Viscoelasticity variation in a biofilm-mediated Bacillus subtilis suspension induced by adding polyethylene glycol
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Recent experiments show that synthetic polymers can influence the degree of microbial aggregation and the rheological properties of bacterial suspensions, the study of which can help us control biofilm formation. In this article, we add polyethylene glycol (PEG) with various molecular weights and concentrations into two types Bacillus subtilis cell cultures, Luria Broth (LB) and Minimal Salts glutamate glycerol (MSgg), respectively. We first observe cell clusters in cell suspensions with various concentrations of PEG, and measure cluster size in both static and dynamic fluid environments. We find that cells gather together into big clusters and most of the cells are arranged longitudinally; and the large cell clusters are divided into smaller aggregates under fluid shear. We then use a rheometer to measure the viscoelastic properties of various cell cultures, to represent the degree of aggregation of the bacterial suspensions. We find the storage modulus, the loss modulus and the viscosity of bacterial suspensions not only depend on the cell aggregation but also depend on the directionality of cellular motion.
KeywordsBacillus subtilis Cell aggregations PEG The depletion interaction Viscoelasticity
The authors would like to thank Harvard University, United States, for their support. The National Natural Science Foundation of China (11772047)—China, Key international collaborating Project from National Natural Science Foundation of China (11620101001)—China. This work is partially supported by the National Key R&D Program of China under Grant No: 2017YFB1002701.
XW: conception and design, final approval of manuscript. XS: conception and design, collection and assembly of data, manuscript writing. ZW, YK: conception.
Compliance with ethical standards
Conflict of interest
The authors declare no competing financial interest.
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