2 CELL STRUCTUREFUNCTION OF PROKARYOTES-文字教案.doc

2. CELL STRUCTURE/FUNCTION OF PROKARYOTES2.1.1 Light microscopy 2.1.2 Electron microscopy2.1.3 Three-Dimensional Imaging2.1.4 Staining and Cell morphology2.2 Cell membranes and cell walls2.2.1 Cell membrane2.2.2 Cell walls2.3 Surface structures and inclusions2.3.1 Surface structures and inclusions 2.3.2 Endospores2.4 Other bacteria2.4.1 Actinomycetes2.4.2 Cyanobacteria2.4.3 Mycoplasmas, Chlamydia, Rickettsias2.1 Microscopy and cell morphology2.1.1 Light microscopy p56Fig 4.10.5 Resolution 分辨率（最小可分辨距离）= n sin 数值孔径值（Numerical Aperture，NA）: n sin n：玻片与物镜间介质的折射率空气 (n=1.0)、水 (n=1.33)、香柏油 (n=1.52)、玻璃 ( n=1.54):为物镜镜口角，它取决于物镜的直径和工作距离用香柏油取代空气的作用：介质折射率提高, 数值孔径值和分辨率均得到提高; 香柏油与玻璃的折射率相近,很多原来由于在透镜及载片表面的反射和折射而损失的光线可以进入物镜，使照明亮度提高，改善观察效果。特性物镜搜索物镜低倍镜高倍镜油镜放大倍数41040-4590-100数值孔径值0.100.250.55-0.651.25-1.4焦距（f）40 mm16 mm4 mm1.8-2.0 mm工作距离17-20 mm4-8 mm0.5-0.7 mm0.1 mm450nm光源（蓝光）时的分辨率2.3 m0.9 m0.35 m0.18 mThe highest resolution possible in a compound light microscope is about 0.2m. Magnifications of about 1500are near the upper limit obtainable光学显微镜一般配置的最大放大倍数：:目镜：10 15 ；物镜： 100 ；总放大倍数 10001500 0.2m 1000 = 0.2mm (人眼的分辨能力0.1-0.2 mm)目镜的作用只是将物镜放大的实象进一步放大形成能见的虚象,目镜不可以提高分辨率Bright-field microscopy (明视野显微镜)照明光线直接进入视野，属透射照明。生活的细菌在明视野显微镜下观察是透明的，不易看清。 Many bacterial cells are difficult to see well with the bright-field microscope because of their lack of contrast with the surrounding medium. Pigmented organisms are an exception, because the color of the organism adds contrast, thus improving visualizationDyes can be used to stain cells and increase their contrastFig.4.2Dark-field microscopy (暗视野显微镜)暗视野显微镜则利用特殊的聚光器实现斜射照明，给样品照明的光不直接穿过物镜，而是由样品反射或折射后再进入物镜，因此，整个视野是暗的，而样品是明亮的反差增大,观察微粒的尺寸可以小于显微镜的分辨率. Phase-contrast microscopy(相差显微镜)相差显微镜配备有特殊的光学装置环状光阑和相差板，利用光的干涉现象，能将光的相位差转变为人眼可以察觉的振幅差（明暗差），从而使原来透明的细胞与 介质表现出明显的明暗差异，对比度增强。相差板,装在相差物镜中,常刻有Ph(红色),或红色圈用于观察活细胞Fig. 4.5Fluorescent microscopy (荧光显微镜)荧光显微镜是利用一个高发光效率的点光源(汞灯)，经过滤色系统发出一定波长的光(如紫外光或紫蓝光)作为激发光,激发标本内的荧光物质发射出各种不同颜色的荧光后，再通过物镜和目镜的放大进行观察。2.1.2 Electron microscopyThe detailed structure of cells p62与光学显微镜差异：1）use electrons instead of photons to image cells or cell structures 波长最短可达到0.005 nm2）the whole system operates in a vacuum 电镜镜筒中要求高真空（在电子的运行中如遇到游离的气体分子会因碰撞而发生偏转，导致物象散乱不清）3）electromagnets function as lenses 用电磁圈来使 “光线”汇聚、聚焦4）electron micrograph 电子像人肉眼看不到，需用荧光屏来显示 Transmission electron microscope (透射电子显微镜): 