Isovaleryl-homoserine lactone, an unusual branched-chain quorum-sensing signal from the soybean symbiont Bradyrhizobium japonicum
Isovaleryl-homoserine lactone, an unusual branched-chain quorum-sensing signal from the soybean symbiont Bradyrhizobium japonicum
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DOI：
10.1073/pnas.1114125108
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发表时间：
2011-10-04
影响因子：
11.1
通讯作者：
Harwood, Caroline S.
中科院分区：
文献类型：
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作者：
Lindemann, Andrea;Pessi, Gabriella;Harwood, Caroline S.
许多变形杆菌通过使用Luxi-LuxR型群体感应系统进行交流，该系统产生和检测酰基高丝氨酸内酯(acyl-HSL)信号。已知的大多数信号是直链脂肪酰基-HSLs，有证据表明鲁西同系物更喜欢脂肪酸-酰基载体蛋白(ACP)而不是脂肪酰基-CoA作为信号合成的酰基底物。沼泽红假单胞菌的两个相关鲁西同源物RPAI和BtaI分别直接产生芳基-HSLs对香豆酰-HSL和肉桂酰基-HSL。本文报道了大豆共生菌慢生菌USDA110的BjaI与RPAI和BtaI密切相关，并催化合成支链脂肪酰基-HSL(IV-HSL)。我们发现IV-HSL诱导bjaI的表达，通过这种方式，IV-HSL的功能类似于许多其他酰基-HSL群体感应信号。纯化的组氨酸标记的BjaI是一种IV-HSL合成酶，它对异戊酰辅酶A有活性，但对异戊基-ACP检测不到。这表明，酰基-HSL合成酶的RPAI-BtaI-BjaI亚家族可能使用CoA-而不是ACP连接的底物来合成酰基-HSL。BjaI连锁的bjaR(1)基因参与了对IV-HSL的反应，并且BjaR(1)在低至10 pm的浓度下对IV-HSL敏感低水平但足够水平的IV-HSL(约5 NM)积累在日本芽孢杆菌的培养液中。低水平的IV-HSL合成可能导致了这种细菌的群体感应信号在其他地方没有被描述。
Many species of Proteobacteria communicate by using LuxI-LuxR-type quorum-sensing systems that produce and detect acyl-homoserine lactone (acyl-HSL) signals. Most of the known signals are straight-chain fatty acyl-HSLs, and evidence indicates that LuxI homologs prefer fatty acid-acyl carrier protein (ACP) over fatty acyl-CoA as the acyl substrate for signal synthesis. Two related LuxI homologs, RpaI and BtaI from Rhodopseudomonas palustris and photosynthetic stem-nodulating bradyrhizobia, direct production of the aryl-HSLs p-coumaroyl-HSL and cinnamoyl-HSL, respectively. Here we report that BjaI from the soybean symbiont Bradyrhizobium japonicum USDA110 is closely related to RpaI and BtaI and catalyzes the synthesis of isovaleryl-HSL (IV-HSL), a branched-chain fatty acyl-HSL. We show that IV-HSL induces expression of bjaI, and in this way IV-HSL functions like many other acyl-HSL quorum-sensing signals. Purified histidine-tagged BjaI was an IV-HSL synthase, which was active with isovaleryl-CoA but not detectably so with isovaleryl-ACP. This suggests that the RpaI-BtaI-BjaI subfamily of acyl-HSL synthases may use CoA-rather than ACP-linked substrates for acyl-HSL synthesis. The bjaI-linked bjaR(1) gene is involved in the response to IV-HSL, and BjaR(1) is sensitive to IV-HSL at concentrations as low as 10 pM. Low but sufficient levels of IV-HSL (about 5 nM) accumulate in B. japonicum culture fluid. The low levels of IV-HSL synthesis have likely contributed to the fact that the quorum-sensing signal from this bacterium has not been described elsewhere.