Ms. 2106 SHORT COMMUNICATION Changes in rhizosphere populations of selected physiological groups of bacteria related to substitution of specific pairs of c h r o m o s o m e s in spring wheat Summary Rhizosphere population characteristics of two cultivars of spring wheat (Tritieum aestivum L. emend Thell.), Rescue (R) and Cadet (C), and the related chromosome substitution lines, C-R5B and C-R5D, were investigated. R e p l a c e m e n t of the chromosome pair, 5 B, in Cadet with 5 B from Rescue made m a n y of the rhizosphere microbial characteristics of C-R5 B similar to or the same as those in the rhizosphere of the donor parent, Rescue. In contrast, substitution of the functionally related chromosome pair, 5D, did not cause marked changes in the rhizosphere microbial population, demonstrating the specificity of the plant's control over factors governing the rhizosphere microbial environment.

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A facultative anaerobic bacterium that rapidly degrades cyanuric acid (CA) was isolated from the sediment of a stream that received industrial wastewater effluent. CA decomposition was measured throughout the growth cycle by using a high-performance liquid chromatography assay, and the concomitant production of ammonia was also measured. The bacterium used CA or cysteine as a major, if not the sole, carbon and energy source under anaerobic, but not aerobic, conditions in a defined medium. The cell yield was greatly enhanced by the simultaneous presence of cysteine and CA in the medium. Cysteine was preferentially used rather than CA early in the growth cycle, but all of the CA was used without an apparent lag after the cysteine was metabolized. Atrazine was also degraded by this bacterium under anaerobic conditions in a defined medium.

A hydrogen-uptake-positive strain of Rhizobium japonicum (6-3I1b6) was demonstrated to grow in absence of oxygen chemolithotrophically, utilizing nitrate as the electron acceptor. Dissimilatory nitrate reduction occurred during growth, as evidenced by the disappearance of nitrate from the medium and production of nitrous oxide. Rhizobium japonicum 120-3I1b120, a hydrogen-uptake-negative strain, showed little or no growth under anaerobic chemolithotrophic growth conditions and did not evolve nitrous oxide. A nitrate-dependent hydrogen-uptake and an oxygen-dependent hydrogen-uptake system was present in cells of strain 6-3I1b6 grown chemolithotrophically under anaerobic conditions with nitrate serving as the electron acceptor.