Biology subjects

Mao, X.

Publications and source records attributed to Mao, X..

5 recordsLinked to original sources

bioRxiv2018

Impact of acetolactate synthase inactivation on 1,3-propanediol fermentation by Klebsiella pneumoniae

1,3-Propanediol (1,3-PDO) is an important compound that is mainly used in industry for polymer production. Fermentation of 1,3-PDO from glycerol by marine Klebsiella pneumoniae is accompanied by formation of 2,3-butanediol (2,3-BDO) as one of the main byproduct. The first step in the formation of 2,3-BDO from pyruvate is catalyzed by acetolactate synthase (ALS), an enzyme that competes with 1,3-PDO oxidoreductase for the cofactor NADH. This study aimed to analyze the impact of engineering the 2,3-BDO formation pathway via inactivation of ALS on 1,3-PDO fermentation by marine K. pneumoniae HSL4. An ALS mutant was generated using Red recombinase assisted gene replacement. The ALS specific activities of K. pneumoniae {Delta}ALS were notably lower than that of the wild-type strain. Fed-batch fermentation of the mutant strain resulted in a 1,3-PDO concentration, productivity and conversion of 72.04 g L-1, 2.25 g L-1 h-1, and 0.41 g g-1, a slightly increase compared with the parent strain. Moreover, inactivation of ALS decreased meso-2,3-BDO formation to trace amounts, significantly increased 2S,3S-BDO and lactate production, and a pronounced redistribution of intracellular metabolic flux was apparent.

microbiology↗

bioRxiv2018

Infectious bronchitis virus attaches to lipid rafts and enters cells via clathrin mediated endocytosis

Due to its economic importance to in poultry industry, the biology and pathogenesis of infectious bronchitis virus (IBV) have been investigated extensively. However, the molecular mechanisms involved in IBV entry are not well characterized. In this study, systematic approaches were used to dissect IBV entry process in various susceptible cells. First, we observed that lipid rafts were involved in IBV attachment. Second, low pH in intracyplasmic vesicles was required for virus entry. By using the specific clathrin mediated endocytosis (CME) inhibitor or knock down of clathrin heavy chain (CHC), we demonstrated that IBV mainly utilized the CME for its entry. Furthermore, GTPase dynamin1 was involved in virus containing vesicle scission and internalization. Surprisingly, CME adaptor Eps15 had no effect on IBV internalization. Third, the penetration of IBV into cells led to active cytoskeleton rearrangement. After internalization, virus particles moved along with the classical endosome/lysosome track, as evidenced by co-localization of R18 labeled IBV with vehicle markers Rab5/Rab7/LAMP1 along with the infection time course. Functional inactivation of Rab5 and Rab7 significantly inhibited IBV infection. VCP, a protein helps early endosome maturation, was involved virus trafficking. Finally, by using the dual R18/DiOC labeled IBV, we observed that membrane fusion with late endosome/lysosome membranes was induced between 2-3 h.p.i.. Taken together, our findings demonstrate that IBV virions attach to lipid rafts and are internalized into cells via CME, move along with early/late endosomes-lysosomes, finally fuse with late endosome-lysosome membranes, release virus genome into cytoplasm. This study provides comprehensive images of IBV attachment-internalization-trafficking-fusion steps.\n\nIMPORTANCEIBV, the avian coronavirus isolated in 1937, infects chicken and causes economic loss in poultry industry. It has been reported that the entry of IBV requires low pH. However, the molecular mechanisms underlying IBV internalization and trafficking remain to be clarified. Therefore, we employed multiple chemical and molecular approaches to dissect the entry mechanisms of IBV in susceptible cells. Our results showed IBV entry was significantly inhibited when clathrin-mediated endocytosis (CME) was blocked by chemical inhibitor or depletion of clathrin protein. Moreover, by using R18-labeled IBV, we found that IBV particles attached to lipid rafts, led to actin rearrangement, and moved along with the entire endosomal system. R18/DiOC labeling method showed that IBV fused with late endosomes or lysosomes. This is the first report to describe the entire entry process of IBV, allowing for a better understanding of the infection process of group III avian coronavirus.

microbiology↗

bioRxiv2018

β-lactam Antibiotics Stimulate the Pathogenicity of Methicillin-resistant Staphylococcus aureus Via SarA-controlled Tandem Lipoprotein Expression

Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of nosocomial infections worldwide. MRSA resists nearly all {beta}-lactam antibiotics that have a bactericidal activity and a signal inducer effect. However, studies have yet to clarify whether the inducer effect of empirically used {beta}-lactams stimulates MRSA pathogenicity in vivo. Here, we showed that a new cluster of tandem lipoprotein genes (tlpps) was upregulated in MRSA in response to the subinhibitory concentrations of {beta}-lactam induction. The increased Tlpps significantly altered immune responses by macrophages with high IL-6 and TNF levels. The deletion of the tlpps mutant (N315{Delta}tlpps) significantly decreased the proinflammatory cytokine levels in vitro and in vivo. The bacterial loads of N315{Delta}tlpps in the mouse kidney were also reduced compared with those of the wild type N315. The {beta}-lactam-treated MRSA exacerbated cutaneous infections with increased lesion size, extended illness, and flake-like abscess-formation compared with those of the nontreatment. The {beta}-lactam antibiotics that promoted the MRSA pathogenicity were SarA dependent, and the increasing expression of tlpps after {beta}-lactam treatment was directly controlled by the global regulator SarA. Overall, our findings suggested that {beta}-lactams should be used carefully because it might lead to a worse outcome of MRSA infection than inaction in the treatment.\n\nAuthor summary{beta}-lactams are widely used in practice to treat infectious diseases, however, {beta}-lactams worsening the outcome of a certain disease is poorly understood. In this study, we have identified a new cluster of tandem lipoprotein genes (tlpps) that is upregulated in the major clinically prevalent MRSA clones in response to the subinhibitory concentrations of {beta}-lactams induction. The major highlight in this work is that {beta}-lactams induce SarA expression, and then SarA directly binds to the tlpp cluster promoter region and upregulates the tlpp expression in MRSA. Moreover, the {beta}-lactam stimulated Tlpps are important virulence factors that enhance MRSA pathogenicity. The deletion of the tlpps mutant significantly decreases the proinflammatory cytokine levels in vitro and in vivo. The {beta}-lactam induced Tlpps enhance the host inflammatory responses by triggering the expression of IL-6 and TNF, thereby promoting bacterial colonization and abscess formation. These data elucidate that {beta}-lactams can worsen the outcome of MRSA infection through the induction of tlpps that are controlled by the global regulator SarA.

pathology↗

bioRxiv2018

Stiffness Sensing and Cell Motility: Durotaxis and Contact Guidance

Mechanical properties of the substrate plays a vital role in cell motility. Cells are shown to migrate up stiffness gradient (durotaxis) and along aligned fibers in the substrate (contact guidance). Here we present a simple mechanical model for cell migration, by placing a cell on lattice models for biopolymer gels and hydrogels. In our model cells attach to the substrate via focal adhesions (FAs). As the cells contract, forces are generated at the FAs, determining their maturation and detachment. At the same time, the cell also allowed to move and rotate to maintain force and torque balance. Our model, in which the cells only take the information of forces at the FAs, without a prior knowledge of the substrate stiffness or geometry, is able to reproduce both durotaxis and contact guidance.

biophysics↗

bioRxiv2018

Anti-BP180 Autoantibodies Are Present in Stroke and Recognize Human Cutaneous BP180 and BP180-NC16A

BackgroundCurrent evidence has revealed a significant association between bullous pemphigoid (BP) and neurological diseases (ND), including stroke, but the incidence of BP autoantibodies in patients with stroke has not previously been investigated.\n\nObjectiveOur study aims to assess BP antigen-specific antibodies in stroke patients.\n\nMethods100 patients with stroke and 100 healthy controls were randomly selected to measure anti-BP180/230 IgG autoantibodies by enzyme-linked immunosorbent assay (ELISA), salt split indirect immunofluorescence (IIF) and immunoblotting against human cutaneous BP180 and BP180-NC16A.\n\nResultsAnti-BP180 autoantibodies were found in 14(14.0%) patients with stroke and 5(5.0 %) of controls by ELISA (p<0.05). Sera from 13(13.0%) patients with stroke and 3(3.0 %) controls reacted with 180-kDa proteins from human cutis extract (p<0.05). 11(11.0%) of stroke and 2(2.0 %) of control sera recognized the human recombinant full length BP180 and NC16A (p<0.05). The anti-BP180-positive patients were significantly younger than the negative patients in stroke (p<0.001).\n\nLimitationsLongitudinal changes in antibody titers and long-term clinical outcome for a long duration were not fully investigated.\n\nConclusionDevelopment of anti-BP180 autoantibodies occur at a higher frequency after stroke, suggesting BP180 as a shared autoantigen in stroke with BP and providing novel insights into BP pathogenesis in aging.

neuroscience↗