Spatiotemporal Dynamics of the Dihydrolipoyl Dehydrogenase LpdA Determine the Intrinsic Autofluorescence in Filamentous Actinobacteria

The hyphal nature of filamentous streptomycetes poses unique challenges to their multicellular lifestyle, since it requires organizing cellular functions at the scale of hundreds of micrometers length. Streptomycetes exhibit a strong and patchy autofluorescence of so far unknown origin in their hyphae that - as we demonstrate - is a natural property of filamentous actinobacteria. The foci are dynamic and evenly distributed throughout the hyphae, including the hyphal tips, where they are cell membrane-associated. Here, we resolved the high spatiotemporal dynamics of these foci during spore germination and vegetative growth in Streptomyces venezuelae. We isolated a fluorescent protein band and identified the responsible protein as dihydrolipoyl dehydrogenase LpdA. An lpdA deletion mutant lacked these fluorescent foci and showed minor deficiencies in growth and development. Heterologous LpdA production in E. coli and characterization of the enzyme verified that a flavin cofactor is responsible for the green autofluorescence. LpdA is highly conserved in actinomycetes as a part of multienzyme complexes involved in central metabolism. Such delocalized metabolic centers provide a potential solution to mycelial multicellular lifestyle, where diffusion becomes a major challenge.