Solvent-free chlorophyll spectrometry in unicellular algal research

Abstract

Scanning spectrophotometers equipped with integrating spheres are now readily available commercially. This study explores the possibility of largely escaping from solvent-based determinations of chlorophylls and bacteriochlorophylls using the in vivo absorption spectra to deduce the chlorophyll/bacteriochlorophyll (Chl/BChl) contents of unicellular photosynthetic organisms. Furthermore, we show that scans from ordinary dual beam spectrometers can also be used to estimate the Chl/BChls of unicells in vivo despite light scattering. Spectra of unicellular algae using integrating sphere spectroscopy can measure the absorbance (A) of turbid cell suspensions and hence the in vivo pigment absorption properties of photosynthetic organisms. These results were compared with those obtained using conventional dual beam spectrophotometry scans on turbid cell suspensions and the in solvent spectra of the photosynthetic pigments. The common unicellular green alga, Chlorella sp., is used as an example of an oxygenic photo-organism with Chl a + b, and comparisons were made to other unicellular algae: a cyanobacterium (Synechococcus), a diatom (Chaetoceros) and Acaryochloris. The anoxygenic photosynthetic bacterium Rhodopseudomonas palustris (BChl a) was included in the study. Empirical algorithms are presented for the solvent-free estimation of Chls a, a + b, a + c1c2, d + a and BChl a for the organisms in the study.