Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD15EH, UK.
Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
Cell. 2014 Feb 13;156(4):844-54. doi: 10.1016/j.cell.2014.01.012.
Formation of Bacillus subtilis biofilms, consisting of cells encapsulated within an extracellular matrix of exopolysaccharide and protein, requires the polyamine spermidine. A recent study reported that (1) related polyamine norspermidine is synthesized by B. subtilis using the equivalent of the Vibrio cholerae biosynthetic pathway, (2) exogenous norspermidine at 25 μM prevents B. subtilis biofilm formation, (3) endogenous norspermidine is present in biofilms at 50-80 μM, and (4) norspermidine prevents biofilm formation by condensing biofilm exopolysaccharide. In contrast, we find that, at concentrations up to 200 μM, exogenous norspermidine promotes biofilm formation. We find that norspermidine is absent in wild-type B. subtilis biofilms at all stages, and higher concentrations of exogenous norspermidine eventually inhibit planktonic growth and biofilm formation in an exopolysaccharide-independent manner. Moreover, orthologs of the V. cholerae norspermidine biosynthetic pathway are absent from B. subtilis, confirming that norspermidine is not physiologically relevant to biofilm function in this species.
枯草芽孢杆菌生物膜的形成是由细胞被细胞外多糖和蛋白质基质包裹而成的，这一过程需要多胺亚精胺。最近的一项研究表明：(1) 相关多胺正精胺是枯草芽孢杆菌利用与霍乱弧菌生物合成途径等同的途径合成的；(2) 25μM 的外源正精胺可防止枯草芽孢杆菌生物膜的形成；(3) 生物膜中存在 50-80μM 的内源性正精胺；(4) 正精胺通过凝结生物膜胞外多糖来阻止生物膜的形成。相比之下，我们发现，在高达 200μM 的浓度下，外源正精胺可促进生物膜的形成。我们发现，在野生型枯草芽孢杆菌生物膜的所有阶段都不存在正精胺，并且较高浓度的外源正精胺最终会以不依赖胞外多糖的方式抑制浮游生长和生物膜的形成。此外，枯草芽孢杆菌中不存在霍乱弧菌正精胺生物合成途径的同源物，这证实了正精胺在该物种的生物膜功能中并不具有生理相关性。
