Biology subjects

Nieves-Morion, M.

Publications and source records attributed to Nieves-Morion, M..

4 recordsLinked to original sources

bioRxiv2025

Intercellular communication in the fern endosymbiotic cyanobacterium Nostoc azollae

The water fern Azolla spp. harbors as an endobiont the N2-fixing, filamentous, heterocyst-forming cyanobacterium Nostoc azollae. N. azollae provide the fern with fixed nitrogen permitting its growth in nitrogen-poor environments. In the filaments of heterocyst-forming cyanobacteria, an intercellular exchange of regulators and metabolites occur in which heterocysts provide vegetative cells with fixed nitrogen and vegetative cells provide heterocysts with reduced carbon. Intercellular molecular exchange takes place by diffusion through septal junctions and can be probed by fluorescence recovery after photobleaching (FRAP) analysis with fluorescent markers such as calcein and 5-carboxyfluorescein. The septal junctions traverse the septal peptidoglycan through nanopores that can be visualized in isolated septal peptidoglycan disks by electron microscopy. Here we obtained N. azollae material from Azolla plants, which contains the symbiotic cyanobacterium in a viable state and with different morphologies, including heterocyst-containing filaments. FRAP analysis showed effective transfer of the fluorescent markers between vegetative cells as well as from vegetative cells to heterocysts. Interestingly, communicating and noncommunicating vegetative cells and heterocysts could be distinguished showing conservation in the endobiont of a regulatory mechanism capable of opening and closing septal junctions. Peptidoglycan sacculi were also isolated and showed septal disks with arrays of nanopores that conform to those visualized in other heterocyst-forming cyanobacteria. However, a wider range of septal disk size was observed in N. azollae. In spite of its eroded genome, N. azollae maintains the intercellular communication system that is key for its growth as a multicellular organism. ImportanceThe water fern Azolla constitutes a unique symbiotic system in which cyanobacterial endobionts capable of fixation of atmospheric nitrogen provide the plant with the nitrogen needed for growth. This symbiosis is an important fertilizer for rice crops worldwide, thereby reducing the reliance on fossil fuel-derived nitrogen fertilizers. The symbiotic cyanobacterium, Nostoc azollae, is a heterocyst-forming strain in which a filament of cells is the organismic unit of growth. Here we show that the intercellular molecular exchange function necessary for the multicellular behavior of the organism is conserved in the endobiotic Nostoc azollae.

microbiology↗

bioRxiv2024

Using gene complementation to identify a SulP-family bicarbonate transporter in an N2-fixing cyanobacterial endosymbiont of an open ocean diatom

Diatom-Diazotrophic Associations (DDAs) contribute significantly to new and primary production in the worlds oceans, yet the understanding of how production is sustained is poorly resolved. These symbioses involve diatoms and N2-fixing, heterocyst-forming cyanobacteria of the genus Richelia, both partners being photosynthetic. Richelia euintracellularis resides in the cytoplasm of Hemiaulus hauckii, whereas Richelia intracellularis is periplasmic in Rhizosolenia clevei. In the ocean, bicarbonate is taken up by phytoplankton to provide CO2 for photosynthesis. The genomes of both Richelia endobionts (ReuHH01 and RintRC01, respectively) contain genes encoding SulP-family proteins, which are oxyanion transporters. To study the possible involvement of these transporters in bicarbonate uptake, we used complementation of a Synechocystis sp. PCC 6803 mutant with its five CO2 uptake systems inactivated, which is unable to grow in air levels of CO2. Three genes from RintRC01 and one gene and a DNA fragment containing four partial gene sequences from ReuHH01 were chemically synthesized, cloned under the control of a strong gene promoter and incorporated in the chromosome of the Synechocystis mutant. One gene from RintRC01, RintRC_3892, complemented the Synechocystis mutant to grow with air levels of CO2 or with low bicarbonate concentrations. The complemented strain showed strong sodium-dependent, low affinity bicarbonate uptake, which, together with phylogenetic analyses, identified RintRC_3892 as a BicA protein. Additionally, RintRC_3892 transcripts were consistently detected in environmental samples from three ocean basins. No evidence for a bicarbonate transporter was found, however, for ReuHH01, suggesting different strategies for inorganic carbon uptake in the periplasmic and cytoplasmic endobionts.

