hus, the Salinispora group of actinobacteria represents the first recorded source of rifamycins from marine bacteria. To discover this source, we used an approach of applying phylogenetic analysis based on polyketide synthase genes to the prediction of synthesis of polyketide antibiotics in a particular chemical class. Such molecular prediction could conceivably preclude the need for time-consuming nontargeted chemical assay. Significantly for biotechnology, the discovery of rifamycin synthesis by Salinispora strains implies that they are a potential new source, outside the genus Amycolatopsis, of rifamycins and of polyketide synthesis gene clusters specific to rifamycin synthesis. Comparative genomic analysis of rifamycin synthesis gene clusters using strains from the two distinct genus level taxa known to harbor strains producing rifamycins will now be possible