Distribution and density of bacteria in subtropical flooded rice growing areas in Brazil.

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.