An insoluble iron complex coated cathode enhances direct electron uptake by Rhodopseudomonas palustris TIE-1

Abstract

Microbial electrosynthesis (MES) is a promising bioelectrochemical approach to produce biochemicals. A previous study showed that Rhodopseudomonas palustris TIE-1 can directly use poised electrodes as electron donors for photoautotrophic growth at cathodic potentials that avoid electrolytic H production (photoelectroautotrophy). To make TIE-1 an effective biocatalyst for MES, we need to improve its electron uptake ability and growth under photoelectroautotrophic conditions. Because TIE-1 interacts with various forms of iron while using it as a source of electrons for photoautotrophy (photoferroautotrophy), we tested the ability of iron-based redox mediators to enhance direct electron uptake. Our data show that soluble iron cannot act as a redox mediator for electron uptake by TIE-1 from a cathode poised at +100mV vs. Standard Hydrogen electrode. We then tested whether an immobilized iron-based redox mediator Prussian blue (PB) can enhance electron uptake by TIE-1. Chronoamperometry indicates that cathodic current uptake by TIE-1 increased from 1.47±0.04 to 5.6±0.09μA/cm (3.8 times). Overall, our data show that immobilized PB can enhance direct electron uptake by TIE-1.

Phototrophic extracellular electron uptake is linked to carbon dioxide fixation in the bacterium Rhodopseudomonas palustris

“…Previously published work from our laboratory, however, suggests no redox active molecule is detectable in the spent-medium 3 . Our laboratory has also shown that a cathode-driven Fe(II)/Fe(III) redox cycle at +100 mV vs. SHE 10 , is also unlikely.…”

“…In such BESs it is difficult to isolate the response of surface-attached cells. This is because other factors like the influence of planktonic cells 3,10 , extracellular enzymes 26 , and abiotic reactions confound the interpretation of electrochemical data 3,10 . Being able to collect electrochemical data from surface-attached cells exclusively would shed light on whether EEU leads to electron transfer into the pETC.…”

“…BESs were configured as previously described 10 . Briefly, FW media (70 mL) was dispensed into sterile, sealed, three-electrode BESs which were bubbled for 60 min with 80%:20% N 2 -CO 2 to remove oxygen, and pressurized to ~50 kPa.…”

“…Furthermore, microbe-electrode interactions have been leveraged for biotechnological applications such as microbial electrosynthesis 9 . Our laboratory 3,10 , and others 11,12 , have recently applied BESs to better understand the molecular details of microbial phototrophic EEU. This has led to the discovery of at least two pure cultures capable of EEU from electrodes, the anoxygenic phototrophs Rhodopseudomonas palustris TIE-1 3 and Prosthecochloris aestuarii 12 .…”

Phototrophic N2 and CO2 Fixation Using a Rhodopseudomonas palustris-H2 Mediated Electrochemical System With Infrared Photons

“…Bacterial–electrochemical hybrid systems offer great potential for sustainable upgrading of both CO 2 and N 2 to higher value chemicals. The use of R. palustris TIE-1 in electrosynthetic systems is not new, with prior examples using Fe(II) as a mediator (Doud and Angenent, 2014; Rengasamy et al, 2018) or direct electron transfer (Bose et al, 2014; Rengasamy et al, 2018; Guzman et al, 2019; Ranaivoarisoa et al, 2019). However, there are some inconsistencies with these reports.…”