Biology subjects

Groussman, R. D.

Publications and source records attributed to Groussman, R. D..

3 recordsLinked to original sources

bioRxiv2022

Divergent functions of two clades of flavodoxin in diatoms mitigate oxidative stress and iron limitation

Phytoplankton rely on diverse mechanisms to adapt to the decreased iron bioavailability and oxidative stress-inducing conditions of todays oxygenated oceans, including replacement of the iron-requiring ferredoxin electron shuttle protein with a less-efficient iron-free flavodoxin under iron limiting conditions. And yet, diatoms transcribe flavodoxins in high-iron regions in contrast to other phytoplankton. Here, we show that the two clades of flavodoxins present within diatoms exhibit a functional divergence, with only clade II flavodoxins displaying the canonical role in adaptation to iron limitation. We created CRISPR/Cas9 knock-outs of the clade I flavodoxin from the model diatom Thalassiosira pseudonana and found these cell lines are hypersensitive to oxidative stress, while maintaining a wild-type response to iron limitation. Within natural diatom communities, clade I flavodoxin transcript abundance is regulated over the diel cycle rather than in response to iron availability, whereas clade II transcript abundances increase either in iron-limiting regions or under artificially induced iron-limitation. The observed functional specialization of two flavodoxin variants within diatoms reiterates two major stressors associated with contemporary oceans and illustrates diatom strategies to flourish in diverse aquatic ecosystems.

evolutionary biology↗

bioRxiv2022

Siderophore production and utilization by microbes in the North Pacific Ocean

Siderophores are strong iron-binding molecules produced and utilized by microbes to acquire the limiting nutrient iron (Fe) from their surroundings. Despite their importance as a component of the iron-binding ligand pool in seawater, data on the distribution of siderophores and the microbes that use them are limited. Here we measured the concentrations and types of dissolved siderophores during two cruises in April 2016 and June 2017 that transited from the iron-replete, low-macronutrient North Pacific Subtropical Gyre (NPSG) through the North Pacific Transition Zone (NPTZ) to the iron-deplete, high-macronutrient North Pacific Subarctic Frontal Zone (SAFZ). Surface siderophore concentrations in 2017 were higher in the NPTZ (4.0 - 13.9 pM) than the SAFZ (1.2 - 5.1 pM), which may be partly attributed to stimulated siderophore production by environmental factors such as dust-derived iron concentrations (up to 0.51 nM). Multiple types of siderophores were identified on both cruises, including ferrioxamines, amphibactins and iron-free forms of photoreactive siderophores, which suggest active production and use of diverse siderophores across latitude and depth. Additionally, the widespread genetic potential for siderophore biosynthesis and uptake across latitude and the variability in the taxonomic composition of bacterial communities that transcribe putative ferrioxamine, amphibactin and salmochelin transporter genes at different latitudes suggest that particular microbes actively produce and use siderophores, altering siderophore distributions and the bioavailability of iron across the North Pacific.

ecology↗

bioRxiv2020

Diel Oscillations of Particulate Metabolites Reflect Synchronized Microbial Activity in the North Pacific Subtropical Gyre

Light is the primary input of energy into the sunlit ocean, driving daily oscillations in metabolism of primary producers. The consequences of this solar forcing have implications for the whole microbial community, yet in situ measurements of metabolites, direct products of cellular activity, over the diel cycle are scarce. We evaluated community-level biochemical consequences of diel oscillations in the North Pacific Subtropical Gyre by quantifying 79 metabolites in particulate organic matter in surface waters every four hours over eight days. Total particulate metabolite concentration peaked at dusk, even when normalized to biomass estimates. The concentrations of 70% of individual metabolites exhibited 24-hour periodicity. Despite the diverse organisms that use them, primary metabolites involved in anabolic processes and redox maintenance had significant 24-hour periodicity. Osmolytes exhibited the largest diel oscillations, implying rapid turnover and metabolic roles beyond cell turgor maintenance. Metatranscriptome analysis revealed the taxa involved in production and consumption of some metabolites, including the osmolyte trehalose. This compound displayed the largest diel oscillations in abundance and was likely produced by the nitrogen-fixing cyanobacterium Crocosphaera for energy storage. These findings demonstrate that paired measurements of particulate metabolites and transcripts resolve strategies microbes use to manage daily energy and redox oscillations.

ecology↗