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EFFECT OF TEMPERATURE ON THE C ISOTOPIC VALUE OF MICROBIAL LIPIDS APPLIED TO DETERMINE C USAGE IN MICROBIAL COMMUNITIES
Citation:
Molina, M, R A. Burke Jr., AND J E. Cox. EFFECT OF TEMPERATURE ON THE C ISOTOPIC VALUE OF MICROBIAL LIPIDS APPLIED TO DETERMINE C USAGE IN MICROBIAL COMMUNITIES. Presented at American Society for Microbiology Annual Meeting, Los Angeles, CA, May 21-25, 2000.
Impact/Purpose:
The overall objective of this task is to develop quantitative relationships for assessing the vulnerability of aquatic resources to global change. The task will contribute experimental and modeling tools for assessments of the interactions of global climate and UV changes with coral reefs and selected watersheds and estuaries in the U.S. These activities are contributing primarily to two APGs in the ecosystems component of the Global Change Research Multiyear Plan: the 2006 APG (APG 3) on building the capacity to assess global change impacts on coastal aquatic ecosystems, including coral reefs and estuaries and the 2004 APG (APG 2) on building capacity to assess and respond to global change impacts on selected watersheds. One major task objective is to assess interactions of global warming and UV exposure that are contributing to the observed coral bleaching and disease. Our lab is working with scientists at the NHEERL Gulf Ecology Lab to characterize UV exposure and effects at several coral reef sites. Other research in this task is examining the interactions between UV-induced breakdown of refractory organic matter in estuaries and coastal areas that enhance UV penetration into the water and concurrently form biologically-labile nitrogen-, phosphorus- and carbon-containing substances that stimulate productivity and microbial activity. This task also involves research in central Brazil that is part of the Large Scale Biosphere Atmosphere Experiment (LBA). The objectives of this project are to assess the impacts of land use and climatic changes on soil nutrient cycles and microbiota, trace gas exchange and water quality in the Brazilian cerrado. This work involves a close collaboration between EPA and a group of scientists from the Department of Ecology, University of Brasilia, Brazil. Other objectives of this task are to assess the interactions of land use and climate changes with the ecological functioning of streams in watersheds of the Piedmont region of the southestern U.S.
Description:
The combination of compound specific stable isotopic analysis with phospholipid fatty acid (PLFAS) analysis is useful in determining the source of organic carbon used by groups of a microbial community. Determination of the effect of certain environmental parameters is important when interpreting C sources utilized by the microbial community in complex ecosystems. In this research, we studied the effects of temperature, substrate, and incubation
time on the abundance and isotopic fractionation of PLFAS. Lipids were extracted from pure bacterial cultures and salt marsh sediments incubated at 10, 20, and 28 degrees C for 5, 10, 15, and 25 days. PLFAs were 2 to 8 per mil more depleted in 13C relative to the substrate, with the cultures grown at 10 degrees C showing the largest fractionation. For instance, Pseudomonas and Mycobacterium lipids were 2 and 4 per mil more depleted in 13C when grown at 10 degrees C than when grown at 28 degrees C. In general, C16:0 showed the greatest fractionation in almost all the cases, while C16:lw7c and C18:lw7c showed the least and were sometimes enriched relative to the substrate. However, there was no consistent trend in the 13C values among the individual lipids extracted from a given bacterial species. Differences in substrates did not affect the "C fractionation. The isotopic values of most PLFAs extracted from the environmental samples indicated that the fractionation was smaller (less than or equal to 4 per mil) than in the pure cultures. In addition, C16:0 was not the most depleted lipid. The results suggest that when using PLFAs to determine the sources of organic C utilized by the microbial community, it is important to consider the effect of temperature on the 13C fractionation of the lipids. Specifically, the effect that lower temperatures may cause greater isotopic fractionation. Although there are significant differences in the lipid isotopic values from pure cultures grown at different temperatures, such a strong temperature dependence is not observed in the environmental samples. Therefore, results from pure laboratory cultures should be applied cautiously when interpreting environmental data.