Carotenoid Analysis of Halophilic Archaea by Resonance Raman Spectroscopy

Abstract

Recently, halite and sulfate evaporate rocks have been discovered on Mars by the NASA rovers, Spirit and Opportunity. It is reasonable to propose that halophilic microorganisms could have potentially flourished in these settings. If so, biomolecules found in microorganisms adapted to high salinity and basic pH environments on Earth may be reliable biomarkers for detecting life on Mars. Therefore, we investigated the potential of Resonance Raman (RR) spectroscopy to detect biomarkers derived from microorganisms adapted to hypersaline environments. RR spectra were acquired using 488.0 and 514.5 nm excitation from a variety of halophilic archaea, including Halobacterium salinarum NRC-1, Halococcus morrhuae, and Natrinema pallidum. It was clearly demonstrated that RR spectra enhance the chromophore carotenoid molecules in the cell membrane with respect to the various protein and lipid cellular components. RR spectra acquired from all halophilic archaea investigated contained major features at approximately 1000, 1152, and 1505 cm ؊1 . The bands at 1505 cm ؊1 and 1152 cm ؊1 are due to in-phase C¨C ( 1 ) and C-C stretching ( 2 ) vibrations of the polyene chain in carotenoids. Additionally, in-plane rocking modes of CH 3 groups attached to the polyene chain coupled with C-C bonds occur in the 1000 cm ؊1 region. We also investigated the RR spectral differences between bacterioruberin and bacteriorhodopsin as another potential biomarker for hypersaline environments. By comparison, the RR spectrum acquired from bacteriorhodopsin is much more complex and contains modes that can be divided into four groups: the C¨C stretches (1600-1500 cm ؊1 ), the CCH in-plane rocks (1400-1250 cm ؊1 ), the C-C stretches (1250-1100 cm ؊1 ), and the hydrogen out-of-plane wags (1000-700 cm ؊1 ). RR spectroscopy was shown to be a useful tool for the analysis and remote in situ detection of carotenoids from halophilic archaea without the need for large sample sizes and complicated extractions, which are required by analytical techniques such as high performance liquid chromatography and mass spectrometry.

Potential and limits of Raman spectroscopy for carotenoid detection in microorganisms: implications for astrobiology

“…In this way, trace pigment detection is sometimes possible using especially the excitation wavelengths 514.5 and 532 nm [12][13][14]. Carotenoids can also be identified in native samples from surface or subsurface colonizations of rocks or sediments using Raman spectroscopy.…”

Performance Evaluation for a Contamination Detection Method Using Multiple Water Quality Sensors in an Early Warning System

“…The first type refers to non-compound specific or conventional water quality sensors, which are normally used for routine water quality parameters, including pH, chlorine, total organic carbon (TOC), oxidation reduction potential (ORP), conductivity and temperature. The second type refers to compound specific water quality sensors or advanced sensors, which are capable of confirmative detection at low concentrations for a specific component [4][5][6][7][8][9].…”

The potential of Raman spectroscopy for the analysis of diagenetically transformed carotenoids

“…Recently, Marshall et al (2007) reported on the identification of carotenoids in halophilic archaea by resonance Raman spectroscopy using 514.5 nm excitation wavelength. The choice of this excitation wavelength is useful when analysing carotenoids owing to its coincidence with an electronic transition in the chromophore portion of carotenoids (p-p * ) resulting in the Raman resonance effect, thus significantly enhancing the Raman signal.…”