Spectroscopic characterization of pigment binding proteins in normal-grown and iron-stressed thermophilic cyanobacteria Synecococcus sp.

Abstract

The results of low temperature absorption, fluorescence and hole burning spectroscopy of pigment binding proteins in normal-grown and iron-stressed thermophilic Synecococcus sp. are reported. These experiments revealed that the growing of Synecococcus sp. under the iron-limited condition affects spectral characteristics and excited energy transfer (EET) in pigment proteins. The comparison of low temperature absorption spectra of normal-grown and iron-stressed thermophilic cyanobacteria well documents major changes in composition of the antenna systems and in composition of the core of photosystem II. The absorption of membrane chlorophyll in particular, is blue-shifted from 679 nm in normal cells to 673 nm which is caused by absorption of chlorophyll binding protein CP 34 in stressed sample. The presence of CP 34 in the photosystem II (PS 1 1 Abbreviations: APC, allophycocyanin; CC, cylindrical core; Chl, chlorophyll; LT, low temperature; PBS, phycobilisomes; PSB, phonon sideband; PC, phycocyanin; PR, peripheral rods; PS, photosystem; RC, reaction center, ZPH, zero phonon hole. II) has also been seen in the low temperature fluorescence spectra where the increased luminescence at 685 nm has been observed. This implies the decreased efficiency of photosynthesis in iron-limited sample. We studied the energy transfer in PS II by the means of fluorescence and absorption hole-burning spectroscopy which enabled to study the influence of iron-stressed condition on energy transfer and pigment–protein interaction (Debye–Waller factor). The stressed cells exhibit the broadened spectral hole width at 682 and 685.5 nm.