THE CHARACTERIZATION AND DESCRIPTION OF REPRESENTATIVES OF G-BACTERIAFROM ACTIVATED-SLUDGE PLANTS

The name Tetracoccus cechii is proposed for two strains of the tetrad arranged cocci, previously known as 'G' bacteria, which were isolated from laboratory scale activated sludge plants in the Czech Republic an d in Italy. They were morphologically, phenotypically and phylogenetic ally characterized and found to comprise a novel lineage in the alpha- 3 group of the proteobacterial phylum in the domain Bacteria. The stra ins are Gram-negative and produce intracellular inclusions of poly-bet a-hydroxybutyrate. Although commonly seen in activated sludge mixed li quor as cocci 1-2 mu m in diameter, arranged in tetrads, in pure cultu re they can also grow in amorphous aggregations and the cells are gene rally more variable in their size and shape with coccobacilli as well as cocci being present. They are not able to grow phototrophically, no r can they reduce nitrate beyond nitrite nor grow anaerobically. The c losest phylogenetic neighbours of T. cechii are Rhodobacter sphaeroide s and R. capsulatus which are 93% similar by 16S rDNA comparison. Tetr acoccus cechii is oxidase- and catalase-positive, non-motile and has a n optimal growth temperature between 25 degrees and 35 degrees C. The 16S rRNA of T. cechii has a 21 nucleotide deletion in the V9 region (E scherichia coli positions 1258-1278) and this feature is a unique mole cular synapomorphy in the alpha-3 group.