The occurrence of harmful Microcystis blooms is increasing in frequency in a myriad of freshwater ecosystems. Despite considerable research pertaining to the cause and nature of these blooms, the molecular mechanisms behind the cosmopolitan distribution and phenotypic diversity in Microcystis are still unclear. We compared the patterns and extent of DNA methylation in three strains of Microcystis, PCC 7806SL, NIES-2549 and FACHB-1757, using Single Molecule Real-Time (SMRT) sequencing technology. Intact restriction-modification (R-M) systems were identified from the genomes of these strains, and from two previously sequenced strains of Microcystis, NIES-843 and TAIHU98. A large number of methylation motifs and R-M genes were identified in these strains, which differ substantially among different strains. Of the 35 motifs identified, eighteen had not previously been reported. Strain NIES-843 contains a larger number of total putative methyltransferase genes than have been reported previously from any bacterial genome. Genomic comparisons reveal that methyltransferases (some partial) may have been acquired from the environment through horizontal gene transfer.

在无数的淡水生态系统中，有害的微囊藻开花的发生频率正在增加。尽管对这些花开的原因和性质进行了大量研究，但微囊藻的世界性分布和表型多样性背后的分子机制仍不清楚。我们使用单分子实时（SMRT）测序技术比较了三株微囊藻，PCC 7806SL，NIES-2549和FACHB-1757中DNA甲基化的模式和程度。从这些菌株的基因组以及两个先前测序的微囊藻菌株中鉴定出完整的限制性修饰（RM）系统。，NIES-843和TAIHU98。在这些菌株中鉴定出大量的甲基化基序和RM基因，不同菌株之间存在很大差异。在确定的35个图案中，有18个以前没有被报道过。NIES-843菌株包含的推定甲基转移酶基因总数比以前从任何细菌基因组中报告的数量大。基因组比较显示甲基转移酶（部分转移酶）可能是通过水平基因转移从环境中获得的。