PT  - JOURNAL ARTICLE
AU  - Anirban Bose
AU  - Sufi O Raja
AU  - Sanhita Ray
AU  - Anjan Kr Dasgupta
TI  - Bistability in Fluorescence from a purple non-sulfur bacteria
AID  - 10.1101/132498
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 132498
4099  - http://biorxiv.org/content/early/2017/05/02/132498.short
4100  - http://biorxiv.org/content/early/2017/05/02/132498.full
AB  - Bistability has been observed for photosynthetic purple non-sulfur bacteria Rhodobacter capsulatus SB1003. The microbes respond to UV excitation (at 365nm) in a switchable manner. A time dependent increase in fluorescence (590-685nm) following roughly a first order kinetics is observed at normal temperature (298K). When either concentration or temperature is lowered the state switches to a steady state first order bleaching. Similar bistability is also observed with respect to temperature variations, as amplification occuring at say 298K disappears below 280K. One can synthetically control bistability and force a re-emergence of fluorescence amplification by exposing the system to a static magnetic field (0.25T). Differential excitability of singlet and triplet states and selective sensitivity of triplets to static magnetic field may explain this result. The triplets dominate at low temperature preventing amplification of emission, and the reversal may be caused by the Zeeman splitting of the triplets, wherein the excitable singlets re-emerge. Evolutionary and ecological implication of bistable photosynthetic system is discussed in the text.PACS numbers: 87.18.Fx, 31.50.Df, 33.50.-j,87.50.C-