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

Summary

We simulated a Precambrian ferruginous marine upwelling system in a lab-scale vertical flow-through column. The goal was to understand how geochemical profiles of O₂ and Fe(II) evolve as cyanobacteria produce O₂. The results show the establishment of a chemocline due to Fe(II) oxidation by photosynthetically produced O₂.

Abstract

A conventional concept for the deposition of some Precambrian Banded Iron Formations (BIF) proceeds on the assumption that ferrous iron [Fe(II)] upwelling from hydrothermal sources in the Precambrian ocean was oxidized by molecular oxygen [O₂] produced by cyanobacteria. The oldest BIFs, deposited prior to the Great Oxidation Event (GOE) at about 2.4 billion years (Gy) ago, could have formed by direct oxidation of Fe(II) by anoxygenic photoferrotrophs under anoxic conditions. As a method for testing the geochemical and mineralogical patterns that develop under different biological scenarios, we designed a 40 cm long vertical flow-through column to simulate an anoxic Fe(II)-rich marine upwelling system representative of an ancient ocean on a lab scale. The cylinder was packed with a porous glass bead matrix to stabilize the geochemical gradients, and liquid samples for iron quantification could be taken throughout the water column. Dissolved oxygen was detected non-invasively via optodes from the outside. Results from biotic experiments that involved upwelling fluxes of Fe(II) from the bottom, a distinct light gradient from top, and cyanobacteria present in the water column, show clear evidence for the formation of Fe(III) mineral precipitates and development of a chemocline between Fe(II) and O₂. This column allows us to test hypotheses for the formation of the BIFs by culturing cyanobacteria (and in the future photoferrotrophs) under simulated marine Precambrian conditions. Furthermore we hypothesize that our column concept allows for the simulation of various chemical and physical environments — including shallow marine or lacustrine sediments.

Introduction

The Precambrian (4.6 to 0.541 Gy ago) atmosphere experienced a gradual build-up of photosynthetically produced oxygen (O₂), perhaps punctuated by step changes at the so-called "Great Oxidation Event" (GOE) at approximately 2.4 Gy ago, and again in the Neoproterozoic (1 to 0.541 Gy ago) as atmospheric O₂ approached modern levels¹. Cyanobacteria are the evolutionary remnants of the first organisms capable of oxygenic photosynthesis². Geochemical evidence and modeling studies support the role of shallow coastal environments in harboring active communities of cyanobacteria or organisms capable of oxygenic photosynthesis ....

Protocol

1. Preparation of Culturing Medium

Note: Information on the required equipment, chemicals and supplies for the preparation of the culture medium is listed in Table 1. 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 NaCO₃. As a source for Fe(II), add 3.5 ml of a 1 M anoxic and sterile FeCl₂-sol....

Results

Control experiment

Abiotic control experiments (10 days) demonstrated consistently low oxygen concentrations (O₂ <0.15 mg/L) with no significant fluctuations in the Fe(II)-profile throughout the upwelling water column. The formation of precipitates (presumably Fe(III)(oxyhydr-)oxides) in the medium reservoir and the slight decrease in the overall Fe(II) concentration from 500 µM to.......

Discussion

Microbial communities in the Precambrian ocean were regulated by, or modified as a result of, their activity and the prevailing geochemical conditions. In interpreting the origins of BIF, researchers generally infer the presence or activity of microorganisms based on the sedimentology or geochemistry of BIF, e.g., Smith et al.²³ and Johnson et al.²⁴. The study of modern organisms in modern environments that have geochemical analogs to ancient environments is also a valuabl.......

