Occurrence and applications of CRISPR-Cas systems in bifidobacteria

Bifidobacterium is a key member of the human gut microbiota, and many strains are widely used as probiotics due to their health-promoting properties. Despite growing interest, genetic studies in Bifidobacterium have been relatively limited, primarily due to the lack of available genome editing tools. Recent advances in genomics and CRISPR-Cas systems provide opportunities for targeted genome modification in this genus. In this review, we provide an overview of the occurrence, diversity, and distribution of CRISPR-Cas systems across Bifidobacterium species and examine the editing tools developed and implemented to date. We also highlight practical challenges such as strain variability and low transformation efficiency and introduce future avenues of research such as large-payload insertion and in situ editing. Expanding the genetic toolbox for Bifidobacterium will broaden our understanding of this important genus and enable the development of next-generation probiotics.