Extracellular Accumulation of Rhodotorulic Acid in Strains of Microbotryum violaceum

Abstract

Siderophore production is an integral component of high-affinity iron uptake by many microorganisms. We examined the extracellular production of the siderophore rhodotorulic acid (RA) in 16 field-collected and seven herbarium strains of Microbotryum violaceum. These strains were collected from a variety of caryophyllaceous host plant species, from many geographical locations, over a period of years. All of the tested strains, when starved for iron, produced detectable levels of RA, which is consistent with a critical function of the high-affinity iron uptake system. We found normal patterns of siderophore secretion accompanying iron starvation as well as repression of siderophore secretion when cells were grown in culture containing adequate levels of iron. We detected a fivefold variation in the extracellular siderophore level (0.33 mM-1.71 mM) among the 23 strains. Levels of extracellular siderophore accumulation correlated with cell density; strains that grew to a greater density (cells/mL) in liquid c...