Biology subjects

Sharan, D.

Publications and source records attributed to Sharan, D..

4 recordsLinked to original sources

bioRxiv2025

DNA-utilization loci enable exogenous DNA metabolism in gut Bacteroidales

The human gut microbiome plays a central role in nutrient metabolism, yet the fate of exogenous nucleic acids within this ecosystem remains poorly understood. Here, we show that multiple Bacteroidales species efficiently metabolize exogenous DNA, with Bacteroides thetaiotaomicron converting it into the deaminated nucleobases uracil and xanthine. Using genetic and biochemical approaches, we identify ddbABCDEF, a six-gene locus encoding secreted nucleases and an outer membrane transporter, essential for exogenous DNA metabolism in B. thetaiotaomicron. Colonization of gnotobiotic mice with ddbABCDEF mutants reveals that this pathway significantly alters nucleobase pools in the gut. Comparative genomics demonstrate that ddbABCDEF is evolutionarily related to a natural transformation system present in Bacteroidota and has diversified into four distinct subtypes, each linked to unique DNA-processing activities in closely related gut Bacteroidales strains. These findings thus establish DNA as a metabolic substrate in the gut microbiome and reveal a distinctive pathway for nucleobase production with implications for host-microbe interactions. SIGNIFICANCE STATEMENTThe gut microbiome plays a crucial role in nutrient metabolism, yet the fate of extracellular DNA within this ecosystem remains poorly understood. This study identifies Bacteroidales species that actively metabolize extracellular DNA, revealing a conserved pathway that converts DNA-derived nucleotides into deaminated nucleobases. We show that Bacteroides thetaiotaomicron utilizes a specialized genetic locus, ddbABCDEF, to facilitate this process, influencing nucleobase availability in the gut. Comparative genomic analyses suggest that ddbABCDEF is evolutionarily linked to bacterial natural transformation systems but has diverged into distinct metabolic subtypes. These findings establish DNA as a metabolic substrate in the gut microbiome, with potential implications for microbial ecology, host-microbe interactions, and gut health.

microbiology↗

bioRxiv2022

Exceptionally versatile respiratory metabolisms drive metabolite production by diverse gut bacteria

Respiratory reductases enable microbes to utilize molecules present in anaerobic ecosystems as energy-generating respiratory electron acceptors. Here we identify three taxonomically distinct families of human gut bacteria (Burkholderiaceae, Eggerthellaceae, Erysipelotrichaceae) that encode large arsenals of tens-to-hundreds of respiratory-like reductases per genome. Screening species from each family (Sutterella wadsworthensis, Eggerthella lenta, and Holdemania filiformis), we discover 22 metabolites used as respiratory electron acceptors in a species-specific manner. Identified reactions transform multiple classes of dietary- and host-derived metabolites, including bioactive molecules resveratrol and itaconate. Products of identified respiratory metabolisms highlight poorly characterized compounds, such as the itaconate-derived 2-methylsuccinate. Reductase substrate-profiling defines enzyme-substrate pairs and reveals a complex picture of reductase evolution, providing evidence that reductases with specificities for related cinnamate substrates independently emerged at least four times. These studies thus establish an exceptionally versatile form of anaerobic respiration that directly links microbial energy metabolism to the gut metabolome.

microbiology↗

bioRxiv2022

Complete identity of the cis-asRNA StfZ and its influence on FtsZ protein level and cell division in Escherichia coli

Bacteria regulate FtsZ protein levels through transcriptional and translational mechanisms for proper cell division. A cis-antisense RNA, StfZ, produced from the ftsA-ftsZ intergenic region was proposed to regulate the FtsZ level in Escherichia coli. However, its structural identity remained unknown. In the present study, we determined the complete sequence, identified the promoters, and effects of StfZ on the FtsZ level. We show that StfZ is expressed at 1:6 ratio of StfZ:ftsZ mRNA at all growth phases from three promoters as three isoforms of 366 nt, 474 nt, and 552 nt. Overexpression of StfZ reduces FtsZ level, increases cell size, and blocks cell division. Thus, the cis-encoded StfZ emerges as a novel factor for maintaining the FtsZ level at different growth phases in E. coli.

microbiology↗

bioRxiv2019

Unveiling the physiological mechanisms that drive the emergence of antibiotic resisters from antibiotic persister population of mycobacteria

The physiological mechanisms behind the emergence of antibiotic-resistant bacteria from their antibiotic-persister population are beginning to be explored. Here we delineate the sequential physiological events that drive the emergence of rifampin-resistant rpoB mutants from rifampin-persister population of mycobacteria during prolonged exposure. The rifampin-persister population generated elevated levels of hydroxyl radical, which inflicted mutations, enabling regrowth of the persister cells to form multi-septated, multi-nucleated elongated cells. These cells, through multiple divisions, produced multiple sister-daughter cells, causing an abrupt, unexpectedly high increase of rifampin-resistant colonies. Similar response was observed against moxifloxacin also. Earlier studies on the rifampin/moxifloxacin-exposed laboratory/clinical M. tuberculosis strains from in-vitro cultures and infected mouse-lung also showed cfu spurt, but went unnoticed/unreported. It is likely that these sequential physiological events may be driving the emergence of antibiotic-resistant tubercle bacilli in TB patients also. Escherichia coli also has been found to respond similarly against subminimal inhibitory concentrations of ciprofloxacin. Thus, the present findings attain broad significance as a general physiological mechanism used by diverse bacterial genera to emerge as drug-resistant strains against antibiotics.

microbiology↗