Biology subjects

Satapathy, S. S.

Publications and source records attributed to Satapathy, S. S..

9 recordsLinked to original sources

bioRxiv2026

Expression-dependent but strand-independent synonymous single-nucleotide polymorphism in the Escherichia coli chromosome

AbstractMutation in genomes is mainly attributed to replication, though transcription is also known to be mutagenic and is a more frequent event than replication in an organism. Recently, there have been reports regarding genome-wide transcription-induced mutagenesis. However, a distinct demonstration of specific mutation being replication-dependent and/or transcription-dependent in genomes is yet to be established. Here, we studied synonymous single-nucleotide polymorphisms (SNPs) in 2091 individual coding sequences (CDS) in the leading strand (LeS) and the lagging strand (LaS) of the Escherichia coli chromosome by comparing across 157 strains. The frequencies of complementary transitions (ti) and complementary transversions (tv) were compared in each CDS to assess parity violation in the context of strand location and gene expression. The C[->]T and G[->]A exhibited the maximum frequency as well as the most prominent strand inequality as these tis were influenced both by the strand location as well as by the gene expression. Interestingly, inequality between T[->]C and A[->]G was expression-dependent but strand-independent. This was a direct demonstration of strand inequality due to expression but not due to replication. A[->]T and G[->]T tvs were universally more frequent than their complementary T[->]A and C[->]A, respectively. The strand-independent but expression-dependent synonymous SNP inequality in CDS, supports the role of transcription-induced mutagenesis contributing to strand inequality in the E. coli chromosome. Significance StatementMutational patterns in bacterial genomes are shaped by both replication and transcription, but their relative roles remain unclear. By analyzing synonymous SNPs across 157 strains of E. coli, we identify strong strand-specific asymmetry consistent with replication-associated biases. A strong asymmetry between the strands regarding C[->]T and G[->]A ti is observed, as it is influenced by replication asymmetry and expression. We further show that gene expression significantly influences mutation types, with T[->]C ti being enriched in the highly expressed genes and A[->]G ti being enriched in the lowly expressed genes. Notably, A[->]T ti is strand independent but exhibits mild dependency on gene expression, revealing a previously unrecognized mutational pattern. These findings highlight how some SNPs are influenced by transcription but not replication

evolutionary biology↗

bioRxiv2026

Regions of genome plasticity are systematically organized into recurrent integration spots that shape accessory-genome functional architecture: insights from a complete genome of strain F1C1 and pangenomic analysis of the Ralstonia solanacearum species complex

1The Ralstonia solanacearum species complex (RSSC) is a highly diverse plant pathogen whose evolution is shaped by horizontal gene transfer. We generated a complete, gap-free hybrid genome assembly of F1C1, a South Asian Phylotype I strain classified as R. pseudosolanacearum. The closed assembly resolves a bipartite genome (3.73 Mb chromosome; 2.03 Mb megaplasmid), enabling precise localization of mobile genetic elements. Using F1C1 together with 142 complete RSSC genomes, we implemented a lineage-stratified pangenome framework that reveals a hierarchically structured gene repertoire and shows that accessory gene content can discriminate host-associated lineages beyond core-genome. Pangenome-informed mapping of genome plasticity identified 651 conserved integration spots that concentrate accessory turnover and are enriched for adaptive functions, including type III secretion system effectors and antiviral defense systems (e.g., Wadjet and CRISPR-Cas). Genes within these spots display elevated Ka/Ks relative to housekeeping functions, consistent with conflict-driven diversification and/or relaxed constraint. Together, these results link RSSC genome architecture to adaptive potential and provide a spot-based framework for genomic surveillance and resistance breeding in bacterial wilt pathosystems.

genomics↗

bioRxiv2024

Higher frequency of transition mutation over transversion mutation in genomes: evidence from the binding energy calculation of base pairs using DFT

Base substitution mutations such as transition (ti) and transversion (tv) in organisms are major driving force in molecular evolution. In this study, different possible types of base pairing that can cause ti and tv were investigated using the density functional theory (DFT) method. The chemical structures of bases as well as base pairs were optimized using B3LYP hybrid functional along with 6-31G(d,p) basis set. We performed single point energy calculation of all optimized species using the same functional but combined with higher diffuse and polarized basis set i.e. 6-311++G(d,p) to get more refined energy of all species. The binding energy of various base pairs was calculated considering basis set superposition error (BSSE) as well as without BSSE. The binding energy of the base pairs leading to ti was found to be more stable than that of the base pairs leading to tv. This was interesting considering the observations in organisms that tis are more frequent than tvs. Among the base pairs leading to the same ti, G(keto): T (enol) base pair was found to be more stable than A(imino):C(amino) base pair. This theoretical study of binding energy of different base pairs using the DFT method has provided additional evidences in support to the biological observations of a higher transition rate than transversion in genomes.

molecular biology↗

bioRxiv2022

Codon degeneracy as well as pretermination codons influence transition to transversion ratio in coding sequences

