Microhabitat partitioning in a diverse assemblage of darters in the Allegheny River system

Synopsis Habitat partitioning among eleven species of darters (Percidae: Etheostomatini) from the Allegheny River system was studied through underwater observation. Percina caprodes and Percina copelandi showed consistent segregation from Etheostoma by occupying deeper habitats. Substrate size, depth, and water velocity were important variables by which Etheostoma species segregated. Analysis of niche breadth values indicated that species differed widely in their degree of specialization in habitat use; based on the variables measured, Etheostoma zonale was a habitat generalist whereas Etheostoma camurum, Etheostoma tippecanoe, and Percina caprodes tended towards habitat specialization. Habitat segregation appears to be an important mechanism allowing the coexistence of these closely related and ecologically similar species. Microhabitat quantification on a fine scale was important in discovering habitat differences in this diverse system.     

MetR-mediated repression of the glyA gene in Escherichia coli

Abstract Both lactic and acetic acids cause mixed inhibition of acid production in mutans streptococci. This inhibition is partly irreversible due to cell death, an important factor when considering acidogenicity and aciduricity of these organisms, and their role in the caries process. Other monocarboxylic end-products may be present and may also be important inhibitors of acid production in dental plaque. This study considered the effects of varying concentrations of the end-product formic acid on acid production rates in Streptococcus mutans R9, measured using the pH-stat. Undissociated formic acid caused mixed inhibition with constants of K _iu (uncompetitive) of 6.07 ± 1.27 mmol 1⁻¹ and K _ic (competitive) of 0.2 ± 10.11 mmol I ⁻¹. Inhibition was found to be fully reversible, with no loss of cell viability. It is concluded that at those concentrations found in vivo, formate is not a significant inhibitor of acid production by S. mutans in dental plaque at any time, and is not important in determining the acidogenicity or aciduricity of this organism.     

Observations of an ash lagoon spill on the new River,Virginia

An estimated 7 million liters of slightly alkaline water (pH = 7.7) and ash entered New River on 23 July 1973 near Pearisburg, Virginia. The rate of dispersion, 1.4 km/hr, allowed qualitative collections of fishes and macroinvertebrates to be made immediately before and after the biological impact of the spill. Diversity and relative abundance indicated that fishes and macroinvertebrates were little affected. Physicochemical parameters from the flyash lagoon, as projected from 1971–1972 data, were within the known tolerance ranges of aquatic biota common to New River.