Metabolic Profiling of Geobacter Sulfurreducens During Scale-Up
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AEM Accepted Manuscript Posted Online 6 March 2015 Appl. Environ. Microbiol. doi:10.1128/AEM.00294-15 Copyright © 2015, American Society for Microbiology. All Rights Reserved. 1 Metabolic profiling of Geobacter sulfurreducens 2 during scale-up 3 4 Howbeer Muhamadali1, Yun Xu1, David I. Ellis1, J. William Allwood1, Nicholas J.W. 5 Rattray1, Elon Correa1, Haitham Alrabiah1,3, Jonathan R. Lloyd2*and Royston Goodacre1* 6 1School of Chemistry, Manchester Institute of Biotechnology, University of Manchester, Manchester, 7 UK 8 2Williamson Research Centre for Molecular Environmental Science, School of Earth, Atmospheric and 9 Environmental Sciences the University of Manchester, Manchester, UK 10 3Current address: Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud 11 University, P.O. Box 2457, Riyadh 11451, Saudi Arabia 12 *Corresponding authors: 13 Royston Goodacre, E-mail: [email protected], Tel: 0161 306-4480 14 Jonathan R. Lloyd, E-mail: [email protected], Tel: 0161 275-7155 15 16 Running title: Metabolomics of G. sulfurreducens 17 Keywords: Geobacter, Scale-up, FT-IR spectroscopy, GC-MS, Metabolic fingerprinting, 18 Biotechnology, Magnetite, Nanoparticles, Bioremediation, Optimisation, Metabolomics 19 20 ABSTRACT 21 During the industrial scale-up of bioprocesses it is important to establish that the 22 biological system has not changed significantly when moving from small laboratory 23 scale shake flasks or culturing bottles to an industrially relevant production level. 24 Therefore during upscaling of biomass production for a range of metal 25 transformations, including the production of biogenic magnetite nanoparticles by 26 G. sulfurreducens, from 100 mL bench scale to 5 L fermenters, we applied Fourier 27 transform infrared (FT-IR) spectroscopy as a metabolic fingerprinting approach 28 followed by the analysis of bacterial cell extracts by gas chromatography mass 29 spectrometry (GC-MS) for metabolic profiling. FT-IR results clearly differentiated 30 between the phenotypic changes associated with different growth phases as well as 31 the two culturing conditions. Furthermore, the clustering patterns displayed by 32 multivariate analysis were in agreement with the turbidimetric measurements, which 1 33 displayed an extended lag phase for cells grown in a 5 L bioreactor (24 h) compared 34 to those grown in 100 mL serum bottles (6 h). GC-MS analysis of the cell extracts 35 demonstrated an overall accumulation of fumarate during the lag phase in both 36 culturing conditions, coinciding with the detected concentrations of oxaloacetate, 37 pyruvate, nicotinamide and glycerol-3-phosphate being at their lowest levels 38 compared to other growth phases. These metabolites were overlaid onto a metabolic 39 network of G. sulfurreducens, and taking into account the levels of these metabolites 40 throughout the entire fermentation process, the limited availability of oxaloacetate and 41 nicotinamide would seem to be the main metabolic bottleneck resulting from this 42 scale-up process. Additional metabolite-feeding experiments were carried out to 43 validate the above hypothesis. Nicotinamide supplementation (1 mM) did not display 44 any significant effects on the lag phase of G. sulfurreducens cells grown in the 100 45 mL serum bottles. However, it significantly improved the growth behaviour of cells 46 grown in the 5 L bioreactor by reducing the lag phase from 24 h to 6 h, whilst 47 providing higher yield in comparison to the 100 mL serum bottles. 2 48 INTRODUCTION 49 Geobacter species are Gram-negative Deltaproteobacteria, which have been 50 recognised as an intrinsic component of a diverse range of natural subsurface 51 environments including soils and groundwater, as well as aquatic sediments (1). 52 Geobacter species are considered to play a vital role in the global recycling of metals 53 and carbon (2) in anaerobic environments, coupling the oxidation of acetate, and other 54 key intermediates from fermentative metabolism of natural complex organic matter, to 55 the reduction of Fe(III) and other metals (3,4). G. metallireducens was the first 56 organism to be isolated with the ability of reducing insoluble Fe(III) oxides in tandem 57 with oxidation of acetate (5,6). 58 G. sulfurreducens strain PCA is another member of the family Geobacteraceae, 59 which also has the ability of coupling the oxidation of acetate to the reduction of 60 sulfur, fumarate, Fe(III) and other metals (7). The availability of its complete genome 61 sequence not only revealed unexpected insights into its complex metabolism 62 (including evidence of aerobic metabolism (8), one-carbon and complex carbon 63 metabolism) but also multiple capabilities in terms of motility and chemotactic 64 behaviour (2). For a detailed introduction to both the physiology and ecology of 65 Geobacter spp. (and other metal reducers), the reader is directed to Lovley, et al. (9). 