Multiscale Investigations of the Effects of Chemical Stimuli on the Composition, Adhesion and Mechanics of Pseudomonas putida Cells and Biofilm

This work provides detailed information on the effect of soil environmental conditions (ionic strength and carbon starvation) on mechanical properties of a soil model microbe, Pseudomonas putida and its adhesion to quartz sand models as well as its biofilm formation via a multiscale approach. To do that, atomic force microscopy (AFM) was used to quantify forces acting between P. putida surface biopolymers and AFM silicon nitride (Si3N4) cantilevers in a range of ionic strength (0.2 M-0.52 M) which brackets the common environmental conditions. Theoretical and statistical models were combined with the AFM data to decouple the adhesion forces into its governing specific (hydrogen bonding and hydrophobic forces) and nonspecific (electrostatic and van der Waals forces) components. Also, mechanical properties (Young's moduli and spring constants) as well as the thicknesses of P. putida surface biopolymer fringes were estimated by applying a model of contact mechanics to AFM data. Finally, biofilms of P. putida were grown in sand short columns for a course of 80 days under both carbon-supplemented and carbon-deprivation conditions. Extracellular polymeric substances (EPS) extracted from biofilms were assessed for their components at different stages of biofilm formation throughout the experiment and adhesion of starved and fed biofilms to silica slides were quantified using AFM technique.;Our results show that specific forces play important role in adhesion of P. putida to sand and this influence is more pronounced at elevated ionic strengths. Also, bacterial surface is stiffer at higher ionic strengths due to having a more collapsed biopolymer fringes at their periphery. Finally, our results show that P. putida is able to maintain viability for at least 80 days under starvation condition in sand short columns. In the absence of glucose, the bacterial preference switched to production of higher protein to carbohydrate ratio compared to when they were fed by glucose, resulting in higher adhesion to sand particles. In summary, the information presented here improved our fundamental understanding of the factors affecting bacterial adhesions to quartz sand, assessing engineers and scientists in designing successful upscale processes which can be used to solve biogeotechnical problems.