Resumen Beber agua subterrµnea no desinfectada supone un riesgo de infección por microorganismos patógenos. Estudios recientes muestran que la mitad de los pozos de abastecimiento analizados en los EEUU presentan evidencia de contaminación fecal. Un porcentaje significativo de la aparición de enfermedades transmitidas por el agua puede asociarse a las aguas subterrµneas, estimµndose que por contaminación de las mismas se registran, sólo en ese país, entre 750.000 y 5.9 millones de personas enfermas y entre 1400-9400 muertos por aaeo. El control de estos patógenos empieza con la protección de la fuente para prevenir la contaminación fecal de pozos y acuíferos. Esto supone evaluar la vulnerabilidad y corregir las posibles deficiencias detectadas, lo que incluye controlar los trabajos de rehabilitación del propio pozo. La desinfección puede servir como una barrera a los microorganismos patógenos, por lo que se recomienda como una política prudente de salud pblica en zonas abastecidas con aguas subterrµneas.

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The red alga Gelidium coulteri Harv. photosynthetically fixed 11'4C bicarbonate at high rates under defined conditions in unialgal laboratory culture. The fixation rate and flow of photosynthate into various end products were dependent on the nitrogen status of the tissue. Plants fed luxury levels of nitrogen (approximately 340 micromolar) showed fixation rates several-fold higher than those seen for plants starved for nitrogen. algal species for both agar and the related polysaccharide, carrageenan (2,17). This effect appears to involve altered allocation of photosynthate as well as changes in overall growth rate.To assess the nature of N regulation of agar biosynthesis, it became of interest to determine the pathways of carbon flow from primary fixation products into agar and other end products. If these pathways were known in detail, the effect of N on the physiological levels ofparticular metabolites could be determined and the branch points for photosynthate flow and enzymic sites of regulation could be pinpointed (7). Previous work in this area with a variety of red algae indicates that carbon is fixed via the reductive pentose phosphate pathway in light (10, 12). Fixation in the dark appears to be primarily via PEP2 carboxykinase (1 1). For Gelidium robustum, a significant fraction of the photosynthate appears in the compound floridoside (2-0-glycerol-a-Dgalactopyranose) (3, 9). However, previous work utilized plants harvested from field populations with limited control for their nutrient levels, environmental condition or reproductive status. Plant to plant variation in field-collected material can significantly affect quantitation and subsequent conclusions. A detailed assessment of the metabolic pathways of carbon flow under defined conditions in the red algae has not been reported.Since it has been possible to grow cloned strains of G. coulteri under defined conditions, experiments were undertaken to characterize carbon fixation and subsequent partitioning of photosynthate into various end products under a variety of environmental conditions. The results reported here detail some of the effects of N and light on carbon fixation and flow.

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