Comprehensive genomic analysis of Bacillus subtilis and Bacillus paralicheniformis associated with the pearl millet panicle reveals their antimicrobial potential against important plant pathogens.

BACKGROUND: Plant microbiome confers versatile functional roles to enhance survival fitness as well as productivity. In the present study two pearl millet panicle microbiome member species Bacillus subtilis PBs 12 and Bacillus paralicheniformis PBl 36 found to have beneficial traits including plant growth promotion and broad-spectrum antifungal activity towards taxonomically diverse plant pathogens. Understanding the genomes will assist in devising a bioformulation for crop protection while exploiting their beneficial functional roles. RESULTS: Two potential firmicute species were isolated from pearl millet panicles. Morphological, biochemical, and molecular characterization revealed their identities as Bacillus subtilis PBs 12 and Bacillus paralicheniformis PBl 36. The seed priming assays revealed the ability of both species to enhance plant growth promotion and seedling vigour index. Invitro assays with PBs 12 and PBl 36 showed the antibiosis effect against taxonomically diverse plant pathogens (Magnaporthe grisea; Sclerotium rolfsii; Fusarium solani; Alternaria alternata; Ganoderma sp.) of crops and multipurpose tree species. The whole genome sequence analysis was performed to unveil the genetic potential of these bacteria for plant protection. The complete genomes of PBs 12 and PBl 36 consist of a single circular chromosome with a size of 4.02 and 4.33 Mb and 4,171 and 4,606 genes, with a G + C content of 43.68 and 45.83%, respectively. Comparative Average Nucleotide Identity (ANI) analysis revealed a close similarity of PBs 12 and PBl 36 with other beneficial strains of B. subtilis and B. paralicheniformis and found distant from B. altitudinis, B. amyloliquefaciens, and B. thuringiensis. Functional annotation revealed a majority of pathway classes of PBs 12 (30) and PBl 36 (29) involved in the biosynthesis of secondary metabolites, polyketides, and non-ribosomal peptides, followed by xenobiotic biodegradation and metabolism (21). Furthermore, 14 genomic regions of PBs 12 and 15 of PBl 36 associated with the synthesis of RiPP (Ribosomally synthesized and post-translationally modified peptides), terpenes, cyclic dipeptides (CDPs), type III polyketide synthases (T3PKSs), sactipeptides, lanthipeptides, siderophores, NRPS (Non-Ribosomal Peptide Synthetase), NRP-metallophone, etc. It was discovered that these areas contain between 25,458 and 33,000 secondary metabolite-coding MiBiG clusters which code for a wide range of products, such as antibiotics. The PCR-based screening for the presence of antimicrobial peptide (cyclic lipopeptide) genes in PBs 12 and 36 confirmed their broad-spectrum antifungal potential with the presence of spoVG, bacA, and srfAA AMP genes, which encode antimicrobial compounds such as subtilin, bacylisin, and surfactin. CONCLUSION: The combined in vitro studies and genome analysis highlighted the antifungal potential of pearl millet panicle-associated Bacillus subtilis PBs12 and Bacillus paralicheniformis PBl36. The genetic ability to synthesize several antimicrobial compounds indicated the industrial value of PBs 12 and PBl 36, which shed light on further studies to establish their action as a biostimulant for crop protection.

Deciphering the thermotolerance of chitinase O from Chitiniphilus shinanonensis by in vitro and in silico studies.

