Shewanella is a gram-negative soil iron reducing bacteria

which has extracellular electron transfer ability. The composition of the extracellular polymer is one of the important factors that can directly influence the electron transfer effect. Extracellular polysaccharide (EPS) is an important component of extracellular polymers. The effect of different concentrations of CaCl

2

(0

0.7，1.4， 2.1 and 5.0 mmol/L) on the EPS of Shewanella oneidensis MR-1 was herein studied by phenol sulfuric acid method combined with spectrophotometry

chromatography and mass spectrometry. The results showed that the amount of EPS would vary with the Ca

2+

concentration. Maximum EPS production of 0.3 g /mL was obtained in the culture medium with 2.1 mmol/L of Ca

2+

concentration

which was 5 times greater than that obtained without Ca

2+

. The amount of EPS obtained with 1.4 mmol/L Ca

2+

concentration was 0.08 g/mL

which was nearly the same to that obtained without Ca

2+

. The concentration of Ca

2+

in the medium did not significantly influence the structure of EPS produced by MR-1. EPS had a repeating unit with a ［→3)-α-D-Manp(1→］ backbone chain. The results of this study provide reference data for the further study of Shewanella extracellular polymers.