Longitudinal changes in microbial assemblages of the Ogeechee River

Abstract

Summary Bacteria are common and important constituents of aquatic ecosystems but little is known about their populations; most measurements commonly employed are at a grosser, assemblage‐level. The purpose of this study was to compare longitudinal patterns in microbial assemblages and populations along a river ecosystem. Water samples were collected under base flow conditions from 13 main stem and four tributary sites along the Ogeechee River spanning the piedmont and coastal plain of Georgia, USA. Based on the detection of active cells with abundant ribosomes, two species of bacteria, Acinetobacter calcoaceticus and Pseudomonas putida, represented 0.4–4.9% of individuals in the Domain Bacteria. The abundance of P. putida was low in the headwater region of the river, perhaps because of lower concentrations of aromatic compounds. The abundance of members of the Domain Bacteria peaked in the upper and lower orders of the river and were low in the mid‐orders, where protozoa were numerous. Higher DOC quality (based on bacterial growth) in the headwaters and peak protozoa numbers in the mid‐section of the river, may have contributed to the spatial patterns observed in the bacterial assemblage. Results suggest that there is a longitudinal pattern of changing relationships between labile DOC, protozoa and bacteria but that, within the bacterial assemblage, species differ in their responses.

Seasonal Response of Stream Biofilm Communities to Dissolved Organic Matter and Nutrient Enrichments

“…In this study, we examined how different bacterial taxa in biofilms responded to DOM and inorganic nutrients by using nutrient diffusing artificial substrates (clay flowerpots), an approach commonly used to demonstrate nutrient limitation in streams (e.g., references 11 and 43). Responses to different treatments (leaf leachate [LL], glucose, algal exudates, and phosphate and nitrate singly and in combination) by different bacterial taxa and algae were compared among seasons.The bacterial taxa examined were selected because they are common in streams (21,25,26) and known to use a wide array of organic compounds (28). The three species targeted (Burkholderia cepacia, Acinetobacter calcoaceticus, and Pseudomonas putida) are gram-negative bacteria that are abundant in water and sediment (22).…”

“…The source, quality, and type of DOM, as well as the quantity, may influence the abundance and distribution of bacteria in stream ecosystems (20,21,24). In addition, other aspects of microbial community function such as respiration, biomass, and extracellular enzyme activity may be limited by dissolved inorganic nutrients and organic matter in streams (49, 51).…”

“…The bacterial taxa examined were selected because they are common in streams (21,25,26) and known to use a wide array of organic compounds (28). The three species targeted (Burkholderia cepacia, Acinetobacter calcoaceticus, and Pseudomonas putida) are gram-negative bacteria that are abundant in water and sediment (22).…”

Abundance of Three Bacterial Populations in Selected Streams

“…Several studies have reported dynamic changes, both spatially, within a watershed, and temporally, in the abundance and distribution of selected stream bacterial populations [11,12,[14][15][16][17]19]. However, differences in stream bacterial populations among watersheds from diverse regions exhibiting differing environmental conditions have not been examined [10].…”

“…In the Ogeechee River (GA, USA), P. putida numbers were higher and more consistent spatially than A. calcoaceticus numbers [11]. Likewise, on decomposing leaves in a stream, numbers of B. cepacia, A. calcoaceticus, and P. putida exhibited different responses [20].…”