电子束穿过薄切片20-60nm点分辨（0.30.5nm）; 晶格分辨（0.10.2nm）Scanning electron microscope (扫描电子显微镜): 观察样品的表面结构 分辨率610nmFig.4.9 An electron microscope which encompasses both transmission and scanning electron microscope functionFig.4.10u Transmission electron microscopy, for observing internal cell structure down to the molecular level u Scanning electron microscopy, for three-dimensional imaging and examining surfaces.2.1.3 Three-Dimensional Imaging p60DIC and CSLM are forms of light microscopy that allow for greater three-dimensional imaging than other forms of light microscopy.1. Differential interference contrast microscopy (DIC) 微分干涉相差显微镜 2. Confocal scanning laser microscopy (CSLM) 激光扫描共聚焦显微镜3. Atomic force microscopy (AFM) 原子力显微镜 Differential interference contrast microscopy (DIC) 微分干涉差显微镜 偏光干涉原理. 偏振镜产生偏振光，偏振光经过样品形成不同折射率，汇合光时由于不同相产生干涉效应，显示结构微小差异。与传统相差显微镜相比，其标本可略厚一点，折射率差别更大，故影像的立体感更强，产生类似于浮雕的效果。 DIC显微镜使细胞的内部结构，特别是一些较大的细胞器，如核、孢子、液泡、颗粒等，立体感特别强 DIC can reveal internal cell structures that are less apparent by bright-field techniques. It is particularly useful for observing unstained cells Fig. 4.7aConfocal scanning laser microscopy (CSLM, 激光扫描共聚焦显微镜)激光扫描共聚焦显微镜是在传统荧光显微镜成像的基础上，采用激光作为光源，加装了激光扫描装置, 并利用计算机的图像处理技术,把光学成像的分辨率提高了30-40%。通过调节激光束聚焦的平面，观察不同层面上的细胞。与传统的光学显微镜相比,它能产生真正具有三维清晰度的图像。广泛用于微生物生态，鉴别微生境中各种微生物类群的存在和分布Confocal microscopy allows imaging through thick specimens; each plane is visualized by adjusting the plane of focus of the laser beamFig.4.83. Atomic force microscopy (AFM,原子力显微镜) 利用原子之间的范德华力作用来呈现样品的表面特性。是利用微小探针与待测物之间交互作用力，来呈现待测物的表面之物理特性。可以观察活的含水样品。The atomic force microscope yields a detailed three-dimensional image of live preparations. 当针尖与样品之间有了交互作用之后，会使得悬臂摆动，所以当激光照射在悬臂的末端时，其反射光的位置也会因为悬臂摆动而有所改变，这就造成偏移量的产生。依靠激光光斑位置检测器将偏移量记录下并转换成电的信号，供控制器信号处理。Fig.4.7b2.1.4 Staining and Cell morphologyStaining :Increasing contrast for bight-field microscopy分辨率: 能辨别两点之间最小距离的能力放大: 放大倍数反差: 被观察物区别于背景的程度Stains improve the contrast between cells and their background 活体观察: 压滴法；悬滴法；菌丝埋片法；小培养法染色观察: Many dyes used in microbiology are positively charged (basic dyes) and combine with negatively charged cellular constituents such as nucleic acids and acidic polysaccharides细菌菌体在中性碱性或弱酸性溶液中带负电荷,易于碱性染料(正电荷)进行结合常用染料:Crystal violet (结晶紫)；Safranin (番红)；Methylene blue (美蓝)等Simple stain染色操作程序制片干燥固定染色水洗干燥镜检Differential stainThe gram stain，革兰氏染色，丹麦医学家 Hans Christian Gram于1884年发明的一种鉴别不同类型细菌的染色方法制片干燥固定染色水洗干燥镜检结晶紫初染 碘液媒染 酒精脱色番红复染 2. Cell morphology: The shape of an organism Fig.4.11Coccus，球状细胞个体呈球形或椭圆形，不同种的球菌在细胞分裂时会形成不同的空间排列方式，常被作为分类依据。