Haase Elaine M, Kou Yurong, Sabharwal Amarpreet, Liao Yu-Chieh, Lan Tianying, Lindqvist Charlotte, Scannapieco Frank A
Department of Oral Biology, School of Dental Medicine, University at Buffalo, State University of New York, Buffalo, NY, USA.
Department of Oral Biology, School of Stomatology, China Medical University, Shenyang, People's Republic of China.
BMC Microbiol. 2017 Apr 20;17(1):94. doi: 10.1186/s12866-017-1005-7.
Successful commensal bacteria have evolved to maintain colonization in challenging environments. The oral viridans streptococci are pioneer colonizers of dental plaque biofilm. Some of these bacteria have adapted to life in the oral cavity by binding salivary α-amylase, which hydrolyzes dietary starch, thus providing a source of nutrition. Oral streptococcal species bind α-amylase by expressing a variety of amylase-binding proteins (ABPs). Here we determine the genotypic basis of amylase binding where proteins of diverse size and function share a common phenotype.
ABPs were detected in culture supernatants of 27 of 59 strains representing 13 oral Streptococcus species screened using the amylase-ligand binding assay. N-terminal sequences from ABPs of diverse size were obtained from 18 strains representing six oral streptococcal species. Genome sequencing and BLAST searches using N-terminal sequences, protein size, and key words identified the gene associated with each ABP. Among the sequenced ABPs, 14 matched amylase-binding protein A (AbpA), 6 matched amylase-binding protein B (AbpB), and 11 unique ABPs were identified as peptidoglycan-binding, glutamine ABC-type transporter, hypothetical, or choline-binding proteins. Alignment and phylogenetic analyses performed to ascertain evolutionary relationships revealed that ABPs cluster into at least six distinct, unrelated families (AbpA, AbpB, and four novel ABPs) with no phylogenetic evidence that one group evolved from another, and no single ancestral gene found within each group. AbpA-like sequences can be divided into five subgroups based on the N-terminal sequences. Comparative genomics focusing on the abpA gene locus provides evidence of horizontal gene transfer.
The acquisition of an ABP by oral streptococci provides an interesting example of adaptive evolution.
成功的共生细菌已经进化到能够在具有挑战性的环境中维持定殖。口腔草绿色链球菌是牙菌斑生物膜的先锋定殖菌。其中一些细菌通过结合唾液α-淀粉酶适应口腔生活，唾液α-淀粉酶可水解膳食淀粉，从而提供营养来源。口腔链球菌通过表达多种淀粉酶结合蛋白（ABP）来结合α-淀粉酶。在此，我们确定了淀粉酶结合的基因型基础，其中不同大小和功能的蛋白质具有共同的表型。
使用淀粉酶配体结合试验对代表13种口腔链球菌的59株菌株进行筛选，在27株菌株的培养上清液中检测到ABP。从代表6种口腔链球菌的18株菌株中获得了不同大小ABP的N端序列。使用N端序列、蛋白质大小和关键词进行基因组测序和BLAST搜索，确定了与每个ABP相关的基因。在测序的ABP中，14个与淀粉酶结合蛋白A（AbpA）匹配，6个与淀粉酶结合蛋白B（AbpB）匹配，11个独特的ABP被鉴定为肽聚糖结合蛋白、谷氨酰胺ABC型转运蛋白、假想蛋白或胆碱结合蛋白。为确定进化关系而进行的比对和系统发育分析表明，ABP至少聚类为六个不同的、不相关的家族（AbpA、AbpB和四个新的ABP），没有系统发育证据表明一组是从另一组进化而来的，并且在每个组中未发现单一的祖先基因。基于N端序列，AbpA样序列可分为五个亚组。对abpA基因座的比较基因组学提供了水平基因转移的证据。
口腔链球菌获得ABP提供了一个适应性进化的有趣例子。
