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Rubellimicrobium thermophilum gen. nov., sp. nov., a red-pigmented, moderately thermophilic bacterium isolated from coloured slime deposits in paper machines Six red-pigmented strains of the Alphaproteobacteria with optimal growth between 45 and 54 6C were previously isolated from coloured biofilms in two fine-paper machines and one pulp dryer. The strains were found to be resistant to 15 p.p.m. 2,2-dibromo-3-nitrilopropionamide, a common industrial biocide. 16S RNA gene sequence similarity of the isolates was 99?7-100 %. Ribotyping using the restriction enzymes PvuII and EcoRI showed that four of the isolates (C-lvk-R2A-1, C-lvk-R2A-2 T , C-R2A-52d and C-R2A-5d) belong to a single species. 16S rRNA gene-based phylogenetic analysis revealed that, together with Rhodobacter blasticus ATCC 33485 T , the isolates form a deep line of descent (94?7-94?9 % sequence similarity) within the family Rhodobacteraceae loosely affiliated with the Rhodobacter/Paracoccus clade. The isolates were strictly aerobic and oxidase-positive (catalase was weakly positive) and utilized a wide range of substrates including pentoses, hexoses, oligosaccharides and sugar alcohols. The predominant constituents in their cellular fatty acid profiles were C 19 : 0 cyclo v8c (39-44 %), C 18 : 0 (21-24 %) and C 16 : 0 (21-23 %). Fatty acids present in smaller amounts included C 18 : 1 v7c, C 10 : 0 3-OH, C 18 : 1 v7c 11-methyl, C 20 : 2 v6,9c and C 17 : 0 cyclo, amongst others. Polar lipids included diphosphatidylglycerol, phosphatidylcholine and an unidentified aminolipid, but not phosphatidylethanolamine. Carotenoid pigments were synthesized but bacteriochlorophyll a was not. The polyamine patterns consisted of the major compounds putrescine, spermidine and sym-homospermidine. The major respiratory lipoquinone was ubiquinone Q-10. The DNA G+C content was 69?4-70?2 mol%. On the basis of the phylogenetic and phenotypic evidence, the biofilm isolates were classified in a new genus, Rubellimicrobium gen. nov.; four of the isolates are assigned to the type species, Rubellimicrobium thermophilum gen. nov., sp. nov. Strain C-lvk-R2A-2 T (=CCUG 51817 T =DSM 16684 T =HAMBI 2421 T ) is the type strain of Rubellimicrobium thermophilum.Coloured microbial slime deposits (biofilms) in the wet end of paper machines are deleterious, particularly for white end products. Bacterial slime deposits on machine surfaces impair the runability of paper machines, because thick biofilms may break loose and cause web breaks or product defects such as holes and coloured spots (Blanco et al., The GenBank/EMBL/DDBJ accession numbers for the 16S rRNA gene sequences of strains A-col-R2A-4, C-lvk-R2A-2 T , C-R2A-52d, E-R2A-8a and C-lvk-R2A-1 are AJ505840 and AJ844281-AJ844284, respectively. Details of the polyamine and fatty acid profiles of the novel strains, characteristics that distinguish the strains from other similar species isolated from paper-machine biofilms, results of riboprint analysis and additional electron micrographs are available as supplementary material in IJSE...