Comparative polyphasic characterization of Weissella strains isolated from beaked whale and rainbow trout (Oncorhynchus mykiss): confirmation of Weissella ceti sp. nov. and description of the novel Weissella tructae sp. nov. isolated from farmed rainbow trout.

The weissellosis agent bacterium (WS08 ^T  = CBMAI 2730) was isolated from diseased rainbow trout (Oncorhynchus mykiss) in Brazil. The whole genome sequence of this strain was compared with the Mexican W-1 strain, also isolated from diseased rainbow trout, and with the Weissella ceti type strain CECT 7719  ^T (= 1119-1A-09  ^T  = CCUG 59653  ^T ), recovered from the beaked whale. Digital DNA-DNA hybridization pairwise analyses scored 98.7% between the Mexican W-1 and Brazilian WS08 ^T but just 24.4% for both fish isolates compared to the W. ceti type strain CECT 7719  ^T . The 16S rRNA gene sequence comparisons with isolates of W. ceti, available at GenBank, were conducted. All rainbow trout-pathogenic isolates grouped close (97% bootstrap confirmation), but when this group was compared to the W. ceti type strain CECT 7719  ^T the similarity varied from 78.9 to 79.1%. Phenotypic assays were also conducted, and the W. ceti type strain diverged from WS08 ^T and W-1 in the hydrolysis of aesculin, D-mannose, and potassium gluconate and in the hydrolysis of hippurate. Moreover, WS08 ^T and W-1 showed weak growth at 5 °C whereas no growth was observed for W. ceti CECT 7719  ^T . The major fatty acids (> 10% total fatty acids) presented by WS08 ^T and W-1 were summed feature 8 (C _18:1 ω7c/C _18:1 ω6c), summed feature 3 (C _16:1 ω6c/C _16:1 ω7c), and C _16:0 . The results of phylogenetic and phenotypic analyses clearly differentiated the W. ceti CECT 7719  ^T type strain from the assessed pathogenic strains obtained from rainbow trout. Therefore, Weissella strains isolated from rainbow trout, here represented by strain WS08 ^T (= CBMAI 2730), should be known as members of a novel species for which the name Weissella tructae sp. nov. is proposed.
(© 2022. The Author(s) under exclusive licence to Sociedade Brasileira de Microbiologia.)