Professional Education


  • Doctor of Philosophy, Washington University (2014)
  • Bachelor of Arts, Simpson College (2008)

Stanford Advisors


All Publications


  • Species-Independent Attraction to Biofilms through Electrical Signaling. Cell Humphries, J., Xiong, L., Liu, J., Prindle, A., Yuan, F., Arjes, H. A., Tsimring, L., Süel, G. M. 2017; 168 (1-2): 200-209 e12

    Abstract

    Bacteria residing within biofilm communities can coordinate their behavior through cell-to-cell signaling. However, it remains unclear if these signals can also influence the behavior of distant cells that are not part of the community. Using a microfluidic approach, we find that potassium ion channel-mediated electrical signaling generated by a Bacillus subtilis biofilm can attract distant cells. Integration of experiments and mathematical modeling indicates that extracellular potassium emitted from the biofilm alters the membrane potential of distant cells, thereby directing their motility. This electrically mediated attraction appears to be a generic mechanism that enables cross-species interactions, as Pseudomonas aeruginosa cells also become attracted to the electrical signal released by the B. subtilis biofilm. Cells within a biofilm community can thus not only coordinate their own behavior but also influence the behavior of diverse bacteria at a distance through long-range electrical signaling. PAPERCLIP.

    View details for DOI 10.1016/j.cell.2016.12.014

    View details for PubMedID 28086091

  • Mutations in the bacterial cell division protein FtsZ highlight the role of GTP binding and longitudinal subunit interactions in assembly and function BMC MICROBIOLOGY Arjes, H. A., Lai, B., Emelue, E., Steinbach, A., Levin, P. A. 2015; 15

    Abstract

    Assembly of the tubulin-like GTPase, FtsZ, at the future division site initiates the process of bacterial cytokinesis. The FtsZ ring serves as a platform for assembly of the division machinery and constricts at the leading edge of the invaginating septum during cytokinesis. In vitro, FtsZ assembles in a GTP-dependent manner, forming straight filaments that curve upon GTP hydrolysis. FtsZ binds but cannot hydrolyze GTP as a monomer. Instead, the active site for GTP hydrolysis is formed at the monomer-monomer interface upon dimerization. While the dynamics of GTP hydrolysis and assembly have been extensively studied in vitro, significantly less is known about the role of GTP binding and hydrolysis in vivo. ftsZ84, a GTPase defective allele of Escherichia coli ftsZ, provides a striking example of the disconnect between in vivo and in vitro FtsZ assembly.Although ftsZ84 mutants are defective for FtsZ ring formation and division under nonpermissive conditions, they are near wild type for ring formation and division under permissive conditions. In vitro, however, purified FtsZ84 is defective in GTP binding, hydrolysis and assembly under standard reaction conditions. To clarify the nature of the FtsZ84 assembly defect, we isolated and characterized three intragenic suppressors of ftsZ84. All three suppressor mutations increased the apparent affinity of FtsZ84 for GTP, consistent with improved subunit-subunit interactions along the longitudinal interface. Although kinetic analysis indicates that the suppressor mutations increase the affinity of FtsZ84 for GTP, all three exhibit reduced rates of GTP hydrolysis and fail to support assembly in vitro.Together, our data suggest that FtsZ, and potentially other enzymes whose assembly is similarly regulated, can compensate for defects in catalysis through increases in substrate binding and subunit-subunit interactions. In addition, these results highlight the dichotomy between commonly used in vitro assembly conditions and FtsZ ring formation in the complex intracellular milieu.

    View details for DOI 10.1186/s12866-015-0544-z

    View details for Web of Science ID 000362707300001

    View details for PubMedID 26463348

  • Failsafe Mechanisms Couple Division and DNA Replication in Bacteria CURRENT BIOLOGY Arjes, H. A., Kriel, A., Sorto, N. A., Shaw, J. T., Wang, J. D., Levin, P. A. 2014; 24 (18): 2149-2155

    Abstract

    The past 20 years have seen tremendous advances in our understanding of the mechanisms underlying bacterial cytokinesis, particularly the composition of the division machinery and the factors controlling its assembly [1]. At the same time, we understand very little about the relationship between cell division and other cell-cycle events in bacteria. Here we report that inhibiting division in Bacillus subtilis and Staphylococcus aureus quickly leads to an arrest in the initiation of new rounds of DNA replication, followed by a complete arrest in cell growth. Arrested cells are metabolically active but are unable to initiate new rounds of either DNA replication or division when shifted to permissive conditions. Inhibiting DNA replication results in entry into a similar quiescent state in which cells are unable to resume growth or division when returned to permissive conditions. Our data suggest the presence of two failsafe mechanisms: one linking division to the initiation of DNA replication and another linking the initiation of DNA replication to division. These findings contradict the prevailing view of the bacterial cell cycle as a series of coordinated but uncoupled events. Importantly, the terminal nature of the cell-cycle arrest validates the bacterial cell-cycle machinery as an effective target for antimicrobial development.

    View details for DOI 10.1016/j.cub.2014.07.055

    View details for Web of Science ID 000342396900034

    View details for PubMedID 25176632