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\bibitem{Saiz-Jimenez_etal1990} {\textquotedblleft}\textit{Endolithic cyanobacteria in Maastricht limestone}{\textquotedblright}. Saiz-Jimenez C, Garcia-Rowe J, Garcia Del Cura MA, Ortega-Camvo JJ, Roekens E, Van Grieken R, The science of the total environment \textbf{94}, 209 (1990).   http://doi.org/10.1016/0048-9697(90)90171-P

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