微生物世界 第四章 微生物世界

非细胞形态的生命体 蛋白粒子(朊病毒) 类病毒 20世纪20年代 英国的一种马铃薯病和相继出现的很多靠传统方法找不到病原体的植物病。 70年代，发现是比病毒还小的、单链的、线形的或环状的裸露的RNA。

一般是由300多个核甘酸构成的RNA 3 病毒 爱滋病毒 流感病毒等

一 病毒 1 大肠杆菌噬菌体T-4噬菌体 2 爱滋病毒

Human Immunodeficiency Virus (AIDS)

Rhinovirus (Common Cold)

Filovirus (Ebola, Hemorrhagic Fever)

Influenza Virus (Flu)

细菌 二 1 古细菌 2 真细菌

古细菌 1

IMAGE CREDIT: Colleen Cavanaugh, Harvard University Symbiont from the Deep: Microbes in Tube Worms from Deep Sea Thermal Vents Microbe Name: not yet known

古细菌出现于38亿年以前的生命诞生之初. 那时的地球,大气中充满了有毒气体(比如硫化氢:H2S),完全没有氧气(即使有那么一点,也会与其它物质反应而被消耗),大气的化学性质是呈还原性的. 在这样奇特的环境影响下,古细菌形成了严格厌氧的特性. 在30多亿年前的地球上繁荣的生长着. 这一下就是10亿多年.

终日沸腾的温泉成了古细菌最后的天堂

Not so inhospitable : It used to be unthinkable that life could exist at temperatures near boiling, but some intrepid archaeans thrive under these conditions. Geysers, like the one shown above, are home to such microbes and may help us understand how life existed when the Earth was young.

Finding Archaea : The hot springs of Yellowstone National Park, USA, were among the first places Archaea were discovered. At left is Octopus Spring, and at right is Obsidian Pool. Each pool has slightly different mineral content, temperature, salinity, etc., so different pools may contain different communities of archaeans and other microbes.

The biologists pictured above are immersing microscope slides in the boiling pool onto which some archaeans might be captured for study.

Salt-lovers : immense bloom of a halophilic ("salt-loving") archaean species at a salt works near San Quentin, Baja California Norte, Mexico.

This archaean, Halobacterium, also lives in enormous numbers in salt ponds at the south end of San Francisco Bay; interested residents of this area should take the Dumbarton Bridge for the best views.

美国的黄石公园,那里最著名的景观便是间歇泉与泉水中五颜六色的细菌群。 它们是地球上最古老的生命形式。古细菌对氧气可是“退避三舍”，哪怕只那么一丁点氧分子就让它们一命呜呼。它们的大多数同伴在20亿年前地球上首次出现氧气时灭绝了，史称“氧的大屠杀”。

唯有那么一点点幸存者在其他生物都不敢涉足、几乎没有溶解氧气的少数温泉中繁衍生息。 它们能氧化硫化氢、硫黄和其他硫化物为硫酸，并利用这类氧化作用释放的能量来同化二氧化碳。

同时，在它们体内累积硫黄粒。使它们带上不同的颜色，如上图。河流中的黄色物质都是古细菌群，当然还有一些硫细菌（Mathanobacillus），它们不属于古细菌。

生活在温泉中的古细菌)

Basic Archaeal Shapes : At far left, Methanococcus janaschii, a coccus form with numerous flagellae attached to one side. At left center, Methanosarcina barkeri, a lobed coccus form lacking flagellae. At right center, Methanothermus fervidus, a short bacillus form without flagellae. At far right, Methanobacterium thermoautotrophicum, an elongate bacillus form.

Basic Archaeal Structure : The three primary regions of an archaeal cell are the cytoplasm, cell membrane, and cell wall. Above, these three regions are labelled, with an enlargement at right of the cell membrane structure

Archaeal cell membranes are chemically different from all other living things, including a "backwards" glycerol molecule and isoprene derivatives in place of fatty acids. See text below for details.

These three groups are now recognized as three distinct domains of life, as shown above at right