中文摘要：

希瓦氏菌是一类革兰氏阴性土壤铁还原菌，具有胞外电子传递能力，其胞外聚合物的组成是直接影响其电子传递效应的重要因素之一。胞外多糖（EPS）是胞外聚合物的重要组成成分，该文以Shewanella oneidensis MR－1为对象，采用苯酚－硫酸法结合光谱法、色谱法及质谱法等系统地研究了含不同浓度（0、0.7、1.4、2.1和5.0 mmol／L） CaCl2培养基对MR－1胞外多糖的影响。结果表明，不同浓度Ca^2＋影响下的MR－1多糖的分泌量各不相同，其中Ca^2＋浓度为2.1 mmol／L时，MR－1分泌多糖质量浓度最高，为0.3 g／mL，是无Ca^2＋影响的EPS分泌量的5倍；而Ca^2＋浓度为1.4 mmol／L 时，EPS为0.08 g／mL，与无Ca^2＋影响时EPS分泌量相近；Ca^2＋对MR－1分泌的EPS结构没有显著性影响，获得的EPS均为由α－D－吡喃甘露糖通过1，3－苷键形成的多糖。研究结果为深入研究希瓦氏菌胞外聚合物提供数据参考。

英文摘要：

Shewanella is a gramnegative soil iron reducing bacteria,which has extracellular electrontransfer ability.The composition of the extracellular polymer is one of the important factors that can directly influence the electron transfer effect.Extracellular polysaccharide （EPS）is an important component of extracellular polymers.The effect of different concentrations of CaCl2 （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 acidmethod combined with spectrophotometry,chromatography and mass spectrometry.The results showedthat the amount of EPS would vary with the Ca^2 ＋ concentration.Maximum EPS production of 0.3 g /mLwas obtained in the culture medium with 2.1 mmol/L of Ca^2 ＋ concentration,which was 5 times greaterthan 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 themedium did not significantly influence the structure of EPS produced by MR -1.EPS had a repeating unit with a [→3） -α-D-Manp （1→]backbone chain.The results of this study provide reference da-ta for the further study of Shewanella extracellular polymers.