Boydston Jeremy A, Yue Ling, Kearney John F, Turnbough Charles L
Department of Microbiology, BBRB 409, University of Alabama at Birmingham, 1530 3rd Ave. S, 35294-2170, USA.
J Bacteriol. 2006 Nov;188(21):7440-8. doi: 10.1128/JB.00639-06. Epub 2006 Aug 25.
The outermost layer of the Bacillus anthracis spore is the exosporium, which is composed of a paracrystalline basal layer and an external hair-like nap. The filaments of the nap are formed by a collagen-like glycoprotein called BclA, while the basal layer contains several different proteins. One of the putative basal layer proteins is ExsY. In this study, we constructed a DeltaexsY mutant of B. anthracis, which is devoid of ExsY, and examined the assembly of the exosporium on spores produced by this strain. Our results show that exosporium assembly on DeltaexsY spores is aberrant, with assembly arrested after the formation of a cap-like fragment that covers one end of the forespore-always the end near the middle of the mother cell. The cap contains a normal hair-like nap but an irregular basal layer. The cap is retained on spores prepared on solid medium, even after spore purification, but it is lost from spores prepared in liquid medium. Microscopic inspection of DeltaexsY spores prepared on solid medium revealed a fragile sac-like sublayer of the exosporium basal layer, to which caps were attached. Examination of purified DeltaexsY spores devoid of exosporium showed that they lacked detectable levels of BclA and the basal layer proteins BxpB, BxpC, CotY, and inosine-uridine-preferring nucleoside hydrolase; however, these spores retained half the amount of alanine racemase presumed to be associated with the exosporium of wild-type spores. The DeltaexsY mutation did not affect spore production and germination efficiencies or spore resistance but did influence the course of spore outgrowth.
炭疽芽孢杆菌孢子的最外层是芽孢外膜，它由一个准晶体基层和外部毛发状绒毛组成。绒毛的细丝由一种名为BclA的胶原蛋白样糖蛋白形成，而基层包含几种不同的蛋白质。一种假定的基层蛋白是ExsY。在本研究中，我们构建了一株缺失ExsY的炭疽芽孢杆菌ΔexsY突变体，并研究了该菌株产生的孢子上芽孢外膜的组装情况。我们的结果表明，ΔexsY孢子上的芽孢外膜组装异常，在形成覆盖前芽孢一端（总是靠近母细胞中部的那一端）的帽状片段后组装停止。该帽状物含有正常的毛发状绒毛，但基层不规则。即使经过孢子纯化，在固体培养基上制备的孢子上仍保留有帽状物，但在液体培养基中制备的孢子上则没有。对在固体培养基上制备的ΔexsY孢子进行显微镜检查发现，芽孢外膜基层有一个脆弱的囊状亚层，帽状物附着在该亚层上。对不含芽孢外膜的纯化ΔexsY孢子进行检查发现，它们缺乏可检测水平的BclA以及基层蛋白BxpB、BxpC、CotY和偏好肌苷 - 尿苷的核苷水解酶；然而，这些孢子保留了假定与野生型孢子芽孢外膜相关的丙氨酸消旋酶量的一半。ΔexsY突变不影响孢子产量、萌发效率或孢子抗性，但确实影响孢子生长的进程。
