Moniruzzaman M, Lai X, York S W, Ingram L O
Department of Microbiology and Cell Science, University of Florida, Gainesville 32611, USA.
J Bacteriol. 1997 Mar;179(6):1880-6. doi: 10.1128/jb.179.6.1880-1886.1997.
Contrary to general concepts of bacterial saccharide metabolism, melibiose (25 to 32 g/liter) and fructose (5 to 14 g/liter) accumulated as extracellular intermediates during the catabolism of raffinose (O-alpha-D-galactopyranosyl-1, 6-alpha-D-glucopyranosyl-beta-D-fructofuranoside) (90 g/liter) by ethanologenic recombinants of Escherichia coli B, Klebsiella oxytoca M5A1, and Erwinia chrysanthemi EC16. Both hydrolysis products (melibiose and fructose) were subsequently transported and further metabolized by all three organisms. Raffinose catabolism was initiated by beta-fructosidase; melibiose was subsequently hydrolyzed to galactose and glucose by alpha-galactosidase. Glucose and fructose were completely metabolized by all three organisms, but galactose accumulated in the fermentation broth with EC16(pLOI555) and P2. MM2 (a raffinose-positive E. coli mutant) was the most effective biocatalyst for ethanol production (38 g/liter) from raffinose. All organisms rapidly fermented sucrose (90 g/liter) to ethanol (48 g/liter) at more than 90% of the theoretical yield. During sucrose catabolism, both hydrolysis products (glucose and fructose) were metabolized concurrently by EC16(pLOI555) and P2 without sugar leakage. However, fructose accumulated extracellularly (27 to 28 g/liter) at early stages of fermentation with KO11 and MM2. Sequential utilization of glucose and fructose correlated with a diauxie in base utilization (pH maintenance). The mechanism of sugar escape remains unknown but may involve downhill leakage via permease which transports precursor saccharides or novel sugar export proteins. If sugar escape occurs in nature with wild organisms, it could facilitate the development of complex bacterial communities which are based on the sequence of saccharide catabolism and the hierarchy of sugar utilization.
与细菌糖类代谢的一般概念相反，在大肠杆菌B、产酸克雷伯菌M5A1和菊欧文氏菌EC16的产乙醇重组体对棉子糖（O-α-D-吡喃半乳糖基-1,6-α-D-吡喃葡萄糖基-β-D-呋喃果糖苷）（90克/升）的分解代谢过程中，蜜二糖（25至32克/升）和果糖（5至14克/升）作为细胞外中间产物积累。两种水解产物（蜜二糖和果糖）随后被这三种微生物转运并进一步代谢。棉子糖分解代谢由β-果糖苷酶启动；蜜二糖随后被α-半乳糖苷酶水解为半乳糖和葡萄糖。葡萄糖和果糖被这三种微生物完全代谢，但半乳糖在EC16(pLOI555)和P2的发酵液中积累。MM2（一种棉子糖阳性大肠杆菌突变体）是从棉子糖生产乙醇（38克/升）最有效的生物催化剂。所有微生物都能将蔗糖（90克/升）快速发酵为乙醇（48克/升），产率超过理论产率的90%。在蔗糖分解代谢过程中，两种水解产物（葡萄糖和果糖）被EC16(pLOI555)和P2同时代谢，没有糖泄漏。然而，在KO11和MM2发酵的早期阶段，果糖在细胞外积累（27至28克/升）。葡萄糖和果糖的顺序利用与碱基利用中的二次生长（pH维持）相关。糖逃逸的机制尚不清楚，但可能涉及通过转运前体糖类的通透酶或新型糖输出蛋白的下坡泄漏。如果野生生物在自然界中发生糖逃逸，它可能会促进基于糖类分解代谢顺序和糖利用层次的复杂细菌群落的发展。
