The marine filamentous N2 fixing (diazotroph) cyanobacteria Trichodesmium spp. form extensive blooms contributing 25 to 50% of the estimated rates of N2 fixation in the oligotrophic subtropical and tropical oceans. Trichodesmium’s dominant role in carbon and nitrogen cycling has prompted investigations examining the effects of rising sea surface temperatures and elevated atmospheric pCO2 (leading to ocean acidification) on the growth and abundance of this organism.
We examined the effect of elevated pCO2 and light on the physiology and gene expression of key genes in Trichodesmium. Genes that participate in nitrogen metabolism, Ci fixation, and photosynthesis were most affected by changes in pCO2, temperature and the time within the diurnal period. High pCO2 shifted transcript patterns of all genes, resulting in a more synchronized diel expression. Concurrently, we found no significant changes in the protein pools or in total cellular allocations of carbon and nitrogen (i.e. C : N ratio remained stable). Moreover, increased temperatures and high pCO2 resulted in higher C : P ratios. The plasticity in phosphorous stoichiometry combined with higher enzymatic efficiencies lead to higher growth rates. We demonstrate that shifted cellular resource and energy allocation among those components will enable Trichodesmium grown at elevated temperatures and pCO2 to extend its niche in the future ocean, through both tolerance of a broader temperature range and higher P plasticity.
Currently we are investigating two other physiological phenomena in Trichodesmium: the mechanisms of colony and bloom formation, and the molecular mechanisms of toxin production.