生防菌Bs-916突变菌株M49芽胞形成和感受态形成能力

摘要：生防枯草芽胞杆菌Bs-916（Bacillus subtilis）在水稻纹枯病的防治上效果显著。应用离子注入突变对Bs-916进行了突变,获得了一系列的突变菌株。其中突变菌株M49,其表面活性素Surfactin分泌量比出发菌株Bs-916大大降低并导致其防效降低。【目的】为了确认影响该菌株防效降低的影响因子,对其表型和相关基因表达水平进行了研究。【方法】应用生孢培养基,通过芽胞形成能力评测方法比较该菌株和野生菌株Bs-916的芽胞形成能力;通过转化质粒的实验评测突变菌株M49和野生型Bs-916的     

X-ray study of competence development in Bacillus subtilis

Summary Pre-competent and competent cultures of Bacillus subtilis were x-irradiated before and after centrifugal separation of cells in a Renografin density gradient. Pre-competent cultures have no cells at the radiosensitivity of the cells in the bulk competent culture, but there is a substantial fraction of cells in a multi-target state, with heterogeneous target numbers. On reaching maximal competence, the survival becomes entirely linear in radiosensitivity. Irradiation of the separated competent cells shows that competence development correlates with disappearance of multi-target cells from the non-competent band of cells and the appearance of single-target cells in the competent band at a radiosensitivity equal to that of the bulk competent culture. Thus the multi-target state may be a required stage in the development of competence in this system.     

A novel SMC-like protein,SbcE (YhaN), is involved in DNA double-strand break repair and competence in Bacillus subtilis

Bacillus subtilis and most Gram positive bacteria possess four SMC like proteins: SMC, SbcC, RecN and the product of the yhaN gene, termed SbcE. SbcE is most similar to SbcC but contains a unique central domain. We show that SbcE plays a role during transformation in competent cells and in DNA double-strand break (DSB) repair. The phenotypes were strongly exacerbated by the additional deletion of recN or of sbcC, suggesting that all three proteins act upstream of RecA and provide distinct avenues for presynapsis. SbcE accumulated at the cell poles in competent cells, and localized as a discrete focus on the nucleoids in 10% of growing cells. This number moderately increased after treatment with DNA damaging agents and in the absence of RecN or of SbcC. Damage-induced foci of SbcE arose early after induction of DNA damage and rarely colocalized with the replication machinery. Our work shows that SMC-like proteins in B. subtilis play roles at different subcellular sites during DNA repair. SbcC operates at breaks occurring at the replication machinery, whereas RecN and SbcE function mainly, but not exclusively, at DSBs arising elsewhere on the chromosome. In agreement with this idea, we found that RecN-YFP damage-induced assemblies also arise in the absence of ongoing replication.     

Cannibalism enhances biofilm development in Bacillus subtilis

Cannibalism is a mechanism to delay sporulation in Bacillus subtilis. Cannibal cells express the skf and sdp toxin systems to lyse a fraction of their sensitive siblings. The lysed cells release nutrients that serve to feed the community, effectively delaying spore formation. Here we provide evidence that the subpopulation of cells that differentiates into cannibals is the same subpopulation that produces the extracellular matrix that holds cells together in biofilms. Cannibalism and matrix formation are both triggered in response to the signalling molecule surfactin. Nutrients released by the cannibalized cells are preferentially used by matrix-producing cells, as they are the only cells expressing resistance to the Skf and Sdp toxins. As a result this subpopulation increases in number and matrix production is enhanced when cannibalism toxins are produced. The cannibal/matrix-producing subpopulation is also generated in response to antimicrobials produced by other microorganisms and may thus constitute a defense mechanism to protect B. subtilis from the action of antibiotics in natural settings.