Complete Genome Sequence And Comparative Analysis Of Probiotic Bacterium Lactobacillus Casei Zhang

Lactobacillus casei Zhang was a probiotic bacterium screened from lactic acid bacteria (LAB) isolated from home-made koumiss in Inner Mongolia of China. It exhibited high resistance against low pH and bile and possessed antibacterial, antioxidative and immunomodulating properties.To systematically investigate the genetic basis of L. casei Zhang probiotic properties, whole genome shot gun strategy was used for genome sequencing of L. casei Zhang and the comparative analysis was performed. The complete chromosome of L. casei Zhang consisted of 2,861,848 bp. 2,804 coding sequences (CDSs) were predicted, and 2,572 of them were assigned functions. Further analysis revealed thirty-one phosphotransferase systems (PTSs) in the chromosome, which was strikingly more abundant than in other LAB species and was reflecting the flexibility of L. casei Zhang in sugar utilization. Moreover, we observed a chromosome-encoded iol cluster involved in the use of myo-inositol (MI) and we presumed it would help the L. casei Zhang cell to grow on plant materials. In addition, identification of two eps clusters revealed the genetic basis of exopolysaccharides (EPSs) biosynthesis.Additionally, the complete 36,487 bp sequence of plasmid plca36 from Lactobacillus casei Zhang was determined. Plca36 contains 44 predicted coding regions, and to 23 of them functions could be assigned. For the first time, a relBE toxin–antitoxin (TA) locus in a Lactobacillus genus was identified, perhaps indicating a potential role for plca36 in host survival under extreme nutritional stress. A region encoding a cluster of conjugation genes (tra) was also identified. The cluster showed high similarity and co-linearity with tra regions of pWCFS103 and pMRC01 from Lactobacillus plantarum and Lactococcus lactis, respectively. Comparative gene analysis revealed that plasmids from the genus Lactobacillus may have contributed to the environmental adaptation mainly by providing carbohydrate and amino acid transporters.The genomic studies on L. casei Zhang provided insights into the genetic basis of its probiotic properties and revealed its value for industrial use. We believe that this study would certainly promote the research on LAB species and contribute to the development of new probiotics. On the other hand, the broad view of the genetic landscape would aid in strain improvement and development.