Microbial interactions with nanoscale features

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)

Divya Shankar Iyer (Creator)

Institution

The University of North Carolina at Greensboro (UNCG )

Web Site: http://library.uncg.edu/

Advisor

Dennis LaJeunesse

Abstract: Bacteria and other microbes interact with their environment through nanoscale mechanical and chemical processes. Understanding these interactions is critical for controlling bacteria, both in preventing biofilm formation and in using these interactions to control bacterial metabolism and behavior in industrially relevant applications such as fermentation and biomaterial generation. Biofilm formation is a key step in the process of biofouling, a process of great importance in shipping and food processing industries and especially in healthcare where it is of utmost importance to prevent the formation of biofilms on medical equipment which would further prevent infections. In this dissertation, I examine the biological responses of the Gram-negative bacterium, Escherichia coli (E. coli) to alterations in the surface nanostructure, persistent photoconductivity, and the stiffness of the surface material. In my characterization of Bacterial interactions with nanostructured surfaces, I examined the behavior of E. coli bacteria, when exposed to twenty-one different nanostructured polymeric substrates etched from seven common and industrially relevant polymers. I demonstrated that in the bacteria respond to the surfaces by changing their adhesion, morphology and biofilm formation. Interestingly neither surface energy nor structure appeared to control these behaviors. The predominant effect on bacterial behavior appeared to be directed by the composition of the surface. To investigate the mechanisms that control the bacterial response to a surface phenomenon known as persistent photoconductivity (PPC), I used E. coli strains that were mutant for genes that encoded specific components of adhesion and/or biofilm formation. One goal of microbial bioelectronics is to develop hybrid organic/inorganic interfaces between living cells and electronic devices. Type III semiconductors such as GaN are a good candidate for such interfaces; Gallium nitride and Oxide materials are biocompatible, a growing material system for electronics, and have a property known as persistent photoconductivity (PPC), which is the persistence of a charge after excitation energy such as ultraviolet light is removed. Work in the Ivanisevic and LaJeunesse labs have shown that PPC changes the physiology of the bacterial cells and results in both an increase in intracellular Ca2+ and alteration to cell adhesion. To determine which cell surface and adhesive components of E. coli are required for the response to PCC, I used a collection of E. coli deletion mutants and examined the loss of these cell structures on the bacteria’s response to PCC. I found that mutation in the synthetic pathways that generate the LPS, curli, and mutations in flagella significantly alter the response of E. coli to PPC. To determine the bacterial adhesive response to material stiffness, I tested the adhesion of E. coli to Polyacrylamide hydrogels of three different stiffnesses (~17kPa, 29kPa and 1547 kPa). Wild type E. coli demonstrated the highest adhesion to the soft PA hydrogel and the least on the hard gel. I used single-gene deletion mutants of E. coli bacterial surface appendages to determine how the loss of these cellular structures would affect bacterial adhesion to these gels. I compared the adhesion trends of the various knockouts to the WT trend and found that they were vastly different, and with no particular pattern. Adhesion of bacteria to the soft gels was significantly lower than the adhesion of the WT except for the csgD mutant. All the knockout bacteria adhered more to the hard gels in comparison to the WT adhesion. Identifying the most important deletion remains a challenge, even though all the deletions resulted in a change in bacterial adhesion. This analysis has provided a framework for the further elucidation of genetic pathways involved in the bacterial responses. [This abstract has been edited to remove characters that will not display in this system. Please see the PDF for the full abstract.]

Microbial interactions with nanoscale features
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Created on 12/1/2019
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Additional Information

Publication

Dissertation

Language: English

Date: 2019

Keywords

Microbe, Nano, Nanotopography, Photoconductivity, Stiffness, Substrate

Subjects

Escherichia coli $x Biotechnology

Microbial biotechnology

Nanostructured materials

Photoconductivity

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