Iron limitation reduces diatom carbon flow to bacteria through shifts in exometabolite consumption.

Iron limitation in the diatom Phaeodactylum tricornutum reduces carbon transfer into bacterial biomass by 80% and shifts bacterial exometabolite use toward less labile compounds.

• Why it matters: Iron scarcity can lower photosynthetic carbon fixation, but how this changes dissolved organic matter composition and bacterial processing through the microbial loop is unclear.
• What they did: Using nanoSIMS single-cell-resolution on a bacterial community dependent on diatom carbon, and ultra-high-resolution exometabolomics, the study quantified carbon fixation and bacterial incorporation under iron-replete versus iron-deplete conditions.
• The result: Iron limitation caused a 43% reduction in carbon fixation and an 80% reduction in bacterial carbon transfer, linked to bacterial consumption of less labile aromatics, specific lipids, and nucleobases.