Article Abstract:
Mutations were introduced in the region upstream of the nifA gene in Azotobacter vinelandii and the fragment cloned and transformed into wild type and lacZ-containing A. vinlandii. The mutants retained their nitrogenase activity even in inhibitory concentrations of ammonium. The mutants were also able to excrete ammonium, with maximum excretion occurring toward the end of the log phase and stationary phase. The mean levels excreted were around 10 mM, accompanied by an increase in pH, reaching a final value of 8.5. The mutated gene was identified as nifL, based on some similarities with nifL of Klebsiella pneumoniae.
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Article Abstract:
Genes involved in competitive nodulation were isolated by examining the DNA-RNA hybridization patterns of two strains of Bradyrhizobium japonicum USDA 438 (competitive) and USDA 110 (less competitive). Differential hybridization was achieved by using RNA probes induced in basal medium, soil extract and root exudate. Results showed specific DNA sequences were expressed in soil extract and root exudate. The gene library of USDA 438 yielded six clones transcribed in response to soil extract or root exudate. One clone, p8B1, when mobilized on USDA 110, enhanced its competitive nodulation ability.
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Article Abstract:
Escherichia coli does not produce a diffusible substance that protects the bacterium from an acid challenge. Acid tolerance appears to involve the induction of glutamate- and arginine-decarboxylase acid survival pathways.
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