Proposal for a method to estimate nutrient shock effects in bacteria

Plating methods are still the golden standard in microbiology; however, some studies have shown that these techniques can underestimate the microbial concentrations and diversity. A nutrient shock is one of the mechanisms proposed to explain this phenomenon. In this study, a tentative method to assess nutrient shock effects was tested. Findings To estimate the extent of nutrient shock effects, two strains isolated from tap water (Sphingomonas capsulata and Methylobacterium sp.) and two culture collection strains (E. coli CECT 434 and Pseudomonas fluorescens ATCC 13525) were exposed both to low and high nutrient conditions for different times and then placed in low nutrient medium (R2A) and rich nutrient medium (TSA). The average improvement (A.I.) of recovery between R2A and TSA for the different times was calculated to more simply assess the difference obtained in culturability between each medium. As expected, A.I. was higher when cells were plated after the exposition to water than when they were recovered from high-nutrient medium showing the existence of a nutrient shock for the diverse bacteria used. S. capsulata was the species most affected by this phenomenon. This work provides a method to consistently determine the extent of nutrient shock effects on different microorganisms and hence quantify the ability of each species to deal with sudden increases in substrate concentration. <br/

Aquatic habitat use by amphibians with specific reference to Rana temporaria at high elevations (Retezat Mountains National Park, Romania)

Alpine areas are extreme habitats that require special adaptations and involve major trade-offs in terms of life history. Amphibians have the ability to adapt both their life history and developmental traits to alpine environments. Temperate amphibians depend on the quality and availability of aquatic habitats for reproduction. We explored the aquatic habitat used by amphibians in the alpine area of Retezat Mountains, Southern Carpathians, Romania. We surveyed 40 aquatic habitats in a 380 ha area delimited by mountain crests and drained by a steep valley. Each aquatic habitat was characterized using 10 environmental variables. Only three amphibian species occur at elevations above 1900 m, the most widespread being the Common Frog Rana temporaria. The Common Frog showed preference for breeding aquatic habitats, the variables of importance being altitude, solar radiation, water chemistry and grazing. Higher elevation and lower solar radiation decreased frog occurrence, while the impact of grazing favored the use of water bodies. Acidification is eminent in the area with pH dropping below 5 in 20% of the water bodies. Overall, amphibian occurrence in alpine area can be partly explained by the characteristics of aquatic habitats