As important genome editing tools, CRISPR/Cas systems, especially those based on type II Cas9 and type V Cas12a, are widely used in genetic and metabolic engineering of bacteria. However, the intrinsic toxicity of Cas9 and Cas12a-mediated CRISPR/Cas tools can lead to cell death in some strains, which led to the development of endogenous type I and III CRISPR/Cas systems. However, these systems are hindered by complicated development and limited applications. Thus, further development and optimization of CRISPR/Cas systems is needed. Here, we briefly summarize the mechanisms of different types of CRISPR/Cas systems as genetic manipulation tools and compare their features to provide a reference for selecting different CRISPR/Cas tools. Then, we show the use of CRISPR/Cas technology for bacterial strain evolution and metabolic engineering, including genome editing, gene expression regulation and the base editor tool. Finally, we offer a view of future directions for bacterial CRISPR/Cas technology.

中文翻译：

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不同类型基于CRISPR / Cas的系统在细菌中的应用。

作为重要的基因组编辑工具，CRISPR / Cas系统，尤其是基于II型Cas9和V型Cas12a的系统，被广泛用于细菌的基因和代谢工程中。然而，Cas9和Cas12a介导的CRISPR / Cas工具的内在毒性可能导致某些菌株中的细胞死亡，从而导致内源性I和III型CRISPR / Cas系统的发展。然而，这些系统由于复杂的开发和有限的应用而受到阻碍。因此，需要进一步开发和优化CRISPR / Cas系统。在这里，我们简要总结了不同类型的CRISPR / Cas系统作为遗传操纵工具的机制，并比较了它们的功能，为选择不同的CRISPR / Cas工具提供了参考。然后，我们展示了CRISPR / Cas技术在细菌菌株进化和代谢工程中的应用，包括基因组编辑，基因表达调控和碱基编辑工具。最后，我们提供了细菌CRISPR / Cas技术的未来方向的看法。