Lecture 5-1 Microbial Growth

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1 Lecture 5-1 Microbial Growth CHAPTER 5 in BROCK BIOLOGY OF MICROORGANISMS Zhao Liping, Chen Feng School of Life Science and Biotechnology Shanghai Jiao Tong University

2 I. Bacterial Cell Division 5.1 Cell Growth and Binary Fission In microbiology, growth 生长 is defined as an increase in the number of cells. By definition, when one cell divides to form two, one generation 世代 has occurred. Shanghai Jiao Tong University

3 Binary fission 二分分裂 Bacterial Growth In most prokaryotes, growth of an individual cell continues until the cell divides into two new cells, a process called binary fission.

4 5.2 Fts proteins and the cell division plane Fts proteins ( filamentous temperature sensitive ) are important in the cell division process of prokaryotes. Fts proteins are universally distributed among prokaryotes, including the Archaea, and FtsZ proteins have been found in mitochondria 线粒体 and chloroplasts 叶绿体. Fts 蛋白广泛存在于原核生物 FtsZ shows structural similarities to tubulin 微管蛋白, the important cell division protein in eukaryotes. Shanghai Jiao Tong University

5 In rod-shaped cells, formation of the divisome begins with the attachment of molecules of FtsZ in a ring around the cell cylinder in the precise center of the cell. 细胞的 分裂装置 称为分裂体 (divisome), 杆菌的分裂体形成于 FtsZ 环, 该环位于细胞柱体的正中央. Shanghai Jiao Tong University

6 The arrangement of individual divisome proteins: ZipA is an FtsZ anchor; FtsI is a peptidoglycan biosynthesis protein; FtsK assists in chromosome separation; FtsA is an ATPase. Phase-contrast Cells stained with a specific reagent against FtsZ Binary fission

7 DNA replication, Min Proteins, and Cell Division Location of the actual cell midpoint by FtsZ is facilitated by Min proteins, especially MinC, MinD, and MinE. Shanghai Jiao Tong University

8 Figure 5.4 FtsZ Cell wall Cytoplasmic membrane MreB Sites of cell wall synthesis MreB and Determinants of Cell Morphology Other kinds of division

9 5.3 Peptidoglycan synthesis and cell division 肽聚糖合成与细胞分裂 2000 chemical reactions in the cell division Energy transformations Biosynthesis of monomers, coenzymes, cofactors etc. Polymerization reactions-synthesis of polymers from monomers Shanghai Jiao Tong University

10 Localization of new cell wall synthesis during cell division. In cocci, new cell wall synthesis (shown in green) is localized at only one point. 球菌新合成的细菌壁 ( 绿色部分 ) 位于中间 Shanghai. Jiao Tong University

11 Review: the peptidoglycan structure. Shanghai Jiao Tong University

12 Review: Overall structure of peptidoglycan illustrating the repeating sugars and cross bridges.

13 5.3.1 Biosynthesis of peptidoglycan Figure 5.7a Bactoprenol 细菌萜醇 is a very hydrophobic C 55 alcohol. Bactoprenol transports peptidoglycan building blocks across the Transport membrane of by peptidoglycan rendering the precursors across sufficiently the cytoplasmic hydrophobic to membrane pass through to the interior growing of point the cytoplasmic of the cell wall. membrane.

14 5.3.2 Transpeptidation: the penicillin target 转肽作用 : 青霉素作用位点 The transpeptidation reaction leads to the final cross-linking of two peptidoglycan chains. Penicillin inhibits this reaction.

