Salinispora tropica

Salinispora tropica rewrote assumptions about actinomycete ecology when it was discovered in 2005 as the first obligate marine actinomycete. Unlike terrestrial species that can tolerate seawater, Salinispora requires seawater for growth—it's truly marine, not just marine-tolerant. This obligate marine lifestyle suggested that ocean sediments harbor distinct actinomycete communities with potentially distinct chemistry.

The prediction proved correct. S. tropica produces salinosporamide A, a proteasome inhibitor that entered clinical trials for multiple myeloma and other cancers. This anticancer compound has no close relatives from terrestrial actinomycetes; the marine environment apparently selected for different chemical solutions. The discovery launched systematic exploration of marine actinomycetes as sources of novel natural products.

S. tropica demonstrates that undiscovered antibiotic-producing bacteria likely remain in underexplored environments. The terrestrial Streptomyces screening that dominated antibiotic discovery for decades represented one ecological niche. Marine sediments, extreme environments, and symbiotic associations likely harbor actinomycetes producing different chemistry for different ecological challenges. The ocean remains largely unsampled for actinomycete diversity, suggesting substantial discovery potential remains.