Department of Chemistry, Temple University, Philadelphia, Pennsylvania.
Department of Chemistry, Temple University, Philadelphia, Pennsylvania.
Biophys J. 2021 Jun 15;120(12):2461-2470. doi: 10.1016/j.bpj.2021.04.018. Epub 2021 Apr 29.
Bacterial surface charge is a critical characteristic of the cell's interfacial physiology that influences how the cell interacts with the local environment. A direct, sensitive, and accurate experimental technique capable of quantifying bacterial surface charge is needed to better understand molecular adaptations in interfacial physiology in response to environmental changes. We introduce here the method of second-harmonic light scattering (SHS), which is capable of detecting the number of molecular ions adsorbed as counter charges on the exterior bacterial surface, thereby providing a measure of the surface charge. In this first demonstration, we detect the small molecular cation, malachite green, electrostatically adsorbed on the surface of representative strains of Gram-positive and Gram-negative bacteria. Surprisingly, the SHS-deduced molecular transport rates through the different cellular ultrastructures are revealed to be nearly identical. However, the adsorption saturation densities on the exterior surfaces of the two bacteria were shown to be characteristically distinct. The negative charge density of the lipopolysaccharide coated outer surface of Gram-negative Escherichia coli (6.6 ± 1.3 nm) was deduced to be seven times larger than that of the protein surface layer of Gram-positive Lactobacillus rhamnosus (1.0 ± 0.2 nm). The feasibility of SHS-deduced bacterial surface charge density for Gram-type differentiation is presented.
细菌表面电荷是细胞界面生理学的一个关键特征，影响着细胞与局部环境的相互作用方式。需要一种直接、灵敏、准确的实验技术来量化细菌表面电荷，以便更好地理解界面生理学中分子适应环境变化的机制。我们在这里介绍二次谐波散射（SHS）的方法，该方法能够检测吸附在细菌外表面作为抗衡电荷的分子离子数量，从而提供表面电荷的测量。在这第一次演示中，我们检测了代表性的革兰氏阳性菌和革兰氏阴性菌表面静电吸附的小分子阳离子孔雀石绿。令人惊讶的是，通过不同细胞超微结构的分子输运速率被证明几乎相同。然而，两种细菌外表面的吸附饱和密度却表现出明显的特征差异。革兰氏阴性大肠杆菌（Escherichia coli）的脂多糖涂层外表面的负电荷密度（6.6 ± 1.3nm）被推断为革兰氏阳性乳杆菌（Lactobacillus rhamnosus）的蛋白质表面层的七倍（1.0 ± 0.2nm）。提出了 SHS 推断的细菌表面电荷密度用于革兰氏类型区分的可行性。
