SEXUAL CO-FLOCCULATION BY HETEROTHALLIC CELLS OF THE FISSION YEAST SCHIZOSACCHAROMYCES-POMBE MODULATED BY MEDIUM CONSTITUENTS

Novel simple synthetic media for inducing sexual co-flocculation in a short time after mixing heterothallic fission-yeast (Schizosaccharomyc es pombe) cells of h(-) and h(+) were devised; The most effective of t hese, mannose synthetic medium (MSM), contains 0.4% mannose as a carbo n source in addition to galactose, KH2PO4 (pH4.0) and 4 vitamins. The addition of galactose to the medium suppressed the asexual self-floccu lation but rather promoted the sexual co-flocculation. By transferring and mixing h(-) and h(+) cells grown in malt-extract broth plus galac tose into MSM, these heterothallic strains were revealed to be sexuall y ready through a long period of the log to stationary phases. Further more, a variety of C sources and NH4Cl at various concentrations in va rious media were examined for their effects upon sexual co-flocculatio n, conjugation and sporulation; it was found that the sugar concentrat ion strictly affected the progress of the sequence of sexual reproduct ion at 26 degrees C but not 30 degrees C and that sexual co-flocculati on of the heterothallic strains was induced only under lower concentra tions of C and N source than that for the homothallic one.