TY - JOUR
T1 - Coxiella burnetii Type 4B Secretion Systemdependent manipulation of endolysosomal maturation is required for bacterial growth
AU - Samanta, Dhritiman
AU - Clemente, Tatiana M.
AU - Schuler, Baleigh E.
AU - Gilk, Stacey D.
N1 - Publisher Copyright:
© 2019 Samanta et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
PY - 2019
Y1 - 2019
N2 - Upon host cell infection, the obligate intracellular bacterium Coxiella burnetii resides and multiplies within the Coxiella-Containing Vacuole (CCV). The nascent CCV progresses through the endosomal maturation pathway into a phagolysosome, acquiring endosomal and lysosomal markers, as well as acidic pH and active proteases and hydrolases. Approximately 24-48 hours post infection, heterotypic fusion between the CCV and host endosomes/ lysosomes leads to CCV expansion and bacterial replication in the mature CCV. Initial CCV acidification is required to activate C. burnetii metabolism and the Type 4B Secretion System (T4BSS), which secretes effector proteins required for CCV maturation. However, we found that the mature CCV is less acidic (pH∼5.2) than lysosomes (pH∼4.8). Further, inducing CCV acidification to pH∼4.8 causes C. burnetii lysis, suggesting C. burnetii actively regulates pH of the mature CCV. Because heterotypic fusion with host endosomes/ lysosomes may influence CCV pH, we investigated endosomal maturation in cells infected with wildtype (WT) or T4BSS mutant (ΔdotA) C. burnetii. In WT-infected cells, we observed a significant decrease in proteolytically active, LAMP1-positive endolysosomal vesicles, compared to mock or ΔdotA-infected cells. Using a ratiometric assay to measure endosomal pH, we determined that the average pH of terminal endosomes in WT-infected cells was pH∼5.8, compared to pH∼4.75 in mock and ΔdotA-infected cells. While endosomes progressively acidified from the periphery (pH∼5.5) to the perinuclear area (pH∼4.7) in both mock and ΔdotA-infected cells, endosomes did not acidify beyond pH∼5.2 in WT-infected cells. Finally, increasing lysosomal biogenesis by overexpressing the transcription factor EB resulted in smaller, more proteolytically active CCVs and a significant decrease in C. burnetii growth, indicating host lysosomes are detrimental to C. burnetii. Overall, our data suggest that C. burnetii inhibits endosomal maturation to reduce the number of proteolytically active lysosomes available for heterotypic fusion with the CCV, possibly as a mechanism to regulate CCV pH.
AB - Upon host cell infection, the obligate intracellular bacterium Coxiella burnetii resides and multiplies within the Coxiella-Containing Vacuole (CCV). The nascent CCV progresses through the endosomal maturation pathway into a phagolysosome, acquiring endosomal and lysosomal markers, as well as acidic pH and active proteases and hydrolases. Approximately 24-48 hours post infection, heterotypic fusion between the CCV and host endosomes/ lysosomes leads to CCV expansion and bacterial replication in the mature CCV. Initial CCV acidification is required to activate C. burnetii metabolism and the Type 4B Secretion System (T4BSS), which secretes effector proteins required for CCV maturation. However, we found that the mature CCV is less acidic (pH∼5.2) than lysosomes (pH∼4.8). Further, inducing CCV acidification to pH∼4.8 causes C. burnetii lysis, suggesting C. burnetii actively regulates pH of the mature CCV. Because heterotypic fusion with host endosomes/ lysosomes may influence CCV pH, we investigated endosomal maturation in cells infected with wildtype (WT) or T4BSS mutant (ΔdotA) C. burnetii. In WT-infected cells, we observed a significant decrease in proteolytically active, LAMP1-positive endolysosomal vesicles, compared to mock or ΔdotA-infected cells. Using a ratiometric assay to measure endosomal pH, we determined that the average pH of terminal endosomes in WT-infected cells was pH∼5.8, compared to pH∼4.75 in mock and ΔdotA-infected cells. While endosomes progressively acidified from the periphery (pH∼5.5) to the perinuclear area (pH∼4.7) in both mock and ΔdotA-infected cells, endosomes did not acidify beyond pH∼5.2 in WT-infected cells. Finally, increasing lysosomal biogenesis by overexpressing the transcription factor EB resulted in smaller, more proteolytically active CCVs and a significant decrease in C. burnetii growth, indicating host lysosomes are detrimental to C. burnetii. Overall, our data suggest that C. burnetii inhibits endosomal maturation to reduce the number of proteolytically active lysosomes available for heterotypic fusion with the CCV, possibly as a mechanism to regulate CCV pH.
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U2 - 10.1371/journal.ppat.1007855
DO - 10.1371/journal.ppat.1007855
M3 - Article
C2 - 31869379
AN - SCOPUS:85077770298
SN - 1553-7366
VL - 15
JO - PLoS pathogens
JF - PLoS pathogens
IS - 12
M1 - e1007855
ER -