Etude comparative par epifluorescence et cytometrie en flux des communautes bacteriennes des eaux de la retenue du barrage Sidi Salem (Tunisie Septentrionale)

Abstract

Two counting techniques by epifluorescence microscopy and flow cytometry were used to assess the spatial and temporal variability of bacterial communities in the Sidi Salem reservoir. This concerned the heterotrophic populations, including the cultivable forms and viable non cultivable (VNC) once; taking into account the influence of environmental parameters (temperature, transparency, dissolved oxygen and nutrients). Thus, a monthly monitoring has been followed during two years (February 2009 to January 2011), to analyze water samples upstream, downstream and into the deepest area of the reservoir. The results show that the observation by epifluorescence microscopy reveals all viable non- Bull. Inst. Natn. Scien. Tech. Mer de Salammbô, Vol. 41, 2014 122 cultivable forms of bacteria, including their abundance ranges from 5.3 x 104 to 1.2 x 106 cells / ml. Also, we recorded the maximum bacterial loads during autumn and spring, especially at the deepest station of the reservoir. Otherwise, bacterial loads upstream of the reservoir are higher than those of downstream and significantly correlated with some physico-chemical factors (pH, dissolved oxygen, total nitrogen and chlorophyll a). For cytometric analysis, bacterial populations are separated according to the state of the DNA "Low DNA" (LDNA) and "High DNA" (HDNA) with respective abundance ranging between 1.3 x105 and 4x107 cells / ml and from 6x104 to 2x107 cells / ml. These results emphasize the high bacterial diversity in the Sidi Salem dam based on the environmental characteristics