Functional analysis of Burkholderia Pseudomallei Sigma N2 and Sigma S in modulating multinucleated giant cell formation in macrophage cell line

Abstract

A human severe infectious disease with high mortality rate in many Tropical countries, melioidosis, is caused by a highly versatile pathogen Burkholderia pseudomallei. The function of the B. pseudomallei sigma S (RpoS) transcription factor in survival during stationary growth phase and conditions of oxidative stress is well documented. Beside rpoS, bioinformatics analysis of B. pseudomallei genome showed the existence of two rpoN genes, rpoN1 and rpoN2. To access the function of RpoN , both rpoN1 and rpoN2 were inactivated, unfortunately only the rpoN2 mutant (rpoN2) strain was successfully constructed and characterized. It may be due to the potential important role of rpoN1 in bacteria survival. In this study, by using the mouse macrophage cell line RAW264.7 as a model of infection, the involvement of B. pseudomallei RpoS and RpoN2 in invasion, intracellular survival leading to the reduction in Multinucleated Giant Cell (MNGC) formation of RAW264.7 cell line was illustrated. The researcher also demonstrated that MNGC formation in RAW264.7 cell line depended on a certain number of intracellular bacteria (at least 104) and that both RpoS and RpoN2 are not directly involved in MNGC formation judging by the same 15% MNGC formation observed in RAW264.7 cells infected with either B. pseudomallei wild type MOI 2 or RpoN2 mutant (?rpoN2) MOI 10 or RpoS mutant (?rpoS) MOI 100. Moreover, the role of B. pseudomallei RpoS and RpoN2 in regulation of Type Three Secretion System bipB-bipC gene expression was hypothesized for the first time.