Characterization of the physiology and cell-mineral interactions of the marine anoxygenic phototrophic Fe(II) oxidizerRhodovulum iodosum- implications for Precambrian Fe(II) oxidation

Abstract

Anoxygenic phototrophic Fe(II)-oxidizing bacteria (photoferrotrophs) are suggested to have contributed to the deposition of banded iron formations (BIFs) from oxygen-poor seawater. However, most studies evaluating the contribution of photoferrotrophs to Precambrian Fe(II) oxidation have used freshwater and not marine strains. Therefore, we investigated the physiology and mineral products of Fe(II) oxidation by the marine photoferrotroph Rhodovulum iodosum. Poorly crystalline Fe(III) minerals formed initially and transformed to more crystalline goethite over time. During Fe(II) oxidation, cell surfaces were largely free of minerals. Instead, the minerals were co-localized with EPS suggesting that EPS plays a critical role in preventing cell encrustation, likely by binding Fe(III) and directing precipitation away from cell surfaces. Fe(II) oxidation rates increased with increasing initial Fe(II) concentration (0.43-4.07 mM) under a light intensity of 12 μmol quanta m(-2) s(-1). Rates also increased as light intensity increased (from 3 to 20 μmol quanta m(-2) s(-1)), while the addition of Si did not significantly change Fe(II) oxidation rates. These results elaborate on how the physical and chemical conditions present in the Precambrian ocean controlled the activity of marine photoferrotrophs and confirm the possibility that such microorganisms could have oxidized Fe(II), generating the primary Fe(III) minerals that were then deposited to some Precambrian BIFs.

Modulation of oxygen production in Archaean oceans by episodes of Fe(II) toxicity

“…Growth was monitored by attenuance (D 750 nm ) measurements for cultures containing ≤100 µM Fe(II). For cultures with >100 µM Fe(II), cells were counted after fixation with paraformaldehyde and dissolution of the Fe(III) precipitates 28 . Data for the counts in Fig.…”

Laboratory Simulation of an Iron(II)-rich Precambrian Marine Upwelling System to Explore the Growth of Photosynthetic Bacteria

“…Italic alphanumerical codes in brackets refer to the equipment itemized in Table 2 and shown in Figure 1. 1. Prepare 5 L of Marine Phototroph (MP) medium (referred to hereafter as "medium") following the protocol of Wu et al 16 . Adjust the pH to 6.8 using anoxic and sterile 1 M HCl or 0.5 M NaCO 3 .…”

“…Prepare 100 ml MP medium following the protocol of Wu et al 16 but substitute ferric chloride with 1 ml/L ferric ammonium citrate at 6 mg/ml. ) and inoculate with 5% of the stock culture.…”

“…Make sure to keep the valve of the gas pack closed. 16. Reduce the pressure of the N 2 /CO 2 gas line (<0.1 mbar) in the headspace gas exchange panel (C in Figure 1; position LLF) to maintain an outflow of gas from the outgassing needle (C.6).…”

Limited Zn and Ni mobility during simulated iron formation diagenesis

“…Cornell and Schwertmann, 2003) and freeze-dried prior to sorption of Ni or Zn. The marine photoferrotroph, Rhodovulum iodosum, was cultivated in artificial seawater medium as described by Wu et al (2014); the phosphate content was reduced to 1 mM to minimize FePO 4 precipitation, with additional NaCl added to maintain the same ionic strength as per Eickhoff (2013 …”