Showing papers by "Åsa Frostegård published in 1997"

Dynamics of a microbial community associated with manure hot spots as revealed by phospholipid fatty acid analyses.

Abstract: Microbial community dynamics associated with manure hot spots were studied by using a model system consisting of a gel-stabilized mixture of soil and manure, placed between layers of soil, during a 3-week incubation period. The microbial biomass, measured as the total amount of phospholipid fatty acids (PLFA), had doubled within a 2-mm distance from the soil-manure interface after 3 days. Principal-component analyses demonstrated that this increase was accompanied by reproducible changes in the composition of PLFA, indicating changes in the microbial community structure. The effect of the manure was strongest in the 2-mm-thick soil layer closest to the interface, in which the PLFA composition was statistically significantly different (P < 0.05) from that of the unaffected soil layers throughout the incubation period. An effect was also observed in the soil layer 2 to 4 mm from the interface. The changes in microbial biomass and community structure were mainly attributed to the diffusion of dissolved organic carbon from the manure. During the initial period of microbial growth, PLFA, which were already more abundant in the manure than in the soil, increased in the manure core and in the 2-mm soil layer closest to the interface. After day 3, the PLFA composition of these layers gradually became more similar to that of the soil. The dynamics of individual PLFA suggested that both taxonomic and physiological changes occurred during growth. Examples of the latter were decreases in the ratios of 16:1 omega 7t to 16:1 omega 7c and of cyclopropyl fatty acids to their respective precursors, indicating a more active bacterial community. An inverse relationship between bacterial PLFA and the eucaryotic 20:4 PLFA (arachidonic acid) suggested that grazing was important.

Phospholipid fatty acid composition of size fractionated indigenous soil bacteria

Abstract: The soil bacterial community is dominated by small cells (< 0.4 μm dia), and most of these “dwarf” cells are unculturable. We have tried to elucidate the character of these cells by determining the amounts and types of phospholipid fatty acids (PLFAs), in comparison with the whole microbial community. Indigenous soil bacteria were extracted from soil and fractionated according to size by sequential filtration, and the PLFA pattern was determined. The PLFA pattern of the different size fractions were different when compared using principal component analysis. This separation was partly due to an increase in branched fatty acids like a15:0 and br18:0 and a decrease in relative amounts of the PLFA 18:1ω7 in the < 0.4 μm size fraction, compared to the whole community, indicating a higher proportion of Gram-positive bacteria among the smaller cells. The amount of PLFA per cell indicated the possibility of intact cell membranes in these small cells.