SREL Reprint #2293




Physiologic and genetic determinants of lotic bacterial distribution and abundance

J Vaun McArthur


Although microbes control most ecosystem level processes, i.e., nutrient cycling, carbon mineralization, oxidative phosphorylation, little is known of their ecology. There are no studies that have described the distribution and abundance of bacterial species along any river system. Studies that have dealt with bacterial types are often at higher taxonomic levels (Trentham & James 1981) or are restricted to a single location and often a single sampling effort. However, densities of bacteria range between 103 and 106 cells per mL in the water column and exceed 108 cells per cm2 of sediment.  Because so many bacteria are either in transport or attached to surfaces in a stream, researchers have assumed that no matter where they conduct their experiments similar microbial effects will be observed.

Current stream theory (Vannote et al. 1980) predicts that biotic changes along a stream continuum are controlled by physical changes in the stream. Specific predictions about the types and functional capabilities of stream blota have been made and tested. Although certain differences have been found for various streams this theoretical construct has been supported in many instances (Minshall et al. 1995). While the river continuum concept has been reworked over the years, little attention has been given to microbes. No predictions are made concerning changes in either the species composition or the functional capabilities of bacteria or other microbes along a stream.

If microinvertebrates, macroinvertebrates and vertebrates change along streams are there similar changes in bacterial species composition and/or functional groups? Are the same species of bacteria found both spatially and temporally along stream continua? What are the origins and fates of bacteria in transport? Can transported bacteria colonize lower reaches and be functional? If the same species are found at multiple sites in a stream are they the same strain or are there genetic differences among sub-populations?

While the above list of questions is not exhaustive of the types of questions needing answers in aquatic microbial ecology they form a framework for the work described in this paper. The purpose of this paper is to present results from previous experiments that address aspects of the question presented above. The studies reviewed were conducted primarily by myself or my students and thus represent a specific sub-set of possible papers that deal with these questions.

SREL Reprint #2293

McArthur, J.V. 1998. Physiologic and genetic determinants of lotic bacterial distribution and abundance. Verh. Internat. Verein. Limnol. 26:1080-1082.

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