CHARACTERISTICS OF MAGNETOTACTIC BACTERIA IN DUANJIAPO LOESS SECTION,SHAANXI PROVINCE AND THEIR ENVIRONMENT SIGNIFICANCE

Magnetotactic bacteria (MB) have been isolated from 61 samples which h ave been collected from S0, L1, S1 and L2 layers in the Duanjiapo loes s section. A few MB (<25 cell counts per sieve mesh) have been found i n loess layers (L1, L2) bow-shaped, each cell containing only two magn etosomes, while much more MB (>125 cells counts per sieve mesh) have b een found from paleosol layers (S0, S1) rod-shaped, each cell containi ng 8-26 magnetosomes arranged in irregular chains. Magnetosomes with F e and Co as the main metallic elements are spheroid-shaped, and mainly round in cross-section. Normal saturated fatty acids in MB ranged fro m C-14 to C-20; almost no monousaturated fatty acids have been identif ied. Most suitable oxygen content for MB growing is 10%, and low conce ntration of organic salt (0.02 mmol/L qunisic iron) is beneficial to t he forming of magnetosomes. Results suggest that the paleosol developm ent stage is suitable for the growing of MB and the climate fluctuatio n periods for magnetosomes formation.