Distribution of Flavobacterium psychrophilum and its gyrA genotypes in a river

Flavobacterium psychrophilum can be divided into three genotypes, G-C type (ayu type), A-C type (multi-fish type), and A-T type (salmon-trout type), by two single-nucleotide polymorphisms in the DNA gyrase subunit A ( gyrA ) gene. We isolated F. psychrophilum from various samples collected from the lower basin of a river flowing into Lake Biwa, as a model for bacterial survey, in Shiga Prefecture in June, September, and December from 2010 to 2013 and investigated their gyrA genotypes. All three types of F. psychrophilum were isolated in June when ayu went up the river from the lake. In September, ayu gathered in the lower river basin for spawning and became high in density, almost all of the isolates were of the G-C genotype and the A-T genotype was never isolated. In December, only the A-T type was isolated from the river samples, when Biwa trout Oncorhynchus masou rhodurus came to the river to spawn and were present in the sampling area. In accordance with the seasonal change of the host fish species in the river, the genotype of F. psychrophilum isolated from the environment seems to have changed as well.