Comparative Enzymology of Sulfite Oxidation in Thiocapsa roseopersicina Strains 6311, M1 and BBS under Chemotrophic and Phototrophic Conditions

Abstract

The purple sulfur bacterium T. roseopersicina is able to grow chemoautotrophically in the dark under micro- to semiaerobic conditions. Under the latter cell yield and growth rate are considerably reduced. During chemo- and phototrophic growth reduced sulfur compounds are metabolized by the same pathway, i.e. oxidized to sulfate via adenylylsulfate. APS reductaseEC 1.8.99.2), ADP sulfurylaseEC 2.7.7.5) and ATP sulfurylaseEC 2.7.7.4) could be shown in all the strains tested. whereas only strain BBS contained an AMP independent sulfite-oxidizing activity under photo- as well as under chemotrophic conditions. Not only ADP but also ATP sulfurylase perform a dissimilatory function proven by their high specific activities. In contrast to the enzyme of T. roseopersicina strain 6311 APS reductases from strains M 1 and BBS are strictly membrane-bound. The enzyme from strain M 1 was solubilized, enriched and characterized. While the KM values of purified APS reductase remain unaffected. specific activities of APS reductase, ATP and ADP sulfurylase are increased substantially under chemotrophic growth conditions. © 1989, Verlag der Zeitschrift. All rights reserved.