基因的横向转移现在已不是很流行的词语了，但是在根瘤菌中的研究却日益如火如荼。特别是不同遗传背景的根瘤菌之间的共生基因之间可通过横向转移的方式由一个菌转移到另一个菌，这方面的证据是越来越多。共生基因的横向转移的结果是尽管一些根瘤菌的遗传背景不同，但它们都有相同或相似的共生基因。下面的这篇文章即是从染色体基因分析和共生基因分析这两个角度证实共生基因的横向转移。

论文题目：Chromosomal and symbiotic relationships of rhizobia nodulating Medicago truncatula and M. laciniata

中文摘要：

多位点序列分型法（MLST）是一种基于序列分析的方法，用于比较细菌的基因组之间的差别。运用这种方法，本文对突尼斯干旱地区的Amra地点与苜蓿结瘤的根瘤菌进行了遗传结构的分析。在这个地方，一年生的M. laciniata 和M. truncatula是这一自然群落的主要物种。本研究的主要目的是要鉴定与M. laciniata结瘤的根瘤菌其染色体是不是一个独特的类群，因为M. laciniata只与特定的根瘤菌结瘤。用MLST分析法对分离自M. laciniata 和M. truncatula的74株菌的10个染色体位点进行了分析。M. truncatula作为能捕捉根瘤菌的阳性对照植物，因为它对根瘤菌的专一性不强，不象M. laciniata严格限定某一类根瘤菌在其上形成根瘤。对于质粒上的nodC也进行了分析。148个分离物被分成26个染色体序列型(Sequence Types, STs)，其中只有3个以前被鉴定过。分离自M. laciniata的根瘤菌是土壤中与苜蓿结瘤的常见根瘤菌种群中的一部分，因为分离物中99.95%的菌株，它们的染色体基因型与重新分离自M. truncatula的菌株的基因型相似。但是，分离自M. laciniata的菌株的多样性与分离自M. truncatula的菌株的多样性相比来说是很小的，并且它们的nodC也是不常见。这可能是不同的nodC基因在同一块地中与苜蓿结瘤的根瘤菌中横向转移的最好例子了。这里提供了一个染色体背景不同的菌株之间基因横向转移的证据。

英文摘要：

MultiLocus Sequence Typing (MLST) is a sequence-based method used to characterize bacterial genomes. This method was used to examine the genetic structure of Medicago-nodulating rhizobia at the Amra site, which is located in an arid region of Tunisia. Here the annual medics M. laciniata and M. truncatula are part of the natural flora. The goal of this study was to identify whether distinct chromosomal groups of rhizobia nodulate M. laciniata because of its restricted requirement for specific rhizobia. The MLST analysis involved the determination of sequence variation in 10 chromosomal loci of 74 isolates each from M. laciniata and M. truncatula. Medicago truncatula was used as a control trap host, because unlike M. laciniata, it is relatively unrestricted in its rhizobial requirements. Allelic diversity among the plasmid-encoded nodC alleles in the isolates was also determined. The 148 isolates were placed into 26 chromosomal Sequence Types (STs), of which only 3 had been identified previously. The rhizobia of M. laciniata were shown to be part of the general Medicago-nodulating population in this soil because 99.95% of the isolates had chromosomal genotypes similar to those recovered from M. truncatula. However, the isolates recovered from M. laciniata were less diverse than those from M. truncatula and they also harbored an unusual nodC allele. This could perhaps be best explained by horizontal transfer of the different nodC alleles among members of the Medicago-nodulating rhizobial population at the field site. Evidence is provided indicating a history of lateral transfer of rhizobial symbiotic genes across distinct chromosomal backgrounds.

全文链接：

Chromosomal and symbiotic relationships of rhizobia nodulating Medicago truncatula and M. laciniata

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