Lecture 13 Metabolic Diversity 微生物代谢的多样性 Chapter 17 in BROCK BIOLOGY OF MICROORGANISMS School of Life Science and Biotechnology Shanghai Jiao Tong University http://micro.sjtu.edu.cn
I. The Phototrophic Way of Life Energy source-light Photosynthesis- conversion of light energy to chemical energy 光合作用 : 将光能转化为化学能的过程
Figure: 17-01 Carbon source- photoautotroph -CO 2 光能自养型 photoheterotroph-organic carbon 光能异养型
13.1 Photosynthesis 光合作用 Green plants, algae, and cyanobacteria use H 2 O as a source of reducing power to reduce NADP + to NADPH and produce O 2 as a by-product. 绿色植物, 藻类, 蓝细菌以水为电子供体, 产生 O 2 为副产物. Some phototrophic bacteria obtain reducing power from other electron donors, typically reduced sulfur sources (H 2 S, S 0, S 2 O 2-3 ) or H 2. 某些光合细菌以还原性硫化物或氢为电子供体
Fig.17.2b oxygenic phototrophs 产氧光合生物, light drives the oxidation of water to oxygen.
Figure: 17-02a anoxygenic phototrophs 不产氧光合生物 : obtain their energy from light (hv). They do not produce O 2.
13.2 Photosynthetic pigments and their location within the cell 光合色素及其细胞内定位 Chlorophyll-Magnesium containing porphyrin 叶绿素 : 含镁的卟啉 Cyanobacteria-chlorophyll a 叶绿素 a Purple bacteria-bacteriochlorophyll a 菌绿素 a
环戊酮 环戊酮 Differences between chlorophyll a and bacteriochlorophyll a
Fig. 17.3 Structure and spectra of chlorophyll a. it shows strong absorption of red light (680nm) and blue light (430nm).
Fig 17.3 Structure and spectra of bacteriochlorophyll a. it shows strong absorption at 870, 800, 590, and 360 nm.
Figure 17.4 Structure of known bacteriochlorophylls. The different substituents present in the positions R1 to R7 are given in the accompanying table. Bacteriochlorophyll diversity 细菌叶 绿素的多样性
Chlorophyll diversity and its ecological significance 色素多样性的生态优势 p.534-535 A strategy to make better use of the energy of the electromagnetic spectrum. 可更充分地利用电磁光谱的能量 Different pigments using light with different wavelength Unrelated bacteria/organisms coexisting in the same habitat, each using wavelengths of light that the other is not using.
Photosynthetic apparatus: Photosynthetic membrane and Chloroplasts 光合膜与叶绿体 Chloroplast in eukaryotes 真核生物 : 叶绿体 Prokaryotes Purple bacteria-invagination of the cytoplasmic membrane 紫细菌 Heliobacteria-cytoplasmic membrane 螺旋杆菌 Green bacteria-cytoplasmic membrane and chlorosomes 绿细菌
Arrangement of bacteriochlorophyll molecules 菌绿素分子的排列 in the photosynthetic membrane 50-300 bacteriochlorophyll molecules form a complex Most pigment molecules are antenna molecules for light harvesting A small number are reaction center molecules Harvesting light under low light intensities Chlorosome in green sulfur bacteria and green nonsulfur bacteria
13.3 Accessory pigments 其它色素 Carotenoids play primarily a photoprotective role 类胡萝卜素起光保护作用 Phycobilins function in light-harvesting 藻胆素起光采集作用
13.4 Anoxygenic Photosynthesis: purple bacteria as example 不产氧光合作用 Photosynthetic apparatus of purple phototrophic bacteria: four membrane-bound pigment-protein complexes and ATPase Reaction center Light harvesting I Light harvesting II Cytochrome bc1 complex ATPase
RC, reaction center; Bchl, bacteriochlorophyll; Bph, bacteriopheophytin; QA, QB, intermediate quinones; Q pool, quinone pool in membrane;cyt, cytochrome Thermodynamic gradient Fig.17.14 Electron flow in anoxygenic photosynthesis in a purple bacterium. (Cyclic electron flow). Light energy converts a weak electron donor, P870, into a very strong electron donor, P870 *. The remaining steps in photosynthetic electron flow are much the same as that of respiratory electron flow.
