Transcriptional responses of Trichodesmium to natural inverse gradients of Fe and P availability

Abstract

The filamentous diazotrophic cyanobacterium Trichodesmium is responsible for a significant fraction of marine di-nitrogen (N2) fixation. Growth and distribution of Trichodesmium and other diazotrophs in the vast oligotrophic subtropical gyres is influenced by iron (Fe) and phosphorus (P) availability, while reciprocally influencing the biogeochemistry of these nutrients. Here we use observations across natural inverse gradients in Fe and P in the North Atlantic subtropical gyre (NASG) to demonstrate how Trichodesmium acclimates in situ to resource availability. Transcriptomic analysis identified progressive upregulation of known iron-stress biomarker genes with decreasing Fe availability, and progressive upregulation of genes involved in the acquisition of diverse P sources with decreasing P availability, while genes involved in N2 fixation were upregulated at the intersection under moderate Fe and P availability. Enhanced N2 fixation within the Fe and P co-stressed transition region was also associated with a distinct, consistent metabolic profile, including the expression of alternative photosynthetic pathways that potentially facilitate ATP generation required for N2 fixation with reduced net oxygen production. The observed response of Trichodesmium to availability of both Fe and P supports suggestions that these biogeochemically significant organisms employ unique molecular, and thus physiological responses as adaptations to specifically exploit the Fe and P co-limited niche they construct.

The response of diazotrophs to nutrient amendment in the South China Sea and western North Pacific

“…4). These results add to increasing evidence for the potentially widespread Fe-P co-limitation of N 2 fixation under elevated Fe supply (Mills et al, 2004;Snow et al, 2015;Cerdan-Garcia et al, 2022).…”

N 2 Fixation in Trichodesmium Does Not Require Spatial Segregation from Photosynthesis

“…In marine diazotrophs, AET can be a complement to linear PET (LPET), in which ATP and NADPH are produced at a molar ratio (1.3:1) that is substantially lower than that (3:1) required by N 2 fixation ( 27 , 28 , 30 – 32 ). AET can therefore benefit N 2 fixation by providing ATP to energetically expensive N 2 fixation while not generating O 2 ( 8 , 26 , 33 , 34 ).…”

Marine Microeukaryote Metatranscriptomics: Sample Processing and Bioinformatic Workflow Recommendations for Ecological Applications

“…Researchers may instead prioritize additional sampling depths, locations, or time points to capture transcript pools with high resolution. Samples collected from similar latitudes and depths may reflect similar biological properties, thus demonstrating oceanographic consistency across space and time (Cerdan- Garcia et al, 2021;Hogle et al, 2021). High frequency sampling may identify metabolic trends that either change on a diel cycle (e.g., energy partitioning), or are unaffected by temporal dynamics (e.g., chronic nutrient stress).…”