Helmholtz Institute for Pharmaceutical Research Saarland, Saarbrücken, Germany.
Appl Microbiol Biotechnol. 2014 Jan;98(2):795-806. doi: 10.1007/s00253-013-5440-6. Epub 2013 Dec 15.
Streptomyces albus J1074 is a derivative of the S. albus G1 strain defective in SalG1 restriction-modification system. Genome sequencing of S. albus J1074 revealed that the size of its chromosome is 6.8 Mb with unusually short terminal arms of only 0.3 and 0.4 Mb. Here we present our attempts to evaluate the dispensability of subtelomeric regions of the S. albus J1074 chromosome. A number of large site-directed genomic deletions led to circularization of the S. albus J1074 chromosome and to the overall genome reduction by 307 kb. Two spontaneous mutants with an activated carotenoid cluster were obtained. Genome sequencing and transcriptome analysis indicated that phenotypes of these mutants resulted from the right terminal 0.42 Mb chromosomal region deletion, followed by the carotenoid cluster amplification. Our results indicate that the right terminal 0.42 Mb fragment is dispensable under laboratory conditions. In contrast, the left terminal arm of the S. albus J1074 chromosome contains essential genes and only 42 kb terminal region is proved to be dispensable. We identified overexpressed carotenoid compounds and determined fitness costs of the large genomic rearrangements.
白色链霉菌 J1074 是 S. albus G1 菌株的衍生物，该菌株在 SalG1 限制修饰系统中存在缺陷。对白色链霉菌 J1074 的基因组测序表明，其染色体大小为 6.8Mb，其末端臂非常短，仅有 0.3 和 0.4Mb。在这里，我们尝试评估白色链霉菌 J1074 染色体端粒区的非必需性。大量的大片段定点基因组缺失导致了白色链霉菌 J1074 染色体的环化，并导致整个基因组减少了 307kb。获得了两个具有激活类胡萝卜素簇的自发突变体。基因组测序和转录组分析表明，这些突变体的表型是由于右末端 0.42Mb 染色体区域缺失，随后类胡萝卜素簇扩增所致。我们的结果表明，在实验室条件下，右末端 0.42Mb 片段是可缺失的。相比之下，白色链霉菌 J1074 染色体的左末端臂包含必需基因，只有 42kb 的末端区域被证明是可缺失的。我们鉴定了过表达的类胡萝卜素化合物，并确定了大规模基因组重排的适应代价。
