摘要：
Hydrogen sulfide is known to be toxic to rice seed- lings in concentrations as low as 2.2 X 10 M. Lowland rice is grown in water - submersed paddies where soluble sulfides are copiously produced by the metabolic activi ties of anaerobic microorganisms, principally Desulfovib- rio s p p. A reduced, aqueous iron-sulfur system was proposed a= a model of the paddy soils of Louisiana and the equilib rium between hydrogen sulfide and precipitated sulfides in this model system was described on the basis of available thermodynamic data. A multiparameter diagram which per mits the continuous mutual variation of the components of the model system was constructed. On the basis of these physico-chemical considerations, it was predicted that m a r ginally toxic conditions of hydrogen sulfide could exist in equilibrium with non-toxic, precipitated sulfides under conditions prevalent in Louisiana rice paddies. The detoxification of hydrogen sulfide by a biologi cal system in the paddy was postulated. B e g g i a t o a. a flexibacterium which is capable of oxidizing hydrogen sul fide to sulfur intracellularly, was isolated from paddy soil in the Crowley, Louisiana area and its physiological char acteristics verified. This bacterium is autointoxicated by hydrogen peroxide and requires that this compound be decomposed externally for optimum growth. The exudation of catalase (EC 1.***.1.6) by rice roots was demonstrated in greenhouse, growth chamber, and gnoto- biotic nutrient solution studies. Beggiatoa was found to grow well in culture with gnotobiotically-germinated rice, whereas it failed to survive in a parallel, control system without rice. ThuB, an ecosystem was elucidated compris ing anaerobic, hydrogen sulfide-forming organisms, hydrogen sulfide-sensitive rice, and an organism which detoxifies hydrogen sulfide while requiring a specific rice root exud ate (catalase). The simplicity of this ecosystem, which has been dis covered in rice paddies, suggests that it may b
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