Biology subjects

Giner-Lamia, J.

Publications and source records attributed to Giner-Lamia, J..

5 recordsLinked to original sources

bioRxiv2026

From Magnetosomes to Vesicles: LemA Proteins as Drivers of Bacterial Membrane Reorganization

The cellular machineries that remodel bacterial membranes during organelle and vesicle formation remain poorly defined. Herein, we report MamQ as a key determinant of the lipid invaginations that enclose the magnetosome. MamQ belongs to the broadly conserved LemA protein family, whose members localize to either the inner or outer membrane. Heterologous overproduction of 13 different LemA proteins in Escherichia coli induced extensive membrane restructuring and vesiculation, indicating a conserved membrane-remodelling activity. In Pseudomonas aeruginosa, overproduction of the inner membrane protein LemA1 (PaLemA1) promoted cytoplasmic membrane vesicle (CMV) formation, whereas the periplasmic-located outer membrane-anchored LemA2 (PaLemA2) drove the formation of bacterial outer-membrane vesicles (OMVs). Conversely, deletion of the corresponding genes reduced extracellular vesicle production. Interactome analyses identified 256 protein partners of PaLemA1 and PaLemA2, including multiple components of the cellular divisome, such as CpoB, FtsE, FtsI, FtsK, FtsN, FtsW, MinE, ParB, ZapG, ZipA. Bacterial two-hybrid assays confirmed interactions between both LemA proteins and the cell division regulator CpoB, whose perturbation markedly altered vesicle formation. Additional interaction partners included PspA, an ESCRT-III-like protein implicated in membrane remodelling. Proteins involved in cell wall metabolism, membrane turnover, lipopolysaccharide (LPS) biogenesis, protein export and maturation, energy metabolism, and stress-responsive gene regulation were also enriched, suggesting a supporting role for PaLemA proteins in coordinating membrane-associated processes. Consistent with this, LemA deletion mutants displayed altered vesicle composition and global changes in gene expression. Furthermore, PalemA2 expression was induced in stationary phase and under envelope stress via the extracytoplasmic sigma factor AlgU, itself an interaction partner of the LemA proteins. Together, our findings indicate the LemA family act as a conserved membrane-remodelling system that, in conjunction with PspA, CpoB and divisome components, organises membrane-localized protein complexes required for bacterial organelle biogenesis and vesicle formation while executing a controlled, protein-machinery-driven mechanism that operates independently of passive chemical blebbing (such as hydrophobic PQS intercalation) or lytic membrane fragmentation.

microbiology↗

bioRxiv2026

A rhizobial extracellular vesicle-conveyed auxin transporter mediates phytohormone mobilization and optimizes rhizobium-legume symbiosis

Bacterial extracellular vesicles (bEVs) are emerging as key players in interkingdom communication, yet their role in delivering functional proteins to host cells during symbiosis remains unexplored. This study shows that Sinorhizobium fredii HH103 packages a PIN-like auxin transporter, AuxT, into bEVs that traffic within the peribacteroid space of soybean nodules. AuxT is chromosomally encoded and constitutively expressed, genetically uncoupled from the flavonoid-inducible auxin biosynthesis machinery located on the symbiotic plasmid. Structural prediction reveals that AuxT adopts an eight-transmembrane-helix architecture with striking homology to plant PIN auxin exporters, despite negligible sequence identity. Molecular docking demonstrates that AuxT binds indole-3-acetic acid within a central cavity, with dimerization inducing ligand-specific conformational changes consistent with transport activity. The auxT mutant exhibits significant symbiotic defects including reduced shoot biomass, nodule number, and nodule mass that are fully restored by complementation. Critically, AuxT-enriched bEVs contain elevated auxin levels, and nodules colonized by the complemented strain accumulate more auxin specifically within the bEVs peribacteroid space, while bacteroids themselves show no auxin retention. We postulate that bEV-associated AuxT mediates localized auxin export into the symbiosome, modulating the host hormonal environment to optimize symbiotic development. This work reveals a previously unrecognized mechanism of interdomain hormonal modulation, where a bacterium uses a structurally convergent transporter and vesicular delivery to actively shape host physiology and to improve the symbiotic performance.

microbiology↗

bioRxiv2025

A photosynthetic checkpoint halts Synechocystis sp. PCC 6803 response to nitrogen deprivation during glucose-mediated metabolic imbalance

