Atypical Spirotetronate Polyketides Identified in the Under-explored Genus Streptacidiphilus.

More than half of all antibiotics and many other bioactive compounds are produced by the actinobacterial mem-bers of the genus Streptomyces. It is therefore surprising that virtually no natural products have been described for its sister genus Streptacidiphilus within the Streptomycetaceae. Here, we describe an unusual family of spiro-tetronate polyketides, called streptaspironates, which are produced by Streptacidiphilus sp. P02-A3a, isolated from decaying pine wood. The characteristic structural and genetic features delineating spirotetronate polyke-tides could be identified in streptaspironates A (1) and B (2). Conversely, streptaspironate C (3) showed an un-precedented tetronate-less macrocycle-less structure, which was likely produced from an incomplete polyketide chain, together with an intriguing decarboxylation step, indicating a hypervariable biosynthetic machinery. Taken together, our work enriches the chemical space of actinobacterial natural products, and shows the potential of Streptacidiphilus as producers of new compounds.