Though few CO2 reduction approaches can rival the energy efficiency and selectivity of biological CO2 fixation, the limited light absorption of natural photosynthesis pales in comparison to that of inorganic semiconductor based photovoltaics. Augmenting the CO2 reduction of biological organisms with inorganic light harvesting combines the best of both worlds. Bacteria, such as acetogens, fix CO2 into acetic acid. This common organic substrate is readily upgraded to a number of fuels, polymers, pharmaceuticals, and commodity chemicals through complementary genetically engineered bacteria, a process poised to supplant traditional petrochemical routes to the same chemicals. While this biological approach mitigates the high energy and material costs of traditional abiotic catalysts, the manufacturing of an inorganic semiconductor light harvester still relies upon non-green fabrication techniques. To address this, this presentation details a completely biological approach to the synthesis and utilization of an inorganic semiconductor light harvester for CO2 reduction at high efficiencies. Upon addition of a simple Cd2+ salt and the sulfur amino acid cysteine, the non-photosynthetic Moorella thermoacetica self-photosensitizes through the synthesis of light absorbing CdS nanoparticles. This hybrid organism, M. thermoacetica-CdS, produces acetic acid from CO2, water, and light at quantum efficiencies above 80%. This biological nature of this system renders it both self-replicating and self-regenerating, extending its operating lifetime and recycling all waste products to make this a zero-waste technology. Spectroscopic insight into the mechanism of the inorganic-biological charge transfer drives the development of subsequent generations of this technology, improving stability and performance. These advances and variations of the inorganic-biological hybrid organism concept drive this work towards outcompeting traditional approaches to chemical production, and augment the ever expanding portfolio of next generation green technologies.

Cyborg bacteria: Inorganic-biological hybrid organisms for solar-to-chemical production

254th National Meeting (2017)

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