Zhang W, Dai W, Tsai Shi-Ming, Zehnder S M, Sarntinoranont M, Angelini T E
Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, USA.
Soft Matter. 2015 May 14;11(18):3612-7. doi: 10.1039/c5sm00148j.
Bacterial biofilms are highly structured, surface associated bacteria colonies held together by a cell-generated polymer network known as EPS (extracellular polymeric substance). This polymer network assists in adhesion to surfaces and generates spreading forces as colonies grow over time. In the laboratory and in nature, biofilms often grow at the interface between air and an elastic, semi-permeable nutrient source. As this type of biofilm increases in volume, an accommodating compression of its substrate may arise, potentially driven by the osmotic pressure exerted by the EPS against the substrate surface. Here we study Bacillus subtilis biofilm force generation by measuring the magnitude and rate of deformation imposed by colonies against the agar-nutrient slabs on which they grow. We find that the elastic stress stored in deformed agar is orders of magnitude larger than the drag stress associated with pulling fluid through the agar matrix. The stress exerted by the biofilm is nearly the same as the osmotic pressure generated by the EPS, and mutant colonies incapable of producing EPS exert much lower levels of stress. The fluid flow rate into B. subtilis biofilms suggest that EPS generated pressure provides some metabolic benefit as colonies expand in volume. These results reveal that long-term biofouling and colony expansion may be tied to the hydraulic permeability and elasticity of the surfaces that biofilms colonize.
细菌生物膜是高度结构化的、与表面相关的细菌菌落，由一种称为EPS（胞外聚合物）的细胞产生的聚合物网络维系在一起。这种聚合物网络有助于细菌附着于表面，并随着菌落的生长产生扩展力。在实验室和自然环境中，生物膜通常生长在空气与弹性、半透性营养源的界面处。随着这种生物膜体积的增加，其底物可能会出现适应性压缩，这可能是由EPS对底物表面施加的渗透压驱动的。在这里，我们通过测量菌落对其生长的琼脂营养平板施加的变形大小和速率，来研究枯草芽孢杆菌生物膜力的产生。我们发现，储存在变形琼脂中的弹性应力比与流体通过琼脂基质的拉动相关的曳力应力大几个数量级。生物膜施加的应力与EPS产生的渗透压几乎相同，而无法产生EPS的突变菌落施加的应力水平要低得多。进入枯草芽孢杆菌生物膜的流体流速表明，随着菌落体积的扩大，EPS产生的压力提供了一些代谢益处。这些结果表明，长期的生物污垢和菌落扩展可能与生物膜所附着表面的水力渗透性和弹性有关。
