Institut des Sciences du Végétal, UPR2355, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France.
PLoS One. 2013 Jun 7;8(6):e65473. doi: 10.1371/journal.pone.0065473. Print 2013.
Quorum-sensing (QS) signals of the N-acylhomoserine lactone (NAHL) class are cleaved by quorum-quenching enzymes, collectively named NAHLases. Here, functional metagenomics allowed the discovery of a novel bacterial NAHLase in a rhizosphere that was treated with γ-caprolactone. As revealed by rrs-DGGE and rrs-pyrosequencing, this treatment increased the percentage of the NAHL-degrading bacteria and strongly biased the structure of the bacterial community, among which Azospirillum dominated. Among the 29 760 fosmids of the metagenomic library, a single one was detected that expressed the qsdB gene conferring NAHL-degradation upon E. coli and decreased QS-regulated virulence in Pectobacterium. Phylogenetic analysis of the 34 orfs of the fosmid suggested that it would belong to an unknown Proteobacterium - probably a γ-proteobacterium. qPCR quantification of the NAHLase-encoding genes attM, qsdA, and qsdB revealed their higher abundance in the γ-caprolactone-treated rhizosphere as compared to an untreated control. The purified QsdB enzyme exhibited amidase activity. QsdB is the first amidase signature (AS) family member exhibiting NAHLase-activity. Point mutations in the AS-family catalytic triad K-S-S abolished the NAHLase activity of QsdB. This study extends the diversity of NAHLases and highlights a common phylogenic origin of AS-family enzymes involved in the degradation of natural compounds, such as NAHLs, and xenobiotics, such as nylon and linuron.
群体感应（QS）信号的 N-酰基高丝氨酸内酯（NAHL）类被群体感应淬灭酶切割，统称为 NAHLases。在这里，功能宏基因组学允许在使用γ-己内酯处理的根际中发现一种新型细菌 NAHLase。如 rrs-DGGE 和 rrs-焦磷酸测序所揭示的，这种处理增加了 NAHL 降解细菌的百分比，并强烈偏向于细菌群落的结构，其中 Azospirillum 占主导地位。在宏基因组文库的 29760 个fosmid 中，检测到一个单 fosmid 表达 qsdB 基因，该基因赋予大肠杆菌 NAHL 降解能力，并降低了 Pectobacterium 中 QS 调节的毒力。fosmid 的 34 个或基因的系统发育分析表明，它可能属于未知的 Proteobacterium-可能是γ-Proteobacterium。NAHLase 编码基因 attM、qsdA 和 qsdB 的 qPCR 定量显示，与未处理对照相比，它们在γ-己内酯处理的根际中丰度更高。纯化的 QsdB 酶表现出酰胺酶活性。QsdB 是第一个表现出 NAHLase 活性的酰胺酶签名（AS）家族成员。AS 家族催化三联体 K-S-S 中的点突变使 QsdB 的 NAHLase 活性丧失。这项研究扩展了 NAHLase 的多样性，并强调了参与天然化合物（如 NAHLs）和异生物质（如尼龙和利谷隆）降解的 AS 家族酶的共同系统发育起源。
