Alcanivorax borkumensis produces an extracellular siderophore in iron-limitation condition maintaining the hydrocarbon-degradation efficiency

Obligate marine hydrocarbonoclastic bacteria possess genetic and physiological features to use hydrocarbons as
sole source of carbon and to compete for the uptake of nutrients in usually nutrient-depletedmarine habitats. In
the present work we have studied the siderophore-based iron uptake systems in Alcanivorax borkumensis SK2
and their functioning during biodegradation of an aliphatic hydrocarbon, tetradecane, under iron limitation
conditions. The antiSMASH analysis of SK2 genome revealed the presence of two different putative operons of
siderophore synthetases. Search for the predicted core structures indicated that one siderophore is clearly affiliated
to the family of complex oligopeptidic siderophores possessing an Orn-Ser-Orn carboxyl motif whereas the second
one is likely to belong to the family of SA (salicylic acid)–based siderophores.
Analyzing the supernatant of SK2 culture, an extracellular siderophore was identified and its structure was resolved.
Thus, along with the recently described membrane-associated amphiphilic tetrapeptidic siderophore
amphibactin, strain SK2 additionally produces an extracellular type of iron-chelating molecule with structural
similarity to pseudomonins. Comparative Q-PCR analysis of siderophore synthetases demonstrated their significant
up-regulation in iron-depleted medium. Different expression patterns were recorded for two operons during the
early and late exponential phases of growth, suggesting a different function of these two siderophores under
iron-depleted conditions.