The light-reaction of the green photosynthetic bacterium Chlorobium limicola f. thiosulfatophilum at cryogenic temperatures

Abstract

1. Introduction The photochemical reaction of the green sulfur photosynthetic bacteria (Chlorobiaceae) is clearly very different from that of the purple sulfur and non-sulfur bacteria (Chromatiaceae and Rhodospiril- laceae). The latter have a quinone-iron complex, with an operating midpoint potential near -175 mV, as the ‘primary acceptor’ [l-3]. These organisms reduce pyridine nucleotides by energy-dependent reversed electron flow [3,4]. In contrast, the midpoint poten- tial of the ‘primary acceptor’ in green bacteria has a substantially lower value, probably near -540 mV [5-71, and these organisms are capable of direct photoreduction of pyridine nucleotides [3,4,8]. However, the chemical identity of the ‘primary acceptor’ in green bacteria, such as