Physiological and spectroscopical changes of the thermophilic cyanobacterium Synechococcus elongatus under iron stress and recovery culture

Abstract

The iron in cyanobacterial cells contributes to energy conversion via electron transport chains, so its availability directly influences all metabolic pathways. Besides exploring cell adaptations and changes occurring with iron insufficient stress, the present work examines profoundly for the first time the metabolic changes accompanied with iron recovery for the thermophilic cyanobacterium Synechococcus elongatus (Nag., var. thermalis Geitl. Strain Kovrov 1972/8). S. elongatus cells were cultivated on two iron deprivation levels, iron-limited (45 nM Fe) and iron-deficient (4.5 nM Fe). Growth, carotenoids/Chlorophyll-a (Car/Chl-a) ratio, transmitting electron images, pigments fractionation analysis, and cell activity were checked. The obtained results demonstrated an astounding decrease in Chl-a content, an increment in β-carotene content, leading to rising the Car/Chl-a ratio, a reduction of phycobilins content, a reduction in cell diameters, a decrease of energy transfer, a depletion of the electron transport chain, and a reduction of photosynthesis and respiration processes under inadequate iron condition. Likewise, the photochemical activity of photosystem II (PSII), determined by Fv/Fm ratio and thermoluminescence estimations, demonstrated that PSII was disabled under iron pressure. With iron recovery by 200 nM Fe, cells regained full metabolic activity within 24 h. Despite the fact that photosynthesis and respiration activity exhibited nearly a similar behavior, S. elongatus under iron-deficiency began to recuperate the activity of the photosynthetic apparatus quicker than the respiratory machinery by regaining their pigment content and activity.