Aiswarya N M, Tabraiz Shamas, Taneja Himani, Ahmed Asma, Aravinda Narayanan R
Department of Physics, Birla Institute of Technology and Science Pilani, Hyderabad Campus, India.
Section of Natural and Applied Sciences, Canterbury Christ Church University, UK.
Biofilm. 2024 Oct 5;8:100227. doi: 10.1016/j.bioflm.2024.100227. eCollection 2024 Dec.
The picture of bacterial biofilms as a colloidal gel composed of rigid bacterial cells protected by extracellular crosslinked polymer matrix has been pivotal in understanding their ability to adapt their microstructure and viscoelasticity to environmental assaults. This work explores if an analogous perspective exists in fungal biofilms with long filamentous cells. To this end, we consider biofilms of the fungus formed on the air-liquid interface, which has shown an ability to remove excess nitrogen and phosphorous from wastewater effectively. We investigated the changes to the viscoelasticity and the microstructure of these biofilms when the biofilms uptake varying concentrations of nitrogen and phosphorous, using large amplitude oscillatory shear flow rheology (LAOS) and field-emission scanning electron microscopy (FESEM), respectively. A distinctive peak in the loss modulus (G″) at 30-50 % shear strain is observed, indicating the transition from an elastic to plastic deformation state. Though a peak in G″ has been observed in several soft materials, including bacterial biofilms, it has eluded interpretation in terms of quantifiable microstructural features. The central finding of this work is that the intensity of the G″ peak, signifying resistance to large deformations, correlates directly with the protein and polysaccharide concentrations per unit biomass in the extracellular matrix and inversely with the shear-induced changes in filament orientation in the hyphal network. These correlations have implications for the rational design of fungal biofilms with tuneable mechanical properties.
将细菌生物膜描绘为由细胞外交联聚合物基质保护的刚性细菌细胞组成的胶体凝胶，这一观点对于理解它们调整微观结构和粘弹性以应对环境冲击的能力至关重要。这项工作探讨了在具有长丝状细胞的真菌生物膜中是否存在类似的观点。为此，我们考虑了在气液界面形成的真菌生物膜，它已显示出有效去除废水中过量氮和磷的能力。我们分别使用大振幅振荡剪切流变学（LAOS）和场发射扫描电子显微镜（FESEM），研究了这些生物膜在摄取不同浓度的氮和磷时其粘弹性和微观结构的变化。在30% - 50%的剪切应变下观察到损耗模量（G″）有一个独特的峰值，表明从弹性变形状态向塑性变形状态的转变。尽管在包括细菌生物膜在内的几种软材料中都观察到了G″的峰值，但从可量化的微观结构特征角度尚未得到解释。这项工作的核心发现是，G″峰值的强度表示对大变形的抵抗力，它与细胞外基质中每单位生物量的蛋白质和多糖浓度直接相关，而与菌丝网络中剪切诱导的细丝取向变化成反比。这些相关性对具有可调机械性能的真菌生物膜的合理设计具有启示意义。
