Bacterial Secretion and the Role of Diffusive and Subdiffusive First Passage Processes

Frank Marten,Krasimira Tsaneva-Atanasova,Luca Giuggioli,Matjaž Perc

doi:10.1371/journal.pone.0041421

Abstract

By funneling protein effectors through needle complexes located on the cellular membrane, bacteria are able to infect host cells during type III secretion events. The spatio-temporal mechanisms through which these events occur are however not fully understood, due in part to the inherent challenges in tracking single molecules moving within an intracellular medium. As a result, theoretical predictions of secretion times are still lacking. Here we provide a model that quantifies, depending on the transport characteristics within bacterial cytoplasm, the amount of time for a protein effector to reach either of the available needle complexes. Using parameters from Shigella flexneri we are able to test the role that translocators might have to activate the needle complexes and offer semi-quantitative explanations of recent experimental observations.

Highlights

The structural and rheological properties of an intracellular medium define the transport characteristics of a variety of molecules, many of which need to be transported within the cell to fulfil their tasks [1,2]
Based on a first-passage framework, here we focus on modelling secretory activities in bacteria and we provide in particular a quantitative analysis of type III secretion [11], a mechanism through which a bacterium invades potential host cells by delivering protein effectors across their membrane
Our analysis indicates that such depletion time scales are possible in either of three plausible scenarios: (1) the values of the effector diffusion coefficient are much smaller than expected [17]; (2) the effector are hampered by obstacles in the cytoplasm [18], making their movement statistics dominated by long waiting times; (3) the measured depletion time scales are the result of progressive needle activation by translocator proteins [13]

Summary

Introduction

The structural and rheological properties of an intracellular medium define the transport characteristics of a variety of molecules, many of which need to be transported within the cell to fulfil their tasks [1,2]. A crucial element in carrying out these tasks is their timing and the spatio-temporal processes that control such timing The importance of this temporal regulation cuts across a broad spectrum of cell biology; from vesicle neurotransmitters containing ribbon synapses in nerve cells [3,4,5] to neurite growth [6] and secretory activities in bacteria Our analysis indicates that such depletion time scales are possible in either of three plausible scenarios: (1) the values of the effector diffusion coefficient are much smaller than expected [17]; (2) the effector are hampered by obstacles in the cytoplasm [18], making their movement statistics dominated by long waiting times; (3) the measured depletion time scales are the result of progressive needle activation by translocator proteins [13]

Methods

Results

Conclusion