Biology subjects

Lopez-Igual, R.

Publications and source records attributed to Lopez-Igual, R..

4 recordsLinked to original sources

bioRxiv2026

The cyanobacterium Anabaena uses pleomorphism as an acclimation strategy to high light stress

O_LIPhytoplankton species display characteristic morphologies that are generally assumed to confer adaptive advantages, yet the functional significance of cell shape remains poorly understood. Here, we investigated whether pleomorphism contributes to acclimation to changing light environments. C_LIO_LIUsing the cyanobacterium Anabaena sp. PCC 7120 as a model system, we combined molecular genetics, microscopy, physiological measurements and biophysical analyses to determine how morphology is regulated and how it affects photosynthetic performance under different light intensities. C_LIO_LIWe show that Anabaena undergoes a reversible light-dependent morphological transition from rod-shaped cells under low light to large globular cells under high light stress. This transition is controlled by the relative activities of the elongasome and class A penicillin-binding proteins and is accompanied by thylakoid reorganization. The globular morphology reduces light absorption and enables cells to maintain photosynthetic activity under photoinhibitory conditions. C_LIO_LIOur findings establish a mechanistic link between cell-wall remodelling, cellular optics and photosynthetic performance, revealing pleomorphism as a dynamic acclimation strategy to high light stress. More broadly, this work provides experimental support for the packaging effect and highlights morphology as an active determinant of phytoplankton fitness. C_LI

plant biology↗

bioRxiv2026

Large-scale recovery of integron cassettes for gene discovery screens

Integrons capture and stockpile adaptive genes encoded in modular mobile genetic elements called integron cassettes (ICs). Present in 17% of bacterial genomes, integrons can harbor hundreds of cassettes, representing a hotspot of genetic variability. Some ICs encode antimicrobial or phage resistance genes, but most remain functionally uncharacterized, representing an untapped source of genes of biotechnological interest. Here, we present two tools, the cassette gatherer and hunter, that allow the swift establishment of libraries of genes either from genetically tractable strains or directly from DNA. By re-engineering a class 1 integron, these platforms capture single cassettes in a sequence and function-independent manner. When applied to Vibrio genomes, they recovered hundreds of single cassettes per assay with >99% specificity. To validate the usability of our tools for the discovery of new genes, we subjected these libraries to screens against phages ICP2 and T4, and identified nine phage-defense systems, including five previously undescribed. Hence, these tools provide a fast and simple method to recover thousands of ICs, in a way amenable to gene-discovery screens.

microbiology↗

bioRxiv2024

Long-term evolution reveals the role of the circadian cycle in the environmental adaptation of cyanobacteria

Circadian clocks synchronize internal cellular states with diurnal rhythms. Widespread in bacteria and eukaryotes, they regulate a variety of physiological processes, from hormone secretion in animals to carbon fixation in photosynthetic organisms. The adaptive role of circadian clocks is assumed to stem from their ability to anticipate environmental change, yet their impact on ecological adaptation remains unclear. Here, we use experimental evolution to study the interplay between fitness and circadian regulation in the model cyanobacterium Synechococcus elongatus PCC 7942. After 1,200 generations under continuous, high-intensity illumination, we obtained a strain that grew six times faster than its ancestral counterpart. Genome sequencing revealed three mutations fixed in the population, two of which replicated the fast-growing phenotype in the wild-type. A deletion in SasA, a key circadian regulator, was essential for fast growth. Transcriptomic and metabolomic analyses revealed that this mutation perturbed the rhythmicity of the cycle, while simultaneously locking the cell in a transcriptomic response to high intensity illumination. A comparison with another fast- growing isolate, UTEX 2973, showed convergent transcriptomic states despite different driving mutations. Our results indicate that the clock acts not only as a timekeeping device, but also as an adaptive mechanism to optimize growth across diverse ecological conditions.

microbiology↗

bioRxiv2023

Identification of the active mechanism of aminoglycoside entry in V. cholerae through characterization of sRNA ctrR, regulating carbohydrate utilization and transport.

The possible active entry of aminoglycosides in bacterial cells has been debated since the development of this antibiotic family. Here we report the identification of their active transport mechanism in Vibrio species. We combined genome-wide transcriptional analysis and fitness screens to identify alterations driven by treatment of V. cholerae with sub-minimum inhibitory concentrations (sub-MIC) of the aminoglycoside tobramycin. RNA-seq data showed downregulation of the small non-coding RNA ncRNA586 during such treatment, while Tn-seq revealed that inactivation of this sRNA was associated with improved fitness in the presence of tobramycin. This sRNA is located near sugar transport genes and previous work on a homologous region in Vibrio tasmaniensis suggested that this sRNA stabilizes gene transcripts for carbohydrate transport and utilization, as well as phage receptors. The role for ncRNA586, hereafter named ctrR, in the transport of both carbohydrates and aminoglycosides, was further investigated. Flow cytometry on cells treated with a fluorescent aminoglycoside confirmed the role of ctrR and of carbohydrate transporters in differential aminoglycoside entry. Despite sequence diversity, ctrR showed functional conservation across the Vibrionales. This system in directly modulated by carbon sources, suggesting regulation by carbon catabolite repression, a widely conserved mechanism in Gram-negative bacteria, priming future research on aminoglycoside uptake by sugar transporters in other bacterial species.

microbiology↗