Abstract
Biohybrids composed of microorganisms and nanoparticles have emerged as potential systems for bioenergy and high-value compound production from CO2 and light energy, yet the cellular and metabolic processes within the biological component of this system are still elusive. Here we dissect the biohybrid composed of the anaerobic acetogenic bacterium Moorella thermoacetica and cadmium sulphide nanoparticles (CdS) in terms of physiology, metabolism, enzymatics and transcriptomic profiling. Our analyses show that while the organism does not grow on l-cysteine, it is metabolized to acetate in the biohybrid system and this metabolism is independent of CdS or light. CdS cells have higher metabolic activity, despite an inhibitory effect of Cd2+ on key enzymes, because of an intracellular storage compound linked to arginine metabolism. We identify different routes how cysteine and its oxidized form can be innately metabolized by the model acetogen and what intracellular mechanisms are triggered by cysteine, cadmium or blue light.
Highlights
Biohybrids composed of microorganisms and nanoparticles have emerged as potential systems for bioenergy and high-value compound production from CO2 and light energy, yet the cellular and metabolic processes within the biological component of this system are still elusive
Cultures did not grow on l- or d-cysteine alone and mixotrophic conditions with substrate-limiting concentrations of d-glucose (10 mM) and l-cysteine as additional growth substrate did not result in an increased growth either (Supplementary Fig. 2C)
We saw a stimulation of light on metabolic activity to some extent, but this was true for cadmium sulphide nanoparticles (CdS) and normal cells
Summary
Biohybrids composed of microorganisms and nanoparticles have emerged as potential systems for bioenergy and high-value compound production from CO2 and light energy, yet the cellular and metabolic processes within the biological component of this system are still elusive. An innovative proof-ofconcept study has recently been described in which a non-photosynthetic anaerobic bacterium becomes photosynthetic by coupling it to CdS nanoparticles[3] This poses a very appealing technology, as the model organism used is an acetogen and these organisms have emerged as microbial platforms for the production of high-value compounds (biofuel, bioplastic) from C O2 and inexpensive energy s ources[4]. The thermophilic acetogen Thermoanaerobacter kivui on the other hand uses an Ech complex, which couples the electron flow of Fd2− onto H + to the establishment of an ion gradient composed of both Na+ and H +, and it is only the latter which fuels a H+-dependent F1FO ATP synthase[8]. In this paper we examine M. thermoacetica in context of the biohybrid system by assessing the influence of cadmium, light and cysteine on microbial growth, metabolic activity, enzyme activity and the transcriptome of M. thermoacetica
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