Characterization of the main colonizer and biogenic pigments present in the red biofilm from La Galea Fortress sandstone by means of microscopic observations and Raman imaging

This work aims to understand the nature of the main colonizer and the composition of the biogenic compounds present in a reddish biofilm located on the sandstone from the Northside of La Galea Fortress (Getxo, North of Spain). For that purpose, microscopic observations of the main colonizer and the biofilm were conducted using Phase Contrast Microscope and a Scanning Electron microscope. These observations allowed to identify the Trentepohlia algae as the main colonizer responsible for the reddish biofilm formation. In order to determine the composition of the organic compounds present in the Trentepohlia algae and those excreted by them, point-by-point and Raman imaging using confocal Raman microscope were applied. These analyses allowed to identify not only beta-carotene as the main biogenic pigment but also additional carotenoids such as bacterioruberin. Moreover, the identification of scytonemin suggests the presence of cyanobacteria on the biofilm. (C) 2015 Elsevier B.V. All rights reserved.