Effect of pH on constitutive immobilization of β-mannanase on the Lactobacillus cell surface

Previously, β-mannanase (ManB) was successfully immobilized on the surface of the Lactobacillus plantarum using two constitutive promoters, Pgm and SlpA. The highest activity of immobilized ManB (3010 U/g dry cell weight) was obtained after 4 hours of induction culture, extending cultivation to 8 hours led to a 4.2-fold decrease. This decline might be due to lactic acid production by L. plantarum, which lowered the pH of the culture medium. This study evaluated the impact of pH-controlled cultivation on the activity of ManB displayed on L. plantarum WCFS1. Under these conditions, the highest ManB activity decreased by only ~1.5-fold after 8 hours. This demonstrates that maintaining a constant pH level is a critical factor for improving bacterial cell growth and enhancing the overall yield of enzymes displayed L. plantarum surface. This is the first study to investivate the effect of pH on constitutive immobilization of ManB on the Lactobacillus cell surface.