肺炎链球菌Streptococcus pneumoniae淋病奈瑟氏球菌Neisseria gonorrhoeae金黄色葡萄球菌Staphylococcus aureusRod，杆状细胞呈杆状或圆柱形，一般其粗细（直径）比较稳定，而长度则常因培养时间、培养条件不同而有较大变化。杆状细菌的排列方式常因生长阶段和培养条件而发生变化，一般不作为分类依据。炭疽病的病原菌-炭疽杆菌Bacillus anthracis铜绿假单胞菌（绿脓杆菌）Pseudomonas aeruginosa结核分枝杆菌Mycobacterium tuberculosis梭状芽孢杆菌ClostridiumSpirilla，螺旋状 Vibrio：弧菌,菌体只有一个弯曲，其程度不足一圈，形似“C”字或逗号，鞭毛偏端生。寄生性弧菌-蛭弧菌Bdellovibrio 霍乱弧菌Vibrio cholerae Spirillum (螺菌): a cell body that twists like a spiral. 螺旋状菌体细胞; having tufts of flagellae at both poles 鞭毛二端生。Spirochaete (also spelled spirochetes) 螺旋体菌：are distinguished from other bacterial phyla by the location of their flagella, sometimes called axial filaments. 用于运动的类似鞭毛的轴丝位于细胞外鞘内梅毒密螺旋体Treponema pallidum Filamentous 丝状，如某些蓝细菌，放线菌（链霉菌） Budding and appendaged bacteria，细胞上有柄（stalk）、菌丝(hyphae)、附器（appendages）等细胞质伸出物，细胞呈杆状或梭状，并有特征性的细柄。一般生活在淡水中固形物的表面，其异常形态使得菌体的表面积与体积之比增加，能有效地吸收有限的营养物星形细菌（star-shaped bacteria ）方形细菌（square-shaped bacteria）环境条件的变化会导致异常形态：物理、化学因子的刺激阻碍细胞正常发育培养时间过长细胞衰老，营养缺乏，自身代谢产物积累过多，环境条件恢复正常，异常形态正常形态 The size of microbial cellsThe dimensions of an average球菌：0.5 1 m （直径）杆菌：0.2 1 m （直径） 1 80 m（长度）螺旋菌：0.3 1 m （直径） 1 50 m（长度）(长度是菌体两端点之间的距离，而非实际长度)例外 Fig.4.12b the largest known prokaryote. A single coccus-shaped cell is about 400 m wide德国科学家1999年在纳米比亚海岸的海底沉积物中发现的一种硫磺细菌, Thiomargarita namibiensis (纳米比亚硫磺珍珠)大小测定：显微镜测微尺: 目镜测微尺：测定；镜台测微尺：标定目镜测微尺；电子显微镜成像后根据标准尺（图片上常标出）进行测算细菌大小测量结果的影响因素：（1）个体差异；（2）干燥、固定后的菌体会一般由于脱水而比活菌体缩短1/3-1/4；（3）染色方法的影响，负染色法观察的菌体大于普通染色法,有时大于活菌体(有荚膜的细菌)；（4）幼龄菌一般比成熟的或老龄的菌大(杆菌长度变化,宽度不变)；（5）环境条件，如培养基中渗透压增加会导致细胞变小。2.2 Cell membranes and cell walls一般构造：一般细菌都有的构造特殊构造：部分细菌具有的或一般细菌在特殊环境下才有的构造2.2.1 Cell membrane (Cytoplasmic membrane) p66The cytoplasmic membrane is a thin structure that completely surrounds the cell. Only about 8nm thick, this vital structure is the barrierBarrier：The barrier separating the inside of the cell from its environmentA high selective barrier enabling a cell to concentrate specific metabolites and excrete waste materialsFig 4.15Structure: Chemical composition of membrane由磷脂（占20%30%）和蛋白质（占50%70%）组成l Phospholipid bilayerl Membrane proteinsFluid mosaic model (流动镶嵌模型) Fig. 4.16The cytoplasmic membrane is quite fluid:phospholipid and protein molecules have significant freedom to move about within the membrane. Integral membrane