Cyclic Metabolism as a Mode of Microbial Existence

The review deals with specific bacterial physiological groups developing under periodically varying ambient conditions and possessing a cyclic type of metabolism (CTM). CTM is characterized by unbalanced two-phase growth occurring during the period less than the generation time. During the first phase, the carbon and/or energy source are accumulated, while during the second phase biomass biosynthesis occurs using the accumulated substrate. Known CTM organisms of the groups of phosphate-accumulating and glycogen-accumulating bacteria are described, and their major biochemical models are discussed. Development of microorganisms with obligate CTM is probably impossible or significantly suppressed under stable ambient conditions, which may be the reason why the major CTM organisms can not be cultured using traditional batch and continuous cultivation, while highly enriched cultures may be obtained by cyclic cultivation. Ecological aspects of CTM are discussed, and the possible environments for CTM microorganisms in natural ecosystems are determined.