Environmental Factors Influencing the Production of an Antibacterial Metabolite from a Marine Dinoflagellate,Prorocentrum minimum

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Abstract
Prorocentrum minimum, an ubiquitous marine dinoflagellate that does not form toxic red tides, produces biologically active extracellular metabolites, one of which is 1-(2,6,6-trimethyi-4-hydroxycyclohexenyl)-1,3-butanedione, a norcarotenoid referred to herein as β-diketone. The β-diketone was released extracellularly in a single "pulse" during the stationary phase of growth, and irradiance and temperature are important in controlling its maximum extracellular concentration. Different concentrations were obtained depending on the limiting nutrient. If cells were P deficient, the final extracellular concentration was twice that of N-deficient cultures. Iron-deficient growth further reduced the amount of the β-diketone produced. The ambient nitrate concentration in the medium had a strong influence on the maximum amount of the β-diketone produced. None of the environmental factors affected the temporal pattern of production. That the β-diketone is an antibiotic metabolite active against marine bacteria is shown by the reduction of the growth rate of three of four marine isolates and the inhibition of the heterotrophic uptake of glucose. The β-diketone in the natural environment may serve to reduce degradation of algae by physically associated bacteria.