Impact of an urban effluent on the bacterial community structure in the Arga River (Spain), with special reference to culturable Gram-negative rods

Abstract

The Arga River is an interesting system in which to study the impact of urban effluent pollution because it receives a single effluent in the form of wastewater discharge from the city of Pamplona. To analyze the extent of this discharge, total bacteria, culturable heterotrophic bacteria, and Gram-negative heterotrophic bacteria were enumerated and 409 isolates of the latter were identified. One sampling station was located upstream from the inflow, while five were located up to 30 km downstream. Bacterial counts increased drastically downstream from the wastewater inflow. Total bacterial numbers decreased along the 30 km downstream, the last station attaining similar values to those recorded upstream from the discharge. However, culturable heterotrophic and Gram-negative heterotrophic bacteria levels generally remained significantly higher within the 30 km zone investigated. Among the 409 isolates identified, Aeromonas spp. were the most frequent both upstream and downstream from the discharge. In contrast, although strains belonging to different genera of Enterobacteriaceae were found in all stations, their occurrence was significantly higher just downstream from the polluted discharge. Acinetobacter spp., which were never found upstream, were detected in all stations below the discharge. Our results clearly show that the bacterial community structure changes definitively downstream from the discharge and that Aeromonas were common throughout the sampling zone. Thus they cannot be considered good indicators of pollution in this setting compared to some genera of Enterobacteriaceae or some species of Acinetobacter, the distribution of which correlated better with the distance from the wastewater discharge.

Microbiological water quality of the Mfoundi River watershed at Yaoundé, Cameroon, as inferred from indicator bacteria of fecal contamination

“…Indicator bacteria are typically found in sewage (Gerba, 2000) and their concentrations in the Mfoundi River watershed were close to the upper range of values reported elsewhere for rivers and streams subjected to wastewater discharge from sewage treatment systems (see comparative Table I in Fernandez-Molina, et al, 2004, Goñi-Urriza, et al, 1999, Jugnia and Nsimé-Ngando, 2001). Hence, it is reasonable to assume that at least part of the source of indicator bacteria in the water bodies of the Mfoundi river watershed were from raw sewage.…”

Wastewater Treatment Effluent Reduces the Abundance and Diversity of Benthic Bacterial Communities in Urban and Suburban Rivers

“…However, it was very surprising that despite the higher concentrations of inorganic nutrients, the numbers of sediment bacteria decreased downstream of the effluent inputs. Previous studies demonstrated that increased concentrations of nitrogen and phosphorus associated with WWTPs stimulate planktonic bacterial growth (6,7) and benthic (9) bacterial numbers. The downstream sites also had lower concentrations of sediment organic matter, which might explain the reduction in bacterial numbers.…”

“…Numerous studies have documented the potential ecosystem effects of WWTP effluent, including increased nutrient loading (4) and eutrophication (5). Several previous studies have also examined the effects of WWTP effluent on bacterial populations within the water column (6)(7)(8), and some have demonstrated the ability of microorganisms contained in the effluent to persist in the water column of the receiving system (8). However, few studies have examined the potential effects of WWTP effluent on benthic microbial communities (9) despite the fact that bacterial numbers are generally much higher in freshwater sediment than in the overlying water (10) and despite the fact that benthic microbial communities are critical components of lotic ecosystems, as they contribute to organic matter decomposition, nutrient cycling, and bioremediation of a variety of pollutants.…”

Effect of Previous Incubation of Aeromonas hydrophila in Wastewater Prior to Its Transfer Into Marine Water Microcosms

“…The strain was streaked on Muller hinton agar plates (BiorAD, france) and incubated at 32°C for 24 h before use. The biochemical features described by the sending laboratory were confirmed using conventional tests (Gram staining, motility, oxidase and catalase) and strips Api 20 NE systems (Biomerieux, france) (BorrEL et al, 1998;GoNi-UrrizA et al, 1999). The whole profile responses of A. hydrophila are shown in table 1.…”

“…Gram staining was carried out to determine eventual cellular shape modifications. for the biochemical characterization, all the enzymatic and metabolic tests were carried out as described previously (BorrEL et al, 1998;GoNi-UrrizA et al, 1999).…”