Biology subjects

Marcus, J. R.

Publications and source records attributed to Marcus, J. R..

3 recordsLinked to original sources

bioRxiv2026

ATP synthase deficiency promotes prolonged hydrogenproduction in Chlamydomonas

Photosynthetic electron transport is tightly regulated to balance ATP and NADPH production and prevent over-reduction of the photosynthetic machinery. How this balance is maintained under severe ATP limitation, particularly under anoxia, is not fully resolved. Here, we used several deletion mutants of chloroplast ATP synthase subunits from Chlamydomonas reinhardtii to examine how electron flow is reorganized under anoxic conditions through the interplay between linear electron flow, cyclic electron flow, and alternative electron sinks. Using a combination of optical spectroscopy methods and membrane inlet mass spectrometry, we characterized changes in photosynthetic electron transport, proton motive force relaxation and gas exchange. Under oxic conditions, the {Delta}atpH mutant (lacking the c-subunit) showed strong acceptor-side limitation at photosystem I (PSI), whereas atpC1-2 (lacking the {gamma}-subunit) resembled the wild type. Under anoxia, this limitation was partially relieved, coinciding with sustained electron transport and prolonged hydrogen production. In particular, the {Delta}atpH mutant exhibited increased cyclic electron flow under oxic conditions and maintained PSI activity under anoxia despite impaired ATP synthesis. Prolonged hydrogen production was also observed in atpC1-2, which did not share the increased respiration of {Delta}atpH. Hydrogenase activity under anoxia is consistent with a role as an electron sink that may help alleviate PSI acceptor-side limitation and rebalance the redox state of the electron transport chain. These findings show that ATP synthase deficiency reorganizes photosynthetic electron flow and promotes prolonged hydrogen production, and point to hydrogenase as a candidate electron sink under energy-constrained conditions.

plant biology↗

bioRxiv2026

Expanding The Algal Hydrogen Toolbox: A Non-GMO Platform Reveals Multiple Physiological Routes To Sustained Hydrogen Production Across Microalgae

Sustainable hydrogen production from microalgae remains limited by intrinsic physiological constraints and the need to preserve biomass value for food and feed applications. Transgenic approaches to overcome these limitations were proven successful, yet result in genetically modified (GMO) strains that face major regulatory and deployment barriers. Here, we present a non-GMO experimental platform that enables systematic isolation of hydrogen-producing phenotypes through high-throughput UV mutagenesis pipline coupled with targeted physiological screening. Applying this approach across phylogenetically distinct algal species, including the industrial strain Chlorella vulgaris and the extremophile Chlorella ohadii, we achieve high discovery efficiency, recovering 0.4-0.6% validated hydrogen-producing mutants and achieving 6.7-25% validation rates among screen-positive candidates, indicating strong enrichment at the primary screening stage. We show that sustained hydrogen production represents a physiologically accessible state emerging across diverse genetic backgrounds. This state is consistently associated with reorganization of photosynthetic electron partitioning, yet arises through multiple distinct configurations that differentially balance hydrogen production, oxygen metabolism, and carbon fixation. This framework provides a scalable route to identify hydrogen-producing strains in industrially relevant algae without introducing foreign DNA and expands the accessible design space for photobiological hydrogen production.

plant biology↗

bioRxiv2025

Decoding host responses: How a freshwater invertebrate defends against a parasitic bacterium

Host-parasite interactions drive coevolutionary dynamics, often leading to reciprocal adaptations between hosts and parasites, a process known as the Red Queen arms race. While the molecular mechanisms underlying vertebrate and insect immune responses have been studied extensively, those of aquatic invertebrates remain unexplored, despite their critical role in ecosystem stability and aquaculture. Here, we use the Daphnia magna-Pasteuria ramosa system to investigate the hosts immune response and the molecular mechanisms underlying host-parasite interactions. We inoculated 800 D. magna hosts with 20,000 mature spores of P. ramosa and tracked the progression of infection by measuring the proportion of infected individuals and the developmental stages of the parasite at multiple time points post-inoculation (hereafter p.i.). RNA sequencing was performed at key infection phases, early (Cauliflower stage), mid (Cauliflower and Grape stages), and terminal (Cauliflower, Grape, and Mature spore stages), to capture gene expression changes linked to infection dynamics. Our transcriptomic analyses revealed key immune genes involved in host defense, including genes involved in Toll signaling pathways, thereby revealing significant changes in pathways related to immune function, host metabolism, and resource allocation. Our findings suggest that iron sequestration may serve as a host defense strategy to restrict parasite growth, representing a form of nutritional immunity. Furthermore, pathways associated with infection-induced phenotypic traits, such as somatic growth, red coloration, and castration, were significantly upregulated, underscoring the impact of the infection on host physiology. Taken together, these findings provide new insights into the interplay between hosts and parasites at a molecular level in an ecologically relevant system, advancing our understanding of infection strategies in aquatic invertebrates.

evolutionary biology↗