Relationship between bacterial flora and occurrence of the Alteromonas sp., the causative agent of red-spots on the culture bed of makonbu Laminaria japonica, in the coastal area of Funka Bay.

The bacterial flora of surface seawater at Osatube station in Funka Bay were investigated from February to December 1986. Marine Moraxella and marine Flavobacterium/Cytophaga were predominant in many samples, and marine Pseudomonas, Vibrio, Alteromonas, terrestrial Moraxella or terrestrial Flavobacterium/Cytophaga increased in some samples. In this area, Alteromonas sp., a bacterial predator and causative agent of red-spot was detected during July to September 1986. On double-layer agar plate, 43.3% of 180 strains isolated during July to December were lysed by Alteromonas sp. strain No. 8, the representative strain of red-spot causing bacterium. Each lytic susceptibility of the dominant genera to No. 8 was follows: marine Moraxella, 66%; marine Flavobacterium/Cytophaga, 17%; Alteromonas, 63%; Vibrio, 53%; marine Pseudomonas, 58% and terrestrial Flavobacterium/Cytophaga, 71%. It was also found that lytic enzyme of the red-spot forming bacterium lysed both gram negative and gram positive bacteria. According to these results, it may be considered that bacterial flora and water temperature are important factors in regulating the distribution of the Alteromonas sp. (red-spot causing bacterium) in coastal waters.