Wotanis Caitlin K, Brennan William P, Angotti Anthony D, Villa Elizabeth A, Zayner Josiah P, Mozina Alexandra N, Rutkovsky Alexandria C, Sobe Richard C, Bond Whitney G, Karatan Ece
Department of Biology, Appalachian State University, Boone, North Carolina, United States of America.
PLoS One. 2017 Oct 18;12(10):e0186291. doi: 10.1371/journal.pone.0186291. eCollection 2017.
The polyamine norspermidine is one of the major polyamines synthesized by Vibrionales and has also been found in various aquatic organisms. Norspermidine is among the environmental signals that positively regulate Vibrio cholerae biofilm formation. The NspS/MbaA signaling complex detects extracellular norspermidine and mediates the response to this polyamine. Norspermidine binding to the NspS periplasmic binding protein is thought to inhibit the phosphodiesterase activity of MbaA, increasing levels of the biofilm-promoting second messenger cyclic diguanylate monophosphate, thus enhancing biofilm formation. V. cholerae can also synthesize norspermidine using the enzyme NspC as well as import it from the environment. Deletion of the nspC gene was shown to reduce accumulation of bacteria in biofilms, leading to the conclusion that intracellular norspermidine is also a positive regulator of biofilm formation. Because V. cholerae uses norspermidine to synthesize the siderophore vibriobactin it is possible that intracellular norspermidine is required to obtain sufficient amounts of iron, which is also necessary for robust biofilm formation. The objective of this study was to assess the relative contributions of intracellular and extracellular norspermidine to the regulation of biofilm formation in V. cholerae. We show the biofilm defect of norspermidine synthesis mutants does not result from an inability to produce vibriobactin as vibriobactin synthesis mutants do not have diminished biofilm forming abilities. Furthermore, our work shows that extracellular, but not intracellular norspermidine, is mainly responsible for promoting biofilm formation. We establish that the NspS/MbaA signaling complex is the dominant mediator of biofilm formation in response to extracellular norspermidine, rather than norspermidine synthesized by NspC or imported into the cell.
多胺亚精胺是弧菌属合成的主要多胺之一，也在各种水生生物中被发现。亚精胺是对霍乱弧菌生物膜形成有正向调节作用的环境信号之一。NspS/MbaA信号复合体可检测细胞外亚精胺并介导对这种多胺的反应。亚精胺与NspS周质结合蛋白结合被认为会抑制MbaA的磷酸二酯酶活性，增加促进生物膜形成的第二信使环二鸟苷单磷酸的水平，从而增强生物膜形成。霍乱弧菌还可利用NspC酶合成亚精胺，也可从环境中摄取。nspC基因的缺失显示会减少生物膜中细菌的积累，从而得出细胞内亚精胺也是生物膜形成正向调节因子的结论。由于霍乱弧菌利用亚精胺合成铁载体弧菌素，因此可能需要细胞内亚精胺来获取足够量的铁，而铁对于强大的生物膜形成也是必需的。本研究的目的是评估细胞内和细胞外亚精胺对霍乱弧菌生物膜形成调节的相对贡献。我们发现亚精胺合成突变体的生物膜缺陷并非源于无法产生弧菌素，因为弧菌素合成突变体的生物膜形成能力并未降低。此外，我们的研究表明，主要是细胞外而非细胞内亚精胺促进生物膜形成。我们确定NspS/MbaA信号复合体是响应细胞外亚精胺而非由NspC合成或导入细胞的亚精胺时生物膜形成的主要介导因子。
