Biology subjects

Munoz-Marin, M. d. C.

Publications and source records attributed to Munoz-Marin, M. d. C..

3 recordsLinked to original sources

bioRxiv2022

Open ocean and coastal strains of the N2-fixing cyanobacterium UCYN-A have distinct transcriptomes

Decades of research on marine N2 fixation focused on Trichodesmium, which are generally free-living cyanobacteria, but in recent years the endosymbiotic cyanobacterium Candidatus Atelocyanobacterium thalassa (UCYN-A) has received increasing attention. However, few studies have shed light on the influence of the host versus the habitat on UCYN-A N2 fixation and overall metabolism. Here we compared transcriptomes from natural populations of UCYN-A from oligotrophic open-ocean versus nutrient-rich coastal waters, using a microarray that targets the full genomes of UCYN-A1 and UCYN-A2 and known genes for UCYN-A3. We found that UCYN-A2, usually regarded as adapted to coastal environments, was transcriptionally very active in the open ocean and appeared to be less impacted by habitat change than UCYN-A1. Across habitats and sublineages, genes for N2 fixation and energy production had high transcript levels, and, intriguingly, were among the minority of genes that kept the same schedule of diel expression. This might indicate different regulatory mechanisms for genes that are critical to the symbiosis for the exchange of nitrogen for carbon from the host. Our results underscore the importance of N2 fixation in UCYN-A symbioses across habitats, with consequences for community interactions and global biogeochemical cycles.

microbiology↗

bioRxiv2021

Differential timing for glucose assimilation in Prochlorococcus and coexistent microbial populations at the North Pacific Subtropical Gyre

The marine cyanobacterium Prochlorococcus can utilize glucose as a source of carbon. However, the relative importance of inorganic and organic carbon assimilation and the timing of glucose assimilation are still poorly understood in these numerically dominant cyanobacteria. Here we investigated whole microbial community and group-specific primary production and glucose assimilation, using incubations with radioisotopes combined with flow cytometry cell sorting. We also studied changes in the microbial community structure in response to glucose enrichments and analyzed the transcription of Prochlorocccus genes involved in carbon metabolism and photosynthesis. Our results showed a circadian rhythm for glucose assimilation in Prochlorococcus, with maximum assimilation during the midday and minimum at midnight, which was different compared with that of the total microbial community. This suggests that rhythms in glucose assimilation have been adapted in Prochlorococcus to couple the active transport to photosynthetic light reactions producing energy, and possibly to avoid competition from the rest of the microbial community. High-light Prochlorococcus strains showed most transcriptional changes upon glucose enrichment. Pathways involved in glucose metabolism as the pentose phosphate, the Entner-Dudoroff, glycolysis, respiration and glucose transport showed an increase in the transcript level. A few genes of the low-light strains showed opposite changes, suggesting that glucose assimilation has been subjected to diversification along the Prochlorococcus evolution.

microbiology↗

bioRxiv2018

A transcriptional cycle suited to daytime N2 fixation in the unicellular cyanobacterium Candidatus Atelocyanobacterium thalassa (UCYN-A)

The symbiosis between a marine alga and a N2-fixing cyanobacterium (UCYN-A) is geographically widespread in the oceans and is important in the marine N cycle. UCYN-A is uncultivated, and is an unusual unicellular cyanobacterium because it lacks many metabolic functions, including oxygenic photosynthesis and carbon fixation, which are typical in cyanobacteria. It is now presumed to be an obligate symbiont of haptophytes closely related to Braarudosphaera bigelowii. N2-fixing cyanobacteria use different strategies to avoid inhibition of N2 fixation by the oxygen evolved in photosynthesis. Most unicellular cyanobacteria temporally separate the two incompatible activities by fixing N2 only at night, but surprisingly UCYN-A appears to fix N2 during the day. The goal of this study was to determine how the unicellular UCYN-A coordinates N2 fixation and general metabolism compared to other marine cyanobacteria. We found that UCYN-A has distinct daily cycles of many genes despite the fact that it lacks two of the three circadian clock genes found in most cyanobacteria. We also found that transcription patterns in UCYN-A are most similar to marine cyanobacteria that are capable of aerobic N2 fixation in the light such as Trichodesmium and heterocyst-forming cyanobacteria, rather than Crocosphaera or Cyanothece species, which are more closely related to unicellular marine cyanobacteria evolutionarily. Our findings suggest that the symbiotic interaction has resulted in a shift of transcriptional regulation to coordinate UCYN-A metabolism with the phototrophic eukaryotic host, thus allowing efficient coupling of N2 fixation (by the cyanobacterium) to the energy obtained from photosynthesis (by the eukaryotic unicellular alga) in the light.\n\nImportanceThe symbiotic N2-fixing cyanobacterium UCYN-A and its eukaryotic algal host, which is closely related to Braarudosphaera bigelowii, have been shown to be globally distributed and important in open ocean N2 fixation. These unique cyanobacteria have reduced metabolic capabilities, even lacking genes for oxygenic photosynthesis and carbon fixation. Cyanobacteria generally use energy from photosynthesis for nitrogen fixation, but require mechanisms for avoiding inactivation of the oxygen-sensitive nitrogenase enzyme by ambient oxygen (O2) or the O2 evolved through photosynthesis. This study shows that the symbiosis between the N2-fixing cyanobacterium UCYN-A and its eukaryotic algal host has led to adaptation of its daily gene expression pattern in order to enable daytime aerobic N2 fixation, which is likely more energetically efficient than fixing N2 at night, as in other unicellular marine cyanobacteria.

ecology↗