Abstract
BackgroundThe well-lit surface waters of oligotrophic gyres significantly contribute to global primary production. Marine cyanobacteria of the genus Prochlorococcus are a major fraction of photosynthetic organisms within these areas. Labile phosphate is considered a limiting nutrient in some oligotrophic regions such as the Caribbean Sea, and as such it is crucial to understand the physiological response of primary producers such as Prochlorococcus to fluctuations in the availability of this critical nutrient.ResultsProchlorococcus strains representing both high light (HL) (MIT9312) and low light (LL) (NATL2A and SS120) ecotypes were grown identically in phosphate depleted media (10 μM Pi). The three strains displayed marked differences in cellular protein expression, as determined by high throughput large scale quantitative proteomic analysis. The only strain to demonstrate a significantly different growth rate under reduced phosphate conditions was MIT9312. Additionally, there was a significant increase in phosphate-related proteins such as PhoE (> 15 fold increase) and a depression of the Rubisco protein RbcL abundance in this strain, whereas there appeared to be no significant change within the LL strain SS120.ConclusionsThis differential response between ecotypes highlights the relative importance of phosphate availability to each strain and from these results we draw the conclusion that the expression of phosphate acquisition mechanisms are activated at strain specific phosphate concentrations.
Highlights
The well-lit surface waters of oligotrophic gyres significantly contribute to global primary production
Neither PhoA nor PhoE was observed with mass spectrometry here, which is surprising as we showed previously that both PhoA and PhoE are greater in abundance alongside PstS in the high light ecotype MED4 [21], as is true with MIT9312 in this study
Prochlorococcus are widely considered to be evolutionarily adept at environmental niche domination, within nutrient poor oligotrophic waters
Summary
The well-lit surface waters of oligotrophic gyres significantly contribute to global primary production. Prochlorococcus is characterised by its small size (~ 1 μm3), and significantly reduced genomes which ranges from 1.64 Mbps (the HL strain MIT9301) to 2.68 Mbps (the LL strain MIT9303) [9]. This diminished volume and genome is hypothesised to be the result of an accelerated evolutionary process adapting to reduced phosphorus in its environment [10,11]. Prochlorococcus is known to replace phospholipids in its membranes with sulpholipids, which dramatically reduce its Pi requirements [12]
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