Materials

Name	Company	Catalog Number	Comments
Widdel flask (5 L)	Ochs	110015	labor-ochs.de
Glass bottles (5 L)	Rotilabo	Y682.1	carlroth.com
Glass pipettes (5 mL)		51714	labor-ochs.de
0.22 µm Steritop filter unit (0.22 µm Polyethersulfone membrane)	Millipore	X337.1	carlroth.com
Aluminum foil
Sterile Luer Lock glass syringe, filled with cotton		C681.1	carlroth.com
Luer Lock stainless steel needles (150 mm, 1.0 mm ID)		201015	labor-ochs.de
NaCl	Sigma	433209	sigmaaldrich.com
MgSO4	Sigma	208094	sigmaaldrich.com
CaCl2	Sigma	C4901	sigmaaldrich.com
NH4Cl	Sigma	A9434	sigmaaldrich.com
KH2PO4	Sigma	P5655	sigmaaldrich.com
KBr	Sigma	P3691	sigmaaldrich.com
KCl	Sigma	P9541	sigmaaldrich.com
Glass cylinder		Y310.1	carlroth.com
Glass wool		7377.2	carlroth.com
Glass beads (ø 0.55 - 0.7 mm)		11079105	biospec.com
Butyl rubber stopper (ø 1.2 cm)		271024	labor-ochs.de
Petri Dish, glass (ø 8.0 cm)		T939.1	carlroth.com
Polymers glue		OTTOSEAL S68	adchem.de
Optical oxygen sensor foil (for oxygen analysis, see below)		– on request –	presens.de
Rubber tubing (35 mm, 7 mm ID)		770350	labor-ochs.de
Luer Lock tube connector (3.0 mm, luer lock male = LLM)		P343.1	carlroth.com
Luer Lock tube connector (3.0 mm, luer lock female = LLF)		P335.1	carlroth.com
Rubber tubing (25 mm, 0.72 mm ID)		2600185	newageindustries.com
Rubber tubing (50 mm, 7 mm ID)		770350	labor-ochs.de
Luer Lock stainless steel needle (150 mm, 1.0 mm ID)		201015	labor-ochs.de
Luer Lock glass syringe (10 mL)		C680.1	carlroth.com
Loose cotton		–
Butyl rubber stopper (ø 1.75 cm)		271050	labor-ochs.de
Stainless steel needle (40 mm, 1.0 mm ID)	Sterican	4665120	bbraun.de
Luer Lock stainless steel needle (150 mm, 1.5 mm ID)		201520	labor-ochs.de
position: Luer Lock female connector part at C.7
Polymers glue		OTTOSEAL S68	adchem.de
Stainless steel needle (120 mm, 0.7 mm ID)	Sterican	4665643	bbraun.de
Rubber tubing (40 mm, 0.74 mm ID)		2600185	newageindustries.com
Heat shrink tubing (35 mm, 3 mm ID shrunk)		541458 - 62	conrad.de
Tube clamp		STHC-C-500-4	tekproducts.com
Luer Lock tube connector (1.0 mm, LLF)		P334.1	carlroth.com
Luer Lock plastic cap (LLM)		CT69.1	carlroth.com
Glass bottle (5 L)	Rotilabo	Y682.1	carlroth.com
Butyl rubber stopper (for GL45)		444704	labor-ochs.de
Stainless steel capillary (300 mm, 0.74 mm ID)		56736	sigmaaldrich.com
Stainless steel capillary (50 mm, 0.74 mm ID)		56737	sigmaaldrich.com
Shrink tubing (35 mm, 3 mm ID shrunk)		541458 - 62	conrad.de
Rubber tubing (100 mm, 0.74 mm ID)		2600185	newageindustries.com
Luer Lock tube connector (1.0 mm, LLF)		P334.1	carlroth.com
Luer Lock glass syringe (10 mL)		C680.1	carlroth.com
Loose cotton		–
Butyl rubber stopper (ø 1.75 cm)		271050	labor-ochs.de
Stainless Steel needle (40 mm, 0.8 mm ID)	Sterican	4657519	bbraun.de
Luer Lock glass syringe (5 mL)		C679.1	carlroth.com
Butyl rubber stopper (ø 1.75 mm)		271050	labor-ochs.de
Stainless steel needle (40 mm, 0.8 mm ID)	Sterican	4657519	bbraun.de
Rubber tubing (40 mm, 0.74 mm ID)		2600185	newageindustries.com
Glass bottle (2 L)	Rotilabo	X716.1	carlroth.com
Butyl rubber stopper (for GL45)		444704	labor-ochs.de
Stainless steel capillary (50 mm, 0.74 mm ID)		56736	sigmaaldrich.com
Rubber tubing (30 mm x 0.74 mm ID)		2600185	newageindustries.com
Rubber tubing (100 mm x 0.74 mm ID)		2600185	newageindustries.com
Luer Lock tube connector (1.0 mm, LLF)		P334.1	carlroth.com
Luer Lock 3-way connector (LLF, 2x LLM)		6134	cadenceinc.com
Light source	Samsung	SI-P8V151DB1US	samsung.com
Peristalic pump	Ismatec	EW-78017-35	coleparmer.com
Pumping tubing (0.89 mm ID)		EW-97628-26	coleparmer.com
Stainless steel capillary (200 mm, 0.74 mm ID)		56736	sigmaaldrich.com
Stainless steel capillary (400 mm, 0.74 mm ID)		56737	sigmaaldrich.com
Supel-Inert Foil (Tedlar - PFC) gas pack (10 L)		30240-U	sigmaaldrich.com
Rubber tube (30 mm, 6 mm ID)		770300	labor-ochs.de
Luer Lock tube connector (3.0 mm, LLM)		P343.1	carlroth.com
Luer Lock tube connector (3.0 mm, LLF)		P335.1	carlroth.com
Gas-tight syringe (20 mL)		C681.1	carlroth.com
Bunsen burner		–
Fiber optic oxygen meter for oxygen quantification	Presens	TR-FB-10-01	presens.de
Vacuum pump		–
Silicone glue for oxygen optodes	Presens	PS1	presens.de