Fe-responsive accumulation of redox proteins ferredoxin and flavodoxin in a marine cryptomonad

Abstract

Fe deficiency has been documented in diverse marine environments ranging from pelagic high-nutrient, low chlorophyll (HNLC) regions to coastal systems. Detection of specific Fe-responsive proteins in phytoplankton has provided a sensitive approach to assessing Fe deficiency in natural waters. Here, we report on the development and applicability of taxon-specific polyclonal antisera to monitor the accumulation of two such Fe-responsive proteins, flavodoxin and ferredoxin (Fd) in cryptomonad algae. Reactivity of these immunoreagents was limited primarily to cryptomonads. Anti-Fd cross-reacted with a broad spectrum of both marine and freshwater cryptophytes whereas anti-flavodoxin recognized only flavodoxin from Rhodomonas lens. Assessment of Fd and flavodoxin accumulation in R. lens grown under various levels of Fe demonstrated an apparent uncoupling of flavodoxin expression from physiological Fe deficiency in this species. It appears that flavodoxin accumulates in response to external Fe availability as supported by results of a chelator addition experiment which demonstrated rapid accumulation of flavodoxin in Fe-replete cells of R. lens without concomitant physiological deficit following addition of the fungal siderophore desferrioxamine B.