来自纽约大学牙科学院(NYUCD)的一组科学家最近发现,一种口腔细菌有力的支持了现代人类最早是从非洲向亚洲迁移的观点。
这一小组是由NYUCD的Page Caufield教授领导的,他们发现这种和龋齿有关的细菌——Streptoccocus mutans随着人类宿主以一条非常清晰的线索进化,并且能追溯到一个大约生活在100000到200000年之前的非洲的共同原始祖先。
该细菌能从母亲传递给她们的婴儿,然后大约在婴儿2岁时首次出现在口腔中。Caufield的这些发现发表在了刊物《Journal of Bacteriology》上。在小组的研究过程中,Caufield利用了DNA指纹以及其它的很多生物标记分子等。科学家曾经利用这些技术来追溯人类的进化,并寻找到了一个共同的人类非洲祖先——ancestral Eve。
Caufield表示:“随着人类在世界范围内的迁移,并且逐渐进化为各种不同的人种,这一口腔细菌也随着它们的人类宿主共同进化。”Caufield在过去的20年间从六大洲的人群中收集了超过600分样本,他的分析主要集中在中国、日本、非洲、非裔美国人、美国的西班牙人和高加索人、瑞典、澳洲、亚马逊印第安人等中。
Caufield说:“追踪细菌比交容易,因为它们用分裂进行繁殖。通过DNA分析,我们重建了进化树,结果显示其发源在非洲,然后主要的一个分支迁移到了亚洲。接着从亚洲向欧洲延伸出一个分支,进化成了现代高加索人种的一支。”下一步Caufield将分析细菌从亚洲向北美及南美共同进化的情况。
译自:physorg.com
部分英文原文:
Journal of Bacteriology, February 2007, p. 1238-1243, Vol. 189, No. 4
0021-9193/07/$08.00+0 doi:10.1128/JB.01183-06
Population Structure of Plasmid-Containing Strains of Streptococcus mutans, a Member of the Human Indigenous Biota
Page W. Caufield,1,2* Deepak Saxena,1 David Fitch,3 and Yihong Li1
College of Dentistry,1 School of Medicine,2 Department of Biology, New York University, New York, New York3
Received 31 July 2006/ Accepted 25 October 2006
There are suggestions that the phylogeny of Streptococcus mutans, a member of the human indigenous biota that is transmitted mostly mother to child, might parallel the evolutionary history of its human host. The relatedness and phylogeny of plasmid-containing strains of S. mutans were examined based on chromosomal DNA fingerprints (CDF), a hypervariable region (HVR) of a 5.6-kb plasmid, the rRNA gene intergenic spacer region (IGSR), serotypes, and the genotypes of mutacin I and II. Plasmid-containing strains were studied because their genetic diversity was twice as great as that of plasmid-free strains. The CDF of S. mutans from unrelated human hosts were unique, except those from Caucasians, which were essentially identical. The evolutionary history of the IGSR, with or without the serotype and mutacin characters, clearly delineated an Asian clade. Also, a continuous association with mutacin II could be reconstructed through an evolutionary lineage with the IGSR, but not for serotype e. DNA sequences from the HVR of the plasmid produced a well-resolved phylogeny that differed from the chromosomal phylogeny, indicating that the horizontal transfer of the plasmid may have occurred multiple times. The plasmid phylogeny was more congruent with serotype e than with mutacin II evolution, suggesting a possible functional correlation. Thus, the history of this three-tiered relationship between human, bacterium, and plasmid supported both coevolution and independent evolution.
* Corresponding author. Mailing address: New York University College of Dentistry, 345 East 24th Street, New York, NY 10010. Phone: (212) 998-9603. Fax: (212) 995-3994. E-mail:pwc2@nyu.edu .
Published ahead of print on 3 November 2006.