Measuring PDH and PK Activities

The activity of PDH was measured as reported (75 (link)–77 (link)), and the PK enzymatic activity was assessed using a commercial assay kit (BC0545, Beijing Solarbio Science and Technology Co., Ltd.). The bacteria were treated as stated above. After incubation with serum or/and mannitol, the bacteria were collected and adjusted to OD600 of 1.0. Moreover, 20 ml of OD600 = 1.0 bacterial solution was collected in a 1.5-ml centrifugation tube, resuspended with 1 ml sterile saline, and disrupted by sonic oscillation (200 W total power with 35% output, 2 s pulse, and 3 s pause over ice) for 3 min. After centrifugation, the supernatants of the enzyme activity assay were collected. Protein concentration was measured with enhanced BCA Protein Assay Kit (P0010, Beyotime, Shanghai, China).