Extended temperature optimum of photosynthetic reaction centers in Rhodobacterales

Temperature is one of the most important physical factors affecting microbial and biochemical processes. We investigated the performance of photosynthetic apparatus of marine photoheterotrophic bacterium Dinoroseobacter shibae under various temperatures. The primary photochemistry and electron transport was measured using variable infra-red fluorometry in the cells grown between 8-35°C. It was found that the photosynthetic electron transport had a broad temperature optimum between 25-50°C. Moreover, the primary charge separation stayed functional even after rising temperature up to 55°C. The same phenomenon was observed also in other phototrophic Rhodobacterales. The psychrotolerant bacterium Roseisalinus antarcticus reached its maximum electron transport rate at 48°C, 30°C above its growth temperature. We propose that the extended temperature stability may be crucial to maintain photosynthetic function under situation when photosynthetic membranes heat up above their ambient temperature due to the heat dissipation of the excess light energy.