Characteristics of magnetotactic bacteria in Duanjiapo loess section, Shaanxi Province and their environment significance

摘要

Magnetotactic bacteria (MB) have been isolated from 61 samples which have been collected from S0, L1, S1 and L2 layers in the Duanjiapo loess section. A few MB ( < 25 cell counts per sieve mesh) have been found in loess layers (L1, L2), bow-shaped, each cell containing only two magnetosomes, while much more MB ( > 125 cells counts per sieve mesh) have been found from paleosol layers (S0, S1), rod-shaped, each cell containing 8-26 magnetosomes arranged in irregular chains. Magnetosomes with Fe and Co as the main metallic elements are spheroid-shaped, and mainly round in cross-section. Normal saturated fatty acids in MB ranged from C_(14) to C_(28); almost no monounsaturated fatty acids have been identified. Most suitable oxygen content for MB growing is 10%, and low concentration of organic salt (0.02 mmol/L qunisic iron) is beneficial to the forming of magnetosomes. Results suggest that the paleosol development stage is suitable for the growing of MB and the climate fluctuation periods for magnetosomes formation.