Russell J B, Cook G M
USDA Agricultural Research Service, Cornell University, Ithaca, New York 14853.
Microbiol Rev. 1995 Mar;59(1):48-62. doi: 10.1128/mr.59.1.48-62.1995.
Biomass formation represents one of the most basic aspects of bacterial metabolism. While there is an abundance of information concerning individual reactions that result in cell duplication, there has been surprisingly little information on the bioenergetics of growth. For many years, it was assumed that biomass production (anabolism) was proportional to the amount of ATP which could be derived from energy-yielding pathways (catabolism), but later work showed that the ATP yield (YATP) was not necessarily a constant. Continuous-culture experiments indicated that bacteria utilized ATP for metabolic reactions that were not directly related to growth (maintenance functions). Mathematical derivations showed that maintenance energy appeared to be a growth rate-independent function of the cell mass and time. Later work, however, showed that maintenance energy alone could not account for all the variations in yield. Because only some of the discrepancy could be explained by the secretion of metabolites (overflow metabolism) or the diversion of catabolism to metabolic pathways which produced less ATP, it appeared that energy-excess cultures had mechanisms of spilling energy. Bacteria have the potential to spill excess ATP in futile enzyme cycles, but there has been little proof that such cycles are significant. Recent work indicated that bacteria can also use futile cycles of potassium, ammonia, and protons through the cell membrane to dissipate ATP either directly or indirectly. The utility of energy spilling in bacteria has been a curiosity. The deprivation of energy from potential competitors is at best a teleological explanation that cannot be easily supported by standard theories of natural selection. The priming of intracellular intermediates for future growth or protection of cells from potentially toxic end products (e.g., methylglyoxal) seems a more plausible explanation.
生物量的形成是细菌新陈代谢最基本的方面之一。虽然有大量关于导致细胞复制的个体反应的信息，但令人惊讶的是，关于生长的生物能量学的信息却很少。多年来，人们一直认为生物量的产生（合成代谢）与可从产能途径（分解代谢）获得的ATP量成正比，但后来的研究表明，ATP产量（YATP）不一定是恒定的。连续培养实验表明，细菌将ATP用于与生长无直接关系的代谢反应（维持功能）。数学推导表明，维持能量似乎是细胞质量和时间的与生长速率无关的函数。然而，后来的研究表明，仅维持能量并不能解释产量的所有变化。由于只有部分差异可以通过代谢物的分泌（溢流代谢）或分解代谢转向产生较少ATP的代谢途径来解释，因此能量过剩的培养物似乎具有能量溢出机制。细菌有可能在无效酶循环中溢出过量的ATP，但几乎没有证据表明这种循环很重要。最近的研究表明，细菌还可以通过细胞膜利用钾、氨和质子的无效循环直接或间接地消耗ATP。细菌中能量溢出的作用一直是个令人好奇的问题。从潜在竞争者那里剥夺能量充其量只是一种目的论解释，很难得到自然选择标准理论的支持。为未来生长启动细胞内中间体或保护细胞免受潜在有毒终产物（如甲基乙二醛）的影响似乎是一个更合理的解释。