Transition (ti) and transversion (tv) are the major causes for genome variation. The accurate estimation of ti to tv ratio [Formula] in genomes is crucial for understanding of mutational and selection processes in organisms as it is influenced by both codon degeneracy and pretermination codons (PTC). Therefore, we developed a method (accessible at https://github.com/CBBILAB/CBBI.git) to estimate [Formula] ratio by accounting codon degeneracy as well as PTC in protein coding sequences. Our findings revealed a distinct impact of codon degeneracy and PTC on the [Formula] ratio in the Escherichia coli genome. We observed a decreasing order among the frequencies of different base substitutions such as synonymous transition (Sti) > synonymous transversion (Stv) > non-synonymous transition (Nti) > non-synonymous transversion (Ntv) in E. coli genome. The correlation was strong between Sti and Stv values (Pearson r value 0.795) whereas the correlation was weak between Sti and Nti (Pearson r value 0.192). Coding sequences with similar Sti values exhibited a wide range of Nti values. This indicated the varying strength of purifying selection acting on the coding sequences. In concordance with the assumption, the genes having higher Nti values were observed with lower codon adaptation index (CAI) values than that of the genes having lower Nti values. Our approach is convenient to visualize the frequency of base substitution variation as well as selection in protein coding sequences. The proposed method is useful to estimate different [Formula] ratios accurately in coding sequences and is insightful from an evolutionary perspective. Article SummaryGenetic diversity is pivotal in evolution, with base substitution as a key driver. Transition (ti) frequency surpasses transversion (tv) frequency in genomes, making [Formula] ratios a valuable metric for studying mutation bias. Our improved estimator for [Formula] calculation accounts for codon degeneracy and nonsense substitutions in pretermination codons. Additionally, we unveil insights into the frequency of different substitutions such as Sti, Stv, Nti, and Ntv and demonstrate the impact of selection on protein coding sequences.

evolutionary biology↗

bioRxiv2022

The transcribed intergenic regions exhibit lower frequency of nucleotide polymorphism than the untranscribed intergenic regions in the genomes of Escherichia coli and Salmonella enterica

The temporary exposure of single-stranded regions in the genome during the process of replication and transcription makes the region vulnerable to cytosine deamination resulting higher rate of C[->]T transitions. Intra-operon intergenic regions undergo transcription along with adjacent co-transcribed genes in an operon, whereas inter-operon intergenic regions only undergo replication. Hence these two types of intergenic regions (IGRs) can be compared to find out the contribution of replication-associated mutations (RAM) and transcription-associated mutations (TrAM) towards bringing variation in genomes. In our work, we performed a polymorphism spectra comparison between intra-operon IGRs and inter-operon IGRs in genomes of two well-known closely related bacteria such as Escherichia coli and Salmonella enterica. In general, the size of intra-operon IGRs was smaller than that of inter-operon IGRs in these bacteria. Interestingly, the polymorphism frequency at intra-operon IGRs was 2.5-fold lesser than that in the inter-operon IGRs in E. coli genome. Similarly, the polymorphism frequency at intra-operon IGRs was 2.8-fold lesser than that in the inter-operon IGRs in S. enterica genome. Therefore, the intra-operon IGRs were often observed to be more conserved. In the case of inter-operon IGRs, the T[->]C transition frequency was a minimum of two times more than T[->]A transversion frequency whereas in the case of intra-operon IGRs, T[->]C transition frequency was similar to that of T[->]A transversion frequency. The polymorphism was purine biased and keto biased more in intra-operon IGRs than the inter-operon IGRs. In E. coli, the Ti/Tv ratio was observed as 1.639 and 1.338 in inter-operon and in intra-operon IGRs, respectively. In S. enterica, the Ti/Tv ratio was observed as 2.134 and 2.780 in inter-operon and in intra-operon IGRs, respectively. The observation in this study indicates that transcribed IGRs might not always have higher polymorphism frequency than the untranscribed IGRs. The lower polymorphism frequency at intra-operon IGRs might be attributed to different events such as the transcription-coupled DNA repair, sequences facilitating translation initiation and avoidance of rho-dependent transcription termination.

evolutionary biology↗

bioRxiv2022

Synonymous polymorphism difference relating to codon degeneracy between co-transcribed genes in the genome of Escherichia coli

The previous findings suggest that replication and transcription are two major reasons behind the different substitution patterns of mutations in genomic DNA. In the current work, we have compared the adjacent co-transcribed gene pairs regarding synonymous polymorphism in five different operons in Escherichia coli. It is interesting that the co-transcribed genes were different from each other regarding the polymorphism spectra. The transition to transversion ratio between gene pairs were different due to their compositional differences regarding two-fold degenerate codon and four-fold degenerate codons. Further, the polymorphism spectra difference between the gene pairs was more prominent in four-fold and six-fold degenerate codons than in the two-fold degenerate codons. In case of rpoB and rpoC, the major difference was found at UCC, GUA, CCG, GCU, GGC and CGC codons. Similarly, in case of the other four pairs of co-transcribed genes, the difference was more prominent in the higher degenerate codons than the two-fold degenerate codons. It may be that the restriction of two-fold degenerate codons to transition substitutions only regarding synonymous polymorphism is making these codons different from the higher degeneracy codons in this study.

