Comparative label-free lipidomic analysis of Mycobacterium tuberculosis during dormancy and reactivation.
ABSTRACT: Mycobacterium tuberculosis employs several strategies to combat and adapt to a variety of adverse conditions encountered inside the host. The non-replicative dormant state of the bacterium is linked to drug resistance and slower response to anti-tubercular therapy. It is known that alterations in lipid content allow dormant bacteria to acclimatize to cellular stress. Employing comparative lipidomic analysis, we profiled the changes in lipid metabolism in a modified Wayne’s model of hypoxia-induced dormancy. Further we subjected the dormant bacteria to resuscitation and analyzed the lipidomes of re-aerated bacteria till the lipid profiles were similar to that of normoxially grown bacteria. An enhanced degradation of cell wall associated and cytoplasmic lipids during dormancy and their gradual restoration during reactivation were clearly evident. This study throws light on distinct lipid metabolic patterns that MTB undergoes to maintain its cellular energetics during dormancy and reactivation.
Project description:Lipid remodeling is crucial for hypoxic tolerance in animals, whilst little is known about the hypoxia-induced lipid dynamics in plant cells. Here we performed a mass spectrometry-based analysis to survey the lipid profiles of Arabidopsis rosettes under various hypoxic conditions. We observed that hypoxia caused a significant increase in total amounts of phosphatidylserine, phosphatidic acid and oxylipins, but a decrease in phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Particularly, significant gains in the polyunsaturated species of PC, PE and phosphatidylinositol, and losses in their saturated and mono-unsaturated species were evident during hypoxia. Moreover, hypoxia led to a remarkable elevation of ceramides and hydroxyceramides. Depletion of ceramide synthases LOH1, LOH2, and LOH3 enhanced plant sensitivity to dark submergence (DS), but displayed more resistance to submergence under light than wild type. Consistently, levels of unsaturated ceramide species (22:1, 24:1, and 26:1) predominantly declined in the loh1, loh2, and loh3 mutants under DS. Evidence that C24:1-ceramide interacted with recombinant CTR1 protein in vitro, enhanced ER-to-nucleus translocation of EIN2-GFP and stabilization of EIN3-GFP in vivo, suggests a role of ceramides in modulating ethylene signaling. The DS-sensitive phenotypes of loh mutants were rescued by a ctr1-1 mutation. Thus, our findings demonstrate that unsaturation of very-long-chain ceramides is a protective strategy for hypoxic tolerance in Arabidopsis. Arabidopsis Affymetrix GeneChip arrays were probed with RNAs isolated from leaves of untreated plants (controls) and plants upon hypoxia under light submergence for 48 h.
Project description:DNA binding profiling of endogenous HIF1A on proximal promoters in human HeLa cells exposed to 1% oxygen (hypoxia), using normoxic cells (21% oxygen) as reference.<br><br>Biological background: The Hypoxia Inducible Factor Family of transcription factors is proposed as the main orchestrator of the cellular response to hypoxia. HIFs are heterodimers of a HIF alpha and a HIF beta subunit. HIF alpha protein stability is regulated by oxygen-dependent proteasomal degradation, and hence HIFs are strongly stabilized in hypoxia.<br><br>Purpose of the study: a number of HIF1 ChIP-chip studies have been reported, employing various cell types, array platforms and HIF antibodies, and the overlap of HIF binding locations in these studies is relatively small. The aim of this study was to characterize HIF1 binding in an additional cell line (HeLa), and employing a different HIFalpha antibody.<br><br>Experimental design: We conducted a total of six hybridizations employing four biological replicates. For two biological replicates, we performed dye-swap technical replicate experiments.<br><br>Results summary: We identified 55 HIF binding locations in HeLa cells (FDR<2%). While this number is relatively low compared to previous studies, presumably due to limiting antibody sensitivity, the overlap with data from other cell lines is comparable to our HeLa data.
Project description:Some intracellular bacteria are known to cause long-term infections for periods of time that last decades without compromising the viability of the host. Although of critical importance, the changes that intracellular bacteria suffer during this long process of residence in a host cell environment remain obscure. Here, we report an experimental approach to study the adaptations of intracellular mycobacteria forced by a long-term intracellular lifestyle. Long-term infection of host macrophages with mycobacteria was maintained for a period of years. Mycobacteria in the long-term infected macrophages underwent an adaptation process leading to impaired phenolic glycolipids (PGL) synthesis, preference for glucose as a carbon source and neutral lipids accumulation. These changes correlated with increased survival of mycobacteria in macrophages and mice during re-infection and specific expression of stress- and survival-related genes. Our findings identify bacterial traits implicated in the establishment of long-term cellular infections and represent a tool for understanding the physiological states of bacteria living in fluctuating intracellular environments. Overall design: We investigated the genes differentially expressed during re-infection that might contribute to the improved survival. Using a microarray, we identified a clear and distinct pattern of gene expression after re-infection comparing ancestral (BCGanc) and selected bacteria (BCGevo)
