Abstract：
Moraxella ovis is a Gram-negative bacterium isolated from sheep conjunctivitis cases and is a rare isolate of infectious bovine keratoconjunctivitis (IBK). This species is closely related to M. bovoculi, another species which can also be isolated from IBK, or cattle upper respiratory tract (URT). Prior to molecular identification techniques, M. bovoculi was frequently misclassified as M. ovis. We previously described the structure of two oligosaccharides (lipooligosaccharide-derived, minor and major glycoforms) from M. bovoculi 237T (type strain, also ATCC BAA-1259T). Here, we have identified the genetic loci for lipooligosaccharide synthesis in M. ovis 354T (NCTC11227) and compared it with M. bovoculi 237T. We identified genes encoding the known glycosyltransferases Lgt6 and Lgt3 in M.ovis. These genes are conserved in Moraxella spp., including M bovoculi. We identified three further putative OS biosynthesis genes that are restricted to M. ovis and M. bovoculi. These encode enzymes predicted to function as GDP-mannose synthases, namely a mannosyltransferase and a glycosyltransferase. Adding insight into the genetic relatedness of M.ovis and M. bovoculi, the M. ovis genes have higher similarity to those in M. bovoculi genotype 2 (nasopharyngeal isolates from asymptomatic cattle), than to M. bovoculi genotype 1 (isolates from eyes of IBK-affected cattle). Sequence analysis confirmed that the predicted mannosyltransferase in M. bovoculi 237T is interrupted by a C>T polymorphism. This mutation is not present in other M. bovoculi strains sequenced to date. We isolated and characterised LOS-derived oligosaccharide from M. ovis 354T. GLC-MS and NMR spectroscopy data revealed a heptasaccharide structure with three β-D-Glcp residues attached as branches to the central 3,4,6-α-D-Glcp, with subsequent attachment to Kdo. This inner core arrangement is consistent with the action of Lgt6 and Lgt3 glycosyltransferases. Two α-D-Manp residues are linearly attached to the 4-linked β-D-Glcp, consistent with the presence of the two identified glycosyltransferases. This oligosaccharide structure is consistent with the previously reported minor glycoform isolated from M. bovoculi 237T.
摘要：
莫拉氏菌是一种从绵羊结膜炎病例中分离出的革兰氏阴性细菌，是一种罕见的传染性牛角膜结膜炎（IBK）分离株。该物种与博沃库利紧密相关，另一种也可以从IBK中分离出来的物种，或牛上呼吸道（URT）。在分子鉴定技术之前，博沃武利分枝杆菌经常被错误分类为Ovis分枝杆菌。我们先前描述了两种寡糖（脂寡糖衍生的，来自M.bovoculi237T的次要和主要糖型（类型菌株，也是ATCCBAA-1259T）。这里,我们已经确定了M.ovis354T（NCTC11227）中脂寡糖合成的遗传基因座，并将其与M.bovoculi237T进行了比较。我们在M.ovis中鉴定了编码已知糖基转移酶Lgt6和Lgt3的基因。这些基因在莫拉氏菌属中保守。,包括MBovoculi.我们确定了三个进一步推定的OS生物合成基因，这些基因仅限于卵黄分枝杆菌和博沃氏菌。这些编码的酶被预测为GDP-甘露糖合酶，即甘露糖基转移酶和糖基转移酶。进一步深入了解M.ovis和M.bovoculi的遗传相关性，M.ovis基因与b.voculi基因型2（无症状牛的鼻咽分离株）具有更高的相似性，比1型（来自受IBK影响的牛的眼睛的分离株）。序列分析证实,预测的博沃木霉237T中的甘露糖基转移酶被C>T多态性中断。该突变不存在于迄今为止测序的其它博沃氏杆菌菌株中。我们从M.ovis354T分离并表征了LOS衍生的寡糖。GLC-MS和NMR光谱数据揭示了七糖结构，其中三个β-D-Glcp残基作为分支连接到中央3,4,6-α-D-Glcp，随后依附Kdo。这种内核排列与Lgt6和Lgt3糖基转移酶的作用一致。两个α-D-Manp残基线性连接到4-连接的β-D-Glcp，与两种鉴定的糖基转移酶的存在一致。该寡糖结构与先前报道的从博沃木霉237T分离的次要糖型一致。
