Biology subjects

Hajra, D.

Publications and source records attributed to Hajra, D..

5 recordsLinked to original sources

bioRxiv2024

Evaporation of bacteria-laden surrogate respiratory fluid droplets: On a hydrophilic substrate versus contact-free environment confers differential bacterial infectivity

The transmission of viruses/ bacteria cause infection predominantly via aerosols. The transmission mechanism of respiratory diseases is complex, including direct or indirect contact, large droplet, and airborne routes apart from close contact transmission. With this pretext, we have investigated two modes of droplet evaporation to understand its significance in airborne disease transmission; a droplet in a contact-free environment, which evaporates and forms droplet nuclei, and a droplet on a hydrophilic substrate (fomite). The study examines mass transport, the deposition pattern of bacteria in the precipitates, and their survival and virulence. The osmotic pressure increases with the salt concentration, inactivating the bacteria embedded in the precipitates with accelerated evaporation. Further, the bacterias degree of survival and enhanced pathogenicity are compared for both evaporation modes. The striking differences in pathogenicity are attributed to the evaporation rate, oxygen availability, and reactive oxygen species (ROS) generation.

microbiology↗

bioRxiv2023

SIRT1 and SIRT3 impact host mitochondrial function and host- Salmonella pH balance during infection

Mitochondria are an important organelle regulating energy homeostasis. Mitochondrial health and dynamics are crucial determinants of the outcome of several bacterial infections. SIRT3, a major mitochondrial sirtuin, along with SIRT1 regulates key mitochondrial functions. This led to considerable interest in understanding the role of SIRT1 and SIRT3 in governing mitochondrial functions during Salmonella infection. Here, we show that loss of SIRT1 and SIRT3 function either by shRNA-mediated knockdown or inhibitor treatment led to increased mitochondrial dysfunction with alteration in mitochondrial bioenergetics alongside increased mitochondrial superoxide generation in the Salmonella-infected macrophages. Consistent with dysfunctional mitochondria, mitophagy was induced along with altered mitochondrial fusion-fission dynamics in S. Typhimurium-infected macrophages. Additionally, the mitochondrial bioenergetic alteration promotes acidification of the infected macrophage cytosolic pH. This host cytosolic pH imbalance skewed the intra-phagosomal and intra- bacterial pH in the absence of SIRT1 and SIRT3, resulting in decreased SPI-2 gene expression. Our results suggest a novel role of SIRT1 and SIRT3 in maintaining the intracellular Salmonella niche by modulating the mitochondrial bioenergetics and dynamics in the infected macrophages. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=84 SRC="FIGDIR/small/557159v2_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@486cbaorg.highwire.dtl.DTLVardef@da2fb0org.highwire.dtl.DTLVardef@70cd46org.highwire.dtl.DTLVardef@1b4d0bd_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2023

A host AAA-ATPase exhibits bacteriolytic activity for clearance of microbial infection

An array of host cytosol guarding factors impede bacterial proliferation and preserve cellular sterility. Amongst them, proteasomal degradation of ubiquitinated pathogens has emerged as a critical mechanism for ensuring cytosolic sanctity. We wondered how proteasomes, with their small size and inability to extract membrane-bound proteins, can eradicate pathogens. Here, we unveil a unique strategy, wherein VCP/p97, a host AAA-ATPase, eliminates pathogens by exerting mechanical force that physically unfolds and pulls out ubiquitinated proteins from bacterial membrane. Combining a single-molecule approach along with molecular dynamic simulation and in-vitro reconstitution, we demonstrate that protein extraction by p97 causes extensive membrane lysis and release of cytosolic contents from phylogenetically diverse microbes. Additionally, in an in-vivo mouse sepsis model, this segregase-dependent bactericidal effect of p97 abrogated microbial proliferation in host tissues. Overall, we discovered a distinct innate antimicrobial function of p97, that protects the host against lethal bacterial infections. One Sentence SummaryA host AAA-ATPase exhibits bacteriolytic activity.

microbiology↗

bioRxiv2022

SIRT1 and SIRT3 mediated immuno-metabolic switch govern Salmonella survival within infected macrophages both in vitro and in vivo.

Sirtuins are the major players in host immuno-metabolic regulation. However, the role of sirtuins in the modulation of the immune metabolism pertaining to Salmonellosis is largely unknown. Here, our investigation focussed on the role of two important sirtuins, SIRT1 and SIRT3, shedding light on their impact on intracellular Salmonellas metabolic switch and pathogenesis establishment. Our study indicated the ability of the live Salmonella Typhimurium to differentially regulate the levels of SIRT1 and SIRT3 for maintaining the high glycolytic metabolism and low fatty acid metabolism in Salmonella. Perturbing SIRT1 or SIRT3 through knockdown or inhibition, resulted in a remarkable shift in the host metabolism to low fatty acid oxidation and high glycolysis. This switch led to decreased proliferation of Salmonella in the macrophages. Further, Salmonella-induced higher levels of SIRT1 and SIRT3 led to a skewed polarization state of the macrophages from a pro-inflammatory M1 state toward an immunosuppressive M2 making it more conducive for the intracellular life of Salmonella. Alongside, governing immunological functions by modulating p65 NF-{kappa}B acetylation, SIRT1, and SIRT3 also skew Salmonella-induced host metabolic switch by regulating the acetylation status of HIF-1 and PDHA1. Interestingly, though knock-down of SIRT1/3 attenuated Salmonella proliferation in macrophages, in in vivo mice-model of infection, inhibition or knockdown of SIRT1/3 led to more dissemination and higher organ burden which can be attributed to enhanced ROS and IL-6 production. Our study hence reports for the first time that Salmonella modulates SIRT1/3 levels to maintain its own metabolism for successful pathogenesis.

microbiology↗

bioRxiv2021

The extracellular loops of Salmonella Typhimurium outer membrane protein A (OmpA) maintain the stability of Salmonella containing vacuole (SCV) in murine macrophages and protect the bacteria from autophagy-dependent lysosomal degradation

After entering the host cells, Salmonella Typhimurium (STM) stays inside a modified membrane-bound compartment called Salmonella containing vacuole (SCV). The biogenesis and stability of SCV are crucial for the intracellular proliferation of Salmonella. Our research has provided a novel mechanistic view on the role of a bacterial porin OmpA in maintaining the stability of SCV. We found that the deletion of OmpA forces the bacteria to escape from the SCV during the immediate early stage of infection. In the absence of OmpA, the bacteria failed to retain the LAMP-1 and came into the host cells cytosol. Subsequently, the cytosolic population of STM{Delta} ompA activated the host autophagy machinery after colocalizing with syntaxin 17 and LC3B. The autophagosomes carrying STM{Delta} ompA were targeted to the lysosomes for degradation. Inhibition of autophagy pathway using bafilomycin A1 restored the intracellular proliferation of STM{Delta} ompA. We further showed that the four extracellular loops of OmpA played a crucial role in holding the LAMP-1 pool around the SCV. We have altered the extracellular loop sequences of Salmonella OmpA by site-directed mutagenesis and observed that the bacteria failed to maintain the LAMP-1 pool around the SCV, which finally resulted in their release into the cytosol of the host macrophages. Surprisingly, the cytosolic population of Salmonella having mutations in the extracellular loops of OmpA didnt activate the lysosomal degradation pathway like STM{Delta} ompA, which helped them to survive within the murine macrophages. In summary, our study revealed an OmpA dependent novel strategy utilized by Salmonella to combat host autophagy by promoting the stability of SCV.

microbiology↗