Prokaryotic Life Cycles
While the normal consequence of bacterial growth is production of identical cells, many prokaryotes generate a cell with a different purpose than the parent. These new cell types have one of three specific functions, dormancy, nutrient acquisition, or dis
- PDF / 2,087,402 Bytes
- 20 Pages / 595.276 x 790.866 pts Page_size
- 30 Downloads / 226 Views
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 Differentiation Leading to Dormancy . . . . . . . . . . . . . . . . . . . . . 318 Endospore Formation in Bacillus subtilis . . . . . . . . . . . . . . . 323 Fruiting Body Development in Myxococcus xanthus . . . . 325 Nutrient Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330 Dispersal Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 Caulobacter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336
Introduction Prokaryotic development generates a cell with a different purpose from the parent particularly (1) dormancy, (2) nutrient acquisition, or (3) dispersal. Some species produce specialized cells that simultaneously perform two of these functions, such as baeocytes and zoospores, which function in both dormancy and dispersal. Some organisms have complex life cycles that produce several different types of specialized cells, such as Anabaena and Rhodomicrobium, and are best viewed with a more holistic bend that focuses on the entire life cycle. This chapter compares the structure, function, and, where known, the mechanism of differentiation of the three classes of specialized cell types. This approach has the advantage of illustrating and emphasizing similarities and differences in origin, means, and mechanics. Resting cells are usually generated in response to nutrient limitation and provide a metabolically quiescent state that permits survival during famine or drought. The Bacillus endospore is the most carefully studied resting cell. However, dormant cells are formed by many mechanisms, each with a unique evolutionary origin, attesting at once to the efficacy of this survival approach (> Table 16.1). An interesting twist to endospore formation is found in the closely related genera Metabacterium, which forms two or more internal endospores, and Epulopiscium, which produces two live offspring internally. In Metabacterium, binary fission is no longer the sole means of reproduction. Instead, endospore formation has become hardwired into the cell division cycle and may be the primary means of proliferation (Angert and Losick 1998). Endospore formation was modified further in Epulopiscium to produce live offspring internally (Angert et al. 1996). With a few modifications to the endospore developmental program, the purpose of the life cycle seems to have shifted from dormancy to reproduction.
Some cyanobacteria produce specialized cells for fixing nitrogen. All living cells require organic nitrogen, but only a few bacteria can reduce atmospheric nitrogen (N2) to ammonia (NH3), an ATP-dependent process that utilizes the enzyme nitrogenase. Nitrogenase is oxygen labile. While some bacteria deal with the O2 sensitivity of nitrogenase by growing in anaerobic or microaero
Data Loading...
