Discovery of carotenoid red-shift in endolithic cyanobacteria from the Atacama Desert

Jacek Wierzchos,Octavio Artieda,María Cristina Casero,Carmen Ascaso,Petr Vítek

doi:10.1038/s41598-017-11581-7

Abstract

The biochemical responses of rock-inhabiting cyanobacteria towards native environmental stresses were observed in vivo in one of the Earth’s most challenging extreme climatic environments. The cryptoendolithic cyanobacterial colonization, dominated by Chroococcidiopsis sp., was studied in an ignimbrite at a high altitude volcanic area in the Atacama Desert, Chile. Change in the carotenoid composition (red-shift) within a transect through the cyanobacteria dominant microbial community (average thickness ~1 mm) was unambiguously revealed in their natural endolithic microhabitat. The amount of red shifted carotenoid, observed for the first time in a natural microbial ecosystem, is depth dependent, and increased with increasing proximity to the rock surface, as proven by resonance Raman imaging and point resonance Raman profiling. It is attributed to a light-dependent change in carotenoid conjugation, associated with the light-adaptation strategy of cyanobacteria. A hypothesis is proposed for the possible role of an orange carotenoid protein (OCP) mediated non-photochemical quenching (NPQ) mechanism that influences the observed spectral behavior. Simultaneously, information about the distribution of scytonemin and phycobiliproteins was obtained. Scytonemin was detected in the uppermost cyanobacteria aggregates. A reverse signal intensity gradient of phycobiliproteins was registered, increasing with deeper positions as a response of the cyanobacterial light harvesting complex to low-light conditions.

Highlights

Endolithic phototrophic microorganisms, dominated by Chroococcidiopsis sp., were first described from the Negev Desert, Israel in the pioneering research study by Imre E
Cyanobacteria protect themselves against light-induced stress, caused by an excess of absorbed energy exceeding the rate of carbon fixation
For the first time, we have demonstrated evidence of the carotenoid red shift attributed to photo-protection is occurring both in situ and in vivo in natural endolithic microbial ecosystems within a rock micro-habitat, provided by a porous ignimbrite of volcanic origin from the hyperarid region of the Atacama Desert

Summary

Introduction

Endolithic (rock-inhabiting) phototrophic microorganisms, dominated by Chroococcidiopsis sp., were first described from the Negev Desert, Israel in the pioneering research study by Imre E. It is based on the interaction between www.nature.com/scientificreports/. Its function was only described in the past decade in 200621 This water-soluble protein is responsible for an increase in heat dissipation induced by intense blue-green light radiation (not by the orange to red wavelengths)[21, 22]. It contains N-terminal and C-terminal domains with a single non-covalently bound keto-carotenoid molecule (echinenone or hydroxyechinenone) spanning both domains[23]

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Conclusion