On the trail of iron uptake in ancestral Cyanobacteria on early Earth.

Cyanobacteria oxygenated Earth's atmosphere ~2.4 billion years ago, during the Great Oxygenation Event (GOE), through oxygenic photosynthesis. Their high iron requirement was presumably met by high levels of Fe(II) in the anoxic Archean environment. We found that many deeply branching Cyanobacteria, including two Gloeobacter and four Pseudanabaena spp., cannot synthesize the Fe(II) specific transporter, FeoB. Phylogenetic and relaxed molecular clock analyses find evidence that FeoB and the Fe(III) transporters, cFTR1 and FutB, were present in Proterozoic, but not earlier Archaean lineages of Cyanobacteria. Furthermore Pseudanabaena sp. PCC7367, an early diverging marine, benthic strain grown under simulated Archean conditions, constitutively expressed cftr1, even after the addition of Fe(II). Our genetic profiling suggests that, prior to the GOE, ancestral Cyanobacteria may have utilized alternative metal iron transporters such as ZIP, NRAMP, or FicI, and possibly also scavenged exogenous siderophore bound Fe(III), as they only acquired the necessary Fe(II) and Fe(III) transporters during the Proterozoic. Given that Cyanobacteria arose 3.3-3.6 billion years ago, it is possible that limitations in iron uptake may have contributed to the delay in their expansion during the Archean, and hence the oxygenation of the early Earth.

A low-cost automized anaerobic chamber for long-term growth experiments and sample handling.

The handling of oxygen sensitive samples and growth of obligate anaerobic organisms requires the stringent exclusion of oxygen, which is omnipresent in our normal atmospheric environment. Anaerobic workstations (aka. Glove boxes) enable the handling of oxygen sensitive samples during complex procedures, or the long-term incubation of anaerobic organisms. Depending on the application requirements, commercial workstations can cost up to 60.000 €. Here we present the complete build instructions for a highly adaptive, Arduino based, anaerobic workstation for microbial cultivation and sample handling, with features normally found only in high cost commercial solutions. This build can automatically regulate humidity, H2 levels (as oxygen reductant), log the environmental data and purge the airlock. It is built as compact as possible to allow it to fit into regular growth chambers for full environmental control. In our experiments, oxygen levels during the continuous growth of oxygen producing cyanobacteria, stayed under 0.03 % for 21 days without needing user intervention. The modular Arduino controller allows for the easy incorporation of additional regulation parameters, such as CO2 concentration or air pressure. This paper provides researchers with a low cost, entry level workstation for anaerobic sample handling with the flexibility to match their specific experimental needs.

An investigation into the effects of increasing salinity on photosynthesis in freshwater unicellular cyanobacteria during the late Archaean.

The oldest species of bacteria capable of oxygenic photosynthesis today are the freshwater Cyanobacteria Gloeobacter spp., belonging to the class Oxyphotobacteria. Several modern molecular evolutionary studies support the freshwater origin of cyanobacteria during the Archaean and their subsequent acquisition of salt tolerance mechanisms necessary for their expansion into the marine environment. This study investigated the effect of a sudden washout event from a freshwater location into either a brackish or marine environment on the photosynthetic efficiency of two unicellular freshwater cyanobacteria: the salt-tolerant Chroococcidiopsis thermalis PCC7203 and the cyanobacterial phylogenetic root species, Gloeobacter violaceus PCC7421. Strains were cultured under present atmospheric levels (PAL) of CO2 or an atmosphere containing elevated levels of CO2 and reduced O2 (eCO2 rO2 ) in simulated shallow water or terrestrial environmental conditions. Both strains exhibited a reduction in growth rates and gross photosynthesis, accompanied by significant reductions in chlorophyll a content, in brackish water, with only C. thermalis able to grow at marine salinity levels. While the experimental atmosphere caused a significant increase in gross photosynthesis rates in both strains, it did not increase their growth rates, nor the amount of O2 released. The differences in growth responses to increasing salinities could be attributed to genetic differences, with C. thermalis carrying additional genes for trehalose synthesis. This study demonstrates that, if cyanobacteria did evolve in a freshwater environment, they would have been capable of withstanding a sudden washout into increasingly saline environments. Both C. thermalis and G. violaceus continued to grow and photosynthesise, albeit at diminished rates, in brackish water, thereby providing a route for the evolution of open ocean-dwelling strains, necessary for the oxygenation of the Earth's atmosphere.