chapt07 - 7 Microbial Growth and Reproduction CHAPTER...

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7 Microbial Growth and Reproduction CHAPTER OVERVIEW This chapter describes the basic nature of microbial growth. Several methods for the measurement of microbial growth are described, as are different systems for studying microbial growth. The influence of various environmental factors on the growth of microorganisms is discussed and the chapter ends with a consideration of microbial growth in natural environments. This latter section sets the stage for more detailed discussions of microbial ecology. CHAPTER OBJECTIVES After reading this chapter you should be able to: name the various phases of growth that occur in closed culture systems and describe what is occurring in each phase determine from experimental data the various parameters (number of generations, specific growth rate constant, mean generation time) that describe microbial growth in mathematical terms compare and contrast the various methods for measuring microbial growth describe the various types of continuous culture systems and explain the differences in their function describe the influence of various environmental factors (water availability, pH, temperature, oxygen concentration, pressure, radiation) on the growth of microorganisms categorize microorganisms according to the environmental factors that are conducive to optimal growth of the organism discuss three growth-related phenomena observed in natural environments (growth limitations by environmental factors, viable but nonculturable cells, and quorum sensing) CHAPTER OUTLINE I.Reproductive Strategies A. Bacteria and archaea tend to be haploid, while eukaryotes can be haploid or diploid B. Most prokaryotes reproduce by binary fission; others reproduce by budding or fragmentation; during binary fission, a parent cell grows, elongates, replicates its genome, and then divides into two equal daughter cells II.The Bacterial Cell Cycle A. The two major phases of the bacterial cell cycle are for replication and partitioning DNA into progeny cells and cytokinesis that separates the progeny cells B. Chromosome replication and partitioning 1. Replication of the circular chromosome through a replisome begins at the origin of replication and ends at the terminus 2. Partitioning of the chromosome copies into the daughter cells is performed with the help of MreB protein that is similar to eukaryotic actin 3. Plasmids replicate independent of the chromosome and carry genes specific for their segregation to daughter cells; ParR, like MreB, is an actin analog C. Cytokinesis is the process by which the parent cell is divided into two daughter cells; a tubulinlike protein (FtsZ) forms a dynamic Z ring that constricts to cause cell division D. Cellular growth and determination of cell shape 1. Bacterial cells have defined shapes that must be created and maintained by the cell wall; turgor pressure generated by cell osmolarity helps maintain cell shape and allow for expansion and growth 67
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2. During peptidoglycan synthesis, NAG and NAM subunits are linked in the cell and moved
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chapt07 - 7 Microbial Growth and Reproduction CHAPTER...

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