Decreasing Amounts Of Extractable Phospholipid-linked Fatty Acids In A Soil During Decline In Numbers Of Pseudomonads

The hypothesis that phospholipid-linked fatty acid methyl ester (PL-FAME) analysis of a soil characterizes lipids from within microbial cells (cellular) as distinct from lipids stabilized in soil organic matter (extracellular) was tested by measuring the sensitivity of PL-FAME analysis to numbers of bacteria in samples of a soil. Autoclaved samples from the Ap horizon of a soil having a sandy loam texture were inoculated with suspensions of a Pseudomonas sp. (day 0) to form bacterial microcosms. On day 2, half of the microcosms were inoculated with an Acanthamoeba sp., a protozoan that grazes on pseudomonads.The numbers of bacteria in the soil samples without or with Acanthamoeba sp. increased about five-fold between days 2 and 4. Between days 4 and 7, the numbers of pseudomonads in grazed microcosms decreased 10-fold and the numbers of Acanthamoeba sp. increased 10-fold, relative to those in nongrazed microcosms. The 10-fold relative difference in numbers of pseudomonads between nongrazed and grazed samp...