Enumeration of bacteria in seawater and sediment from the Seto Inland Sea of Japan that promote sperm formation in Coscinodiscus wailesii (Bacillariophyceae)

Using the extinction dilution method with tissue culture microplates, we examined conditions for the enumeration of viable bacteria that promote sperm formation in Coscinodiscus wailesii Gran (Bacillariophyceae) (BPSF-Cw; bacteria-promoting sperm formation in C. wailesii). Samples of bacteria were collected from the surface and bottom (1 m above the bottom) layers of seawater from Harima-Nada, eastern Seto Inland Sea, Japan, during August 1993 and from a sediment sample collected June 1994. The most probable numbers (MPN) of BPSF-Cw in the samples of seawater (surface and bottom) and the sediment were calculated to be 9.5 X 10(3) cells ml(-1), 4.8 X 10(3) cells ml(-1), and 6.3 X 10(4) cells g(-1) wet sediment, respectively. This finding suggests that BPSF-Cw are abundant in the marine environment and that it should be possible to investigate the interaction between C. wailesii and BPSF-Cw in nature using this microplate MPN method.