Switchable amplification of fluoresence from a photosynthetic microbe

Abstract

AbstractOne known attribute of the photosynthetic apparatus is photon capture and generation of metabolic energy. The thermodynamic implications of fluorescence, invariably associated with the photosynthetic components is however poorly understood. In this paper we report a density dependent amplification of such fluorescence which can be interpreted as a thermodynamic strategy of controlled energy release by the cell. We show in support of this hypothesis that prolonged photo-exitation of cell free extract ofRhodobacter capsulatusSB1003 at 395 nm, induces fluorescence emission amplifying with time as long as the fluorophore density is above a critical level. The fact that the amplification disappears at low temperature and at dilute condition, is in accordance with the thermodynamic interpretation that energy is released as per requirement. Live cell imaging is also validation of the phenomenon even at the cellular level. Single cells ofRhodobacter capsulatusSB1003 shows time dependent loss of fluorescence, the process being reversed for cellular clusters. To explain the mechanism of this bistable fluorescence (F) amplification, variation of the scale free kinetic constant k=1/F (dF/dt) is studied at varying temperatures in presence and absence of static magnetic field. The sign of k shifts from positive to negative if T is lowered or if the system is diluted. But at low T, k again switches from negative to positive value, if static magnetic field is applied. The chain of events can be explained by a simple model assuming excretion of a porphyrin by the microbe and possible photon dependent aggregation behavior of such porphyrin complex, differential temperature and magnetic field sensitivity of the monomeric or aggregated forms of porphyrin being reported earlier.