Vitolins and Swaby [74] isolated T. intermedius, T. neopolitanus, T. thiooxidans ...... 1984. Sulphur oxidation by a Streptomyces sp. growing in a carbon-deficient.
1 Biochemistry of Sulfur Cycling in Soil University of Saskatchewan, Saskatoon, Saskatchewan, Canada
JAMES J. GERM IDA
MIL TON WAINWRIGHT
University of Sheffield, Sheffield, England
VANDAKATTU V. S. R. GUPTA*
University of Saskatchewan,
Saskatoon, Saskatchewan, Canada
I.
INTRODUCTION
Sulfur (S) is an essential element for the growth and activity of organisms. It is abundant throughout the earth's crust (ca. 0.1%), and in soil it is derived from the atmosphere, weathered rock, fertilizers, pesticides, irrigation water, and such [ 1] . Since the industrial revolution, the increased burning of fossil fuels has resulted in a greater input of atmospheric S to the soil budget [2-4]. In addition, volatilization of S (as hydrogen sulfide, carbon disulfide, carbonyl sulfide, methyl mercaptan, dimethyl sulfide, dimethyl disulfide, sulfur dioxide) from marine algae, marsh lands, mud flats, plants, and soils contributes to the global circulation of S through the atmosphere, Sulfur exists in a number of oxidation states ( +6 to -2), and for biological systems, it is the most oxidized and most reduced states that are important. The most oxidized form is a component of the
*Present affiliation: Commonwealth Scientific and Industrial Research Organization (CSIRO), Canberra, Australia. 1
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Biochemistry of Sulfur Cycling in Soil
Germida et al.
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nervous system (sulfatides) and connective tissue (sulfated polysaccharides), whereas the most reduced form is required by all microorganisms for storage and transformations of energy, synthesis of amino acids and proteins, enzyme reactions, and as a constituent of coenzymes, ferridoxins, vitamins, and others [ 5]. Sulfur is considered to be a macronutrient in most ecosystems, but in some ecosystems, the availability of S to the biota is limiting. For example, sulfur-deficient soils (> 100 million ha) are found in many parts of the world [ 6] , and over 8 million ha in western Canada are either deficient or potentially deficient [ 7]. Plants need substantial amounts of S for growth and grain production, with their requirements varying according to species. As a result, to manage effectively the S needs of crops, it is important to understand the nature and quantities of different S pools in soil and the various transformation processes of the S cycle (Fig. 1) . This review discusses the major pools and transformations of the soil S cycle, with particular emphasis given to biological and biochemical processes.
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