Fang Chun, Cao Tong, Shan Ying, Xia Ye, Xin Yongping, Cheng Changyong, Song Houhui, Bowman John, Li Xiaoliang, Zhou Xiangyang, Fang Weihuan
Zhejiang University Institute of Preventive Veterinary Medicine, and Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Hangzhou, Zhejiang 310058, P.R. China.
College of Animal Science and Technology, Zhejiang A&F University, Lin'an, Zhejiang 311300, P.R. China.
J Microbiol Biotechnol. 2016 Jan;26(1):197-206. doi: 10.4014/jmb.1504.04075.
Listeria monocytogenes is a foodborne pathogen of considerable genetic diversity with varying pathogenicity. Initially, we found that the strain M7 was far less pathogenic than the strain Lm850658 though both are serovar 4a strains belonging to the lineage III. Comparative genomic approaches were then attempted to decipher the genetic basis that might govern the strain-dependent pathotypes. There are 2,761 coding sequences of 100% nucleotide identity between the two strains, accounting for 95.7% of the total genes in Lm850658 and 92.7% in M7. Lm850658 contains 33 specific genes, including a novel 20K prophage whereas strain M7 has 130 specific genes, including two large prophages (38K and 44K). To examine the roles of these specific prophages in pathogenicity, the 20K and 38K prophages were deleted from their respective strains. There were virtually no differences of pathogenicity between the deletion mutants and their parent strains, although some putative virulent factors like VirB4 are present in the 20K region or holin-lysin in the 38K region. In silico PCR analysis of 29 listeria genomes show that only strain SLCC2540 has the same 18 bp integration hotspot as Lm850658, whereas the sequence identity of their 20K prophages is very low (21.3%). The 38K and 44K prophages are located in two other different hotspots and are conserved in low virulent strains M7, HCC23, and L99. In conclusion, the 20K and 38K prophages of L. monocytogenes serovar 4a strains Lm850658 and M7 are not related to virulence but contribute to genetic diversity.
单核细胞增生李斯特菌是一种食源性病原体，具有相当大的遗传多样性和不同的致病性。最初，我们发现菌株M7的致病性远低于菌株Lm850658，尽管两者都是属于III系的血清型4a菌株。随后尝试采用比较基因组学方法来解读可能决定菌株依赖性致病型的遗传基础。两株菌之间有2761个编码序列的核苷酸同一性为100%，占Lm850658总基因的95.7%，占M7总基因的92.7%。Lm850658包含33个特异性基因，包括一个新的20K原噬菌体，而菌株M7有130个特异性基因，包括两个大的原噬菌体（38K和44K）。为了研究这些特异性原噬菌体在致病性中的作用，从各自的菌株中删除了20K和38K原噬菌体。缺失突变体与其亲本菌株在致病性上几乎没有差异，尽管在20K区域存在一些假定的毒力因子如VirB4，或在38K区域存在孔蛋白-溶素。对29个李斯特菌基因组的电子PCR分析表明，只有菌株SLCC2540具有与Lm850658相同的18bp整合热点，而它们20K原噬菌体的序列同一性非常低（21.3%）。38K和44K原噬菌体位于另外两个不同的热点，并且在低毒力菌株M7、HCC23和L99中保守。总之，单核细胞增生李斯特菌血清型4a菌株Lm850658和M7的20K和38K原噬菌体与毒力无关，但有助于遗传多样性。
