中文摘要：

CRISPR—Cas系统作为获得性免疫系统能够保护乳酸菌免受噬菌体等外源基因元件的入侵，旨在对乳酸菌中CRISPR—Cas系统的活性与近期发生水平基因转移的程度是否呈负相关进行检验。预测了乳酸菌中的CRISPR—Cas系统、前噬菌体及基因岛，并分别分析乳酸菌中CRISPR与前噬菌体及与基因岛在数量上的相关性。研究发现CRISPR序列的长度（能反映该免疫系统的活性）与预测的近期发生的水平基因转移事件的数目之间没有明显的相关性。结果表明乳酸菌中的CRISPR—Cas系统并不抑制水平基因转移事件的发生。

英文摘要：

We aimed to test that whether the activity of CRISPR - Cas in microbes is negatively correlated with the extent of recent HGT or not. We predict the CRISPR - Cas systems, prophages and genomic islands to analysis the correlations between CRISPR spacer count and HGT measures. We found no significant dependence between the length of CRISPR arrays, which reflects the activity of the immune system, and the estimated number of recent HGT events. No evidence of inhibition of horizontal gene transfer by CRISPR - Cas on evolu- tionary timescales.