proteins likely span a highly mobile, yet highly ordered, phospholipid bilayer（1）membrane strengthening agents: sterols and hopanoids 甾醇类物质和类何帕烷Sterols are rigid, planar molecules, whereas fatty acids are flexible. The association of sterols with the membrane serves to stabilize its structure and make it less flexible.Molecules similar to sterols, called hopanoids, may play a role similar to that of sterols in eukaryotic cellsFig. 4.17甾醇(sterol)的一般结构真核生物细胞膜中一般含有胆固醇(cholesterol)等甾醇，含量为5%-25%。原核生物（Mycoplasma 除外）细胞膜中一般不含甾醇，而是含有hopanoids（类何帕烷）。古生菌不含此类物质。Sterols are rigid, planar molecules, whereas fatty acids are flexible. The association of sterols with the membrane serves to stabilize its structure and make it less flexible.Molecules similar to sterols, called hopanoids（类何帕烷）, may play a role similar to that of sterols in eukaryotic cells.（2）. Archaeal membranes 古生菌的细胞质膜 p68The lipids of Archaea differ from those of other organisms The lipids of Archaea have ether linkages between glycerol and their hydrophobic side chains. (ester linkages bond the fatty acids to glycerol in Bacteria and Eukarya. 亲水头（甘油）与疏水尾（烃链）间是通过醚键而不是酯键连接的 Fig. 4.18Archaeal lipids lack fatty acids. Instead, their side chains are composed of repeating units of the five-carbon hydrocarbon isoprene. Glycerol diethers and glycerol tetraethers are the major lipids present in Archaea组成疏水尾的长链烃是异戊二烯的重复单位（如四聚体植烷、六聚体鲨烯等），它与亲水头通过醚键连接成甘油二醚（glycerol diether）或二甘油四醚(diglycerol tetraether)等Fig. 4.19A lipid monolayer instead of a lipid bilayer cytoplasmic membrane 古生菌的细胞质膜中存在着独特的单分子层膜或单、双分子层混合膜。当磷脂为二甘油四醚时，连接两端两个甘油分子间的两个植烷（phytanyl）侧链间会发生共价结合，形成了二植烷(diphytanyl)，这时就形成了独特的单分子层膜。目前发现，单分子层膜多存在于嗜高温的古生菌中，其原因可能是这种膜的机械强度要比双分子层质膜更高 Fig. 4.19在甘油的3C分子上，可连接多种与真细菌和真核生物细胞质膜上不同的基团，如磷酸酯基、硫酸酯基以及多种糖基等。 （3）. Function：p70 Discussion in Section 4.3 Transport of nutrients into the cell（4）. Internal membrane systems 内膜系统间体,或中体(mesosome)Mesosomes are folded invaginations in the plasma membrane of gram-positive bacteria that are produced by the chemical fixation techniques used to prepare samples for electron microscopy. Although several functions were proposed for these structures in the 1960s, they were recognized as artifacts by the late 1970s and are no longer considered to be part of the normal structure of bacterial cells. 1960s, 化学固定(四氧化锇)后电子显微镜观察细胞时发现的由细胞质膜内褶形成的囊状构造，多见于革兰氏阳性细菌。功能可能与DNA的复制、分配以及与细胞分裂有关。1970s, 有学者发现，“间体”仅是电镜制片时因化学固定导致的细胞膜或者细胞壁损坏而引起的一种赝像。