Mechanisms of in vivo transformation between K+ and K- phenotypes in Streptococcus iniae

2014 Fiscal Year Final Research Report

• Project/Area Number: 24580271
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: General fisheries
• Research Institution: Nagasaki University
• Principal Investigator: KANAI Kinya 長崎大学, 水産・環境科学総合研究科(水産), 教授 (40145222)
• Project Period (FY): 2012-04-01 – 2015-03-31
• Keywords: Streptococcus iniae / 莢膜 / 型変異 / 莢膜合成遺伝子 / IS981 / 魚体内

Outline of Final Research Achievements

The fish pathogen Streptococcus iniae is classified into K+ (capsulated) and K- (non-capsulated) phenotypes. To clarify the structure of genetic loci for capsular polysaccharide (cps) biosynthesis of the phenotypes, PCR amplification of their cps gene clusters was conducted. As a result, 29 out of 40 strains of K- phenotype produced the amplicons whose length was 1~2 kbp longer than those of K+ phenotype and were found to harbor IS981 or other insertion sequence in or between their cps genes, suggesting this structure caused the inhibition of cps biosynthesis. When Japanese flounder Paralichthys olivaceus were challenged with S. iniae strains of K+ or K- phenotype, the bacteria that switched their phenotype were detected after 1 to 2 weeks in the challenged fish, indicating phenotypic switch is easily occurred in vivo.

Free Research Field

魚病学