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Microbe-Mineral Interaction and Novel Proteins for Iron Oxide Mineral Reduction in the Hyperthermophilic Crenarchaeon Pyrodictium delaneyi.

ABSTRACT: Dissimilatory iron reduction by hyperthermophilic archaea occurs in many geothermal environments and generally relies on microbe-mineral interactions that transform various iron oxide minerals. In this study, the physiology of dissimilatory iron and nitrate reduction was examined in the hyperthermophilic crenarchaeon type strain Pyrodictium delaneyi Su06. Iron barrier experiments showed that P. delaneyi required direct contact with the Fe(III) oxide mineral ferrihydrite for reduction. The separate addition of an exogenous electron shuttle (anthraquinone-2,6-disulfonate), a metal chelator (nitrilotriacetic acid), and 75% spent cell-free supernatant did not stimulate growth with or without the barrier. Protein electrophoresis showed that the c-type cytochrome and general protein compositions of P. delaneyi changed when grown on ferrihydrite relative to nitrate. Differential proteomic analyses using tandem mass tagged protein fragments and mass spectrometry detected 660 proteins and differential production of 127 proteins. Among these, two putative membrane-bound molybdopterin-dependent oxidoreductase complexes increased in relative abundance 60- to 3,000-fold and 50- to 100-fold in cells grown on iron oxide. A putative 8-heme c-type cytochrome was 60-fold more abundant in iron-grown cells and was unique to the Pyrodictiaceae There was also a >14,700-fold increase in a membrane transport protein in iron-grown cells. For flagellin proteins and a putative nitrate reductase, there were no changes in abundance, but a membrane nitric oxide reductase was more abundant on nitrate. These data help to elucidate the mechanisms by which hyperthermophilic crenarchaea generate energy and transfer electrons across the membrane to iron oxide minerals.IMPORTANCE Understanding iron reduction in the hyperthermophilic crenarchaeon Pyrodictium delaneyi provides insight into the diversity of mechanisms used for this process and its potential impact in geothermal environments. The ability of P. delaneyi to reduce Fe(III) oxide minerals through direct contact potentially using a novel cytochrome respiratory complex and a membrane-bound molybdopterin respiratory complex sets iron reduction in this organism apart from previously described iron reduction processes. A model is presented where obligatory H₂ oxidation on the membrane coupled with electron transport and either Fe(III) oxide or nitrate reduction leads to the generation of a proton motive force and energy generation by oxidative phosphorylation. However, P. delaneyi cannot fix CO₂ and relies on organic compounds from its environment for biosynthesis.

SUBMITTER: Kashyap S

PROVIDER: S-EPMC8105010 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Fe(III) (oxyhydr)oxides are electron acceptors for some hyperthermophilic archaea in mildly reducing geothermal environments. However, the kinds of iron oxides that can be used, growth rates, extent of iron reduction, and the morphological changes that occur to minerals are poorly understood. The hyperthermophilic iron-reducing crenarchaea Pyrodictium delaneyi and Pyrobaculum islandicum were grown separately on six different synthetic nanophase Fe(III) (oxyhydr)oxides. For both organisms, growth on ferrihydrite produced the highest growth rates and the largest amounts of Fe(II), although P. delaneyi produced four times more Fe(II) (25 mM) than P. islandicum (6 mM). Both organisms grew on lepidocrocite and akaganéite and produced 2 and 3 mM Fe(II). Modest growth occurred for both organisms on goethite, hematite, and maghemite where ≤1 mM Fe(II) was produced. The diameters of the spherical mineral end-products following P. delaneyi growth increased by 30 nm for ferrihydrite and 50-150 nm for lepidocrocite relative to heated abiotic controls. For akaganéite, spherical particle sizes were the same for P. delaneyi-reacted samples and heated abiotic controls, but the spherical particles were more numerous in the P. delaneyi samples. For P. islandicum, there was no increase in grain size for the mineral end-products following growth on ferrihydrite, lepidocrocite, or akaganéite relative to the heated abiotic controls. High-resolution transmission electron microscopy of lattice fringes and selected-area electron diffraction of the minerals produced by both organisms when grown on ferrihydrite showed that magnetite and/or possibly maghemite were the end-products while the heated abiotic controls only contained ferrihydrite. These results expand the current view of bioavailable Fe(III) (oxyhydr)oxides for reduction by hyperthermophilic archaea when presented as synthetic nanophase minerals. They show that growth and reduction rates are inversely correlated with the iron (oxyhydr)oxide crystallinity and that iron (oxyhydr)oxide mineral transformation takes different forms for these two organisms.

Project description:A novel hyperthermophilic, anaerobic filamentous archaeon, Thermofilum adornatum strain 1910bT, is capable of growing with cellulose as its sole carbon and energy source. This strain was isolated from a terrestrial hot spring in Kamchatka, Russia. The isolate 1910bT grew optimally at a temperature of 80°C and a pH of 5.5-6.0, producing cell-bound inducible cellulases. During genome analysis, genes, encoding various glycosidases (GHs) involved in oligo- and polysaccharide hydrolysis and genes for the fermentation of sugars were identified. No homologs of currently known cellulase families were found among the GHs encoded by the 1910bT genome, suggesting that novel proteins are involved. To figure this out, a proteomic analysis of cells grown on cellulose or pyruvate (as a control) was performed. Both in-depth genomic and proteomic analyses revealed four proteins (Cel25, Cel30, Cel40, and Cel45) that were the most likely to be involved in the cellulose hydrolysis in this archaeon. Two of these proteins (Cel30 and Cel45) were hypothetical according to genome analysis, while the other two (Cel25 and Cel40) have GH3 and GH1 domains, respectively. The respective genes were heterologously expressed in Escherichia coli BL21 (DE3), and enzymatic activities of recombinant proteins were measured with carboxymethyl cellulose (CMC), Avicel and cellobiose as substrates. It was revealed that the Cel30 and Cel25 proteins were likely exoglucanases with side beta-glucosidase and endoglucanase activities, that Cel40 was a multifunctional glucanase capable of hydrolyzing beta-1,4-glucosides of various lengths, and that Cel45 was an endoglucanase with side exoglucanase activity. Taking into account that the cellulolytic activity of T. adornatum 1910bT surface protein fractions was inducible, that recombinant Cel25 and Cel30 were much less active than Cel40 and Cel45, and that their gene expressions were (almost) non-induced by CMC, we suggest that Cel40 and Cel45 play a major role in the degradation of cellulose, while Cel25 and Cel30 act only as accessory enzymes.

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Microbe-Mineral Interaction and Novel Proteins for Iron Oxide Mineral Reduction in the Hyperthermophilic Crenarchaeon Pyrodictium delaneyi.

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