Biology subjects

Shrivastava, M.

Publications and source records attributed to Shrivastava, M..

4 recordsLinked to original sources

bioRxiv2025

Crosstalk between the Ino80 complex and TOR signaling drives fungal adaptation to hypoxia through chromatin remodeling

In the human host, the opportunistic yeast Candida albicans must adapts to niches that vary markedly in oxygen tension, ranging from the hypoxic gastrointestinal and vaginal tracts to more oxygen-rich niches such as the skin. Thriving across this spectrum requires the capacity to dynamically rewire core metabolic pathways in response to fluctuating oxygen levels. Yet, despite the central role of oxygen in shaping fungal metabolism and fitness, the genetic basis underlying hypoxic adaptation in C. albicans remains incompletely understood. Here, we performed a genetic screen to identify genes required for adaptation to hypoxia (5% O2). This comprehensive approach revealed numerous genes spanning diverse metabolic and stress-related functions that are essential for optimal growth under oxygen-limiting conditions. Notably, this study uncovers a previously unrecognized role for the TOR (Target of Rapamycin) signaling pathway and the chromatin-remodeling complex Ino80 in orchestrating the fungal adaptive response to hypoxia. Integration of ino80 mutant transcriptomic data with Ino80 DNA-binding and nucleosome-occupancy profiles under conditional INO80 depletion revealed that this chromatin remodeler regulates the cellular phosphate demand associated with hypoxic exposure. The similarity between chromatin accessibility changes following TOR1 and INO80 depletion further suggests that Ino80 acts in concert with the TOR pathway to support growth and maintain phosphate homeostasis under low-oxygen conditions. Collectively, these findings provide new insight into how nutrient and oxygen signaling converge on chromatin remodeling, offering a mechanistic framework for understanding the regulatory logic underlying hypoxic adaptation in pathogenic fungi. ImportanceCandida albicans is an opportunistic fungal pathogen that colonizes diverse host niches, many of which are oxygen-limited. Understanding how this organism adapts to hypoxia is critical for elucidating the mechanisms underpinning both commensalism and pathogenicity of this yeast. Here, we reveal that the TOR signaling pathway and the Ino80 chromatin-remodeling complex are key regulators of fungal growth under low-oxygen conditions. Our data show that Ino80 coordinates phosphate homeostasis during hypoxia and functions in concert with TOR to maintain chromatin accessibility and metabolic adaptation. Our results uncover how oxygen and nutrient cues converge on chromatin remodeling, providing a framework for understanding how C. albicans and other human-associated fungi modulate their physiology to thrive and evolve in diverse host environments.

microbiology↗

bioRxiv2024

An envelope stress response governs long-chain fatty acid metabolism via a small RNA to maintain redox homeostasis in Escherichia coli

Long-chain fatty acids (LCFAs) are a tremendous source of energy for several bacteria but are complex to use because they induce redox stress. We previously showed that LCFA degradation impedes oxidative protein folding in the Escherichia coli envelope, an issue that arises due to the insufficiency of ubiquinone, a lipid-soluble electron carrier in the electron transport chain (ETC). To maintain redox homeostasis, E. coli activates the CpxAR two-component system; however, the nature of feedback imparted by this envelope stress response (ESR) remained unknown. Here, we show that contrary to the well-recognized remedial mode of Cpx restoring envelope integrity by upregulating protein quality control factors, in LCFA-grown cells, it uses a preventive measure to maintain homeostasis. Cpx increases ubiquinone availability for oxidative protein folding by suppressing LCFA metabolism and directly increasing ubiquinone levels. Further, rather than using its conventional mode of imparting regulation via CpxR working as a transcriptional regulator, during LCFA metabolism, Cpx mainly uses its non-coding arm to counteract envelope redox stress. The Cpx-regulated small RNA CpxQ represses fad genes involved in LCFA transport and {beta}-oxidation, downregulates components of glyoxylate shunt, gluconeogenesis, and ETC, and increases ubiquinone content. Corroborating with its role in repressing LCFA metabolism and maintaining redox homeostasis, CpxQ overexpression impairs growth of E. coli in LCFAs and CpxQ deletion renders LCFA-grown E. coli hypersensitive to a thiol agent. Our foremost work studying the interconnection between LCFA metabolism, redox stress, and ESR in E. coli provides a rationale for investigating similar networks in other LCFA-utilizing bacteria. Significance StatementLong-chain fatty acids (LCFAs) are energy-rich nutrients for Escherichia coli; however, their utilization hampers disulfide bond (DSB) formation in secreted proteins, an essential process that occurs in the envelope compartment. Here, we show that an envelope stress response manipulates LCFA metabolism in E. coli and uses a small RNA (sRNA) to restore homeostasis. Several bacteria with a huge impact on human health use host-derived LCFAs during infection. Because many virulence factors require DSB formation, the present study offers a basis to examine whether sRNAs play a role in governing envelope redox balance during LCFA metabolism in pathogens. The sRNA-mediated control is likely an ideal strategy both for rapid response to and quick recovery from LCFA-induced stress.

