Aislamiento e identificación de bacterias fotosintéticas en el monimolimnion del Estany de Cullera (Valencia)

Abstract

The Estany of Cullera is a coastal lagoon with a tendency to stratification. In the year of the study was meromictic, consisting in two distinct waters layers: freshwater of fluvial origin in the surface and marine water in the bottom. The high contents of sulphide in the anoxic marine water layer, makes possible the growth of important populations o f photosyntheric bacteria, that in summer present two density maxima: one in the chemocline and another near the bottom. The dominant organism in these maxima was identified as Chl»robiun/ phueoz,ibrioder. Other phototrophic bacteria have been isolated from these water layers, using enrichment techniques based on the modification o f the concentrarion of sulfide, p H and ligth intensity and specrra, as welI as isolation in solid mediurn. These bacteria1 strains were identified in axenic cultures by means of the absortion spectra of their pigments, morphology and ultrastrucrure as pertaining to the species Chlorobiurn limicolu. Chromatitlm zino.rum and Rhodomicrobium zunnielli. The presence of Tbio i p i ~ t I I i ' ~ t ~ ~ sp. was also observed but axenic cultures for its study and identification could not be obtained. The environmental conditions characteristic o f the chemocline of ttiis lagoon determine LI notorious and constant dominante of Chlorobiu?~ phueozibrioides over al1 the other photosynthetic bacteria that are always in low nurnber. Only in early summer, an important growth of Chlorobir~m limicolu is apparent, and it is possible to observe a grcen water layer in the chemocline, just above the brown layer of Chlorobii~nl phdeot~ibriotdei. INTRODUCCION E n estuarios cerrados y lagunas litorales con flujo d e agua dulce superficial, cuando la profundidad lo permite, s e establece con frecuencia una picnoclina, capaz d e separar p o r una quimioclina estable, una zona monimolimnética d o n d e s e agota el oxígeno y u n mixolimnion oxigenado. La presencia d e sulfuro d e hidrhgeno e n el moni-m o l i m n i ó n d e estas lagunas, procedentes m a y o r m e n-te d e la reducción d e sulfatos, posibilita el desarrollo d e g r a n d e s poblaciones d e bacterias fototrofas del azufre, s i e m p r e q u e dispongan d e una intensidad luminosa suficiente e n estas zonas anóxicas del lago (P f e n n i g , 1967). Estas bacterias fotosintéticas f o r m a n con frecueii-cia una capa e n la quimioclina d e los lagos merorníc-ticos, debido e n t r e otras causas al efecto d e auto-sombra, p e r o e n ocasiones los fotosintéticos bac-terianos s e extienden a todo el m o n i m o l i m n i o n con densidades variables. E n algunos lagos mesotróficos someros s e encuentran f o r m a n d o una fina película e n contacto con el s e d i m e n t o (Czeczuga, 1958), mien-tras que bajo espciales condiciones hidrográficas, particularmente e n cuencas pequeñas, las bacterias invaden todo el cuerpo del agua. .Esto último piiede Lirnnktica 1: 78-85 (1984) O Asociación Espanola de Limnologla, Madrid. Spain