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CO-Dependent Hydrogen Production by the Facultative Anaerobe Parageobacillus Thermoglucosidasius

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CO-Dependent Hydrogen Production by the Facultative Anaerobe Parageobacillus Thermoglucosidasius Mohr et al. Microb Cell Fact (2018) 17:108 https://doi.org/10.1186/s12934-018-0954-3 Microbial Cell Factories RESEARCH Open Access CO‑dependent hydrogen production by the facultative anaerobe Parageobacillus thermoglucosidasius Teresa Mohr1,4* , Habibu Aliyu1, Raphael Küchlin1, Shamara Polliack2, Michaela Zwick1, Anke Neumann1, Don Cowan2 and Pieter de Maayer3 Abstract Background: The overreliance on dwindling fossil fuel reserves and the negative climatic efects of using such fuels are driving the development of new clean energy sources. One such alternative source is hydrogen (H­ 2), which can be generated from renewable sources. Parageobacillus thermoglucosidasius is a facultative anaerobic thermophilic bacte- rium which is frequently isolated from high temperature environments including hot springs and compost. Results: Comparative genomics performed in the present study showed that P. thermoglucosidasius encodes two evolutionary distinct ­H2-uptake [Ni-Fe]-hydrogenases and one ­H2-evolving hydrogenases. In addition, genes encod- ing an anaerobic CO dehydrogenase (CODH) are co-localized with genes encoding a putative ­H2-evolving hydroge- nase. The co-localized of CODH and uptake hydrogenase form an enzyme complex that might potentially be involved in catalyzing the water-gas shift reaction (CO ­H2O ­CO2 ­H2) in P. thermoglucosidasius. Cultivation of P. thermo- glucosidasius DSM ­2542T with an initial gas atmosphere+ → of 50%+ CO and 50% air showed it to be capable of growth at elevated CO concentrations (50%). Furthermore, GC analyses showed that it was capable of producing hydrogen at an equimolar conversion with a fnal yield of 1.08 ­H2/CO. Conclusions: This study highlights the potential of the facultative anaerobic P. thermoglucosidasius DSM 2542­ T for developing new strategies for the biohydrogen production. Keywords: Biohydrogen production, Parageobacillus thermoglucosidasius, Carbon monoxide dehydrogenase, Hydrogenase, Water-gas shift reaction Background Hydrogen ­(H2) has recently become prominent as In the next 30 years, the global energy demand will a very attractive clean and sustainable energy source, expand by ca. 30% and the vast majority (ca. 85%) of the especially when generated via ‘eco-friendly’ strategies. energy resources required to ofset the rising demand will In comparison to other fuels, ­H2 has the highest energy come from non-renewable sources such as natural gas content (141.9 MJ/kg higher heating value) [2]. Addi- and crude oil [1]. Tis will result in increased pressure on tionally, its complete combustion with pure oxygen pro- the dwindling fossil fuel reserves and in greater emission duces only water (2 ­H2 + O2 → 2 ­H2O) as a by-product. of greenhouse gases into the Earth’s atmosphere. Tere is Te majority of current industrial ­H2 production strat- thus an urgent need for further development and imple- egies, such as coal gasifcation, steam reformation and mentation of clean and renewable alternative energy partial oxidation of oil, are unsustainable, harmful to sources [2, 3]. the environment, energy intensive and expensive [4, 5]. As such, over the past few years, the production of *Correspondence: [email protected] ­H via microbial catalysis has drawn increasing inter- 4 Section II: Technical Biology, Institute of Process Engineering in Life 2 Science, Karlsruhe Institut für Technologie (KIT), Kaiserstrasse 12, est. Several diferent strategies to produce biohydro- 76131 Karlsruhe, Germany gen, such as photofermentation of organic substances Full list of author information is available at the end of the article © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat​iveco​mmons​.org/licen​ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creat​iveco​mmons​.org/ publi​cdoma​in/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Mohr et al. Microb Cell Fact (2018) 17:108 Page 2 of 12 by photosynthetic bacteria, bio-photolysis of water by Methods algae and dark fermentation of organic substances by Microorganisms anaerobic microorganism, have been explored [6]. Tese Te production of H2 by P. thermoglucosidasius when strategies have the advantage of lower energy expendi- grown in the presence of CO was tested using P. ther- ture, lower cost and higher yields than the industrial moglucosidasius DSM 2542T. Two related strains, methods [7]. Another advantage is the potential to use Geobacillus thermodenitrifcans DSM 465T and P. toe- cheap feedstocks, such as lignocellulosic waste bio- bii DSM 14590 T, which lack orthologues of the three mass, which can be converted into a gas mixture termed hydrogenase loci as well as the CODH locus, were ‘synthesis gas’. Tis gas consists primarily of carbon included as controls. All strains were obtained from monoxide (CO), carbon dioxide (CO2) and H2 [8]. In a the DSMZ (Deutsche Sammlung von Mikroorganismen further step, the CO can react with water to generate und Zellkulturen GmbH, Braunschweig, Germany). H2 via a biologically- or chemically-mediated water-gas shift (WGS) reaction: CO + H2O → CO2 + H2. During the biologically mediated reaction, a carbon monoxide Culture conditions and media dehydrogenase (CODH) oxidizes CO and electrons are Pre-cultures and cultures were grown aerobically in released. Subsequently, a coupled hydrogenase reduces mLB (modifed Luria–Bertani) medium containing the released electrons to molecular hydrogen [9]. Sev- tryptone (1% w/v), yeast extract (0.5% w/v), NaCl (0.5% eral mesophilic, anaerobic prokaryotic taxa, including w/v), 1.25 ml/l NaOH (10% w/v), and 1 ml/l of each of Rhodospirillum rubrum and Rhodopseudomonas palus- the flter-sterilized stock solutions: 1.05 M nitrilotri- tris, are known for the ability to perform the WGS reac- acetic acid, 0.59 M MgSO4·7H2O, 0.91 M CaCl2·2H2O tion [10]. and 0.04 M FeSO4·7H2O. Te frst pre-culture was It has been observed that higher yields of H2 can be inoculated from glycerol stock (20 µl in 20 ml mLB) and obtained in higher temperature fermentations [11]. cultivated for 24 h at 60 °C and rotation at 120 rpm in Thus, there has been increasing interest in the use of an Infors Termotron (Infors AG, Bottmingen, Swit- thermophilic anaerobic bacteria, such as Carboxydo- zerland). A second pre-culture was inoculated from the thermus hydrogenoformans and Thermosinus carboxy- frst one to an OD600 of 0.1 and incubated as above for divorans [12, 13], as well thermophilic archaea (e.g. 12 h. For the experiments, 250 ml serum bottles were Thermococcus onnurineus) [7]. prepared with 50 ml mLB and a gas phase of 50% CO An industrial process utilizing CO-oxidizing bacte- and 50% atmospheric air at 1 bar atmospheric pressure, ria for biohydrogen production has not yet been real- which were inoculated with 1 ml from the second pre- ized, although many CO-using hydrogenogenic species culture. Te experiments were conducted in quadrupli- have been isolated. This may largely be attributed to cate for a total duration of 84 h. the sensitivity of both the hydrogenase and CODH enzymes to oxygen [6, 14]. For example, the hydro- genase of Thermotoga maritima lost 80% of its activ- Analytical methods ity after flushing with air for 10 s [15]. Removal of O 2 Samples were taken at diferent time points during the from industrial waste gases or from bioreactors is pro- experimental procedure. Before and after the sampling hibitively expensive, making the use of strictly anaero- the pressure was measured using a manometer (GDH bic CO-oxidizing hydrogenogens unfeasible [16]. Here, 14 AN, Greisinger electronic, Regenstauf, Germany). we have analysed the hydrogenogenic capacity of the To monitor the growth of the cultures, 1 ml of the cul- facultative anaerobe Parageobacillus thermoglucosi- ture was aspirated through the stopper and absorb- dasius. Comparative genomics revealed the presence ance was measured at OD600 using an Ultrospec 1100 of three distinct hydrogenases, two uptake hydroge- pro spectrophotometer (Amersham Biosciences, USA). nases as well as one H2-evolving hydrogenase, which Te determination of the gas compositions at diferent is linked to an anaerobic CODH. Evolutionary analy- time points was conducted using a 3000 Micro GC gas sis showed that this combination of hydrogenases is analyzer (Infcon, Bad Ragaz, Switzerland) with the col- unique to P. thermoglucosidasius and suggests that umns Molsieve and PLOT Q. A total of 3 ml was sam- H2 plays a pivotal in the bioenergetics of this organ- pled from the head space and injected into the GC. A ism. Furthermore, fermentations and downstream GC constant temperature of 80 °C was maintained during analysis showed that this facultative anaerobe is capa- the total analysis time of 180 s. Te gas compositions at ble of utilizing CO in the WGS reaction to generate an the diferent sampling points were calculated using the equimolar amount of H2 once most of the oxygen in formulas in Additional fle 1. the medium has been exhausted. Mohr et al. Microb Cell Fact (2018) 17:108 Page 3 of 12 Comparative genomic analyses 1d uptake hydrogenase (E-value = 0.0). Tis unidirec- Te large hydrogenase subunits were identifed from the tional, membrane-bound, O2-tolerant hydrogenase is annotated genome of P. thermoglucosidasius DSM 2542T present in a broad range of obligately aerobic and facul- (CP012712.1) by comparison against the Hydrogenase tatively anaerobic soil-borne, aquatic and host-associated DataBase (HyDB) [17]. Te full hydrogenase loci were taxa such as Ralstonia eutropha, Escherichia coli and identifed by searching the genome up- and downstream Wolinella succinogenes [25, 26]. Te H 2 molecules con- of the large subunit gene, extracted and mapped against sumed by group 1d hydrogenases are coupled to aerobic the genome using the CGView server [18].
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