Complete genome sequence and characterization of virulence genes in Lancefield group C Streptococcus dysgalactiae isolated from farmed amberjack (Seriola dumerili)

Abstract

Lancefield group C Streptococcus dysgalactiae causes infections in farmed fish. Here, the genome of S. dysgalactiae strain kdys0611, isolated from farmed amberjack (Seriola dumerili) was sequenced. The complete genome sequence of kdys0611 consists of a single chromosome and five plasmids. The chromosome is 2,142,780 bp long and has a GC content of 40%. It possesses 2061 coding sequences and 67 tRNA and 6 rRNA operons. One clustered regularly interspaced short palindromic repeat, 125 insertion sequences, and four predicted prophage elements were identified. Phylogenetic analysis based on 126 core genes suggested that the kdys0611 strain is more closely related to S. dysgalactiae subsp. dysgalactiae than to S. dysgalactiae subsp. equisimilis. The genome of kdys0611 harbors 87 genes with sequence similarity to putative virulence-associated genes identified in other bacteria, of which 57 exhibit amino acid identity (>52%) to genes of the S. dysgalactiae subsp. equisimilis GGS124 human clinical isolate. Four putative virulence genes, emm5 (FGCSD_0256), spg_2 (FGCSD_1961), skc (FGCSD_1012), and cna (FGCSD_0159), in kdys0611 did not show significant homology with any deposited S. dysgalactiae genes. The chromosomal sequence of kdys0611 has been deposited in GenBank under Accession No. AP018726. This is the first report of the complete genome sequence of S. dysgalactiae isolated from fish.