microbiology↗

bioRxiv2023

Evolution of Multicellularity Genes in the Lead Up to the Great Oxidation Event

Cyanobacteria are among the most morphologically diverse prokaryotic phyla on Earth. Their morphotypes range from unicellular to multicellular filaments, yet mechanisms underlying the evolution of filamentous morphologies remain unknown. Here, we implement phylogenomic, Bayesian molecular clock and gene-tree-species-tree reconciliation analyses to estimate when genes encoding cell-cell joining structures first evolved. We also characterise septal structures and measure intercellular communication rates in non-model and early-branching filamentous strains. Our results suggest that genes encoding septal proteins (namely sepJ, sepI, and fraE) and potentially pattern formation (hetR) evolved in the Neoarchaean [~]2.6-2.7 billion years (Ga) ago. Later, at the start of the Great Oxygenation Event [~]2.5 Ga, genes involved in cellular differentiation (namely hetZ, patU3 and hglK) appeared. Our results predict that early-branching lineages like Pseudanabaena were capable of intercellular communication, but further innovations in cellular differentiation were needed to drive ecological expansion on a scale large enough to permanently oxygenate Earths atmosphere.

evolutionary biology↗

bioRxiv2023

Heterologous expression of genes from a heterocystous cyanobacterial endosymbiont highlights organic carbon exchange with its diatom host

A few genera of diatoms are widespread and thrive in low nutrient waters of the open ocean due to their close association with N2-fixing, filamentous heterocyst-forming cyanobacteria. In one of these symbioses, the symbiont, Richelia euintracellularis, has penetrated the cell envelope of the host, Hemiaulus hauckii, and lives inside the host cytoplasm. How the partners interact, including how the symbiont sustains high rates of N2 fixation is unstudied. Since R. euintracellularis has evaded isolation, heterologous expression of genes in model laboratory organisms was performed to identify the function of proteins from the endosymbiont. Gene complementation of a cyanobacterial invertase mutant and expression of the protein in Escherichia coli showed that R. euintracellularis HH01 possesses a neutral invertase that splits sucrose producing glucose and fructose. Several solute binding proteins (SBPs) of ABC transporters encoded in the genome of R. euintracellularis HH01 were expressed in E. coli and their substrates were characterized. The selected SBPs directly linked the host as the source of several substrates, e.g., sugars (sucrose, galactose), amino acids (glutamate, phenylalanine) and a polyamine (spermidine), to support the cyanobacterial symbiont. Finally, transcripts of genes encoding the invertase and SBPs were consistently detected in wild populations of H. hauckii collected from multiple stations and depths in the western tropical North Atlantic. Our results support the idea that the diatom host provides the endosymbiotic cyanobacterium with organic carbon to fuel N2 fixation. This knowledge is key to understand the physiology of the globally significant H. hauckii-R. euintracellularis symbiosis. SIGNIFICANCEDiatom diazotroph associations (DDAs) between diatoms and N2-fixing bacteria (diazotrophs) have a relevant impact on N2 fixation-based production, but the mechanisms underlying their integrated N2 and CO2 fixation remain unstudied. In the association between the diatom Hemiaulus hauckii (host) and the N2-fixing, heterocyst-forming cyanobacterium Richelia euintracellularis (endosymbiont), the cyanobacterium is uncultivable. Here we used heterologous expression of genes from the endosymbiont to identify the function of proteins involved in the utilization of organic carbon from the host. The importance of these proteins was also confirmed by estimating gene expression in environmental samples. Our results show that the metabolisms of the symbiotic partners are integrated allowing the host to sustain the physiology of the endosymbiont for an important ecological role.

molecular biology↗