Availability of Deep Seawater and Effects of Bacteria Isolated from Deep Seawater on the Mass Culture of Food Microalga Chaetoceros ceratosporum.

The possible availability of deep seawater (DSW; seawater under the euphotic layer) and bac-teria isolated from DSW (BDS) for the mass culture of food microalga Chaetoceros ceratosporum was investigated. Seawater samples pumped up from a depth of 320m at the kochi Deep Seawater Laboratory in Muroto, Kochi Prefecture, were collected and used for cultivation of C. ceratos-porum. Growth rate (μ: reciprocal of the dubling time) and maximum cell yields (MCY) of the alga in untreated DSW were 1.25-2.22 (average 1.72).day-1 and 2-11 (average 6) x 105 cells/ml, respectively. When compared with those obtained by ASP6 medium, the average, μin DSW was about 90% and the values of MCY were 5-20% of those in ASP6. The values of MCY, however, showed a relatively large variance according to the sampling season of DSW. When some BDS were added to DSW, the growth of C. ceratosporum was often stimulated significantly; the μ values were 1.82-2.86 (average 2.27). day-1 and MCYs were 4-12 (average 8) x 105 cells/ml. Moreover, the variance of μ and MCY according to the sampling season tended to decrease when BDS were added. These results suggest that DSW has a high potential for cultivating food micro-algae, and it can be made more stable and effective by adding BDS.