66 It is perhaps not surprising that these multiple and complex metabolic and 67 physiological capabilities make this fascinating species an ideal candidate for 68 bioremediation applications (amongst others). Of particular interest is the treatment 69 and removal of subsurface metal contaminants (10,11), such as U(VI) (12,13), Cr(VI) 70 (14) and Tc(VII) (15,16). For a comparative review of the microbial reduction of 71 metals and metalloids see Lloyd (17), and for a recent review of systems-level and 3 72 modelling approaches to bioremediation of uranium contaminated groundwater see 73 Williams, et al. (18). 74 Other related biotechnical applications linked to Geobacter species include the 75 production of magnetite nanoparticles (19-21) and the potential role of this magnetic 76 material in a wide range of applications such as cancer therapy (22), drug delivery 77 (23), bioseparation (24,25), catalysis (26), reductive bioremediation of contaminants 78 (27), as well as the production of nanomaterials for magnetic data storage devices 79 (28). However, the ability to exploit these microorganisms to their full potential 80 requires a deeper understanding of the basis of their biochemical composition, 81 genetics, and metabolic behaviour in a range of process environments (29), especially 82 at scale. 83 There are a range of approaches available to optimize the biotechnological potential 84 of bacteria such as genetic modification, adjustment of media components and/or 85 incubation conditions; any of which could be applied to improve, for example, the 86 growth kinetics and yields of these extremely useful microorganisms, particularly 87 when there is a requirement to scale-up for industrial/biotechnological applications. 88 Here, we demonstrate a metabolomics approach for achieving this goal. 89 The metabolome is described as being the complement of all low molecular weight 90 metabolites found within a biological sample, such as a single organism, which 91 encompasses the end products of gene expression that are necessary for the 92 maintenance, growth and normal function of a cell (i.e. metabolic intermediates, 93 signalling molecules, and secondary metabolites) (30). The field of metabolomics is 94 accelerating at a considerable rate, which is perhaps not surprising considering 4 95 improvements in the ability to measure multiple metabolites from complex biological 96 systems with a high degree of accuracy and precision (31). 97 Since the metabolome is downstream from the genome, proteome and transcriptome 98 in biological systems, and is affected via the changes and interactions of the above 99 processes, it is said to reflect the activities of the cells at functional levels (32). 100 Therefore, metabolomic approaches are considered complementary to genomics, 101 transcriptomics and proteomics (33) and have been used for optimising microbial 102 processes (34-36). 103 Metabolic fingerprinting is generally employed as a rapid, global, and high- 104 throughput approach to provide sample classification, and is also used as a screening 105 tool to discriminate samples of different biological status (37) (such as the 106 physiological state in this case) or origin, which may pertain to disease diagnostics 107 (case/control) or longitudinal intervention, both aimed at biomarker discovery (38,39). 108 FT-IR is a vibrational spectroscopy technique based on the principle of the absorption 109 of infrared light by the sample of interest, causing intermolecular bond vibrations, 110 which can be detected and directly correlated to (bio)chemical species. FT-IR in 111 comparison to other metabolic fingerprinting techniques, offers the advantages of 112 minimal sample preparation, high-throughput microbial analysis, and is extremely 113 rapid (spectral acquisition, 10 s – 1 min), highly reproducible, low-cost and 114 portability. Since its potential for microbial analysis was first widely recognised by 115 Naumann, et al. (40), FT-IR spectroscopy has been applied to a wide range of areas 116 within microbiology (40) including clinical (41,42), food (43-45), environmental (46- 117 49), and biotechnological applications (50). 5 118 Whilst FT-IR spectroscopy is a global, holistic approach, it does not of course have 119 the sensitivity or specificity of MS approaches. Therefore in this study we also 120 employed GC-MS as a metabolic profiling method which yields information on 121 central carbon as well as amino acid metabolism (51), and has been used to analyse 122 industrial bioprocesses and aid in metabolic engineering (34,36). 123 This study is focused on the first part