisms in activated sludge. (C) 1998 IAWQ. P ublished by Elsevier Science Ltd.