15 Penicillin Shanghai Jiao Tong University

16 II. Growth of Bacterial Populations 细菌群体生长

17 What s the difference between growth of macroorganisms and microorganisms? Macroorganisms 大型生物 Growth and reproduction can be distinct for individuals 个体的生长与繁殖不同 Growth is increase in size and reproduction is increase in number Microorganism 微生物 Growth and reproduction is the same thing Growth is an increase in the number of cells 生长 / 繁殖就是细胞数量的增长 Shanghai Jiao Tong University

18 Bacteria exist as populations Individual cells have a short life span, but Populations are the way bacteria exist as individuals. 个体细胞生命短暂, 群体是细菌作为 个体 生存的方式. In microbiology, growth/ reproduction is an increase in the number (or mass) of cells Shanghai Jiao Tong University

19 5.4 Growth terminology and the concept of exponential growth Growth- an increase in the number (mass) of microbial cells in a population Growth rate-the change in cell number or cell mass per unit time 生长率 : 单位时间细胞数量的变化 Generation-the interval for the formation of two cells from one 世代 : 一个细胞生成两个细胞的过程 Shanghai Jiao Tong University

20 Exponential growth 对数生长 Growth of a microorganism where the number of cells doubles during each unit time period is called exponential growth. 对数生长 : 在每一单位时间里细胞的数量均加倍的生长阶段 Shanghai Jiao Tong University

21 Figure 5.8 Growth rate is ever increasing in exponential growth. 对数生长过程中, 生长速率是不断提高的

22 5.5 The mathematics of exponential growth Generation time 代时 the time required for one generation to occur, for the cell to double in a population 一个世代产生所需的时间 In a time of t, a population grow n generations to increase its cell number from N 0 to N N=N 0 2 n The generation time g=t/n=t/3.3(logn-logn 0 ) If you can measure the growth time, initial cell number, end cell number, generation time can then be calculated Shanghai Jiao Tong University

23 Figure 5.9 K=0.3465/h k=0.1155/h Method of estimating the generation times (g) of exponentially growing populations with generation times of (a) 6 h and (b) 2 h from data plotted on semilogarithmic graphs. The slope of each line is equal to 0.301/g and n equals the number of generations that have occurred in the time, t.

24 Growth rate constant 生长速率常数 (specific growth rate) The number of generations that occur per unit time in an exponentially growing culture. 在对数生长过程中, 单位时间里的世代数 k=log2n/t=0.301n/t=0.301/g

25 What would happen if a cell grow exponentially for a long time? Start from a single cell Generation time 20 min Grow exponentially for 48 hr How many cells can we get in the end? = = X How much do they weight? X cells X gram/cell= X gram= X ton That s 4000 times the weight of the earth Shanghai Jiao Tong University

26 5.6 The Growth Cycle 生长周期 In an enclosed vessel, referred to as a batch culture, a typical growth curve for a population of cells can be divided into several distinct phases: 批量培养的典型生长曲线可分为以下四个时期 : Lag phase 迟滞期 Exponential phase 对数期 Stationary phase 稳定期 Death phase 衰亡期 Shanghai Jiao Tong University

27 Typical growth curve of bacterial populations in batch culture 批量培养的典型生长曲线

28 5.6.1 Lag Phase 迟滞生长期 time required for exponential growth to begin depending on the history of inoculum and growth conditions 迟滞期的长短与接种物状态及生长条件有关 The way to shorten lag phase: If the inoculum is in exponential growth phase, growth conditions are the same, lag period is negligible. If the inoculum has been stored in fridge, warm it to growth temperature can shorten the lag phase.

29 5.6.2 Exponential Phase 对数期 period that the number of cells doubles during each unit time Cells in mid-exponential phase are Fresh Thin cell wall used for enzyme research, for genetic transformation and for purification of cell components

30 5.6.3 Stationary Phase 稳定期 Period that exponential growth stops and cell number remain constant What stops exponential growth? 1. Essential nutrients depletion (an essential nutrient is used up) 必需营养成份的消耗 2. Wastes accumulation 废物的积累 Cryptic growth- death rate and growth rate equals 隐性生长 : 死亡率与生长率相等

31 5.6.4 Death Phase 衰亡期 Period of Cell death and lysis Death phase is also exponential; but in most cases, the rate of cell death is much slower than that of exponential growth. Growth Curve

32 How fast can a cell grow? Factors that influence the grow rate Nutritional factors 营养因素 Energy yield methods 能量产生的方式 Fermentation or respiration Nutrient availability 营养可用性 Glucose or lactose Genetic factors 遗传因素 Gene expression and regulation Genome replication Shanghai Jiao Tong University

33 Shanghai Jiao Tong University