Broad-spectrum antifungal metabolites produced by the soil bacterium Serratia plymuthica A 153

Chlorinated macrolides, haterumalide NA, B and NE, and a new haterumalide X, were produced by the soil bacterium Serratia plymuthica. Haterumalides NA, B and NE caused complete suppression of apothecial formation in sclerotia of Sclerotinia sclerotiorum at a concentration of 0.5 μg ml−1. Ascospore germination of this fungus was inhibited in the concentration range 0.8–3.0 μg ml−1. Haterumalides NA, B and NE prevented spore germination of several other filamentous fungi as well as Oomycetes at concentrations ranging from 0.4 to 40 μg ml−1, but did not show any effect against the yeast Candida albicans. Inhibition data could not be collected for haterumalide X due to its rapid conversion to haterumalide NA. The bacterium also produced two other antifungal metabolites: pyrrolnitrin and 1-acetyl-7-chloro-1-H-indole, which in contrast to the haterumalides, did not inhibit the apothecial formation on sclerotia. Pyrrolnitrin, and haterumalide NA, B and NE effectively inhibited spore germination of tested filamentous fungi at concentrations ranging from 0.06 to 50 μg ml−1, whereas 1-acetyl-7-chloro-1-H-indole inhibited spore germination only at concentrations above 50 μg ml−1. The minimal inhibitory concentrations of the respective compounds needed for total inhibition of spore germination varied for the fungal species tested.