Lima Wanessa C, Van Sluys Marie-Anne, Menck Carlos F M
Department of Microbiology, Institute of Biomedical Sciences, University of São Paulo, ICB II, São Paulo, SP, Brazil.
OMICS. 2005 Summer;9(2):160-72. doi: 10.1089/omi.2005.9.160.
Horizontal gene transfer, a process through which genomes acquire sequences from distantly related organisms, is believed to be a major source of genetic diversity in bacteria. A central question concerning the impact of gene transfer on bacterial genome evolution is the proportion of horizontally transferred sequences within genomes. Through BLAST search, we found that the genomes of two phytopathogens, Xanthomonas campestris pv. campestris and Xanthomonas axonopodis pv. citri, have close to 40% of the genes with the highest similarity to genes from phylogenetically distant organisms (non-gamma-proteobacteria). Most of these genes are found to be contiguous in the genome, forming genome islands, which may have been transferred from other organisms. Overall, the total number of genes within genome islands corresponds to almost one quarter of the entire xanthomonad genomes. Interestingly, many of the genes in these islands are functionally related to plant pathogenesis and virulence. Thus, these results suggest that horizontally transferred genes are clustered in the genome, and may facilitate fitness in new environments, as in the case of plant-bacteria interaction.
水平基因转移是基因组从远缘生物获取序列的过程，被认为是细菌遗传多样性的主要来源。关于基因转移对细菌基因组进化影响的一个核心问题是基因组中水平转移序列的比例。通过BLAST搜索，我们发现两种植物病原菌——野油菜黄单胞菌野油菜致病变种和柑橘溃疡病菌的基因组中，近40%的基因与系统发育上距离较远的生物（非γ-变形菌）的基因具有最高相似度。这些基因中的大多数在基因组中是连续的，形成基因组岛，这些基因组岛可能是从其他生物转移而来的。总体而言，基因组岛中的基因总数几乎相当于整个黄单胞菌基因组的四分之一。有趣的是，这些岛屿中的许多基因在功能上与植物致病和毒力相关。因此，这些结果表明水平转移基因在基因组中聚集，并且可能像在植物-细菌相互作用的情况下那样，促进在新环境中的适应性。
