Transcriptome response of high- and low-light-adapted Prochlorococcus strains to changing iron availability

Area of Science:

• Marine microbiology
• Ocean primary productivity
• Biogeochemical cycles

Background:

• Prochlorococcus is a vital marine cyanobacterium responsible for significant ocean primary productivity.
• Iron availability is a critical factor limiting Prochlorococcus growth in many oceanic regions.
• The genetic basis for variations in iron metabolism among Prochlorococcus ecotypes remains largely unknown.

Purpose of the Study:

• To investigate the ecotypic variation in iron metabolism between two Prochlorococcus strains, MED4 and MIT9313.
• To elucidate the molecular mechanisms underlying differential iron utilization and adaptation in Prochlorococcus.

Main Methods:

• Comparative growth analysis of Prochlorococcus strains MED4 and MIT9313 under varying iron concentrations.
• Whole-genome transcriptional profiling (RNA sequencing) to assess gene expression changes in response to iron starvation and repletion.
• Bioinformatic analysis of genomic regions, including those near the iron-deficiency-induced gene (idiA).

Main Results:

• MIT9313 demonstrated sustained growth at iron concentrations one order of magnitude lower than MED4.
• A limited number of orthologous genes (4/1159) showed differential iron-responsive expression in both strains.
• Each strain exhibited significant changes in expression for over a hundred non-orthologous genes, with many located in labile genomic regions.
• MED4 lacks three idiA-associated genes present and induced by iron stress in MIT9313.

Conclusions:

• Significant ecotypic variation exists in Prochlorococcus iron metabolism, impacting their ecological niche.
• Lateral gene transfer is a likely mechanism contributing to the diversity of iron metabolism pathways.
• The idiA-associated genes in MIT9313 represent key targets for understanding Prochlorococcus adaptation to iron-limited marine environments.