Biology subjects

Kabyashree, K.

Publications and source records attributed to Kabyashree, K..

5 recordsLinked to original sources

bioRxiv2026

Mutation in Ralstonia pseudosolanacearum F1C1 cytochrome p450 homologue impairs virulence through root but not through shoot of tomato plants

Ralstonia pseudosolanacearum causes a lethal bacterial wilt disease in many plants. The pathogen enters through roots and systemically colonizes the xylem tissue, resulting in wilting and eventual death of the host. Using transposon mutagenesis followed by screening in tomato seedlings, we identified a mutant exhibiting virulence deficiency by root inoculation, but not by leaf inoculation. The mutation was recreated in the wild-type genome via natural transformation to prove the linkage of virulence deficiency with the transposon insertion. Whole genome sequencing revealed that the transposon insertion was in a cyp450 homologue, encoding cytochrome P450 monooxygenase. Two independent targeted mutations were generated in the cyp450 gene, and both the mutants recapitulated the root-specific virulence deficiency. The mutants rarely cause disease in mature plants following soil drenching but remained fully virulent upon petiole pricking inoculation. Complementation with the full length cyp450 gene amplified from the wild-type strain F1C1 restored virulence in the mutant. Compared to the wild-type F1C1, the cyp450 mutants exhibited greater sensitivity to tomato root extracts. HR-LCMS of tomato root extracts revealed the occurrence of several antimicrobial compounds. Cytochrome P450 enzymes are known to mediate the degradation or biosynthesis of diverse metabolites in bacteria. Considering the virulence difference due to the mode of inoculation, our findings indicate that cyp450 contributes to tissue-specific adaptation of the pathogen during infection has opened an avenue for integrating tissue metabolomics with bacterial wilt susceptibility research.

pathology↗

bioRxiv2026

Thioesterase modulates antibacterial Type VI secretion system via alteration in oxidative stress responses in Burkholderia

Bacteria utilize specialized protein secretion systems, particularly the type VI secretion system (T6SS), to dominate interbacterial competitions and kill the prey bacteria in a contact-dependent manner. Here, we report that disruption of the thioesterase gene encoded in the gramibactin (a bacterial siderophore) biosynthetic gene cluster activates the T6SS in the Burkholderia gladioli strain NGJ1, even in the absence of prey. The thioesterase mutant exhibits enhanced antibacterial activity, and ectopic expression of the gene complements the phenotype. Notably, thio mutant as well as thioesterase-complement strains show enhanced sensitivity to oxidative stress. The qRT-PCR analysis showed that the thio mutant had upregulated expression of RpoN1, a sigma factor, which positively regulates T6SS functions. We demonstrate that rpoN1 mutant is hypersensitive to oxidative stress and defective in T6SS activation, whereas overexpression of RpoN1 enhances oxidative stress tolerance in NGJ1 and activates T6SS. We propose that, during interbacterial conflicts encountered during plant colonization, NGJ1 faces an oxidative-stress-enriched environment that modulates thioesterase expression, induces RpoN1, and activates T6SS. Overall, our study exemplifies the broader physiological role of Thioesterase in maintaining intracellular ROS homeostasis in bacteria and stimulating antibacterial activity.

microbiology↗

bioRxiv2024

Tissue-independent nature of plant susceptibility: a comparative pathogenicity study of the systemic phytopathogen Ralstonia pseudosolanacearum in eggplant and tomato seedlings through root and leaf

Ralstonia pseudosolanacearum causes a lethal bacterial wilt disease in many plant species, posing significant economic challenges. Although tomato has been a primary model host for investigating the pathogenicity and systemic infection of this bacterium, this manuscript presents a comparative pathogenicity study between two closely related solanaceous hosts, tomato and eggplant, revealing differential host responses to the same pathogen, specifically through leaves and roots. Interestingly, eggplant seedlings exhibited a significantly higher susceptibility to cotyledon leaf inoculation than tomato seedlings. In the case of tomato, a few seedlings escaped wilting (called escapees), which was usual at a high pathogen load, unlike the case of eggplant seedlings where escapees could not be observed even at a 100-fold lower pathogen concentration. The greater susceptibility of eggplant was further demonstrated by performing both single- and double-leaf inoculations in the seedlings. Surprisingly, root inoculations resulted in a significantly lower mortality for eggplant than for tomato seedlings. The contrasting susceptibility between the two hosts regarding root and leaf regions indicates the tissue-dependent nature of susceptibility. The study underscores the value of employing multiple host species to uncover new insights into pathogen behaviour and host-pathogen interactions.

pathology↗

bioRxiv2024

Arabidopsis AtGELP53 modulates polysaccharide acetylation and defense response through oligosaccharide-mediated signaling

O-acetylation is a crucial substitution found in hemicelluloses and pectin which are necessary for maintaining the flexibility and structural integrity of the cell. A balanced polysaccharide O-acetylation level is maintained by cell wall acetyl transferases and esterases present in different cell organelles. Specifically, the role of esterases in cell wall acetylation metabolism is less explored. Therefore, we investigated the role of AtGELP53 from the GELP family of esterases or lipases. Here, we show that AtGELP53 is localized in the plasma membrane. Analysis of AtGELP53 overexpressing independent transgenic lines revealed a decrease in xyloglucan acetylation, changes in other polysaccharide acetylation and alteration in cell wall composition. The series of elicitor-based, transcriptomic and proteomic analyses in AtGELP53 overexpressing lines suggested that oligosaccharide-mediated signalling activates the cell wall and defence-related genes primarily because of xyloglucan deacetylation. Furthermore, AtGELP53 overexpression plants showed resistance against Pseudomonas syringae and Ralstonia solanacearum through activation of elicitor-mediated defense response. Overall, our findings outline the role of AtGELP53 in polysaccharide acetylation, cell wall remodelling and defense through the activation of plant cell wall integrity.

plant biology↗

bioRxiv2022

Micro-colony observation: A rapid and simple approach to count bacterial colony forming units

For enumerating viable bacteria, traditional dilution plating to count colony forming units (CFU) has always been the preferred method in microbiology owing to its simplicity, albeit laborious and time-consuming. Similar CFU counts can be obtained by quantifying growing micro-colonies in conjunction with the perks of a microscope. Here, we employed a simple method of five microliter spotting of differently diluted bacterial culture multiple times on a single Petri dish followed by finding out CFU by counting micro-colonies using a phase-contrast microscope. In this method, the CFU of an Escherichia coli culture can be estimated within a four-hour period. Further, within a ten-hour period, CFU in a culture of Ralstonia solanacearum, a bacterium with a generation time of around 2 h, can be estimated. The CFU number determined by micro-colonies observed is comparable with that obtained by the dilution plating method. Micro-colonies number observed in the early hours of growth (2 h in case of E. coli and 8 h in case of R. solanacearum) were found to remain consistent at later hours, though there was a noticeable increase in the size of the colonies. It suggested that micro-colonies observed in the early hours indeed represent the bacterial number in the culture. Practical applications to this counting method were employed in studying the rifampicin-resistant mutation rate as well as performing the fluctuation test in E. coli. The method described here results in a 90% reduction of labour, time and resources. Thus, the method is likely to be adopted by many microbiologists in their routine laboratory research.

microbiology↗