Biology subjects

Khokhani, D.

Publications and source records attributed to Khokhani, D..

3 recordsLinked to original sources

bioRxiv2025

Refining the root-associated microbial consortia for enhanced biocontrol of the root-rot pathogen of corn

Microbial consortia play a crucial role in plant protection by suppressing soil-borne pathogens. A previously studied root-associated microbial consortium consisting of seven bacterial strains (C7) demonstrated biocontrol activity against seedling blight in corn caused by Fusarium verticillioides. To enhance its biocontrol potential, we incorporated a free-living bacterial strain (S8) exhibiting biocontrol activity, forming a modified community (C8). We evaluated the biocontrol efficacy of S8, C7, and C8 against four major corn pathogens: Pythium torulosum, Fusarium graminearum, Fusarium subglutinans, and Rhizoctonia solani. Plate assays revealed that S8 and C8 exhibited the highest inhibition against P. torulosum (>65% growth inhibition) but were less effective against Fusarium species (25-30%), while none of the communities restricted R. solani growth. In pot assays under growth chamber conditions S8 alone exhibited superior pathogen suppression compared to C7 and C8. However, integrating S8 into C7 did not enhance overall biocontrol efficacy. Community analysis via 16S amplicon sequencing revealed no significant shifts in C7 community strain abundance upon S8 introduction, suggesting a lack of establishment of S8 into the C7 community. Given that some individual strains exhibited stronger pathogen suppression than C7 and had variable effects on root biomass and plant height, we designed three sub-communities (SC1, SC2, SC3) based on the highest inhibitory activity. Plant assays demonstrated that inoculation with SC1 and SC2 restored plant height and root biomass, indicating that biocontrol efficacy is primarily driven by specific strain combinations rather than the broader community. Our findings underscore the importance of refining microbial consortia to maximize synergistic interactions and minimize antagonism, advancing sustainable disease management in agriculture.

microbiology↗

bioRxiv2022

Plant pathogenic Ralstonia phylotypes evolved divergent respiratory strategies and behaviors to thrive in xylem

Bacterial pathogens in the Ralstonia solanacearum species complex (RSSC) infect the water-transporting xylem vessels of plants, causing bacterial wilt disease. Strains in RSSC phylotypes I and III can reduce nitrate to dinitrogen via complete denitrification. The four-step denitrification pathway enables bacteria to use inorganic nitrogen species as terminal electron acceptors, supporting their growth in oxygen-limited environments like biofilms or plant xylem. Reduction of nitrate, nitrite, and nitric oxide all contribute to virulence of a model phylotype I strain. However, little is known about the physiological role of the last denitrification step, the reduction of nitrous oxide to dinitrogen by NosZ. We found that phylotypes I and III need NosZ for full virulence. However, strains in phylotypes II and IV are highly virulent despite lacking NosZ. The ability to respire by reducing nitrate to nitrous oxide does not greatly enhance growth of phylotype II and IV strains. These partial denitrifying strains reach high cell densities during plant infection and cause typical wilt disease. However, unlike phylotype I and III strains, partial denitrifiers cannot grow well under anaerobic conditions or form thick biofilms in culture or in tomato xylem vessels. Furthermore, aerotaxis assays show that strains from different phylotypes have different oxygen and nitrate preferences. Together, these results indicate that the RSSC contains two subgroups that occupy the same habitat but have evolved divergent energy metabolism strategies to exploit distinct metabolic niches in the xylem. IMPORTANCEPlant pathogenic Ralstonia spp. are a heterogeneous globally distributed group of bacteria that colonize plant xylem vessels. Ralstonia cells multiply rapidly in plants and obstruct water transport, causing fatal wilting and serious economic losses of many key food security crops. Virulence of these pathogens depends on their ability to grow to high cell densities in the low-oxygen xylem environment. Plant pathogenic Ralstonia can use denitrifying respiration to generate ATP. The last denitrification step, nitrous oxide reduction by NosZ, contributes to energy production and virulence for only one of the three phytopathogenic Ralstonia species. These complete denitrifiers form thicker biofilms in culture and in tomato xylem, suggesting they are better adapted to hypoxic niches. Strains with partial denitrification physiology form less biofilm and are more often planktonic. They are nonetheless highly virulent. Thus, these closely related bacteria have adapted their core metabolic functions to exploit distinct micro-niches in the same habitat.

microbiology↗

bioRxiv2022

Cell-density regulated adhesins contribute to early disease development and adhesion in Ralstonia solanacearum

Adhesins (adhesive proteins) help bacteria stick to and colonize diverse surfaces and often contribute to virulence. The genome of the bacterial wilt pathogen Ralstonia solanacearum (Rs) encodes dozens of putative adhesins, some of which are upregulated during plant pathogenesis. Little is known about the role of these proteins in bacterial wilt disease. During tomato colonization, three putative Rs adhesin genes were upregulated in a {Delta}phcA quorum sensing mutant that cannot respond to high cell densities: radA (Ralstonia adhesin), rcpA (Ralstonia collagen-like protein), and rcpB. Based on this differential gene expression, we hypothesized that adhesins repressed by PhcA contribute to early disease stages when Rs experiences a low cell density. During root colonization Rs upregulated rcpA and rcpB, but not radA, relative to bacteria in the stem at mid-disease. Root attachment assays and confocal microscopy with {Delta}rcpA/B and {Delta}radA revealed that all three adhesins help Rs attach to tomato seedling roots. Biofilm assays on abiotic surfaces found that Rs does not require RadA, RcpA, or RcpB for interbacterial attachment (cohesion), but these proteins are essential for anchoring aggregates to a surface (adhesion). However, Rs did not require the adhesins for later disease stages in planta, including colonization of the root endosphere and stems. Interestingly, all three adhesins were essential for full competitive fitness in planta. Together, these infection stage-specific assays identified three proteins that contribute to adhesion and the critical first host-pathogen interaction in bacterial wilt disease. ImportanceEvery microbe must balance its need to attach to surfaces with the biological imperative to move and spread. The high-impact plant pathogenic bacterium Ralstonia solanacearum can stick to biotic and abiotic substrates, presumably using some of the dozens of putative adhesins encoded in its genome. We confirmed the functions and identified the biological roles of several afimbrial adhesins. By assaying the competitive fitness and the success of adhesin mutants in three individual plant compartments, we identified the specific disease stages and host tissues where three previously cryptic adhesins contribute to bacterial success. Combined with tissue-specific regulatory data, this work indicates that R. solanacearum deploys distinct adhesins that help it succeed at different stages of plant pathogenesis. Research AreasPlant Microbiology, Host-Microbial Interactions, Microbial Pathogenesis

microbiology↗