Screening for yeast mutants defective in recipient ability for transkingdom conjugation with Escherichia coli revealed importance of vacuolar ATPase activity in the horizontal DNA transfer phenomenon

Proteobacterium Escherichia coli strains harboring wide-transfer-range conjugative plasmids are able to transfer these plasmids to several yeast species. Whole plasmid DNA is mobilizable in the transkingdom conjugation phenomenon. Owing to the availability of various conjugative plasmids in bacteria, the horizontal DNA transfer has potential to occur between various bacteria and eukaryotes. In order to know host factor genes involved in such conjugation, we systematically tested the conjugability of strains among a yeast library comprising single-gene-knockout mutants in this study. This genome-wide screen identified 26 host chromosomal genes whose absence reduced the efficiency of the transkingdom conjugation. Among the 26 genes, 20 are responsible for vacuolar ATPase activity, while 5 genes (SHP1, CSG2, CCR4, NOT5, and HOF1) seem to play a role in maintaining the cell surface. Lack of either ZUO1 gene or SSZ1 gene, each of which encodes a component of the ribosome-associated cytoplasmic molecular chaperone, also strongly affected transkingdom conjugation.This work was supported in part by Japanese Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (#20570221)

Complete Genomic Structure of the Bloom-forming Toxic Cyanobacterium Microcystis aeruginosa NIES-843

The nucleotide sequence of the complete genome of a cyanobacterium, Microcystis aeruginosa NIES-843, was determined. The genome of M. aeruginosa is a single, circular chromosome of 5 842 795 base pairs (bp) in length, with an average GC content of 42.3%. The chromosome comprises 6312 putative protein-encoding genes, two sets of rRNA genes, 42 tRNA genes representing 41 tRNA species, and genes for tmRNA, the B subunit of RNase P, SRP RNA, and 6Sa RNA. Forty-five percent of the putative protein-encoding sequences showed sequence similarity to genes of known function, 32% were similar to hypothetical genes, and the remaining 23% had no apparent similarity to reported genes. A total of 688 kb of the genome, equivalent to 11.8% of the entire genome, were composed of both insertion sequences and miniature inverted-repeat transposable elements. This is indicative of a plasticity of the M. aeruginosa genome, through a mechanism that involves homologous recombination mediated by repetitive DNA elements. In addition to known gene clusters related to the synthesis of microcystin and cyanopeptolin, novel gene clusters that may be involved in the synthesis and modification of toxic small polypeptides were identified. Compared with other cyanobacteria, a relatively small number of genes for two component systems and a large number of genes for restriction-modification systems were notable characteristics of the M. aeruginosa genome

ヒス束内triple pathway機能的縦解離が示唆された高度房室ブロックの1症例

症例は81歳、男性。高度房室ブロックで、洞性P波が房室伝導した際は右脚ブロック型(+30°)のQRS波(以下、心室捕捉A)が現れ、2種類の補充収縮[右脚ブロック型(以下、補充収縮B)、左脚ブロック型(以下、補充収縮C)]が出現し、様々な融合収縮(以下、融合収縮D)を呈する複雑な不整脈を経験した。補充収縮Bは、II誘導でR波が高く、心室捕捉Aに比べてやや右方に偏位(+60°)していた。補充収縮Bおよび補充収縮CのRR間隔は、それぞれ1.65秒、1.68秒と極めて近似した自動能周期であった。心室捕捉Aに続いて、洞性P波と先行心拍とのRP間隔が0.89秒より長くなる補充収縮Bの場合は、順行性に伝導し、補充中枢を脱分極して周期更新するが、0.88秒以下と短くなる補充収縮Cの場合は、ヒス束下部に回り込み、逆行性に不顕伝導して補充中枢を脱分極するため、次の補充収縮は本来の自動能周期よりも長いRR間隔で出現したと考えられた。以上から、本症例はヒス束内triple pathway機能的縦解離が存在しており、心室捕捉Aは左脚後枝束を伝導し、補充収縮Bは左脚前枝束、補充収縮Cは右脚束に補充中枢が局在すると考えられた。We reported a patient with high-degree atrio-ventricular block with various QRS complexes. While the ventricular captured beats showed right bundle branch block（RBBB）axis +30°（A）, 2 patterns of escape beats, i.e. RBBB axis +60°（B）and left bundle branch block（LBBB）（C）, were observed with cycle lengths 1.65 and 1.68 sec, respectively. Fusion beats of various degrees between B and C were also observed. When RP interval was ＞ 0.89 sec, the P wave depolarized the escape focus antegradely. When RP interval was ≤ 0.88 sec, the P wave did not antegradely depolarize the escape focus but retrogradely depolarized it with some delay, conducting via the lower portion of His bundle transversely. QRS axis of B showed mild rightward shift compared with that of A. With the aforementioned electrocardiographic findings, we concluded that His bundle was functionally dissociated into triple pathway. In addition, the P wave conducting through the bundle connecting to the left posterior bundle branch caused A, and two escape focuses localized in the bundles connecting to the left anterior bundle branch and right bundle branch caused B and C, respectively

単発または2連発の心室期外収縮により惹起された非通常型房室結節リエントリー頻拍

単発または2連発の心室期外収縮により房室結節内で機能的縦解離したslow pathway(S路)を逆伝導し、fast pathway(F路)を下行する非通常型房室結節リエントリー頻拍が再現性をもって惹起されたと考えられた2例を報告した。症例1は50歳代女性、単発の心室期外収縮によりQRS直前に陰性P波を伴う房室結節リエントリー頻拍が惹起されたが、頻拍の第1拍は洞性P波でも、また洞性P波と陰性P波との心房融合でも惹起された。症例2は50歳代男性で、心室期外収縮2連発によりQRS直前に陰性P波を伴う非通常型房室結節リエントリー頻拍が惹起された。症例2も頻拍の第1拍は洞性P波でも頻拍は惹起されたことから、洞性刺激がリエントリー回路に進入する前にS路からF路への回帰が生じたと考えられた。症例2は頻拍QRSの立ち上がり部分にデルタ波を思わせる盛り上がりがあるように見えることから、bystander WPWとの鑑別診断についても述べ、考察した