Magnetic Tweezers: Measuring the Stickiness of Marine Extracellular Polymeric Substances
Chi-Shuo Chen
Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu 30013, Taiwan
chen.cs@mx.nthu.edu.tw
Abstract
Organic particle dynamics in the surface ocean plays a critical part in the marine carbon cycle. Aggregation of marine organic particles drives their downward transport to support various marine organisms on their transit to the sediments. Extracellular polymeric substances (EPS) from various microbes are a major contributor to the oceanic organic particle pool. The stickiness of EPS is expected to play a determining role in the aggregation process of particles; however, stickiness parameters are usually indirectly estimated through data fitting without direct assessment. Here a magnetic tweezer method was developed to quantitatively assess the stickiness of three model EPS produced by: Amphora sp., (diatom), Emiliania huxleyi (coccolithophore), and Sagittula stellate (bacteria), under different in vitro environmental conditions (salinity or EDTA complexed cations) and surface matrices (EPS-EPS and bare glass). Our results showed the stickiness of three microbial EPS decreasing for S. stellata>E. huxleyi >Amphora sp., in line with their decreasing protein-to-carbohydrate (P/C) ratios (related to their relative hydrophobicity). The data not only emphasize the importance of hydrophobicity on EPS stickiness, but also demonstrates that salinity and the nature of the substrate surface can influence the stickiness. Furthermore, we investigated stickiness between various types of EPS, and the observed selective stickiness of EPS between species may shed light on the interactions among heterogeneous marine microorganisms. Overall, this newly developed system provides a platform to assess the EPS stickiness to advance our understanding of the aggregation and sedimentation process of organic particles that are critical for the fate of organic carbon as well as for biofilm formation and microbial colonization of surfaces in the ocean.
Short Bio
Chi-Shuo Chen is an Assistant Professor of Department of Biomedical Engineering and Environmental Sciences at National Tsing Hua University. He received his B.S in Atomic Science and the M.S in Molecular Biophotonics from National Tsing Hua University, and Ph.D. in Biological Engineering from University of California, Merced. He was the Postdoctoral Researcher in Dermatology at Feinberg School of Medicine, Northwestern University. His current research focus is to study how mechanical signals propagate between cells from cell-matrix and cell-cell contacts, and the related mechanotransduction responses at cellular level. By integrating with various engineering platforms, such as microfluidic, optical tweezers system, and different microscopy technologies, the works developed in his laboratory aims to further understand the impacts of physical microenvironments on cell physiology.