Microbial I Abundance of Three Bacterial Populations in Selected Streams

The population sizes of three bacterial species, Acinetobacter calcoaceticw, Burkholderia cepacia, and Pseudomonas putida, were examined in water and sediment from nine streams in different parts of the United States using fluorescent in situ hybridization (FISH). Population sizes were determined from three sites (upstream, midstream, and downstream) in each stream to compare differences in the occurrence and distribution of the species within each stream and among streams. Physical and chemical variables measured reflected differences in environmental conditions among the streams. In the water, B. cepada numbers were highest in the agricultural, Iowa stream. P. putida numbers were highest in the southern coastal plain streams, Black Creek (GA) and Meyers Branch (SC). Compared to the other two species, the abundance of A. calcoaceticus was similar in all the streams. In sediment, the greatest abundance of all three species was found in the Iowa stream, while the lowest was in Hugh White Creek (NC). Detrended correspondence analysis (DCA) explained 95.8% and 83.9% of the total variation in bacterial numbers in water and sediment of the streams, respectively. In sediments and water, B. cepacia numbers were related to nitrate concentrations. A. calcoaceticus in water clustered with several environmental variables (i.e., SRP, pH, and conductivity) but benthic populations were less well correlated with these variables. This study reveals the potential influence of various environmental conditions on different bacterial populations in stream communities. Present address for X Gao: Florida Department of Environmental Protection, 2600 Blair Stone Road, Tallahassee, FL 32399, USA Co~apundence to: O.A. Olapade at present address: Great Lakes WATER Institute, Wisconsin Aquatic Technology and Environmental Research, University of Wisconsin, Milwaukee, WI 53204, USA; E-mail: [email protected] Introduction Several studies have reported dynamic changes, both spatially, within a watershed, and temporally, in the abundance and distribution of selected stream bacterial populations [ 1 1, 12, 14-17, 191. However, differences in stream bacterial populations among watersheds from diverse regions exhibiting differing environmental conditions have not been examined [lo]. Factors such as nutrient and organic matter availability, anthropogenic disturbance, turbidity, and precipitation [ 12, 16, 20, 301 are thought to influence bacteria in streams. These effects are likely to vary among ecosystems and thus, responses of the bacterial populations to these factors are predicted to differ among streams. In this study, abundance of three bacterial species, Acinetobacter calcoaceticus, Burkholderia cepacia, and Pseudomonas putida, in the water and sediment of nine streams in midwestern, eastern, and southern parts of the United States were examined using fluorescent in situ hybridization (FISH). Population sizes of the species (defined as the abundance of a given species at a particular location, given that the spatial boundaries of bacterial populations have not been defined in lotic systems) were also compared among sites (upstream, midstream, and downstream) within each stream. Each of these species is a Gram-negative member of the proteobacteria group. P. putida had been described as a cosmopolitan opportunist par excellence and is commonly found in soil and water [27]. B. cepacia is common in soil, water, and in association with plants and is an opportunist pathogen of cystic fibrosis patients; this taxon contains a complex of genomovars and recently described species, such as B. cenocepacia [5, 281. A. calcoaceticus is a strict aerobe that is nonmotile whose high frequency of transformation [23] and degradation of hydrocarbons have been well studied (reviewed by [I]). These three species vary spatially and temporally in abundance and distribution; specifically, P. putida numbers changed sporadically in the water of the Cuyahoga River (OH, USA), while changes in A. calcoaceticus DOI: 10.1007/~00248-004-0030-x Volume 49, 461467 (2005) O Springer Science+Business Media, Inc. 2005 461 462 O.A. OLAPADE ET AL.: ABUNDANCE OF THREE BACTERIAL POPULATIONS I TREAMS population size correlated with water temperature [19]. In the Ogeechee River (GA, USA), P. putida numbers were higher and more consistent spatially than A. calcoaceticus numbers [ 1 11. Likewise, on decomposing leaves in a stream, numbers of B. cepacia, A. calcoaceticus, and P. putida exhibited different responses [20]. A. calcoaceticus was not affected by leaf leachate, whereas phenolic compounds (e.g., tannic acids) appeared to limit P. putida and enhance B. cepacia populations. In contrast, in sediments of Four Mile Creek (SC, USA) population sizes of these three species were similar to each other and did not vary greatly temporally or spatially [21]. Overall, prior studies suggest that A. calcoaceticus is relatively well suited for the water column and benthic habitats and that P. putida is best suited for terrestrial environments, perhaps entering the streams from allochthonous sources, based on abundance in floodplain soil [14] and correlations of temporal changes in abundance with turbidity [19]. B. cepacia is an exceptionally versatile species in terms of DOM use and seems particularly responsive to leaf leachate [13, 201, and thus its abundance may relate to DOM pool composition. This study focused on comparing the abundance of the three target bacterial species among nine streams located in the southeastern and midwestern United States. Streams were selected based on differences in their organic matter dynamics and use in prior studies [3, 7, 9, 13, 15, 22, 26, 291. Streams examined included coastal plain blackwater streams (with high amounts of DOM, in VA, GA, and SC), well-canopied streams (Appalachian Mountain, NC, and northeast OH), more open canopied streams (prairie, KS, and agricultural, IA), a stream with large populations of macrophytes (WI), and a stream in a watershed with forests, agricultural fields, and wetlands (MI). Differences among the streams in DOM sources, inorganic nutrient concentrations, and other environmental features were hypothesized to likely influence the abundance of the bacterial species examined. In addition, to provide a frame of reference for looking at interstream differences, intrastream variation was assessed by collecting samples from three sites within each stream.