Respiratory Membrane endo-Hydrogenase Activity in the Microaerophile Azorhizobium caulinodans Is Bidirectional

BACKGROUND: The microaerophilic bacterium Azorhizobium caulinodans, when fixing N(2) both in pure cultures held at 20 µM dissolved O(2) tension and as endosymbiont of Sesbania rostrata legume nodules, employs a novel, respiratory-membrane endo-hydrogenase to oxidize and recycle endogenous H(2) produced by soluble Mo-dinitrogenase activity at the expense of O(2). METHODS AND FINDINGS: From a bioinformatic analysis, this endo-hydrogenase is a core (6 subunit) version of (14 subunit) NADH:ubiquinone oxidoreductase (respiratory complex I). In pure A. caulinodans liquid cultures, when O(2) levels are lowered to <1 µM dissolved O(2) tension (true microaerobic physiology), in vivo endo-hydrogenase activity reverses and continuously evolves H(2) at high rates. In essence, H(+) ions then supplement scarce O(2) as respiratory-membrane electron acceptor. Paradoxically, from thermodynamic considerations, such hydrogenic respiratory-membrane electron transfer need largely uncouple oxidative phosphorylation, required for growth of non-phototrophic aerobic bacteria, A. caulinodans included. CONCLUSIONS: A. caulinodans in vivo endo-hydrogenase catalytic activity is bidirectional. To our knowledge, this study is the first demonstration of hydrogenic respiratory-membrane electron transfer among aerobic (non-fermentative) bacteria. When compared with O(2) tolerant hydrogenases in other organisms, A. caulinodans in vivo endo-hydrogenase mediated H(2) production rates (50,000 pmol 10(9)·cells(-1) min(-1)) are at least one-thousandfold higher. Conceivably, A. caulinodans respiratory-membrane hydrogenesis might initiate H(2) crossfeeding among spatially organized bacterial populations whose individual cells adopt distinct metabolic states in response to variant O(2) availability. Such organized, physiologically heterogeneous cell populations might benefit from augmented energy transduction and growth rates of the populations, considered as a whole

Prey preference in a kleptoplastic dinoflagellate is linked to photosynthetic performance

Dinoflagellates of the family Kryptoperidiniaceae, known as “dinotoms”, possess diatom-derived endosymbionts and contain individuals at three successive evolutionary stages: a transiently maintained kleptoplastic stage; a stage containing multiple permanently maintained diatom endosymbionts; and a further permanent stage containing a single diatom endosymbiont. Kleptoplastic dinotoms were discovered only recently, in Durinskia capensis; until now it has not been investigated kleptoplastic behavior and the metabolic and genetic integration of host and prey. Here, we show D. capensis is able to use various diatom species as kleptoplastids and exhibits different photosynthetic capacities depending on the diatom species. This is in contrast with the prey diatoms in their free-living stage, as there are no differences in their photosynthetic capacities. Complete photosynthesis including both the light reactions and the Calvin cycle remain active only when D. capensis feeds on its habitual associate, the “essential” diatom Nitzschia captiva. The organelles of another edible diatom, N. inconspicua, are preserved intact after ingestion by D. capensis and expresses the psbC gene of the photosynthetic light reaction, while RuBisCO gene expression is lost. Our results indicate that edible but non-essential, “supplemental” diatoms are used by D. capensis for producing ATP and NADPH, but not for carbon fixation. D. capensis has established a species-specifically designed metabolic system allowing carbon fixation to be performed only by its essential diatoms. The ability of D. capensis to ingest supplemental diatoms as kleptoplastids may be a flexible ecological strategy, to use these diatoms as “emergency supplies” while no essential diatoms are available.Open Access funding enabled and organized by Projekt DEAL.We are grateful to Dr Benjamin Bailleul for discussing the photoactivity possibility of N. inconspicua, and to Prof Dieter Spiteller and Dr Adrien Lapointe for suggesting the feeding experiment of D. capensis with four selected diatoms. We also thank Dr Martin Stöckl, from the Bioimaging Centre at University of Konstanz, for technical support of the CLSM. Our thanks also go to Ms Selina Pucher and Mr Alexander H. Fürst for discussing the RT-qPCR data analyses and evaluation, and to Mr Niccolo Mosesso for discussing the TEM protocol improvement. This research was supported by the Bridging Stipend of University of Konstanz (No.638/20, granted to NY), the DFG Research Grant (No. YA 577/2-1, granted to NY), and the Symbiosis Model Systems Award (No. GBMF9360, granted to NY, RT, DGM, PGK) of the Gordon and Betty Moore Foundation. The CERCA Programme of Generalitat of Catalonia is also acknowledged. The Royal Botanic Garden Edinburgh is supported by the Scottish Government’s Rural and Environment Science and Analytical Services Division.info:eu-repo/semantics/publishedVersio

Publisher Correction: Genetic tool development in marine protists: emerging model organisms for experimental cell biology.

An amendment to this paper has been published and can be accessed via a link at the top of the paper

Genetic tool development in marine protists: emerging model organisms for experimental cell biology

Abstract: Diverse microbial ecosystems underpin life in the sea. Among these microbes are many unicellular eukaryotes that span the diversity of the eukaryotic tree of life. However, genetic tractability has been limited to a few species, which do not represent eukaryotic diversity or environmentally relevant taxa. Here, we report on the development of genetic tools in a range of protists primarily from marine environments. We present evidence for foreign DNA delivery and expression in 13 species never before transformed and for advancement of tools for eight other species, as well as potential reasons for why transformation of yet another 17 species tested was not achieved. Our resource in genetic manipulation will provide insights into the ancestral eukaryotic lifeforms, general eukaryote cell biology, protein diversification and the evolution of cellular pathways

<i>A. caulinodans</i> Nuo (NADH:quinone oxidoreductase) and Hyq (<i>endo</i>-hydrogenase) structural homologs.

†<p>5′-end of <i>hyqG</i> encodes residues 1–156;</p>‡<p>3′-end of <i>hyqG</i> encodes residues 157–504;</p>††<p>CLUSTAL 2.1 pairwise alignments.</p

<i>Azorhizobium caulinodans</i> strains.

<p><i>Azorhizobium caulinodans</i> strains.</p

Structure-function rendering of L-type Hyq <i>endo</i>-hydrogenase by analogy and homology to respiratory complex I.

<p>Inferred membrane ubiquinone (Q) or ubiquinol (QH₂) binding at the interface of HyqC, HyqG and Hyq I requires partial (14Å) extraction from the respiratory membrane hydrophobic phase; yellow rods represent linked transmembrane and transverse α-helices <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036744#pone.0036744-Efremov1" target="_blank">[14]</a>. Any HyqG catalytic site remains speculative; <i>in vivo</i> activity is in principle fully reversible (see Discussion).</p

H₂ evolution by <i>A. caulinodans</i> diazotrophic cultures.

†<p>pmol 10⁹·cells⁻¹ min⁻¹ (typical, single experiment);</p>‡<p>multiple experiments.</p