Bacterial Physiology: Pseudomonas aeruginosa

Pseudomonas aeruginosa is a significant human pathogen. Pathogenicity of P. aeruginosa resides in its high versatility and the intrinsically high antibiotic resistance. Only a handful of antibiotics are effective against P. aeruginosa, and the emergence of drug resistant strains renders this bacterium virtually immune to existing antibiotics. The Center investigates cell biology of P. aeruginosa seeking to understand mechanisms that underlie its pathogenicity and looking for novel ways to control it. The Center focuses on three aspects of P. aeruginosa physiology.

Chromosome structure and segregation

Chromosome plays a central role in the life of all living cells. In P. aeruginosa, correct folding of the chromosome is essential for the robust response to diverse environmental challenges. Rybenkov group studies organization and segregation of P. aeruginosa chromosome with an emphasis on condensins.

Condensins play a unique role in chromosome folding. These multisubunit cellular ATPases act as macromolecular clamps that bridge distant DNA segments and have an intrinsic ability to self-organize into the chromosome scaffold. Condensins are also involved in other aspects of cell physiology. In P. aeruginosa, they mediate the global layout and segregation of the chromosome, control gene expression and are integrated into adaptive behavior of the bacterium.

Petrushenko, Z.M., W. She, and V.V. Rybenkov, A new family of bacterial condensins. Mol Microbiol, 2011. 81(4): p. 881-96. DOI: 10.1111/j.1365-2958.2011.07763.x
Rybenkov, V.V., Maintenance of chromosome structure in Pseudomonas aeruginosa. FEMS Microbiol Lett, 2014. 356(2): p. 154-65. DOI:  10.1111/j.1365-2958.2011.07763.x

Multidrug efflux

Active efflux transporters are ubiquitous in all living organisms and have diverse physiological functions. They define intracellular steady-state concentrations of metabolites, toxins and signaling molecules. In bacteria, active efflux also plays a critical role in establishment and progression of infections and development of antibiotic resistance. Several groups in the Center are involved in studies of functions, assemblies and mechanisms of multidrug efflux pumps using both experimental (mechanistic studies) and computational (drug recognition and transport, macromolecular assemblies) approaches.

Multidrug efflux pumps come from several superfamilies of transporters and vary by structures and mechanisms. Some of them transport substrates across the inner membrane, others act across the outer membrane and a few span both membranes and export various molecules from the cytoplasm directly into the external medium. Transporters belonging to Resistance-Nodulation-Division (RND) superfamily of proteins are of particular interest as these pumps are major contributors to pathogenicity and antibiotic resistance of P. aeruginosa and other Gram-negative pathogens.

Lopez, C.A., T. Travers, K.M. Pos, Z. H.I., and S. Gnanakaran, Dynamics of Intact MexAB-OprM Efflux Pump: Focusing on the MexA-OprM Interface. Sci Rep, 2017. 7(1): p. 16251 DOI: 10.1038/s41598-017-16497-w
Ramaswamy, V.K., A.V. Vargiu, G. Malloci, J. Dreier, and P. Ruggerone, Molecular Rationale behind the Differential Substrate Specificity of Bacterial RND Multi-Drug Transporters. Sci Rep, 2017. 7(1): p. 8075 DOI: 10.1038/s41598-017-08747-8
Zgurskaya, H.I., J.W. Weeks, A.T. Ntreh, L.M. Nickels, and D. Wolloscheck, Mechanism of coupling drug transport reactions located in two different membranes. Front Microbiol, 2015. 6: p. 100 DOI: 10.3389/fmicb.2015.00100

Adaptation and differentiation

During adaptation to hostile environment or colonization of a human host, P. aeruginosa cells undergo clonal diversification and produce colonies with distinct morphologies, such as small colony variants and biofilms. These morphologies are intricately linked to chromosome structure. The two P. aeruginosa condensins, SMC-ScpAB and MksBEF, are integrated into both the global chromosome dynamics and the regulatory switch between planktonic and sessile growth. Rybenkov  group investigates the mechanism of this link.

Zhao, H., et al., Pseudomonas aeruginosa Condensins Support Opposite Differentiation States. J Bacteriol, 2016. 198(21): p. 2936-2944. DOI: 10.1128/JB.00448-16

Both adaptation and differentiation of P. aeruginosa are under the control of quorum sensing signals. These signals often have dual roles, functioning as toxins to some cells and as oxidative-stress protectors for their producer cells. Hence, their internal and external concentrations should be tightly controlled. Zgurskaya lab analyzes the role of the multidrug efflux transporters in quorum sensing and adaptation of P. aeruginosa.