This study investigated the biological characteristics of 43 actinomycete isolates from saline and alkaline soils in Xinjiang, Hebei and Qinghai and representative strains of four genera under differing conditions of pH and varying concentrations of the mineral salts Na + , K + , Mg 2+ and Ca 2+ . The results indicated that halotolerant actinomycetes have extensive adaptability to Na + , K + and Mg 2+ , but that few strains can grow even in low concentrations of CaCl 2 . Halophilic

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... have extensive adaptability to Na + ; for most, Na + may be replaced by K + or Mg 2+ , but not by Ca 2+ . Certain halophilic actinomycetes require Na + to grow. It was also clear that the growth of all halophilic actinomycetes is dependent on different concentrations of Na + , K + or Mg 2+ . We believe that only kaliumophilic or magnesiumophilic or calciumphilic actinomycetes may be found in high salt environments. In addition, the range of pH values in which growth occurred was 6.0~10.0; optimum pH values were 7.0~8.0 for both halophilic and halotolerant actinomycetes. The distribution of halophilic actinomycetes was also found to be related to sample sources.