Arcicella gelida sp. nov. and Arcicella lustrica sp. nov., isolated from streams in China and re-examining the taxonomic status of all the genera within the families Spirosomataceae and Cytophagaceae .

Three Gram-stain-negative, aerobic, rod-shaped, non-motile strains (DC2W ^T , DC25W ^T , and LKC2W) were isolated from streams in China. Comparisons based on the 16S rRNA gene sequences showed that these three strains share 16S rRNA gene sequence similarity values over 97.0 % with the species of genus Arcicella . There was confusion due to the fact that all species of genera Flectobacillus , Aquirufa , and Sandaracinomonas show 16S rRNA gene sequence similarity of over 90.0 % to the above three strains, but the genus Flectobacillus belongs to the family Spirosomataceae and the genera Aquirufa and Sandaracinomonas belong to the family Cytophagaceae . Observing the phylogenetic trees, strains DC2W ^T , DC25W ^T , and LKC2W cluster closely with the species of genus Arcicella , but some species within the families Spirosomataceae and Cytophagaceae are not monophyletic. The phylogenomic tree also showed a confused phylogenetic relationships among these non-monophyletic species. Combining the phylogenetic relationships and average nucleotide identity values, the current taxonomic status of all the genera within the families Spirosomataceae and Cytophagaceae were re-examined. The genera ' Chryseosolibacter ', ' Dawidia ', and Chryseotalea should belong to the new family Chryseotaleaceae fam. nov., the genera Arcicella , Flectobacillus , Pseudarcicella , Aquirufa , and Sandaracinomonas should belong to the new family Flectobacillaceae fam. nov., the genera Fluviimonas , Taeseokella , Arcticibacterium , Emticicia , Jiulongibacter , Marinilongibacter , Lacihabitans , and Leadbetterella should belong to the new family Leadbetterellaceae fam. nov., the genus Litoribacter should be reassigned to the family Cyclobacteriaceae , and the genera Arundinibacter and Tellurirhabdus should be reassigned to the family Spirosomataceae . Strains DC2W ^T and DC25W ^T are reported to represent two novel species of the genus Arcicella , for which the names Arcicella gelida sp. nov. (type strain DC2W ^T =GDMCC 1.3209 ^T =KCTC 92559 ^T ) and Arcicella lustrica sp. nov. (type strain DC25W ^T =GDMCC 1.3210 ^T =KCTC 92557 ^T ) are proposed.