pXO16, a large plasmid from Bacillus thuringiensis serovar israelensis, exhibits unique features. Not only is pXO16 able to transfer at high frequencies within few minutes, but it is also able to transfer among virtually all members of the Bacillus cereus group. Among the proteins encoded in the tip transfer locus of pXO16, TipB displays an atypical organization compared to known conjugative cell wall hydrolases with the large central soluble lytic transglycosylase (SLT) domain missing from the protein. We constructed a tipB deletion mutant which led to significant reduction in transfer efficiencies in both liquid and filter mating. The initial transfer frequencies could be restored when complementing tipB in trans thus showing the TipB implication in pXO16 conjugative transfer. Additionally, truncated versions of TipB were expressed in Escherichia coli to assess the protein lytic activity. When applied exogenously, TipB-2TM, in which the two N-terminal TM domains were removed, yielded a decrease of ca. 40% in optical density of B. thuringiensis sv. israelensis, a lytic activity that could partially be explained by the C-terminal CHAP-like domain. These results confirm TipB conjugative hydrolase function and provide new insights into pXO16 unique conjugative apparatus.

pXO16，从一个大质粒苏云金芽孢杆菌血清变型以色列亚，表现出独特的功能。pXO16 不仅能够在几分钟内以高频率进行转移，而且还能够在蜡状芽孢杆菌群的几乎所有成员之间转移。在pXO16的尖端转移基因座中编码的蛋白质中，与已知的结合细胞壁水解酶相比，TipB 显示出一种非典型的组织，蛋白质中缺少大的中央可溶性裂解转糖基酶 (SLT) 结构域。我们构建了一个tipB缺失突变体，它导致液体和过滤器交配的转移效率显着降低。互补时可以恢复初始传输频率TIPB在反从而表示pXO16接合转移的TIPB含义。此外，TipB 的截短版本在大肠杆菌中表达，以评估蛋白质裂解活性。当外源应用时，去除了两个 N 端 TM 结构域的 TipB-2TM 减少了约 B. thuringiensis sv.光密度为 40% 。israelensis，一种裂解活性，可以部分解释为 C 端 CHAP 样结构域。这些结果证实了 TipB 结合水解酶的功能，并为 pXO16 独特的结合装置提供了新的见解。