Periplasmic sulphide dehydrogenase (Sud) from Wolinella succinogenes: isolation, nucleotide sequence of the sud gene and its expression in Escherichia coli

Wolinella succinogenes contains a periplasmic sulphide dehydrogenase when grown with formate and polysulphide as catabolic substrates. The isolated enzyme catalyzes the reduction of dimethylnaphthoquinone with sulphide at high values of both apparent Km and turnover number. The active enzyme consists of two identical subunits (14 kDa) and amounts to approximately 1% of the soluble cell protein. Prosthetic groups such as flavin, haem or molybdenum are missing. The corresponding gene (sud) encodes a signal peptide together with the mature subunit that consists of 129 amino acid residues including one single cysteine. The sud gene is expressed from a plasmid in Escherichia coli. The resulting enzyme catalyzes sulphide oxidation with dimethylnaphthoquinone and is located in the periplasm of E. coli

Ecophysiology and application of acidophilic sulfur-reducing microorganisms

Sulfur-reducing prokaryotes play an important role in the sulfur biogeochemical cycle, especially in deep-sea vents, hot springs and other extreme environments. The reduction of elemental sulfur is not very favorable thermodynamically, but still provides enough energy for growth of microorganisms. Currently known sulfur reducers are spread over about 69 genera within 9 phyla in the Bacteria domain and 37 genera within 2 phyla in the Archaea domain. Elemental sulfur reduction can occur with polysulfide as an intermediate or via direct cell attachment to the solid substrate. At least four different enzymes are involved in those pathways, and these enzymes are also detected in several microorganisms that are potential sulfur reducers, but not reported as such in literature so far. The ecological distribution of sulfur respiration seems to be more widespread at high temperatures with neutral pH. However, some sulfur reducers can grow at pH as low as 1. The sulfide produced from sulfur reduction can selectively precipitate metals by varying the pH values from 2 to 7, depending on the target metal. Therefore, acidophilic sulfur reducers are of particular interest for application in selective precipitation and recovery of heavy metals from metalliferous waste streams. This chapter explores the ecology and physiology of elemental sulfur reducers, and discusses technologies that can be set up to exploit acidophilic sulfur reducers.The doctoral study program of A.P. Florentino is supported by the organization of the Brazilian Government for the development of Science and Technology CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico). Research of I. Sánchez-Andrea and A.J.M. Stams is financed by ERC grant project 323009 and by Gravitation grant project 024.002.002 from the Netherlands Ministry of Education, Culture and Science