Díaz-Muñiz I, Banavara D S, Budinich M F, Rankin S A, Dudley E G, Steele J L
Microbiology Doctoral Training Program, University of Wisconsin-Madison, Madison, WI 53706, USA.
J Appl Microbiol. 2006 Oct;101(4):872-82. doi: 10.1111/j.1365-2672.2006.02965.x.
To identify potential pathways for citrate catabolism by Lactobacillus casei under conditions similar to ripening cheese.
A putative citric acid cycle (PCAC) for Lact. casei was generated utilizing the genome sequence, and metabolic flux analyses. Although it was possible to construct a unique PCAC for Lact. casei, its full functionality was unknown. Therefore, the Lact. casei PCAC was evaluated utilizing end-product analyses of citric acid catabolism during growth in modified chemically defined media (mCDM), and Cheddar cheese extract (CCE). Results suggest that under energy source excess and limitation in mCDM this micro-organism produces mainly L-lactic acid and acetic acid, respectively. Both organic acids were produced in CCE. Additional end products include D-lactic acid, acetoin, formic acid, ethanol, and diacetyl. Production of succinic acid, malic acid, and butanendiol was not observed.
Under conditions similar to those present in ripening cheese, citric acid is converted to acetic acid, L/D-lactic acid, acetoin, diacetyl, ethanol, and formic acid. The PCAC suggests that conversion of the citric acid-derived pyruvic acid into acetic acid, instead of lactic acid, may yield two ATPs per molecule of citric acid. Functionality of the PCAC reductive route was not observed.
This research describes a unique PCAC for Lact. casei. Additionally, it describes the citric acid catabolism end product by this nonstarter lactic acid bacteria during growth, and under conditions similar to those present in ripening cheese. It provides insights on pathways preferably utilized to derive energy in the presence of limiting carbohydrates by this micro-organism.
确定干酪乳杆菌在类似于成熟奶酪的条件下柠檬酸分解代谢的潜在途径。
利用基因组序列和代谢通量分析生成了干酪乳杆菌的假定柠檬酸循环（PCAC）。虽然有可能构建出干酪乳杆菌独特的PCAC，但其完整功能尚不清楚。因此，在改良化学限定培养基（mCDM）和切达干酪提取物（CCE）中生长期间，通过柠檬酸分解代谢的终产物分析对干酪乳杆菌的PCAC进行了评估。结果表明，在mCDM中能量源过量和受限的情况下，这种微生物分别主要产生L-乳酸和乙酸。在CCE中两种有机酸均有产生。其他终产物包括D-乳酸、3-羟基丁酮、甲酸、乙醇和双乙酰。未观察到琥珀酸、苹果酸和丁二醇的产生。
在类似于成熟奶酪的条件下，柠檬酸转化为乙酸、L/D-乳酸、3-羟基丁酮、双乙酰、乙醇和甲酸。PCAC表明，柠檬酸衍生的丙酮酸转化为乙酸而非乳酸，每分子柠檬酸可能产生两个ATP。未观察到PCAC还原途径的功能。
本研究描述了干酪乳杆菌独特的PCAC。此外，还描述了这种非发酵剂乳酸菌在生长过程中以及在类似于成熟奶酪的条件下柠檬酸分解代谢的终产物。它提供了关于这种微生物在碳水化合物有限的情况下优先用于获取能量的途径的见解。
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