Biochemical and biophysical studies revealed that chitinase O from Chitiniphilus shinanonensis (CsChiO) exhibits considerable thermotolerance, possibly due to the formation of a stable structural conformation. CsChiO is an exochitinase with a temperature optimum of 70 °C. The secondary structures of CsChiO and its catalytic domain (Cat-CsChiO) are only marginally affected upon heating up to 90 °C, as revealed by circular dichroism (CD) spectroscopy. Differential scanning calorimetric (DSC) studies revealed that CsChiO exhibits two endothermic transitions at ca. 51 °C (Tm1) and 59 °C (Tm2), whereas Cat-CsChiO shows a single endothermic transition at 52 °C. Together, the CD and DSC analyses suggested that the catalytic domain of CsChiO undergoes a thermotropic transition at ~52 °C from native state to another stable structural conformation. Results from molecular dynamic simulations corroborated that Cat-CsChiO adopts a stable structural conformation above 50 °C by partial unfolding. Thermotolerant CsChiO would be useful for the conversion of chitin, which is highly abundant, to biologically active COS. This study unveiled the adaptability of enzymes/proteins in nature to perform biological functions at elevated temperatures.

Alterations of Primary Metabolites in Root Exudates of Intercropped Cajanus cajan-Zea mays Modulate the Adaptation and Proteome of Ensifer (Sinorhizobium) fredii NGR234.

Legume-cereal intercropping systems, in the context of diversity, ecological function, and better yield have been widely studied. Such systems enhance nutrient phytoavailability by balancing root-rhizosphere interactions. Root exudates (RE) play an important role in the rhizospheric interactions of plant-plant and/or plant-microbiome interaction. However, the influence of the primary metabolites of RE on plant-rhizobia interactions in a legume-cereal intercrop system is not known. To understand the plant communication with rhizobia, Cajanus cajan-Zea mays intercropped plants and the broad host range legume nodulating Ensifer fredii NGR234 as the model plants and rhizobium used respectively. A metabolomics-based approach revealed a clear separation between intercropped and monocropped RE of the two plants. Intercropped C. cajan showed an increase in the myo-inositol, and proline, while intercropped Z. mays showed enhanced galactose, D-glucopyranoside, and arginine in the RE. Physiological assays of NGR234 with the RE of intercropped C. cajan exhibited a significant enhancement in biofilm formation, while intercropped Z. mays RE accelerated the bacterial growth in the late log phase. Further, using label-free proteomics, we identified a total of 2570 proteins of NGR234 covering 50% annotated protein sequences upon exposure to Z. mays RE. Furthermore, intercropped Z. mays RE upregulated bacterioferritin comigratory protein (BCP), putative nitroreductase, IlvD, LeuC, D (branched-chain amino acid proteins), and chaperonin proteins GroEL2. Identification offered new insights into the metabolome of the legume-cereal intercrop and proteome of NGR234-Z. mays interactions that underline the new molecular candidates likely to be involved in the fitness of rhizobium in the intercropping system.

Elicitation of defense response by transglycosylated chitooligosaccharides in rice seedlings.

Long-chain chitooligosaccharides (COS) with degree of polymerization (DP) more than 4 are known to have potential biological activities. A hyper-transglycosylating mutant of an endo-chitinase from Serratia proteamaculans (SpChiD-Y28A) was used to synthesize COS with DP6 and DP7 using COS DP5 as substrate. Purified COS with DP5-7 were tested to elicit the defense response in rice seedlings. Among the COS used, DP7 strongly induced oxidative burst response as well as peroxidase, and phenylalanine ammonia lyase activites. A few selected marker genes in salicylic acid (SA)- and jasmonic acid-dependent pathways were evaluated by real-time PCR. The expression levels of pathogenesis-related (PR) genes PR1a and PR10 and defense response genes (chitinase1, peroxidase and ß -1,3-glucanase) were up regulated upon COS treatment in rice seedlings. The DP7 induced Phenylalanine ammonia lyase and Isochorismate synthase 1 genes, with concomitant increase of Mitogen-activated protein kinase 6 and WRKY45 transcription factor genes indicated the possible role of phosphorylation in the transmission of a signal to induce SA-mediated defense response in rice.

Genomic Diversity of Pigeon Pea (Cajanus cajan L. Millsp.) Endosymbionts in India and Selection of Potential Strains for Use as Agricultural Inoculants.

