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Periodic Report Summary 1 - EUENDOLIGHT (Mineral excavation by photosynthetic microbes, a geochemical survey of a biological paradox.)

The evolution of oxygenic photosynthesis by a member of the cyanobacterial lineage, allowing water to be utilized as an electron donor and producing dioxygen constitutes a turning point in the evolution of our bio-geosphere (Buick, 2008). In fact, the success of this lineage deeply transformed our environment through the accumulation of O2 in our ocean and atmosphere, modified geochemical cycles and deeply influenced the evolution of life. The destiny of the cyanobacterial lineage has been fundamentally linked with the carbonate system.
It is expected that autotrophic carbon-fixing activity of cyanobacteria will enhance carbonate precipitation. It is well known that cyanobacterial dominated communities are able to calcify forming a variety of carbonate organo-sedimentary deposits, including stromatolites (Kamennaya et al., 2012). However a large number of modern cyanobacterial species do not calcify in nature and some are even able to actively dissolve carbonate mineral (Garcia-Pichel et al., 2010; Ramirez-Reinat and Garcia-Pichel, 2011), thus being called euendolitic. The latter process seems paradoxical and one can ask how these organisms are able to reconcile alkalinity production related to their metabolism along with the decrease of carbonate saturation index (Cockell and Herrera, 2008; Garcia-Pichel et al., 2010).

Project objectives
My main objective is to better understand mechanisms involved in cyanobacteria euendolithic activity, detail, its phylogenetic distribution and to characterized the mineral and geochemical signatures of this process, in order to give new strong diagnosis tools in the interpretation of environmental and paleobiological records.

Objective 1- Phylogenetic distribution and boring ability of endolithic cyanobacteria
Goal : What is the taxonomic extent of boring ability in cyanobacteria ? Are unicellular cyanobacteria also able to bore? What is their mineral boring, spectrum? Is it specific?
Objective 2-Toward a better understanding of microboring process
Goal : Is the metal-pump mechanism universal? Are the mechanisms depending on the substratres and/or of the strain? What is the link between boring activity, carbon concentrating mechanisms (CCM) and photosynthesis?
Objective 3-Microbe-mineral relationship during the boring activity
Goal : What are the geochemical/isotopic/textural variation during boring ? Are there secondary mineral phases formed? If, so, which ones? What is the fate of material mobilized and organic matter?

Work performed since the beginning of the project and main results achieved so far
Since the beginning of the project I focused my effort on the Objective 1 and 2.
Objective 1: This objective was successfully carried out. In a first phase I collected samples from various carbonate outcrops. I could therefore systematically describe them (including their mineralogy and microbial community composition.), and look for evidence of substrate preference in the field. I also isolated new euendolithic strains including various unicellular, filamentous Cyanobacteria and an alga. All together this material allowed me to answer the questions raised in the Objective 1 and to move forward to the Objective 2.
Objective 2: Despite my effort to image calcium dependent boring mechanism (using calcium binding fluorescent dyes) in the new isolated strains, I could never reliably repeat the results obtained for the model strain Mastigocoleus testarum (Ramirez-Reinat and Garcia-Pichel, 2011) therefore I could not conclude on the boring mechanism and decided to take another approach more exploratory to try to answer this important question. I used a combination of genomic and transcriptomic data to unravel the genes that are being turned ON and OFF during the process. I am currently analyzing this dataset.

Expected final results and their potential impact and use
Altogether, this study will start shedding light on the global importance of endolithic communities and provide invaluable material to explore in more details the boring mechanisms by Cyanobacteria and algae. We expect at least 5 publications directly related to this project and to the unexpected finding that we made while studying endolithic communities.

Buick R. (2008). When did oxygenic photosynthesis evolve? Philos Trans R Soc London B Biol Sci 363: 2731–2743.
Cockell CS, Herrera A. (2008). Why are some microorganisms boring? Trends Microbiol 16: 101–106.
Garcia-Pichel F, Ramirez-Reinat E, Gao QJ. (2010). Microbial excavation of solid carbonates powered by P-type ATPase-mediated transcellular Ca(2+) transport. Proc Natl Acad Sci U S A 107: 21749–21754.
Kamennaya N, Ajo-Franklin C, Northen T, Jansson C. (2012). Cyanobacteria as Biocatalysts for Carbonate Mineralization. Minerals 2: 338–364.
Ramirez-Reinat EL, Garcia-Pichel F. (2011). Ca2+-ATPase mediated carbonate dissolution is prevalent among cyanobacterial euendoliths. Appl Environ Microbiol. doi:10.1128/aem.06633-11.

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Rapahel Bretin, (European projects manager)
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