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 degrees 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 omega 7c/C-18:1 omega 6c), summed feature 3 (C-16:1 omega 6c/C-16:1 omega 7c), 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.

Automated summary

In this study, a strain of Weissellosis agent bacterium was isolated from diseased rainbow trout in Brazil, and its whole genome sequence was compared with strains from diseased rainbow trout in Mexico and beaked whales. The results showed low similarity between the Mexican and Brazillian strains, as well as low similarity between fish isolates and the Weissella ceti type strain. Furthermore, phenotypic assays revealed differences in hydrolysis abilities and growth characteristics. Based on these findings, a novel species named Weissella tructae sp. nov. is proposed for the Weissella strains isolated from rainbow trout.