Engineering the iron‐oxidizing chemolithoautotroph Acidithiobacillus ferrooxidans for biochemical production

Abstract

There is growing interest in developing non-photosynthetic routes for the conversion of CO2 to fuels and chemicals. One underexplored approach is the transfer of energy to the metabolism of genetically modified chemolithoautotrophic bacteria. Acidithiobacillus ferrooxidans is an obligate chemolithoautotroph that derives its metabolic energy from the oxidation of iron or sulfur at low pH. Two heterologous biosynthetic pathways have been expressed in A. ferrooxidans to produce either isobutyric acid or heptadecane from CO2 and the oxidation of Fe(2+). A sevenfold improvement in productivity of isobutyric acid was obtained through improved media formulations in batch cultures. Steady-state efficiencies were lower in continuous cultures, likely due to ferric inhibition. If coupled to solar panels, the photon-to-fuel efficiency of this proof-of-principle process approaches estimates for agriculture-derived biofuels. These efforts lay the foundation for the utilization of this organism in the exploitation of electrical energy for biochemical synthesis.

Enhancing isobutyric acid production from engineered Acidithiobacillus ferrooxidans cells via media optimization

“…Further increasing initial Fe 2þ concentration to 288 mM and increasing pH to 2.2 along with 50 mM gluconate resulted in the highest energy efficiency achieved in this work (1.3%), compared to 0.93 % reported by Kernan et al (2015) ( Table II). Higher initial Fe 2þ concentrations led to improved IBA yields, while higher initial pH increased cell yields.…”

“…Genetically modified A. ferrooxidans (AF-KDC) cells were obtained by transforming wild-type cells (ATCC 23270) with a synthetic 2-ketoacid decarboxylase (KDC) gene which enables production isobutyric acid (IBA) from CO 2 , as previously described (Kernan et al, 2015). Cells were propagated and maintained in batches with ATCC 2039 A. ferrooxidans media as previously described (Li et al, 2014b).…”

Harnessing a methane‐fueled, sediment‐free mixed microbial community for utilization of distributed sources of natural gas

“…In addition to building a symbiosis with ANME to enable methane consumption, sulfate‐reducing bacteria can remediate heavy metals (García, Moreno, Ballester, Blázquez, & González, ; Joo, Choi, Kim, Kim, & Oh, ) and produce plastic precursor storage molecules (Hai, Lange, Rabus, & Steinbüchel, ; Wang, Yin, & Chen, ). Sulfide generated through this process can be used as feedstock for genetically tractable chemoautotrophs (Kernan, West, & Banta, ; Nybo, Khan, Woolston, & Curtis, ), which can make high‐value chemical products (Kernan et al, ). Finding a conductive physical scaffold to enable industrially‐relevant reactions within the context of an ecophysiologicaly sustainable system—whereby microbial communities can take advantage of natural electrical and chemical gradients (e.g., Pfeffer et al, )—would decrease transport and scale‐up costs while building a robust, customizable system.…”

Missing Iron-Oxidizing Acidophiles Highly Sensitive to Organic Compounds

“…Previous studies have used agarose plates for the colony isolation and purification of acidithiobacilli, including strain ATCC 23270 T and its derivatives (7, 13). However, when serial dilutions of the resultant culture were streaked on Fe9K agarose plates, no colony formed on them.…”

“…A recent study engineered A. ferrooxidans for the production of isobutyrate from carbon dioxide (13). This indicates the potential of acidithiobacilli for the production of value-added chemicals, whereas productivity is lower than that required for commercial production primarily due to their low growth capacities.…”