Biology subjects

Nürnberg, D. J.

Publications and source records attributed to Nürnberg, D. J..

5 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

ExocubeBio: an in-situ fluidic platform for microbial exposure on the International Space Station

Space-based platforms currently represent the most accurate means to experimentally assess the influence of the space environment on biological systems. However, performing such experiments remains technically challenging and requires highly specialized instrumentation. This study describes the current development and hardware qualification of ExocubeBio, a miniaturized experimental platform for in-situ biological space exposure. This experiment is scheduled for installation on the exterior of the International Space Station in 2027, as part of Exobio, the European Space Agencys new generation exobiology exposure facility. ExocubeBio will expose live microbial samples to the low Earth orbit environment, and combine autonomous in-situ optical density and fluorescence measurements, with the capacity to return preserved samples to Earth. Achieving these experimental goals requires a specialized, robust and reliable hardware system. The ExocubeBio hardware testing described here includes assessment of material biocompatibility and durability, functional validation of the miniaturized fluidic system, and optimization of the integrated optical subsystem for optical density and fluorescence measurements. These results demonstrate that the ExocubeBio experimental hardware components can each execute their core functional and operational requirements; subsystems allow for sample exposure, in-situ measurements of microbial cultures, and the chemical preservation of samples for post-flight analysis. As ExocubeBio transitions from hardware development to mission readiness, the results presented here validate the overall design and engineering approaches utilized. By combining the strengths of in-situ monitoring and sample return, ExocubeBio represents a significant advancement in space-based experimentation, and will provide new insights into microbial responses to the space environment.

microbiology↗

bioRxiv2025

Synthesis of C8-vinyl chlorophylls d and f impairs far-red light photoacclimation and growth under far-red light

The inducible biosynthesis of chlorophylls d and f enables a subset of specialised cyanobacteria to perform oxygenic photosynthesis under far-red light--in the absence of visible wavelengths--via a process termed far-red light photoacclimation. These pigments, like the more common chlorophylls a and b, typically carry an ethyl substituent at the C8 position of the macrocycle, formed by reduction of a vinyl group by an 8-vinyl reductase enzyme. Here, we disrupted the gene encoding BciB, an 8-vinyl reductase found in the majority of cyanobacteria, in Chroococcidiopsis thermalis PCC 7203, a model for the study of far-red light photoacclimation. Disruption of bciB results in the synthesis of 8-vinyl chlorophyll a when the cells are grown in white light; on switching to far-red light, synthesis of 8V-forms of chlorophylls d and f, which have not been detected in nature, are synthesised in this strain. The bciB mutant exhibits sensitivity to high irradiance under both light regimes. Pigment analysis and whole-cell absorption and fluorescence spectroscopy reveal decreased synthesis of far-red absorbing chlorophylls, reduced photosystem assembly and an impaired acclimation to far-red light, and transmission electron microscopy demonstrates altered thylakoid membrane morphology in the mutant when compared to the wild type. These results demonstrate the importance of 8-vinyl group reduction for acclimation to far-red light.

biochemistry↗

bioRxiv2024

The ancient evolution of far-red light photoacclimation in cyanobacteria

Cyanobacteria oxygenated the atmosphere of early Earth and continue to be key players in global carbon and nitrogen cycles. A phylogenetically diverse subset of extant cyanobacteria can perform photosynthesis with far-red light through a process called far-red light photoacclimation, or FaRLiP. This phenotype is enabled by a cluster of [~]20 genes, and involves the synthesis of red-shifted chlorophylls f and d, together with paralogues of the ubiquitous photosynthetic machinery used in visible light. The FaRLiP gene cluster is present in diverse, environmentally important cyanobacterial groups but its origin, evolutionary history, and connection to early biotic environments have remained unclear. This study takes advantage of the recent increase in (meta)genomic data to clarify this issue; sequence data mining, metagenomic assembly, and phylogenetic tree networks were used to recover more than 600 new FaRLiP gene sequences, corresponding to 52 new gene clusters. These data enable high-resolution phylogenetics and - by relying on multiple gene trees, together with gene arrangement conservation - support FaRLiP appearing early in cyanobacterial evolution. Sampling information shows that considerable FaRLiP diversity can be observed in microbialites to the present day, and the process may have been associated with microbial mats and stromatolite formation in the early Paleoproterozoic. The ancestral FaRLiP cluster was reconstructed, revealing a conserved intergenic regulatory sequence that has been maintained for billions of years. Taken together, our results indicate that oxygenic photosynthesis using far-red light may have played a significant role in Earths early history.

evolutionary biology↗

bioRxiv2019

A cytoskeletal network maintains filament shape in the multicellular cyanobacterium Anabaena sp. PCC 7120

Polymerizing and filament-forming proteins are instrumental for numerous cellular processes such as cell division and growth. Their function in stabilization and localization of protein complexes and replicons is achieved by a filamentous structure. Known filamentous proteins assemble into homopolymers consisting of single subunits - e.g. MreB and FtsZ in bacteria - or heteropolymers that are composed of two subunits, e.g. keratin and /{beta} tubulin in eukaryotes. Here, we describe two novel coiled-coil-rich proteins (CCRPs) in the filament forming cyanobacterium Anabaena sp. PCC 7120 (hereafter Anabaena) that assemble into a heteropolymer and function in the maintenance of the Anabaena multicellular shape (termed trichome). The two CCRPs - Alr4504 and Alr4505 (named ZicK and ZacK) - are strictly interdependent for the assembly of protein filaments in vivo and polymerize nucleotide-independently in vitro, similar to known intermediate filament (IF) proteins. A {Delta}zicK{Delta}zacK double mutant is characterized by a zigzagged cell arrangement and hence a loss of the typical linear Anabaena trichome shape. ZicK and ZacK interact with themselves, with each other, with the elongasome protein MreB, the septal junction protein SepJ and the divisome associate septal protein SepI. Our results suggest that ZicK and ZacK function in cooperation with SepJ and MreB to stabilize the Anabaena trichome and are likely essential for the manifestation of the multicellular shape in Anabaena. Our study reveals the presence of filament-forming IF-like proteins whose function is achieved through the formation of heteropolymers in cyanobacteria.

microbiology↗