Cabello, A. M. | Search bioRxiv

bioRxiv2023

Gene expression response to temperature acclimation in a model photoheterotrophic marine flavobacterium (Dokdonia sp. MED134)

Temperature stands as one of the key factors influencing the community structure and distribution of marine microorganisms. Yet, the physiological adaptations of marine bacteria to rising temperatures remain underexplored. This study examines the transcriptional response of Dokdonia sp. MED134, a proteorhodopsin-based phototrophic organism within the class Flavobacteriia, to a gradient of temperature acclimation conditions from 10 to 34{degrees}C. Light availability during day/night cycles exerted minimal influence on the transcriptional patterns of this strain, with only a few genes mostly related to light sensing, light protecting mechanisms and phototrophy being upregulated during daytime. By contrast, temperature significantly impacted the expression of a large fraction of MED134 genes (>60%), including components of the stress response, cellular translation, DNA replication, and some metabolic pathways such as the anaplerotic carbon fixation and the glyoxylate shunt, suggesting intracellular carbon flow adjustments to temperature. Notably, the expression of some highly expressed TonB transporters, prominent in flavobacteria, was also temperature-sensitive. Our findings provide insights into the transcriptional adjustments of Dokdonia sp. MED134 in response to temperature variations, suggesting potential implications for carbon cycling and organic matter processing in marine environments.

microbiology↗

bioRxiv2021

Nitrogen fixation in mesoscale eddies of the North Pacific Subtropical Gyre: patterns and mechanisms

1.Mesoscale eddies have been shown to support elevated dinitrogen (N2) fixation rates (NFRs) and abundances of N2-fixing microorganisms (diazotrophs), but the mechanisms underlying these observations are not well understood. We explored relationships among NFRs and cyanobacterial diazotroph abundances in eddy pairs of opposite polarity sampled in the North Pacific Subtropical Gyre and compared our observations to seasonal trends from the Hawaii Ocean Time-series (HOT) program. Consistent with previous reports, we found that NFRs were anomalously high for this region (up to 3.7-fold above previous monthly HOT observations) in the centers of the sampled anticyclones, coinciding with elevated abundances of Crocosphaera in the summertime. We then coupled our field-based observations, together with transcriptomic analyses of nutrient stress marker genes and ecological models, to evaluate potential mechanisms controlling diazotroph abundance and activity at the mesoscale. Specifically, we evaluated the role of biological (via estimates of growth and grazing rates) and physical controls on populations of Crocosphaera, Trichodesmium, and diatom symbionts. Our results suggest that increased Crocosphaera abundances associated with summertime anticyclones resulted from the alleviation of phosphate limitation, allowing cells to grow at rates exceeding grazing losses. In contrast, distributions of larger, buoyant taxa (Trichodesmium and diatom symbionts) appeared less affected by eddy-driven biological controls. Instead, they appeared driven by physical dynamics along frontal boundaries that separate cyclonic and anticyclonic eddies. Together, the interplay of eddy-specific changes in bottom-up control, top-down control, and the physical accumulation of cells likely explains the elevated diazotroph abundances and NFRs associated with anticyclones and eddy fronts.

ecology↗