但之后还是有少数研究者认为不完全是赝像The mesosome of Bacillus subtilis as affected by chemical and physical fixation. J. Cell Biol. 48 (1): 21924. 其他内膜系统细胞膜存在内摺延伸而形成的囊状、管状或层状结构 光合膜: 某些光合细菌中，广泛存在内膜系统，又称载色体(Chromatophore)。细菌叶绿素II和类胡萝卜素以及光捕获蛋白（light-harvesting proteins）分布在内膜上, 进行光合作用Chromatophores are found in membranes of phototrophic bacteria. Used primarily for photosynthesis, they contain bacteriochlorophy ll pigments and carotenoids. In purple bacteria, the light-harvesting proteins are intrinsic to the chromatophore membranes. Fig12.3, Fig 17.12 硝化细菌（Nitrobacter）中，具有复杂的内膜系统-细胞质膜极冠 (a polar cap of intracytoplasmic membranes)；亚硝化球菌 （Nitrosococcus）中，丰富的内膜系统成片状在细胞中部 NH3 、NO2的氧化位点（location of key enzymes in nitrification）。Fig 12.7; Fig 12.8 methane-oxidising bacteria (methanotrophs)一碳化合物代谢酶所在位点。Fig. 12.15Paired membranes running along the periphery of the cellArranged as bundles of disc-shaped vesicles distributed throughout the cell2.2.2 Cell walls p74The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. To withstand the pressure of about 2 atmospheres 维持细胞膨胀压力 To give shapes and rigidity to the cell 固定细胞外形和提高机械强度Gram-positiveGram-negative Fig.4.27The gram-negative cell wall is a multilayered structure and quite complex, whereas the gram-positive cell wall primarily consists of a single type of molecule, and is often much thicker1. Gram-Positive wall, 革兰氏阳性细菌的细胞壁 特点：厚度大（2080nm）化学组分简单，一般只含90%肽聚糖和10%磷壁酸。(1) Peptidoglycanmucopeptide(粘肽)、murein(胞壁质)、mucocomplex(粘质复合物)Is present only in species of Bacteria 真细菌细胞壁中的特有成分Fig. 4.29N-acetylmuramic acid (M) N-乙酰胞壁酸，细菌所特有的已糖 N-acetylglucosamine (G) N-乙酰葡糖胺双糖单位中的-1,4-糖苷键很容易被溶菌酶(lysozyme)所水解，从而引起细菌因肽聚糖细胞壁的“散架”而死亡。Tetrpeptide 四肽尾由四个氨基酸分子按L型与D型交替方式连接而成Fig. 4.28 Cross-linking amino acids in peptidoglycan. Diaminopimelic acid, DAP,二氨基庚二酸; Lysine，赖氨酸Fig. 4.30Staphylococcus aureus 的肽桥Gly五肽。More than 100 different peptidoglycan types are known, with the variations occurring in the interbridge (肽桥). Any of the amino acids present in the tetrapeptide can also occur in the interbridge. A number of other amino acids such as glycine, threonine, serine, and aspatic acid can be found in the interbridge. Branched-chain amino acids, aromatic amino acids, sulfur-containing amino acids, and histidine, arginine, and proline are never found in the interbridge.(2)Teichoic acid磷壁酸:革兰氏阳性细菌细胞壁上特有的化学成分，主要成分为glycerophosphate (甘油磷酸)or ribitol phosphate (核糖醇磷酸) 。