PtsN regulates the type III secretion system in Pseudomonas aeruginosa

Pseudomonas aeruginosa (PA) is an opportunistic pathogen that is responsible for causing a variety of infections and poses a threat to immunocompromised individuals. One of the key mechanisms contributing to the virulence and pathogenicity of PA is the type 3 secretion system (T3SS), which contributes to the establishment and maintenance of the infection. The T3SS is a complex molecular apparatus that functions like a hypodermic needle. This system allows for PA to inject effector proteins directly into the cytoplasm of a host cell, leading to a negative impact in immune response and an enhanced opportunity of survival for the bacterial pathogen. A transcriptomic analysis had revealed that the protein PtsN, the terminal component of the nitrogen-related phosphotransferase system (Nitro-PTS) in PA, plays a regulatory role in T3SS gene expression. In particular, ΔptsN mutants, there was evidence for significant upregulation in the T3SS gene expression. T3SS expression is generally regulated through a well-established network that allows for environmental cues to trigger a partner switching mechanism within the system. This process leads to the release of ExsA, the master activator of T3SS, from an anti-activator which allows for expression to be initiated. To determine the extent of its involvement in T3SS gene expression, we deleted ptsN in strains with either constitutively active or inactive T3SS expression. We discovered that the absence of ptsN did not restore activity in strains containing the constitutively inactive systems, but did find that the ptsN deletion further enhanced the T3SS gene expression in constitutively active systems. We hypothesize that PtsN may interact with ExsA that reduces its ability to activate T3SS genes. We are currently testing the direct interaction between PtsN and ExsA by using co-immunoprecipitation.