PHOSPHOLIPID FATTY-ACID COMPOSITION OF SIZE-FRACTIONATED INDIGENOUS SOIL BACTERIA

The soil bacterial community is dominated by small cells (<0.4 mu m di al, and most of these ''dwarf'' cells are unculturable. We have tried to elucidate the character of these cells by determining the amounts a nd types of phospholipid fatty acids (PLFAs), in comparison with the w hole 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 si ze fractions were different when compared using principal component an alysis. This separation was partly due to an increase in branched fatt y acids like a15:0 and br18:0 and a decrease in relative amounts of th e PLFA Is:1 omega 7 in the < 0.4 mu m size fraction, compared to the w hole community, indicating a higher proportion of Gram-positive bacter ia among the smaller cells. The amount of PLFA per cell indicated the possibility of intact cell membranes in these small cells. (C) 1997 El sevier Science Ltd.