microbiology↗

bioRxiv2023

The Adr1 transcription factor directs regulation of the ergosterol pathway and azole resistance in C. albicans

Transcription factors play key roles in cellular regulation and are critical in the control of drug resistance in the fungal pathogen Candida albicans. We found that activation of the transcription factor C4_02500C_A (Adr1) conferred significant resistance against fluconazole. In Saccharomyces cerevisiae, Adr1 is a carbon-source-responsive zinc-finger transcription factor required for transcription of the glucose-repressed gene ADH1 and of genes required for ethanol, glycerol, and fatty acid utilization. Motif scanning of promoter elements suggests that Adr1 may be rewired in fungi and governs the ergosterol synthesis pathway in C. albicans. Because previous studies have identified the zinc-cluster transcription factor Upc2 as a regulator of the ergosterol pathway in both fungi, we examined the relationship of Adr1 and Upc2 in sterol biosynthesis in C. albicans. Phenotypic profiles of either ADR1 and UPC2 modulation in C. albicans showed differential growth in the presence of fluconazole; either adr1 or upc2 homozygous deletion results in sensitivity to the drug while their activation generates a fluconazole resistant strain. The rewiring from ergosterol synthesis to fatty acid metabolism involved all members of the Adr1 regulon except the alcohol dehydrogenase Adh1, which remains under Adr1 control in both circuits and may have been driven by the lifestyle of S. cerevisiae, which requires the ability to both tolerate and process high concentrations of ethanol.

genetics↗

bioRxiv2020

Metabolism of long-chain fatty acids affects disulfide bond formation in Escherichia coli and activates envelope stress response pathways as a combat strategy

The envelope of gram-negative bacteria serves as the first line of defense against environmental insults. Therefore, its integrity is continuously monitored and maintained by several envelope stress response (ESR) systems. Due to its oxidizing environment, the envelope represents an important site for disulfide bond formation. In Escherichia coli, the periplasmic oxidoreductase, DsbA introduces disulfide bonds in substrate proteins and transfers electrons to the inner membrane oxidoreductase, DsbB. Under aerobic conditions, the reduced form of DsbB is re-oxidized by ubiquinone, an electron carrier in the electron transport chain (ETC). Given the critical role of ubiquinone in transferring electrons derived from the oxidation of reduced cofactors, we were intrigued whether metabolic conditions that generate a large number of reduced cofactors render ubiquinone unavailable for disulfide bond formation. To test this, here we investigated the influence of metabolism of long-chain fatty acid (LCFA), an energy-rich carbon source, on the redox state of the envelope. We show that LCFA degradation increases electron flow in the ETC. Further, we find that whereas cells metabolizing LCFAs exhibit several characteristics of insufficient disulfide bond formation, these hallmarks are averted in cells exogenously provided with ubiquinone. Importantly, the ESR pathways, Cpx and {sigma}E, are activated by envelope signals generated during LCFA metabolism, and these systems maintain proper disulfide bond formation. We find that {sigma}E downregulation hampers disulfide bond formation only in the absence of Cpx, and amongst the two ESR systems, only Cpx senses redox-dependent signal and is induced to a greater extent by LCFAs. Therefore, we argue that Cpx is the primary ESR that senses and maintains envelope redox homeostasis. Taken together, our results demonstrate an intricate relationship between cellular metabolism and disulfide bond formation dictated by ETC and ESR, and provide the basis for examining whether similar mechanisms control envelope redox status in other gram-negative bacteria. Author summaryDisulfide bonds contribute to the folding and stability of many extracytoplasmic proteins in all domains of life. In gram-negative bacteria, including Escherichia coli, disulfide bond formation occurs in the oxidizing environment of the periplasmic space enclosed within the outer and inner membrane layers of the envelope. Because disulfide-bonded proteins are involved in diverse biological processes, bacteria must monitor the envelope redox status and elicit an appropriate response when perturbations occur; however, these mechanisms are not well elucidated. Here, we demonstrated that the metabolism of an energy-rich carbon source, long-chain fatty acid (LCFA) hampers disulfide bond formation in E. coli. An envelope stress response (ESR) system, Cpx, senses this redox imbalance and maintains proper disulfide bond formation. The {sigma}E pathway, another ESR system, plays an ancillary role in maintaining redox homeostasis. LCFA metabolism, disulfide bond formation, and ESR systems have independently been implicated in the pathogenesis of several gram-negative bacteria. The present study sets the basis to explore whether LCFA metabolism impacts the virulence of these bacteria by influencing the redox status of their envelope and activation of ESR pathways.

microbiology↗