. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 110 M. DURAND-CLEMENT J 1500 1000 500. 1 CAP 10 mgjhil FIGURE 1. Effect of chloramphenicol (CAP) on Gambierdiscus toxicus growth in MPP. Strain previously treated with CAP. Strain without previous CAP treatment. layer. Cell density reached 4000 cells/ml (algal biomass equals 2 to 4-106 cells/1 liter Fernbach flask). Agitation of the cultures inhibited G. toxicus growth. Just prior to stationary growth, cultures were harvested and washed by centrifuga- tion(1500Xg, 5min). Influence of bacteria on G. toxicus growth De
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 110 M. DURAND-CLEMENT J 1500 1000 500. 1 CAP 10 mgjhil FIGURE 1. Effect of chloramphenicol (CAP) on Gambierdiscus toxicus growth in MPP. Strain previously treated with CAP. Strain without previous CAP treatment. layer. Cell density reached 4000 cells/ml (algal biomass equals 2 to 4-106 cells/1 liter Fernbach flask). Agitation of the cultures inhibited G. toxicus growth. Just prior to stationary growth, cultures were harvested and washed by centrifuga- tion(1500Xg, 5min). Influence of bacteria on G. toxicus growth Decreasing the bacterial flora improved the growth of G. toxicus cultures in our laboratory, from 500-1000 cells/ml final algal yield, to 4000 cells/ml. We used two methods for this purpose: serial washing in sterile medium and antibiotic treatment. To select the most efficient antibiotics, we tested the cultures with antibiograms (mul- tidisk Sobioda 12GR422), then treated the cultures with either a large dose of antibi- otics (5-20 mg/1) for a few hours in darkness (after which the drug was washed out), or with a smaller amount ( mg/1) added directly to the culture medium. In the first case, bacterial spore germination was promoted by adding neopeptone one or two days prior to treatment. The best results were obtained with rifampicine, mino- cycline, and chloramphenicol at 5 mg/1 for 24 h. (See Fig. 1 for an example of the effect of chloramphenicol on G. toxicus.} The number of bacterial species was de- creased, from more than 50 at the origin, to 3-5. We obtained a batch in which no bacteria could be detected during two months of growth. Presently, the use of chloramphenicol (5 mg/1) results in less than one bacterium per G. toxicus cell. Such cultures produce only a small amount of mucilage relative to contaminated cultures. Culture media and nutrient supplementation assays Adjusting media to study the nutritional requirements of G. toxicus and to en- hance its grow
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