Wolbachia is an obligate intracellular alphaproteobacterium that occurs in arthropod and nematode hosts. Wolbachia presumably provides a fitness benefit to its hosts, but the basis for its retention and spread in host populations remains unclear. Wolbachia genomes retain biosynthetic pathways for some
vitamins, and the possibility that these
vitamins benefit host cells provides a potential means of selecting for Wolbachia-infected cell lines. To explore whether
riboflavin produced by Wolbachia is available to its host cell, we established that growth of uninfected C7-10 mosquito cells decreases in
riboflavin-depleted culture medium. A well-studied inhibitor of
riboflavin uptake,
lumiflavin, further inhibits growth of uninfected C7-10 cells with an LC50 of approximately 12 μg/ml. Growth of C/wStr1 mosquito cells, infected with Wolbachia from the planthopper, Laodelphax striatellus, was enhanced in medium containing low levels of
lumiflavin, but Wolbachia levels decreased.
Lumiflavin-enhanced growth thus resembled the improved growth that accompanies treatment with
antibiotics that deplete Wolbachia, rather than a metabolic advantage provided by the Wolbachia
infection. We used the polymerase chain reaction to validate the decrease in Wolbachia abundance and evaluated our results in the context of a proteomic analysis in which we detected nearly 800 wStr
proteins. Our data indicate that Wolbachia converts
riboflavin to
FMN and
FAD for its own metabolic needs, and does not provide a source of
riboflavin for its host cell.