13.4.1 ATP formation of anoxygenic photosynthesis in purple bacteria Photophosphorylation 光合磷酸化 Synthesis of ATP during electron flow occurs as a result of the formation of a proton motive force and the activity of ATPase.ATP 的产生 : 质子动势形成及 ATP 酶 Cyclic photophosphorylation 环式光合磷酸化 Electrons are repeatedly moved around a closed circle. There is no net input or consumption of electrons
Cyclic photophosphorylation 环式光合磷酸化 Electrons are repeatedly moved around a closed circle. There is no net input or consumption of electrons Fig.17.15
13.4.2 Autotrophy in Purple Bacteria: Electron donors 自养紫细菌的电子供体 Reducing power (NADH) must be made so that CO 2 can be reduced to the level of cell material. Electron donors from environment Reduced sulfur source-h 2 S, S 0, S 2 O 3 2- H 2 Fe 2+
Reverse electron flow to produce NAD(P)H. Electrons from the quinone pool must be forced against the thermodynamic gradient to reduce NAD + to NADH 反向电子流 : 电子必须逆热力学梯度转移给 NAD +
13.5 Oxygenic photosythesis 产氧光合作用 Electron flow in oxygenic phototrophs involves two distinct, but interconnected, photochemical systems (photosystem I and photosystem II). 产氧光合作用包括两个光合系统
Fig 17.19 Electron flow in oxygenic photosynthesis, the Z scheme. Two photosystems (PS) are involved, PS I and PS II. P680 and P700 are the reaction center chlorophylls of PS II and PS I, respectively. Ph, Pheophytin; Q, quinone; Chl, chlorophyll a; Cyt, cytochrome; PC, plastocyanin; FeS, nonheme iron-sulfur protein; Fd, ferredoxin; Fp, flavoprotein;
An electron from water is donated to the oxidized P680 molecule following the absorption of a quantum of light. Later the electron is accepted by the P700 of PSI, which has previously absorbed light quanta and begins the steps that lead to the reduction of NADP +. 来自水的电子供给 P680, 然后再交给 P700, 由它开始 NADP + 的还原过程
13.5.1 ATP Synthesis in Oxygenic Photosynthesis ATP was generated by noncyclic photophosphorylation. 非环式光合磷酸化产生 ATP. Electrons whose transport results in ATP formation do not cycle back to reduce the oxidized P680, they are used in the reduction of NADP + (reducing power). 电子在 ATP 形成过程中不流回到氧化态 P680, 而用于形成还原力
13.5.2 Anoxygenic photosynthesis in oxygenic phototrophs 产氧光合生物的不产氧光合作用 When sufficient reducing power is present, ATP can also be produced in oxygenic phototrophs by cyclic photophosphorylation involving only PSI. 当还原力充足时,ATP 也可通过 PS1 的环式光合磷酸化产生.
13.6 Autotrophic CO 2 fixation: The Calvin cycle 卡尔文循环固定 CO 2 What does a cell require to convert CO 2 into fructose in the Calvin cycle? NAD(P)H (reducing power) ATP (energy) Two key enzymes Ribulose biphosphate carboxylase (RubisCO) 二磷酸核酮糖羧化酶 Phosphoribulokinase 磷酸核酮糖激酶 Detail
13.7 Autotrophic CO 2 fixation: Reverse Citric Acid Cycle and the Hydroxypropionate Cycle Reverse Citric Acid Cycle presents in green sulfur bacteria Chlorobium. 绿硫细菌的绿菌属 : 反向三羧酸循环 Hydroxypropionate Cycle presents in green nonsulfur bacteria Chloraflexus. 绿色非硫菌的绿屈挠菌属 : 羟基丙酸循环 Detail
The reverse citric acid cycle 反向三羧酸循环 Figure: 17-24a Ferredoxin red indicates carboxylation reactions requiring reduced ferredoxin (2 H each). Reduced ferredoxin is generated in Chlorobium by light-driven reactions. Starting from oxalacetate, each turn of the cycle results in three molecules of CO 2 being incorporated and pyruvate as the product. The cleavage of citrate by the ATP-dependent enzyme citrate lyase regenerates the C 4 acceptor oxalacetate and produces acetyl-coa for biosynthesis.
Acetyl-CoA is carboxylated twice to yield methylmalonyl-coa 甲基丙二酰 CoA. This intermediate is rearranged to yield acetyl-coa and glyoxylate 乙醛酸. The latter is converted to cell material probably through a serine or glycine intermediate. The hydroxypropionate pathway 羟基丙酸途径 Figure: 17-24b