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Hydrogen Sulfide Production from Cysteine (Cystine) in Soil

Dep. of Plant, Soil, and Entomological Sciences, Univ. of Idaho, Moscow, ID 83843

W. A. Dick^*

Dep. of Agronomy, Ohio State Univ. and Ohio Agric. Res. and Development Ctr. (OSU/OARDC), Wooster, OH 44691

* Corresponding author.

ABSTRACT

Hydrogen sulfide (H₂S) production in aerobic soils amended with cysteine (cystine) is thought to result from cystathionase -lyase (EC 4.4.1.1) activity. This enzyme yields thiocysteine (2-amino-2-carboxylethyl hydrodisulfide), which reacts spontaneously with free sulfhydryl groups to produce H₂S. Hydrogen sulfide, however, may also be produced in soil as a result of sulfate reduction. This work was conducted to evaluate the physical and chemical parameters that affect H₂S production in cystine-amended soil and to test the hypothesis that sulfate reduction is involved. Hydrogen sulfide, evolved from 4 g of soil placed in a 25-mL Erlenmeyer flask, was trapped in a center well containing pleated filter paper and 0.5 mL of 1 M zinc acetate. Three soils brought to a water potential of –0.033 MPa and incubated at 37 °C with 50 µmol L-cystine evolved 2.08 to 3.62 mg H₂S-S kg^–1 soil 24 h^–1. Maximum rate of H₂S evolution occurred at 57°C. Propargylglycine (12.5 mmol kg^–1 soil), a specific inhibitor of cystathionine -lyase, reduced H₂S evolution by 90 to 98%. Incubating the soils under waterlogged conditions also reduced H₂S evolution in two of the three soils studied, with no change observed in the third soil. Hydrogen sulfide evolution was not affected by the addition of 12.5 mmol kg^–1 soil of sulfate or nitrate, thus providing additional evidence that sulfate reduction was not involved. The apparent Michaelis constant (K_m) value for H₂S production from cystine in soil was 2.3 mmol kg^–1 soil. It is concluded that production of H₂S in soil, which is a significant reaction of the S cycle, can occur as a result of the mineralization of cysteine (cystine) via participation of the enzyme cystathionine -lyase.

Journal Article no. 63-88. Salaries and research support provided by the Ohio Air Quality Development Authority (OSURF 714851) and by state and federal funds appropriated to OSU/OARDC.

Received for publication March 24, 1988.