生物谷报道：澳大利亚昆士兰大学的研究人员在地球上一些保存最久的有机材料中发现了有35亿年历史的一些最古老的微生物遗体。这个由Miryam Glikson等人领导的研究队伍首次确定性地证实了这些有机材料的本质和来源。这项研究的结果发表在近期的Precambrain Research杂志上。
Golding博士表示，之前的研究利用间接的分析方法进行研究，而这类方法只能揭示出微生物的内含物而不能证实它就是微生物。
该研究组利用了复杂且耗时的电子显微镜技术来确定微生物遗体。他们将观察分析技术和微生物分析技术结合起来进行鉴定。
研究人员还对化石微生物结构和在海底发现的距今35亿年前的原始微生物进行了比较。结果发现，培养的微生物体在瓦解阶段的结构和那些古老的微生物遗体存在很多相似之处。
有关谁是地球上最古老的生命形式一直存在争议。在过去的10多年里，研究生命起源的研究人员将这个头衔给了一群生活在80到90度高温的地热口和温泉的细菌——超耐温菌。但是2002年的一项研究则挑战了这个认识，该研究发现这个头衔应该给一种存活条件更温和的细菌。
越来越多的证据表明，耐热细菌并非第一个出现在地球的生命形式。研究发现位于进化数基部的物种实际上一种耐寒细菌类群——浮霉状菌目（planctomycetales）。这种细菌具有一些奇怪的特征，如染色体外包被一个单层或双层膜。
法国巴黎的研究人员从现存的浮霉状菌中提取核糖体RNA进行测序，并利用一种计算机程序来分析测序数据。因为所有细胞生物都含有核糖体RNA，所以核糖体RNA被视为研究生命进化的一个强有力的依据。研究人员将研究的重点放在了核糖体RNA分子突变速度很慢的部分，由于这个部分在进化中保守性较高，因此能够揭示出生物体之间的古老关系。
事实上，在20多年前就有研究人员提出浮霉状菌才是最古老最早的细菌，但后来被超耐热菌所取代。
英文原文：
Source: University of Queensland
Date: August 7, 2007
More on: Microbes and More, Origin of Life, Organic, Microbiology, Fossils, Soil Types
Microbial Remains Of Some Of The Oldest Forms Of Life Discovered
Science Daily — University of Queensland researchers have identified microbial remains in some of the oldest preserved organic matter on Earth, confirmed to be 3.5 billion years-old.
The UQ team, led by School of Physical Sciences scientists Dr Miryam Glikson and Associate Professor Sue Golding as well as Associate Professor Lindsay Sly from the School of Molecular & Microbial Sciences, are the first to conclusively confirm the nature and source of the organic material.
"What we have found is the first visual confirmation of primitive microbial communities in what is considered to be the best preserved ancient organic matter on our planet," Dr Glikson, the instigator of the research, said.
Dr Golding, Director UQ's Stable Isotope Laboratory in the Division of Earth Sciences, said previous studies used indirect analytical methods that were only able to suggest microbial involvement, not confirm it.
TEM micrograph of carbonaceous matter concentrate after demineralisation of rock. Single 'cell' bodies showing micro porosity and central cavity following dissolution of mineral matter (which filled the cavities in the whole rock; the mineral was silica). (Credit: Image courtesy of University of Queensland)
"We used difficult and time-consuming electron microscope techniques to conclusively confirm the microbial remains," Dr Golding said.
"The integration of observational and micro-analytical techniques is unique to our approach."
The core drilling samples from Western Australia's Pilbara region were collected by PhD student Lawrie Duck who said it was an amazing experience to "hold in your hands rocks that contain remains of some of the earliest forms of life on Earth."
"The Pilbara region is such a good research site as it has ancient forms of the white smokers active at plate margins today and black sulfidic smokers found in sea floor vent systems in tectonically active sites," he said.
"These are the places where scientists believe life on Earth might have had its origins."
Dr Glikson said the UQ team had then taken the study further by comparing the fossil microbial structures to primitive microbes found today in seafloor environments similar to those existing 3.5 billion years ago.
"The microbiologists on the team, led by Dr Sly, cultured currently existing primitive microbes under simulated conditions to those of the ancient forms of life," Dr Glikson said.
"A remarkable resemblance was found between the structures of the cultured microbial entities at their stage of disintegration and those of the ancient microbial remains."The other members of the UQ research team were Robyn Webb, from the Centre for Microscopy and Microanalysis, a specialist in transmission electron microscopical techniques; Justice Baiano, from the School of Molecular & Microbial Sciences, who developed special facilities to culture primitive microbes derived from seafloor mineral-laden hot springs active at plate margins today; and Kim Baublys, from the Stable Isotope Laboratory, who undertook analysis of products from the culture experiments.
A comparison with organic matter from rocks of similar age in South Africa also yielded microbial remains identical to those from the Pilbara, further confirming the UQ work. This was achieved with the collaboration of Dr Axel Hofmann from the University of Kwazulu, South Africa and Dr Robert Bolhar formerly of the University of Canterbury, New Zealand.
Aspects of the research have been published in Precambrian Research.
The research was funded by an Australian Research Council Discovery grant awarded to Dr Glikson and Dr Sly.