Cyanobacteria adapt to nitrogen starvation by undergoing chlorosis, a regulated bleaching process involving the degradation of phycobilisomes, the light harvesting antennae complexes, and accumulation of glycogen. While this response is well-characterized under photoautotrophic conditions, its modulation by external organic carbon sources such as glucose remains poorly characterized. Here, we investigated how glucose affects chlorosis onset in the model cyanobacterium Synechocystis sp. PCC 6803. Using an integrative approach combining physiological assays, targeted metabolomics, RNA-sequencing, chlorophyll fluorescence and absorbance spectroscopy, we studied the underlying regulatory mechanisms, focusing on redox control and photosynthetic electron transport. Glucose supplementation prevented bleaching, even when added after nitrogen deprivation symptoms had begun. This effect was associated with excess glycogen accumulation, disrupted carbon partitioning, and buildup of metabolic intermediates, indicating a metabolic overflow. Despite these physiological differences, transcriptomic responses to nitrogen deprivation were largely similar regardless of glucose supplementation, suggesting regulation at the post-transcriptional or metabolic level. Glucose also impaired photosynthetic electron transport by creating a redox bottleneck at the photosystem II (PSII) acceptor side, leading to decreased electron transport to photosystem I (PSI) and oxidation of the P700 pool. These findings suggest that reduction of the P700 acceptor side is required to trigger chlorosis. Our results demonstrate that glucose uncouples nitrogen sensing from the bleaching process by altering redox balance and photosynthetic electron flow. We propose the existence of a redox-sensitive checkpoint that integrates metabolic state with photosynthetic performance, offering new insights into stress adaptation in cyanobacteria.

plant biology↗

bioRxiv2022

Functional and evolutionary significance of unknown genes from uncultivated taxa

Most microbes on our planet remain uncultured and poorly studied. Recent efforts to catalog their genetic diversity have revealed that a significant fraction of the observed microbial genes are functional and evolutionary untraceable, lacking homologs in reference databases. Despite their potential biological value, these apparently unrelated orphan genes from uncultivated taxa have been routinely discarded in metagenomics surveys. Here, we analyzed a global multi-habitat dataset covering 151,697 medium and high-quality metagenome assembled genomes (MAGs), 5,969 single-amplified genomes (SAGs), and 19,642 reference genomes, and identified 413,335 highly curated novel protein families under strong purifying selection out of previously considered orphan genes. These new protein families, representing a three-fold increase over the total number of prokaryotic orthologous groups described to date, spread out across the prokaryote phylogeny, can span multiple habitats, and are notably overrepresented in recently discovered taxa. By genomic context analysis, we pinpointed thousands of unknown protein families to phylogenetically conserved operons linked to energy production, xenobiotic metabolism and microbial resistance. Most remarkably, we found 980 previously neglected protein families that can accurately distinguish entire uncultivated phyla, classes, and orders, likely representing synapomorphic traits that fostered their divergence. The systematic curation and evolutionary analysis of the unique genetic repertoire of uncultivated taxa opens new avenues for understanding the biology and ecological roles of poorly explored lineages at a global scale.

microbiology↗

bioRxiv2020

A copper activated protease regulates photosynthetic soluble electron carriers in cyanobacteria

After the Great Oxidation Event (GOE), iron availability was greatly decreased and photosynthetic organisms evolved several alternative proteins and mechanisms. One of these proteins, plastocyanin, is a type I blue-copper protein that can replace cytochrome c6 as a soluble electron carrier between cytochrome b6f and photosystem I. In most cyanobacteria, expression of these two alternative proteins is regulated by copper availability, but the regulatory system remains unknown. Herein, we provide evidence that the regulatory system is composed of a BlaI/CopY family transcription factor (PetR) and a BlaR membrane protease (PetP). PetR represses petE (plastocyanin) expression and activates petJ (cytochrome c6), while PetP controls PetR levels in vivo. Using whole-cell extracts, we demonstrated that PetR degradation requires both PetP and copper. Transcriptomic analysis revealed that the PetRP system regulates only four genes (petE, petJ, slr0601, and slr0602), highlighting its specificity. Furthermore, the presence of petE and petRP in early branching cyanobacteria indicates that acquisition of these genes could represent an early adaptation to decreased iron bioavailability following the GOE. Significance StatementAfter the appearance of oxygenic photosynthesis, Fe became oxidized and its solubility and availability were greatly decreased. This generated a problem for most organisms since they are strongly dependent on Fe, especially photosynthetic organisms. In response, organisms evolved alternatives to Fe-containing proteins such as plastocyanin, a copper protein that substitutes for cytochrome c6 in photosynthesis. Expression of these two proteins in cyanobacteria is regulated by Cu availability, but the regulatory system remains unknown. Herein, we describe the regulatory system for these alternative proteins in photosynthesis in cyanobacteria. The mechanism involves a transcription factor (PetR) and a membrane protease (PetP) that degrades PetR in the presence of Cu.

microbiology↗