Project description:The capacity of Mycobacterium tuberculosis (Mtb) to sense, respond and adapt to variable and hostile environment within the host, has made it one of the most successful human pathogens. During different stages of infection, the bacillus is surrounding by a plethora of lipid rich molecules and current evidence points out the relevance of fatty acids during the Mtb infectious process. In this study, we have compared the transcriptional response of Mtb to hypoxia in cultures grown in both, a mix of even long-chain fatty acids and dextrose as carbon sources. Using RNA sequencing, we have identified the differential expressed genes in early and late hypoxia defined according to the in vitro Wayne model and compared the results with the exponential phase of growth in both carbon sources. Our results showed that, different to dextrose, the number of genes overexpressed in hypoxia in the lipid medium was quite low in both, early and late hypoxia in all functional categories describes for Mtb. The exception were the transcripts of stable and non-coding RNAs which were more expressed in the fatty acid medium. We found that SigB and SigE were overexpressed in the early phase of hypoxia, confirming their pivotal role in early adaptation to low oxygen concentration independently of the carbon source. A drastic contrast was found with the transcriptional regulatory factors at early hypoxia. Only 2 transcriptional factors were overexpressed in early hypoxia in the lipid medium compared to 37 that were overexpressed in the dextrose medium. Instead of Rv0081, known to be the central regulator of hypoxia in dextrose, Rv2745c, (ClgR), is playing a main role in hypoxia in the fatty acids medium. The low level of genes associated to stress-response, showed by Mtb during their adaptation to hypoxia in fatty acids, suggested that this lipid environment makes hypoxia a less stressful condition for the tubercle bacilli. Therefore, when the bacillus is surviving in that environment, its metabolism seemed to be already adapted to different stresses within the host, including hypoxia. This fact could explain the success of Mtb to establish long-term survival during latent infection. Overall design: Examination of transcription profiles of M. tuberculosis H37Rv under hypoxic conditions
Project description:One of the key functions of the mammalian liver is lipid metabolism. During fasting, lipid storage in the liver increases in order to reserve and provide energy for cellular functions. Upon re-feeding, this reserve of lipids is rapidly depleted; this change is visible, as the organelles responsible for lipid storage – lipid droplets (LDs) – drastically decrease in size following re-feeding. Little is known regarding LD proteome, or how it changes during the fasting/re-feeding transition. Our study investigated the hepatic LD proteome and how it changes between fasting and re-feeding conditions. For this purpose, LDs were isolated from 4 month-old C57BL/6 mice after a 24 hour fasting period, or a 24 hour fasting period followed by 6 hours of re-feeding. Proteins isolated from these LDs were subject to SDS-PAGE followed by in-gel trypsinization and LC-MS/MS. We identified a combined total of 941 proteins on hepatic LDs, of which 817 had quantifiable extracted ion chromatograms in at least 2 samples (n=6 total) and were not deemed contaminants. 777 of the 817 proteins were observed in both energetic states, with 33 being uniquely observed in fasted LDs, and 7 being uniquely observed in re-fed LDs.
Project description:Tuberculosis, caused by Mycobacterium tuberculosis, still remains a major global health problem. The main obstacle in eradicating this disease is the ability of this pathogen to remain dormant in macrophages, and to get reactivated later under immuno-compromised conditions. The physiology of hypoxic nonreplicating M. tuberculosis is well studied using many in vitro dormancy models. However, the physiological changes that take place during the shift from dormancy to aerobic growth (reactivation) have rarely been subjected to a detailed investigation. In this study, we developed an in vitro reactivation system by re-aerating bacteria that were made dormant employing Wayne’s dormancy model, and compared the proteome profiles of dormant and reactivated bacteria using label-free one-dimensional LC/MS/MS analysis.
Project description:Bacillus amyloliquefaciens FZB42 is a representative organism for Gram positive soil bacteria associated with plant roots and beneficial to plant growth. It is of immense importance to understand mechanisms of this class of bacteria adapting to rhizosphere. In this work employing differential RNA sequencing (RNA-seq) and Northern blot, we systematically identified transcription start sites of mRNAs as well as non-coding regulatory RNAs in FZB42. The genes regulated at different growth phases and located in polycistronic operons were also identified. A set of genes were re-annotated. In addition, a sRNA named Bas01 was identified to be involved in Bacillus sporulation and biofilm formation. The result we obtained provides valuable data for investigation of Bacillus gene expression and molecular details of rhizobacterial interaction with host plants. Examination of transcriptome profile of rhizobacterium B. amyloliquefaciens FZB42 grown under six conditions.
Project description:The absence of oxygen (O2) is a stress condition for aerobic organisms and requires extensive acclimation responses. Previously, Chlamydomonas reinhardtii has been used as a reference organism for understanding these acclimation responses. In this work, we use RNA-Seq for a whole genome view of the acclimation of the organism to dark-anoxic conditions. To distinguish the responses dependent on the COPPER RESPONSE REGULATOR 1 (CRR1), which is also involved in hypoxic gene regulation, we compared the transcriptome of crr1 mutants to that of complemented strains. Nearly 10% of the genome (~ 1,400 genes) are affected by hypoxia based on pairwise comparisons of all strains and two time-points. Comparing transcript profiles from early (hypoxic) with those from late (anoxic) time-points indicated that the cells activated oxidative energy generation pathways before employing fermentative enzymes. Probable substrates included not only carbohydrates but also amino acids and fatty acids (FAs). Lipid profiling of the C. reinhardtii cells revealed that they degraded FAs but also accumulated triacylglycerols (TAGs). In contrast to N-deprived cells, the TAGs accumulating in hypoxic cells are enriched in desaturated FAs, which distinguishes the contribution of individual pathways for Chlamydomonas TAG accumulation. In crr1 mutants, about 140 genes were aberrantly regulated , re-affirming the importance of CRR1 for the hypoxic response, but indicating also the contribution of additional O2-sensors and signaling strategies to account for the remaining differentially regulated transcripts. We conclude that nitric oxide (NO) dependent signaling cascades, employing both known and novel components, are operative in C. reinhardtii. The transcriptome of four different Chlamydomonas strains (wild type CC-124, crr1 mutant, crr1:CRR1 rescued strain and crr1dCys rescued strain) are profiled by RNA-Seq in the dark at different times after the transition from light-oxic to dark-anoxic conditions