赋予革兰氏阳性细菌以特异的表面抗原,表面负电荷Fig. 4.31a核糖醇磷酸 通过磷酸酯键相连。Lipoteichoic acid: 膜磷壁酸(脂磷壁酸)跨越肽聚糖层并与细胞膜相交联，与细胞膜上的磷脂共价结合形成。壁磷壁酸，它与肽聚糖分子间共价结合.Summerizes Fig 4.31b2. Gram-Negative wall, 革兰氏阴性细菌的细胞壁 (1) Peptidoglycan, 肽聚糖它的肽聚糖埋藏在外膜层之内，是仅由12层肽聚糖网状分子组成的薄层(23nm)，含量约占细胞壁总重的10%，故对机械强度的抵抗力较革兰氏阳性菌弱。 Fig.4.30四肽尾的第3个氨基酸不是L-lys，而是内消旋二氨基庚二酸(m-DAP),一种只有在原核微生物细胞壁上才有的氨基酸。没有特殊的肽桥，其前后两个单体间的连接仅通过甲四肽尾的第4个氨基酸D-ala的羧基与乙四肽尾的第3个氨基酸mDAP的氨基直接相连 ,只形成较为疏稀、机械强度较差的肽聚糖网套。 (2) Outer membrane,外膜位于革兰氏阴性细菌细胞壁外层，由脂多糖、磷脂和脂蛋白等若干种蛋白质组成的膜，有时也称为外壁。Fig 4.35a 脂多糖（lipopolysaccharide, LPS）位于革兰氏阴性细菌细胞壁最外层的一层较厚（810nm）的类脂多糖类物质，由类脂A、核心多糖(core polysaccharide)和O-特异侧链（O-specific side chain，或称O-多糖或O-抗原）三部分组成。Fig.4.34O-特异侧链决定了革兰氏阴性细菌细胞表面抗原决定簇的多样性.根据LPS抗原性的测定，沙门氏菌属(Salmonella)的抗原型多达2000多种，一般都源自O-特异侧链种类的变化。核心多糖,负电荷的物质基础，有吸附Mg2+、Ca2+等阳离子以提高其在细胞表面浓度的作用类脂A是一种革兰氏阴性细菌致病物质内毒素(endotoxin)的物质基础；外膜蛋白（ outer membrane protein ）脂蛋白复合体（Lipoprotein complex）: on the inner side of the outer membrane.Anchor between the outer membrane and peptidoglycan孔蛋白（porins）是由三个相同分子量蛋白亚基组成的一种三聚体跨膜蛋白，中间有一直径约1nm的孔道，通过孔的开闭，可对进入外膜层的物质进行选择。Nonspecific porins (非特异性孔蛋白)：可通过分子量小于800900的任何亲水性分子Specific porins (特异性孔蛋白)：只容许一种或少数几种相关物质通过，如维生素B12和核苷酸等。Fig 4.36(3) Periplasm (周质空间 ) 又称壁膜间隙。The periplasmic space or periplasm is a space between the inner cytoplasmic membrane and external outer membrane of Gram-negative bacteria or the equivalent space outside the inner membrane (or inner wall zone, IWZ ) of Gram-positive bacteria.The periplasm may constitute up to 40% of the total cell volume in Gram-negative species, whereas the IWZ is drastically smaller in Gram-positive species周质空间是进出细胞的物质的重要中转站和反应场所在周质空间中，存在着多种周质蛋白(periplasmic proteins)：Hydrolytic enzymes (水解酶类)；Binding proteins (结合蛋白)；Chemoreceptors (化学受体).革兰氏阳性细菌与革兰氏阴性细菌的细胞壁组分比较成分占细胞壁干重的%革兰氏阳性细菌革兰氏阴性细菌肽聚糖含量很高（5090）含量很低（10）磷壁酸含量较高（50）无类脂质一般无（2）含量较高（20）蛋白质无含量较高革兰氏染色原理 p81Insoluble crystal violet-iodine complex（结晶紫-碘复合物） is formed inside the cell, and this complex is extracted by alcohol from gram-negative but not from gram-positive bacteria. Gram-positive bacteria have very thick cell walls consisting of several layers of peptidoglygan. These become dehydrated by the alcohol, causing the pores in the walls to close and preventing the insoluble crystal violet-iodine complex from escaping. In gram-negative bacteria, alcohol readily penetrates the lipid-rich outer membrane and extracts the crystal violet-iodine complex from the cell.3. Cell walls of acid-fast bacteria (p388) 抗酸性细菌细胞壁抗酸性染色： 涂片石炭酸复红加热染色5 min冷却后酸性酒精脱色（脱色至成淡粉红色，约1 min）水洗吕氏美兰复染2-3min抗酸性细菌红色，非抗酸性细菌蓝色抗酸性细菌是一类细胞壁中含有大量分枝菌酸（mycolic acid）的特殊革兰氏阳性细菌。