Diurnal Fe(II)/Fe(III) cycling and enhanced O2 production in a simulated Archean marine oxygen oasis

A J Herrmann,J Sorwat,J M Byrne,M M Gehringer,N Frankenberg-Dinkel

doi:10.1038/s41467-021-22258-1

A J Herrmann, J Sorwat + Show 3 more

Open Access

https://doi.org/10.1038/s41467-021-22258-1

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Abstract

The oxygenation of early Earth’s atmosphere during the Great Oxidation Event, is generally accepted to have been caused by oceanic Cyanobacterial oxygenic photosynthesis. Recent studies suggest that Fe(II) toxicity delayed the Cyanobacterial expansion necessary for the GOE. This study investigates the effects of Fe(II) on two Cyanobacteria, Pseudanabaena sp. PCC7367 and Synechococcus sp. PCC7336, in a simulated shallow-water marine Archean environment. A similar Fe(II) toxicity response was observed as reported for closed batch cultures. This toxicity was not observed in cultures provided with continuous gaseous exchange that showed significantly shorter doubling times than the closed-culture system, even with repeated nocturnal addition of Fe(II) for 12 days. The green rust (GR) formed under high Fe(II) conditions, was not found to be directly toxic to Pseudanabaena sp. PCC7367. In summary, we present evidence of diurnal Fe cycling in a simulated shallow-water marine environment for two ancestral strains of Cyanobacteria, with increased O2 production under anoxic conditions.

Highlights

The oxygenation of early Earth’s atmosphere during the Great Oxidation Event, is generally accepted to have been caused by oceanic Cyanobacterial oxygenic photosynthesis
The growth systems were either closed bottles with a single injection of nitrogen with 10% CO2 and 5% H2 at the start of the experiment or an open system with ventilated culture flasks inside an anoxic chamber filled with forming gas (N2 with ≤ 5% H2) and constant removal of O2 while maintaining 0.2% of CO2, which is on the lower end of the proposed CO2 concentrations of an Archaean atmosphere[24, 25]
Previous studies have proposed that Fe(II) at concentrations thought to have existed in the Archaean ocean were toxic to modern-day marine Cyanobacteria, when grown in a closed system with a single addition of Fe(II)[12]

Summary

Introduction

The oxygenation of early Earth’s atmosphere during the Great Oxidation Event, is generally accepted to have been caused by oceanic Cyanobacterial oxygenic photosynthesis. Many hypotheses exist as to why the occurrence of oxygenic photosynthesis and the timing of the GOE are temporally uncoupled, including the consumption of released oxygen by redox-sensitive elements, such as sulphur, or cell respiration[3], the time needed to adapt to a pelagic life style necessary to produce O2 on a large scale[10, 11] or the toxicity of an anoxic, ferruginous Archaean ocean[12] All of these proposed processes may have contributed towards restricting the expansion of Cyanobacteria to a few highly productive niches, thereby generating the occasional ‘oxygen oases’ recorded in the rock record[13, 14].

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