Bacteria are the most diverse living beings on earth and only a fraction of them have been identified. This paper aims at the analysis of the diversity of mesophilic and heterotrophic bacteria found in samples of irrigation water from rice-fields areas in Rio Grande do Sul State, Brazil. Sample collection was carried out in five rice crop regions areas and followed by isolation, multiplication and bacterial characterization. The species' identification was based on biochemical tests (API-System, bioMérieux). Bacterial diversity was determined by the Shannon & Weaner and Pielou index. The results regarding bacterial diversity revealed 26 species. The most abundant representatives belonged to the Bacillus, Corynebacterium, Staphylococcus and Lactobacillus genera, homogeneously distributed in all studied rice crop areas, and in those areas corresponding to the irrigation channel and the rice growing plot as well. The water of the irrigation channel showed the greatest diversity (H'= 1.00) when compared to the plot (H'= 0.77). The channel also presented a more even species distribution (e = 0.73), while the plot (e = 0.59) had the greatest prevalence represented by the Bacillus genus. The areas and the cultivation phases did not significantly affect the bacterial diversity in the study areas (F4,12=1.04; P>0.05). The results showed that culture management could affect water bacterial populations.

A presença de bactérias heterotróficas em ambientes aquáticos, como os agroecossistemas de produção de arroz irrigado, é determinada por processos bióticos e abióticos, onde se destacam os fatores físico-químicos e as interações de elevada complexidade com outros organismos. Nesse trabalho são abordados aspectos relacionados a estas bactérias, tais como: diversidade bacteriana em áreas orizícolas, coliformes totais e termotolerantes como indicadores ambientais. Também são mencionados tópicos relacionados aos wetlands naturais e artificiais, a viabilidade de bactérias entéricas, os impactos, a reutilização e o monitoramento da água nos ecossistemas orizícolas. Palavras-chave: Agroecossistemas; coliformes; qualidade microbiológica. ABSTRACT BACTERIA AND BIOINDICATORS OF THE WATER QUALITY IN IRRIGATED RICE FIELD ECOSYSTEMS IN THE SOUTHERN REGIONS OF BRAZIL.The presence of heterotrophic bacteria in aquatic environments, such as those in the agricultural systems of irrigated rice fields, is determined by biotic and abiotic processes, with the focus on physical-chemical factors and highly complex interactions with other organisms. In this study, we address aspects related to these bacteria, such as: bacterial diversity in rice growing areas, total coliforms and thermotolerant as environmental indicators. Are also mentioned topics related to natural and artificial wetlands, the viability of enteric bacteria, the environmental impacts, reuse and monitoring of water in rice fields ecosystems. Key words: Agroecosystems; coliforms; microbiological quality. RESUMEN BACTERIAS Y BIO-INDICADORES DE LA CALIDAD DE AGUA DE LOS ECOSISTEMAS DE LOS CULTIVOS ARROZ IRRIGADO EN LA REGIÓN SUR DE BRASIL. La presencia de bacteriasheterotróficas en ambientes acuáticos, como los agroecosistemas de producción de arroz irrigado, esta determinada por procesos bióticos y abióticos, en los que destacan factores fisico-químicos e interacciones muy complejas con otros organismos. En este trabajo se discuten algunos aspectos relacionados a estas bacterias, como la diversidad bacteriana en zonas de cultivo de arroz y coliformes totales y termotolerantes considerados como indicadores ambientales. También se discuten tópicos relacionados a humedales naturales y artificiales, a la viabilidad de bacterias entéricas, a los impactos causados y a la reutilización y monitoreo del agua en los ecosistemas de cultivo de arroz.

This paper presents the results of the statistical analysis of microbiological, physical and chemical parameters related to the quality of the water used in rice fi elds in Southern Brazil. Data were collected during three consecutive crop years, within structure of a comprehensive monitoring program. The indicators used were: potential hydrogen, electrical conductivity, turbidity, nitrogen, phosphorus, potassium, calcium, total and fecal coliforms. Principal Component and Discriminant Analysis showed consistent differences between the water irrigation and drainage, as the temporal variation demonstrated a clear reduction in the concentration of most of the variables analyzed. The pattern of this reduction is not the same in the two regions -that is, the importance of each of the different variables in the observed differentiation is modifi ed in two locations. These results suggested that the variations in the water quality utilized for rice irrigation was infl uenced by certain specifi c aspects of each rice region in South Brazilian -such as anthropic action or soil/climate conditions in each hydrographic basin.

Since microorganisms are important components in the structure and function of water systems, the present paper reports work done to identify groups making up bacterial communities present in rice irrigation water. To this end, water samples were collected in five rice-growing areas of Rio Grande do Sul State, Brazil. The identification of the main bacterial groups found in flooded areas was carried out based on colony morphology, taking into account shape, elevation, and edges. Internal and external cell structure was characterized as cocci or rod, gram-positive or gram-negative, and spore forming or not. The results obtained regarding density and bacterial distribution in the water samples from rice growing areas of RS showed a higher abundance of morphotypes of bacterial colonies in the irrigation channels (F(1,12) = 8.74; p < 0.05) when compared to the culture plots in the five production regions, and in the final culture phase (F(1,12) = 8.86; p < 0.05). In the five rice production areas the occurrence of gram-positive and spore-forming rods was prevalent. Rods showed more abundance (F(1,26) = 15.12; p < 0.05) in the early culture phase, with a significant prevalence of gram-positive rods (F(1,26) = 25.99; p < 0.05) in all rice growing regions under investigation. The group of spore-forming bacteria was significantly more abundant (F(1,30) = 14.06; p < 0.05) when compared with the non-spore-forming ones in all investigated regions. Data showed that the irrigated rice crop affects the density and morphotype colonies in the bacteria found in the water used to flood rice-growing plots.

In this study, we assessed the diversity of Gram-negative bacteria found in water used for irrigation of rice crops in two growing areas of southern Brazil. Samples were collected from the main irrigation channel and field drain area. Twenty-two bacterial species were found in Cachoeirinha and 28 in Camaquã. In both areas, the most frequent bacterial families were Enterobacteriaceae and Aeromonadaceae. Differences in microbial diversity were observed in both study areas. Thirty-five Gram-negative species were identified; however, only 15 were common in both locations. In addition, there were found pathogenic and drug-resistant species, such as Acinetobacter sp., Brucella spp., and Chryseobacterium meningosepticum. This study demonstrates the existence of a number of pathogenic species in aquatic ecosystems analyzed in three consecutive crop years, especially water used for rice production.