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AIMS: Identify novel bacterial taxa that could increase the availability of branched-chain amino acids and the amount of distinctive volatiles during skim milk fermentation. METHODS AND RESULTS: We recovered 344 bacterial isolates from stool samples of healthy and breastfed infants. Five were selected based on their ability to produce branched-chain amino acids. Three strains were identified as Escherichia coli, one as Klebsiella pneumoniae and other as Klebsiella variicola by molecular and biochemical methods. HPLC and solid-phase microextraction with GC-MS were used for the determination of free amino acids and volatile compounds respectively. The consortium formed by K. variicola and four Lactobacillus species showed the highest production of Leu and Ile in skim milk fermentation. In addition, the production of volatile compounds, such as acetoin, ethanol, 2-nonanone, and acetic, hexanoic and octanoic acids, increased in comparison to commercial yogurt, Emmental and Gouda cheese. Also, distinctive volatiles, such as 2,3-butanediol, 4-methyl-2- hexanone and octanol, were identified. CONCLUSION: The use of K. variicola in combination with probiotic Lactobacillus species enhances the availability of Leu and Ile and the amount of distinctive volatiles during skim milk fermentation. SIGNIFICANCE AND IMPACT OF THE STUDY: The identified consortium increases the functional potential of fermented dairy products.

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An in vitro presymbiotic system between mesquite [Prosopis laevigata(Willd.) M.C. Johnst], a semi-arid leguminous plant, and pregerminated spores of Gigaspora rosea Nicol. & Schenck was established. After characteristic hyphal branching, high performance liquid chromatographic analyses of methanol extracts from P. laevigata roots revealed a concentration change in one ultraviolet-detectable product. This product was identified by nuclear magnetic resonance and mass spectrometry as trigonelline, a pyridine alkaloid. The concentration of trigonelline was constant in the aerial parts of the plant with or without G. rosea, but its concentration in the roots increased 1.8-fold when G. roseawas present. Trigonelline may be a regulatory factor during early signal events in the establishment of the arbuscular mycorrhizal symbiosis in P. laevigata.

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For the first time, the production of transgenic plants of the forage grass blue grama, Bouteloua gracilis [H.B.K.] Lag. ex Steud., is reported. Transgenic plants containing a gus Colon, two colons nptll fusion driven by a double CaMV35S promoter were obtained by microprojectile bombardment of the highly chlorophyllous embryogenic cell line 'TIANSJ98'. Transformed B. gracilis cell lines resisted a lethal concentration of 160 mg/l of kanamycin for at least 8 months. Chlorophyll development and growth rate were used as useful criteria for discriminating transformed from non-transformed clones. Stable integration of the transgene in the blue grama genome was demonstrated by PCR and Southern-hybridization analysis. Expression of the NPTll protein in transgenic plants grown under greenhouse conditions was confirmed indirectly by spraying kanamycin (150-250 mg/l) on plant foliage, and directly by ELISA immunological tests. Control plants sprayed with kanamycin showed foliar necrosis and reduced growth (tillering) compared to plants containing the transgene. NPTll was found in transgenic plants in levels ranging between 12.6 and 29.6 ng/mg FW of cells, as determined by ELISA reactions.

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A finely dispersed, homogeneous and highly chlorophyllous cell suspension (TIANSJ98 cell line) was obtained from shoot apices of Bouteloua gracilis (H.B.K.) Lag. ex Steud. cultured on MPC medium containing MS salts supplemented with 2,4-D (1 mg/l), BAP (2 mg/l) and adenine (40 mg/l). When the TIANSJ98 cell line was grown in this medium with shaking at 180 rpm it had doubling times of 7.2 and 3.7 days in terms of fresh and dry weight, respectively. Total chlorophyll content in this cell culture ranged from 121.6 to 18.3 µg/g FW at 12 and 21 days following culture initiation. Plants regenerated from the TIANSJ98 cell line, via somatic embryogenesis, were grown to maturity and produced seeds. Although different cell culture systems have been described for cereals and grasses, to the best of our knowledge this is the first report of a highly chlorophyllous and regenerable cell suspension in Poaceae.

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Among isolates of Rhizoctonia solani Kühn collected as sclerotia from potato (Solanum tuberosum L.) tubers harvested from the Toluca Valley in 1995 was one isolate (MexND) of anastomosis group 7 (AG-7). Virulence of this and other isolates of R. solani representing AG-3 (four isolates) or AG-7 (four isolates), was determined on developing potato plants (cv. Russet Burbank) in growth chamber studies at 10 and 21°C by methods used previously (1). A control treatment was inoculated with sterile disks of potato dextrose agar (PDA). Seed tubers were placed on a layer of pasturized sand-soil mix near the bottom of 6- × 25-cm black plastic tubes, then covered with 2 to 3 cm of the sand-soil mix. Seed tubers used in virulence tests carried no R. solani as they had been surface disinfested by immersing for 2 min in a 1.85% solution of formaldehyde. Inoculum, in the form of one 7-mm agar disk cut from the growing edge of appropriate colonies growing on PDA, was placed 2 to 3 cm above the seed and covered with 7 to 10 cm of sand-soil mix (1). Each treatment had five replications. Plants were harvested after control plants had emerged, 29 days at 21°C and 36 days at 10°C, and damage to roots and shoots was assessed according to Carling and Leiner (1). All four isolates of AG-3, one from the U.S. and three from Mexico, caused major damage to roots and shoots at both temperatures. The two isolates of AG-7 from the U.S. caused superficial discoloration to shoots at both temperatures but the two isolates of AG-7 from Japan caused no damage to shoots. None of the four isolates of AG-7 damaged roots at either temperature. MexND caused no damage to roots or shoots at 21°C but produced lesions (< 1 mm in diameter) on roots and shoots at 10°C. Thus, MexND caused less damage to potato than AG-3, more damage than other isolates of AG-7, and appears more aggressive at lower temperatures. This is the first reported occurrence of R. solani AG-7 in Mexico and its first reported recovery from a potato tuber-borne sclerotium. Reference: (1) D. E. Carling and R. H. Leiner. Phytopathology 80:930, 1990.

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Mycorrhizal enhancement of drought resistance of two woody plant species, loblolly pine (Pinus taeda L.) and rose (Rosa hybrida L. cv. Ferdy), occurred independently of phosphorus nutrition. Mycorrhizae tended to alter root morphology and carbon allocation patterns of shoots and roots. Increased drought resistance of mycorrhizal plants was in part attributed to drought-induced colonization by mycorrhizae and the ability of the mycorrhizal plants to maintain high transpiration rates as a result of greater lateral root formation and lower shoot mass (in ectomycorrhizal loblolly pine), and a higher root/shoot ratio and leaf abscission (in endomycorrhizal roses). Neither the endo- nor ectomycorrhizal symbionts affected osmotic adjustment of droughted plants.