evolutionary biology↗

bioRxiv2022

Modified dN/dS for accounting transition and transversion frequency difference and non-sense substitution in genomes

The dN/dS value is estimated in homologous protein coding gene sequences between two closely related organisms for studying selection on the genes. In the usual method of calculation of synonymous (S) and non-synonymous (NS) sites in codons, the transition and transversion rates are considered same as well as no difference of pretermination codons from the other codons regarding NS substitutions is considered. In this study we are proposing a modification in the method by estimating the S and the NS sites in codons by considering difference between the transition and transversion rates and the NS substitutions leading to non-sense codons in pretermination codons. So, the dN/dS value calculated by our approach was higher than that calculated by the earlier method. The modified method was applied in estimating dN/dS in 29 homologous gene sequences of Escherichia coli and Salmonella enterica. Impact of codon degeneracy and pretermination codons on the dN/dS values estimated by our method were observed clearly. Our method of estimation that considers the above features is a realistic representation of dN/dS values in coding sequences.

evolutionary biology↗

bioRxiv2021

Polymorphism at four-fold degenerate site, but not at the intergenic regions, explains nucleotide compositional strand asymmetry in bacteria

We investigated single nucleotide polymorphism in intergenic regions (IRs) and four-fold degenerate sites (FFS) in genomes of three {gamma}-Proteobacteria and two Firmicutes to understand the mechanism of nucleotide compositional asymmetry between the leading and the lagging strands. Pattern of the polymorphism spectra were alike regarding transitions but variable regarding transversions in the IRs of these bacteria. Contrasting trends of complementary polymorphisms such as C[->]T vs G[->]A as well as A[->]G vs T[->]C in the IRs vindicated similar replication-associated strand asymmetry regarding cytosine and adenine deamination, respectively, across these bacteria. Surprisingly, the polymorphism pattern at FFS was different from that of the IRs and its frequency was always more than the IRs in these bacteria. Further, the polymorphism patterns within a bacterium were inconsistent across the five amino acids, which neither the replication nor the transcription-associated mutations could explain. However, the polymorphism at FFS coincided with amino acid specific codon usage bias in the five bacteria. Further, strand asymmetry in nucleotide composition could be explained by the polymorphism at FFS, not at the IRs. Therefore, polymorphisms at FFS might not be treated as nearly neutral unlike that in IRs in these bacteria.

molecular biology↗

bioRxiv2020

Entner-Doudoroff pathway and Non-OxPPP bypasses glycolysis and OxPPP in Ralstonia solanacearum

In Ralstonia solanacearum, a devastating phytopathogen whose metabolism is poorly understood, we observed that Entner-Doudoroff (ED) pathway and NonOxidative pentose phosphate pathway (OxPPP) bypasses glycolysis and OxPPP under glucose oxidation. Evidences derived from 13C stable isotopes feeding and genome annotation based comparative metabolic network analysis supported the observations. Comparative metabolic network analysis derived from the currently available 53 annotated R. solanacearum strains also including the recently reported strain (F1C1), representing the four phylotypes confirmed the lack of key genes coding for phosphofructokinase (pfk-1) and phosphogluconate dehydrogenase (gnd) enzymes that are relevant for glycolysis and OxPPP respectively. R. solanacearum F1C1 cells fed with 13C Glucose (99%[1-13C]- or 99%[1,2-13C]- or 40%[13C6]-glucose) followed by GC-MS based labelling analysis of fragments from amino acids, glycerol and ribose provided clear evidence that rather than Glycolysis and OxPPP, ED pathway and NonOxPPP are the main routes sustaining metabolism in R. solanacearum. The 13C incorporation in the mass ions of alanine (m/z 260, m/z 232); valine (m/z 288, m/z 260), glycine (m/z 218), serine (m/z 390, m/z 362), histidine (m/z 440, m/z 412), tyrosine (m/z 466, m/z 438), phenylalanine (m/z 336, m/z 308), glycerol (m/z 377) and ribose (m/z 160) mapped the pathways supporting the observations. The outcomes help better defining the central carbon metabolic network of R. solanacearum that can be integrated with 13C metabolic flux analysis as well as flux balance analysis studies for defining the metabolic phenotypes. ImportanceUnderstanding the metabolic versatility of Ralstonia solanacearum is important as it regulates the tradeoff between virulence and metabolism (1, 2) in a wide range of plant hosts. Due to a lack of clear evidence until this work, several published research papers reported on potential roles of Glycolysis and Oxidative pentose phosphate pathways (OxPPP) in R. solanacearum (3, 4). This work provided evidence from 13C stable isotopes feeding and genome annotation based comparative metabolic network analysis that Entner-Doudoroff pathway and Non-OxPPP bypasses glycolysis and OxPPP during the oxidation of Glucose, one of the host xylem pool that serves as a potential carbon source (5). The outcomes help better defining the central carbon metabolic network of R. solanacearum that can be integrated with 13C metabolic flux analysis as well as flux balance analysis studies for defining the metabolic phenotypes. The study highlights the need to critically examine phytopathogens whose metabolism is poorly understood.

systems biology↗