An H2S-producing variant of Escherichia coli (strain 142) isolated from a urinary tract infection was found to be resistant to high levels of tetracycline, ampicillin, streptomycin, and sulfonamide. The H2S trait segregated spontaneously at a frequency of 2.5 x 10-3. No segregation was observed for the drug resistance determinants. Neither ethidium bromide nor acridine orange affected the rate of segregation of the drug resistance determinants or the trait for H2S production. Antibiotic resistance and hydrogen sulfide production were conjugally transferred to E. coli K-12 recipients at a frequency of approximately 1i-5 per donor cell. Antibiotic resistance and hydrogen sulfide production were also transduced as a single unit with phage P1L4. Genetic data, based on the segregation of resistance determinants and the H2S trait among transconjugant and transductant classes, suggested the presence of two R plasmids. Plasmid DNA was isolated by cesium chloride-ethidium bromide centrifugation. Two plasmid species were detected by agarose gel electrophoresis of purified plasmid DNA, a large molecule of about 80 x 106 daltons (designated pSR12) and a small molecular species of approximately 5.5 x 106 daltons (designated pSR13). Transformation studies using purified plasmid DNA showed that the large pSR12 plasmid confers resistance to ampicillin, tetracycline, and streptomycin and also carries the gene(s) for H2S production. The small pSR13 plasmid confers resistance to streptomycin and sulfonamide.

Germ-free mice contaminated with selected Escherichia coli strains were used for experiments designed to demonstrate gene transfer and recombinant formation in vivo. The well-characterized conjugation system of E. coli K-12 was examined in these experiments. Contamination of germ-free mice with a polyauxotrophic Fstrain followed by the addition of isogenic Hfr, F', or F+ strains resulted in the appearance of all recombinant classes at frequencies that would be expected from an in vitro mating experiment. Inheritance of unselected donor markers occurred at frequencies that were dependent on linkage relationships established in experiments in vitro. The presence of Lactobacillus had no influence on gene transfer and recombinant formation in an F' x Fin vivo mating. The R factor ROR-1 was transferred from E. coli strain M7-18 to an E. coli F-strain in the mouse intestine.

Escherichia coli K-12 X971 was crossed with a smooth Salmonella typhimurium donor, HfrK6, which transfers early the ilv-linked rfa region determining lipopolysaccharide (LPS) core structure. Two ilv+ hybrids differing in their response to the LPS-specific phages FO and C21 were then crossed with S. typhimurium HfrK9, which transfers early the rfb gene cluster determining 0 repeat unit structure. Most recombinants selected for his+ (near rfb) were agglutinated by Salmonella factor 4 antiserum. Transfer of an F' factor (FS400) carrying the rfb-his region of S. typhimurium to the same two ilv+ hybrids gave similar results. LPS extracted from two ilv+,his+, factor 4-positive hybrids contained abequose, the immunodominant sugar for factor 4 specificity. By contrast, his+ hybrids obtained from X971 itself by similar HfrK9 and F'FS400 crosses were not agglutinated by factor 4 antiserum, indicating that the parental E. coli X971 does not have the capacity to attach Salmonella 0 repeat units to its LPS core. It is concluded that the Salmonella rfb genes are expressed only in E. coli X971 hybrids which have also acquired ilv-linked genes (presumably rfa genes affecting core structure or 0-translocase ability, or both) from a S. typhimurium donor. When E. coli X971 was crossed with a smooth E. coli donor, Hfr59, of serotype 08, which transfers his early, most his+ recombinants were agglutinated by E. coli 08 antiserum and lysed by the 08-specific phage, Q8. This suggests that, although the parental E. coli K-12 strain X971 cannot attach Salmonella-specific repeat units to its LPS core, it does have the capacity to attach E. coli 08-specific repeat units.

Agronomic and horticultural crop species experience reductions in growth and harvestable yield after exposure to physical agitation (also known as mechanical stress), as by wind or rain. A greenhouse study was conducted to test the influence of mechanical stress on soybean yield and to determine if exposure to mechanical stress during discrete growth periods has differential effects on seed yield. A modified rotatory shaker was used to apply seismic (i.e., shaking) stress. Brief, periodic episodes of seismic stress reduced stem length, total seed dry weight, and seed number of soybean [Glycine max (L.) Merr.]. Lodging resistance was greater for plants stressed during vegetative growth or throughout vegetative and reproductive growth than during reproductive growth only. Seed dry weight yield was reduced regardless of the timing or duration of stress application, but was lowest when applied during reproductive development. Seismic stress applied during reproductive growth stages R1 to R2 (Days 3 to 4) was as detrimental to seed dry weight accumulation as was stress applied during growth stages R1 to R6 (Days 39 to 42). Seed dry weight per plant was highly correlated with seed number per plant, and seed number was correlated with the seed number of two- and three-seeded pods. Dry weight per 100 seeds was unaffected by seismic-stress treatment. Growth and yield reductions resulting from treatments applied only during the vegetative stage imply that long-term mechanical effects were induced, from which the plants did not fully recover. It is unclear which yield-controlling physiological processes were affected by mechanical stress. Both transient and long-term effects on yield-controlling processes remain to be elucidated.