Investigating the roles of Fe(II)-silicate and Fe(III)-silicate complexes and nanoparticles in the survival of early cyanobacteria and photoferrotrophic bacteria
Final Report Abstract
The Archean ocean was an inhospitable environment for early life, due to a combination of the weaker young Sun, coupled with a 1000–10000 x higher flux of damaging UV radiation, compared with modern levels. UV radiation is toxic to cells. It irreparably damages DNA causing cell death. Despite these difficulties, it is accepted that early microbes were reliant on sunlight as an energy source, requiring the overcome the difficulties of this environment to survive. Mineral particles suspended in the water column, which could attenuate UV, have been proposed as a solution to this dilemma. The first step in this research program was to synthesize and characterize environmentally-relevant Fe(II)-Si particles. The ambient conditions for the creation of the Fe(II)-Si colloids were approximated to 25°C and broadly similar seawater composition to modern. 2 µM dissolved organic carbon (as Pony Lake Fulvic Acid), 0.5 mM Fe(II) (As FeCl2), and 2.2 mM Si (as monomeric Si). These precipitates were then characterized using Mössbauer spectroscopy, cryo-TEM, ICP-OES, XRD, and EXAFS. The precipitated solid is an amorphous Fe-Si gel with a monomer diameter range of 3–10 nm. The colloids are light green in colour and translucent. Some variation in crystal habit is observed, but in general the chemistry of the colloid particles is consistent. The Fe(II)/Fe(III) ratio is 2.3, indicating a mostly reduced phase. The Fe:Si ratio of the solid is approx. 1:4. The optical properties of the particulates were compared to the background media, and each component solution and the colloids successfully attenuated the 200– 400 nm wavelength range, while transmitting longer wavelength, photosyntheticallyactive light. UV-exposure experiments with representative microorganisms (photoferrotrophs and cyanobacteria) in the presence and absence of Fe(II)-Si particles were completed to assess the impact of these colloids on survivability. Cultures of the photoferrotroph Rhodovulum iodosum as well as the cyanobacteriae Synechococcus sp. (PCC7002) and Leptolyngbya sp. (PCC7376) were exposed to an 8W UV light at 254 nm, 15 cm distance from plate surface, for 1, 10, and 20 minutes. The exposed microbes were then inoculated into a series of Hungate tubes (R. iodosum) and 96-well plates (cyanobacteria), and diluted by a factor of 10 6 times to create MPNs. Exposure experiments indicated that the presence of environmentally-relevant Fe-Si colloids dramatically increases survival rates from UV exposure. The MPN results for each condition were calculated based on 9 replicates per condition. There appears to be a 1–2 order of magnitude increase in survivorship in the presence of the Mg-Fe-Si colloids.
Publications
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(2018) Were early marine photic environments protected from UV fluxes? Nature Communications, 9, 3088
Mloszewska, A.M., Cole, D., Planavsky, N.J., Kappler, A., Whitford, D.S., Owttrim, G.W., Konhauser, K.O.