Fig 12.69a 60-90个碳原子分枝长链b-羟基脂肪酸Fig 12.71 Structure of cord factor, a mycobacterial glycolipid: 6,6-dimycolyltrehalose. 6,6-二分枝菌酸海藻糖（索状因子）沈萍图3-9“蜡质”细胞表面枝菌酸连结在由ara和gal交替连接的杂多糖链上，并通过磷酯键与肽聚糖相连。沈萍图3-10Fig 12.69b The dye used in the acid-fast stain. The fuchsin dye combines with the mycolic acid via ionic bonds between COO and NH2+. The mycolic acid is covalently bound to peptidoglygan in the mycobacterial wall, and this complex leaves the cell surface with a waxy, hydrophobic consistency(“蜡质”细胞表面). Mycobacteria are not readily stained by the Gram stain method because of the high surface-lipid content. If the lipoidal portion of the cell is removed with alkaline ethanol, however, the intact cell remaining is non-acid-fast but instead is gram-positive抗酸性细胞本身不易被革兰氏染色。碱性酒精脱去细胞壁中的“蜡质”组分后，细胞会变成非抗酸性，革兰氏染色阳性。例：结核分枝杆菌(Mycobacterium tuberculosis) Side-by side arrangement“serpentine cord” 蛇形绳索Compact, wrinkled appearance of the colony，致密的、皱的菌落麻风分枝杆菌(M. leprae) Hansens disease 麻风病通过飞沫、皮肤接触均能传染，患者导致神经末梢坏死(不知疼痛 )手脚溃烂肌肉萎缩4Cell walls of Archaea, 古细菌的细胞壁 p78在古生菌中，与真细菌类似功能但化学成分差别甚大的细胞壁。已研究过的一些古生菌，它们细胞壁中没有真正的肽聚糖，而是下列构成：u pseudopeptidoglycan (假肽聚糖)、u polysaccharides(多糖)、u glycoprotein(糖蛋白) or protein(蛋白质) （1）假肽聚糖(pseudopeptidoglycan)细胞壁 甲烷杆菌属(Methanobacterium)古生菌的细胞壁是由假肽聚糖组成的. Fig.4.33a 多糖骨架：N-乙酰葡糖胺和 N-acetyl-talosaminuronic acid (NAT), N-乙酰塔罗糖胺糖醛酸组成二糖单位，b-1，3-糖苷键，不被溶菌酶水解 3肽尾：L-GluL-AlaL-Lys，全部为L-型氨基酸 肽桥：L-Glu（2）Polysaccharides(多糖) 两类： 甲烷八叠球菌(Methanosarcina)的细胞壁含有独特的多糖，并可染成革兰氏阳性。这种多糖含半乳糖胺、葡糖醛酸、葡萄糖和乙酸, 不含磷酸或硫酸。 嗜盐球菌(Halococcus）的细胞壁含有硫酸化多糖细胞壁.（3）Glycoprotein(糖蛋白) or protein(蛋白质)The most common cell wall type among Archaea is the paracrystalline surface layer (S-layer). It consists of protein or glycoprotein and generally has a hexagonal symmetry. 一种由蛋白质或糖蛋白组成的类结晶表面层（六角形均质层），S-layers, 普遍存在于古生菌中，在某些细菌中也存在同样结构Fig.4.33b5. 缺壁细菌 Cells with no walls (p78)（1）L型细菌（L-form of bacteria）：细菌在某些环境条件下（实验室或宿主体内）通过自发突变而形成的遗传性稳定的细胞壁缺陷变异型。没有完整而坚韧的细胞壁，细胞呈多形态；有些能通过细菌滤器，故又称“滤过型细菌”; 对渗透敏感，在固体培养基上形成“油煎蛋”似的小菌落（直径在 0.1mm左右）英国李斯德（Lister）预防研究所首先发现而得名（1935年，念珠状链杆菌 Streptobacillus moniliformis）大肠杆菌、变形杆菌、葡萄球菌、链球菌、分枝杆菌和霍乱弧菌等20多种细菌中均有发现，被认为可能与针对细胞壁的抗菌治疗有关。（2）原生质体（protoplast）用溶菌酶人工处理而形成的仅由一层细胞膜包裹的圆球形、对渗透压变化敏感的细胞，一般由革兰氏阳性细菌形成。