MetE and MetH are two distinct enzymes that catalyze a similar biochemical reaction during the last step of methionine biosynthesis, MetH being a cobalamin-dependent enzyme whereas MetE activity is cobalamin-independent. In this work, we show that the last step of methionine synthesis in the plant pathogen Ralstonia solanacearum is under the transcriptional control of the master pathogenicity regulator HrpG. This control is exerted essentially on metE expression through the intermediate regulator MetR. Expression of metE is strongly and specifically induced in the presence of plant cells in a hrpG- and metR-dependent manner. metE and metR mutants are not auxotrophic for methionine and not affected for growth inside the plant but produce significantly reduced disease symptoms on tomato whereas disruption of metH has no impact on pathogenicity. The finding that the pathogen preferentially induces metE expression rather than metH in the presence of plant cells is indicative of a probable metabolic adaptation to physiological host conditions since this induction of metE occurs in an environment in which cobalamin, the required co-factor for MetH, is absent. It also shows that MetE and MetH are not functionally redundant and are deployed during specific stages of the bacteria lifecycle, the expression of metE and metH being controlled by multiple and distinct signals.

Bacterial wilt (brown rot) disease of potato caused by Ralstonia solanacearum is one of the most important bacterial diseases and a major constraint on potato production worldwide. Through a comparative genomic analysis between R. solanacearum'race 3 biovar 2' (R3bv2) strains, we identified a 77 kb region in strain UW551 which is specifically absent in the hypoaggressive strain IPO1609. We proved that IPO1609 indeed carries a 77 kb genomic deletion and provide genetic evidence that occurrence of this deletion is responsible for almost complete loss of pathogenicity of this strain. We carried out a functional analysis of this 77 kb region in strain UW551 using a combination of gene deletion and functional complementation approaches which identified the methionine biosynthesis genes metER as having a major contribution to IPO1609 pathogenesis. Deletion of the metER genes significantly impacts pathogenicity of R3bv2 strains but does not lead to methionine auxotrophy nor reduced ability to multiply in planta. In addition, this study indicated that three type III secretion system effectors or a type VI secretion system present within the 77 kb region have no or very minor contribution to pathogenicity.

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ResumenSe estudió el efecto de la carboximetilcelulosa y la temperatura en las propiedades termofísicas, los coeficientes de transferencia de calor y masa, pérdida de humedad y ganancia de aceite durante la fritura de trozos de batata. El calor específico, conductividad térmica y densidad se determinaron mediante ecuaciones experimentales y la difusividad térmica se determinó según su definición física a partir de los valores de las otras propiedades termofísicas. Los coeficientes de transferencia de calor y masa se determinaron gráficamente basados en las soluciones de las ecuaciones diferenciales de conducción de calor y de concentración de humedad, en una dimensión y utilizando la regla de la superposición para ajustarla a un plato finito. Los resultados indicaron que las propiedades termofísicas de la batata varían significativamente durante la etapa de freído. El coeficiente de transferencia de calor h es mayor cuando aumenta la temperatura del aceite y se utiliza recubrimiento. El coeficiente de transferencia de masa kc es mayor cuando aumenta la temperatura del aceite y no se utiliza recubrimiento comestible. Además, se observó que el recubrimiento comestible disminuye más del 30 % el contenido de aceite final para todas las temperaturas de freído utilizadas, lo que hace que sea una excelente elección para mejorar la calidad nutricional de los productos fritos. ABSTRACTThe effect of temperature on Carboxymethylcellulose and thermophysical properties, heat transfer coefficients and mass, moisture loss and oil uptake during frying of potato chips was studied. The specific heat, thermal conductivity and density were determined using experimental equations and the thermal diffusivity was determined by their physical definition from the values of other thermophysical properties. The heat transfer coefficients and mass were determined graphically based on the solutions of the differential equations of heat conduction and high moisture, and using one-dimensional overlap rule to conform to a finite plate. The results indicated that the thermophysical properties of sweet potatoes vary significantly during the frying stage. The heat transfer coefficient h is greater when the oil temperature increases and coating used. The mass transfer coefficient kc is greater as the temperature increases and no edible oil is used. Moreover, the edible coating decreases more than 30% oil content for all end frying temperatures used, which makes it an excellent choice for improving the nutritional quality of the fried products.