Biology subjects

Karmakar, K.

Publications and source records attributed to Karmakar, K..

5 recordsLinked to original sources

bioRxiv2026

Maltose aids in the growth of Salmonella Typhimurium in nitrogen-deficient conditions

Enteric pathogens, such as Salmonella, encounter uncertain nutrients in both the host and the environment. Nutrients such as carbon and nitrogen are essential for growth, and when these nutrients are limited, bacteria have developed various mechanisms to overcome stress and thrive in nutrient-rich environments. In this study, we investigated the role of the disaccharide sugar maltose in the growth and pathogenicity of Salmonella Typhimurium (STM) under nitrogen-deficient culture conditions. Throughout the study, we used Burks medium to mimic nitrogen-deficient conditions. STM growth in Burks medium was minimal, and maltose supplementation enhanced STM growth in both liquid and solid Burks media. The STM grown in Burks medium had a reduced bacterial cell length, which increased upon the addition of maltose and became comparable to that of LB-grown STM WT. Growth was dependent on the NtrBC two-component system and sigma factor RpoE. Deletion of ntrB and rpoE significantly reduced the growth in Burks medium during the log phase. Salmonella grown in Burks medium with maltose had reduced invasion in Caco-2 cells, phagocytosis in RAW 264.7 macrophages, and organ burden in C57BL/6 mice. Our findings revealed the role of maltose in enhancing the growth and length of Salmonella under nitrogen-deficient conditions. However, Salmonella grown in Burks medium with maltose is defective in pathogenesis.

microbiology↗

bioRxiv2025

Maltose facilitates Salmonella growth under nitrogen stress while impairing adhesion to epithelial cells

The composition of nutrients in the intestine defines a niche for colonising gut pathogens. The lack of nutrients suitable for pathogens due to competition from resident intestinal microbiota or dietary preferences leads to colonisation failure by pathogens. In this study, we investigated the impact of the disaccharide sugar maltose on Salmonella Typhimurium (STM) pathogenicity during the early phases of infection in C57BL/6 mice and human colon carcinoma cells (Caco-2). We found that supplementation of maltose at lower concentrations inhibited STM colonisation in the ileum of mice. To understand this, we investigated the role of maltose metabolism in human colon epithelial (Caco-2) cells. Deleting the maltose metabolism gene (malQ) increased adhesion to Caco-2 cells. The increased adhesion was due to increased expression of type 1 fimbriae. Inhibiting the type 1 fimbriae-mediated binding to host epithelial cells by incubating with mannose resulted in similar adhesion of STM WT and STM {Delta}malQ. We further identified that malQ regulates the adhesion of Salmonella through the sigma factor RpoE. Overall, malQ in Salmonella inhibits infection in epithelial cells by reducing its adhesion to host epithelial cells.

microbiology↗

bioRxiv2023

Control of neuronal excitation-inhibition balance by BMP-SMAD1 signaling

Throughout life, neuronal networks in the mammalian neocortex maintain a balance of excitation and inhibition which is essential for neuronal computation. Deviations from a balanced state have been linked to neurodevelopmental disorders and severe disruptions result in epilepsy. To maintain balance, neuronal microcircuits composed of excitatory and inhibitory neurons sense alterations in neural activity and adjust neuronal connectivity and function. Here, we identified a signaling pathway in the adult mouse neocortex that is activated in response to elevated neuronal network activity. Over-activation of excitatory neurons is signaled to the network through the elevation of BMP2, a growth factor well-known for its role as morphogen in embryonic development. BMP2 acts on parvalbumin-expressing (PV) interneurons through the transcription factor SMAD1, which controls an array of glutamatergic synapse proteins and components of peri-neuronal nets. PV interneuron-specific disruption of BMP2-SMAD1 signaling is accompanied by a loss of PV cell glutamatergic innervation, underdeveloped peri-neuronal nets, and decreased excitability. Ultimately, this impairment of PV interneuron functional recruitment disrupts cortical excitation - inhibition balance with mice exhibiting spontaneous epileptic seizures. Our findings suggest that developmental morphogen signaling is re-purposed to stabilize cortical networks in the adult mammalian brain.

neuroscience↗

bioRxiv2019

A Hox code defines spinocerebellar neuron subtype regionalisation

Coordinated body movement requires the integration of many sensory inputs. This includes proprioception, the sense of relative body position and force associated with movement. Proprioceptive information is relayed to the cerebellum via spinocerebellar neurons, located in the spinal cord within a number of major neuronal columns or as various scattered cell populations. Despite the importance of proprioception to fluid movement, a molecular understanding of spinocerebellar relay interneurons is only beginning to be explored, with limited knowledge of molecular heterogeneity within and between columns. Using fluorescent reporter knock-in mice, neuronal tracing and in situ hybridisation, we identify widespread expression of Hox cluster genes, including both protein-coding genes and microRNAs, within spinocerebellar neurons. We reveal a \"Hox code\" based on axial level and individual spinocerebellar column, which, at cervico-thoracic levels, is essential for subtype regionalisation. Specifically, we show that Hoxc9 function is required in most, but not all, cells of the major thoracic spinocerebellar column, Clarkes column, revealing heterogeneity reliant on Hox signatures.

developmental biology↗

bioRxiv2018

Transcriptomic analyses with the progress of symbiosis in ‘crack-entry’ legume Arachis hypogaea highlight its contrast with ‘Infection thread’ adapted legumes

In root-nodule symbiosis, rhizobial invasion and nodule organogenesis is host controlled. In most legumes, rhizobia enter through infection-threads and nodule primordium in the cortex is induced from a distance. But in dalbergoid legumes like Arachis hypogaea, rhizobia directly invade cortical cells through epidermal cracks to generate the primordia. Herein we report the transcriptional dynamics with the progress of symbiosis in A. hypogaea at 1dpi: invasion; 4dpi: nodule primordia; 8dpi: spread of infection in nodule-like structure; 12dpi: immature nodules containing rod-shaped rhizobia; and 21dpi: mature nodules with spherical symbiosomes. Expression of putative orthologue of symbiotic genes in crack-entry legume A. hypogaea was compared with infection thread adapted model legumes. The contrasting features were (i) higher expression of receptors like LYR3, EPR3 as compared to canonical NFRs (ii) late induction of transcription factors like NIN, NSP2 and constitutive high expression of ERF1, EIN2, bHLH476 and (iii) induction of divergent pathogenesis responsive PR-1 genes. Additionally, symbiotic orthologues of SymCRK, FLOT4, ROP6, RR9, NOOT and SEN1 were not detectable and microsynteny analysis indicated the absence of RPG and DNF2 homologues in diploid parental genomes of A. hypogaea. The implications are discussed and a molecular framework that guide crack-entry symbiosis in A. hypogaea is proposed.

plant biology↗