The napEDABC gene cluster that encodes the periplasmic nitrate reductase from Bradyrhizobium japonicum USDA110 has been isolated and characterized. napA encodes the catalytic subunit, and the napB and napC gene products are predicted to be a soluble dihaem c and a membrane-anchored tetrahaem c-type cytochrome, respectively. napE encodes a transmembrane protein of unknown function, and the napD gene product is a soluble protein which is assumed to play a role in the maturation of NapA. Western blots of the periplasmic fraction from wild-type cells grown anaerobically with nitrate revealed the presence of a protein band with a molecular size of about 90 kDa corresponding to NapA. A B. japonicum mutant carrying an insertion in the napA gene was unable to grow under nitrate-respiring conditions, lacked nitrate reductase activity, and did not show the 90 kDa protein band. Complementation of the mutant with a plasmid bearing the napEDABC genes restored both nitrate-dependent anaerobic growth of the cells and nitrate reductase activity. A membrane-bound and a periplasmic c-type cytochrome, with molecular masses of 25 kDa and 15 kDa, respectively, were not detected in the napA mutant strain incubated anaerobically with nitrate, which identifies those proteins as the NapC and the NapB components of the B. japonicum periplasmic nitrate reductase enzyme. These results suggest that the periplasmic nitrate reductase is the enzyme responsible for anaerobic growth of B. japonicum under nitrate-respiring conditions. The promoter region of the napEDABC genes has been characterized by primer extension. A major transcript initiates 66?5 bp downstream of the centre of a putative FNR-like binding site.

A modABC gene cluster that encodes an ABC-type, high-affinity molybdate transporter from Bradyrhizobium japonicum has been isolated and characterized. B. japonicum modA and modB mutant strains were unable to grow aerobically or anaerobically with nitrate as nitrogen source or as respiratory substrate, respectively, and lacked nitrate reductase activity. The nitrogen-fixing ability of the mod mutants in symbiotic association with soybean plants grown in a Mo-deficient mineral solution was severely impaired. Addition of molybdate to the bacterial growth medium or to the plant mineral solution fully restored the wild-type phenotype. Because the amount of molybdate required for suppression of the mutant phenotype either under free-living or under symbiotic conditions was dependent on sulphate concentration, it is likely that a sulphate transporter is also involved in Mo uptake in B. japonicum. The promoter region of the modABC genes has been characterized by primer extension. Reverse transcription and expression of a transcriptional fusion, P modA -lacZ, was detected only in a B. japonicum modA mutant grown in a medium without molybdate supplementation. These findings indicate that transcription of the B. japonicum modABC genes is repressed by molybdate.

Se estudió la frecuencia del aislamiento de Campylobacter spp. en pollos domésticos y pollos mantenidos en confinamiento permanente, en la ciudad de Iquitos (Perú). Campylobacter spp. fue aislado en 54,0% en el primer grupo y 35,0% en el segundo (p<0,05). De las especies termotolerantes clásicas, las más frecuentes fueron C. jejuni y C. coli. La presencia de C. lari en estas aves, señala la importancia de ellas como reservorio natural de este microorganismo. Campylobacter, isolation. Pollos, microbiología. Reservorio de enfermedades. IntroducciónEn los últimos años, las especies termotolerantes de Campylobacter han emergido como una causa común de diarrea en humanos 4,5,11 . Estos microorganismos, ampliamente distribuidos en el mundo, tienen como reservorios naturales una gran variedad de especies animales, tanto domésti-cas como de vida libre, siendo las aves domésticas una de las principales fuentes de infección para el hombre 1,3,4,9,11,13,16,19,21,23 . En Iquitos(Amazonía Peruana, 3°45'05" lat. sur), un alto porcentaje (23,0%) de los cuadros diarreicos son producidos por especies de Campylobacter. Sin embargo, aunque el pollo constituye una importante fuente de alimentación humana, no se tiene información sobre la importancia de estas aves como reservorio de Campylobacter spp. en esta región. Teniendo presente estos antecedentes y considerando que el tipo de habitat y el modo de crianza de estos animales son factores que podrían influir en la proporción de aves portadoras de estas bacterias 13,23 , nos propusimos determinar la frecuencia de aislamiento de Campylobacter spp. en dos poblaciones de pollos criados en distintas condiciones ambientales. Material y MétodoFueron estudiadas 200 muestras fecales de pollos obtenidas mediante hisopado cloacal. De ellas, 100 fueron de pollos criados sin confinamiento, pertenecientes a familias de bajo nivel socioeconómico, residentes en la periferia de la ciudad.

In order to know the importance of chicken as natural reservoir of Campylobacter lari in Iquitos, Peru; samples were obtained by cloacal swabs from 200 chickens and immediately placed into a semisolid enrichment medium; these were streaked on modified Skirrow Agar. The organism was isolated from 21 (10.5%) samples, corresponding 58.8% to biovar I and 41.2% to biovar II (Lior scheme). The results provide evidence that chicken appear to be prominent reservoirs of Campylobacter lari in Iquitos.

The isolation rate of thermotolerant campylobacters in pet monkeys and wild monkeys was established. Campylobacter spp. were isolated in 31.9'Yn of the first (pet) group, being less frequent (20.9 %) in the second (wild) ( I ' > 0.05). In both groups, only biovars I and I1 of Cjquni sspjquni and both biovars of C coli were isolated (Lior's scheme). Campylobacter lati was not isolated. The results show that domestic and wild monkeys can harbour Cumpylobucter in their intestinal tract and would be considered as reservoirs of these bacteria.