Pigeon pea (Cajanus cajan L. Millsp. ) is a legume crop resilient to climate change due to its tolerance to drought. It is grown by millions of resource-poor farmers in semiarid and tropical subregions of Asia and Africa and is a major contributor to their nutritional food security. Pigeon pea is the sixth most important legume in the world, with India contributing more than 70% of the total production and harbouring a wide variety of cultivars. Nevertheless, the low yield of pigeon pea grown under dry land conditions and its yield instability need to be improved. This may be done by enhancing crop nodulation and, hence, biological nitrogen fixation (BNF) by supplying effective symbiotic rhizobia through the application of "elite" inoculants. Therefore, the main aim in this study was the isolation and genomic analysis of effective rhizobial strains potentially adapted to drought conditions. Accordingly, pigeon pea endosymbionts were isolated from different soil types in Southern, Central, and Northern India. After functional characterisation of the isolated strains in terms of their ability to nodulate and promote the growth of pigeon pea, 19 were selected for full genome sequencing, along with eight commercial inoculant strains obtained from the ICRISAT culture collection. The phylogenomic analysis [Average nucleotide identity MUMmer (ANIm)] revealed that the pigeon pea endosymbionts were members of the genera Bradyrhizobium and Ensifer. Based on nodC phylogeny and nod cluster synteny, Bradyrhizobium yuanmingense was revealed as the most common endosymbiont, harbouring nod genes similar to those of Bradyrhizobium cajani and Bradyrhizobium zhanjiangense. This symbiont type (e.g., strain BRP05 from Madhya Pradesh) also outperformed all other strains tested on pigeon pea, with the notable exception of an Ensifer alkalisoli strain from North India (NBAIM29). The results provide the basis for the development of pigeon pea inoculants to increase the yield of this legume through the use of effective nitrogen-fixing rhizobia, tailored for the different agroclimatic regions of India.

Poor Competitiveness of Bradyrhizobium in Pigeon Pea Root Colonization in Indian Soils.

Pigeon pea, a legume crop native to India, is the primary source of protein for more than a billion people in developing countries. The plant can form symbioses with N2-fixing bacteria; however, reports of poor crop nodulation in agricultural soils abound. We report here a study of the bacterial community associated with pigeon pea, with a special focus on the symbiont population in different soils and vegetative and non-vegetative plant growth. Location with respect to the plant roots was determined to be the main factor controlling the bacterial community, followed by developmental stage and soil type. Plant genotype plays only a minor role. Pigeon pea roots have a reduced microbial diversity compared to the surrounding soil and select for Proteobacteria, especially for Rhizobium spp., during vegetative growth. While Bradyrhizobium, a native symbiont of pigeon pea, can be found associating with roots, its presence is dependent on plant variety and soil conditions. A combination of 16S rRNA gene amplicon survey, strain isolation, and co-inoculation with nodule-forming Bradyrhizobium spp. and non-N2-fixing Rhizobium spp. demonstrated that the latter is a much more successful colonizer of pigeon pea roots. Poor nodulation of pigeon pea in Indian soils may be caused by a poor Bradyrhizobium competitiveness against non-nodulating root colonizers such as Rhizobium. Hence, inoculant strain selection of symbionts for pigeon pea should be based not only on their nitrogen fixation potential but, more importantly, on their competitiveness in agricultural soils. IMPORTANCE Plant symbiosis with N2-fixing bacteria is a key to sustainable, low-input agriculture. While there are ongoing projects aiming to increase the yield of cereals using plant genetics and host-microbiota interaction engineering, the biggest potential lies in legume plants. Pigeon pea is a basic food source for a billion low-income people in India. Improving its interactions with N2-fixing rhizobia could dramatically reduce food poverty in India. Despite the Indian origin of this plant, pigeon pea nodulates only poorly in native soils. While there have been multiple attempts to select the best N2-fixing symbionts, there are no reliable strains available for geographically widespread use. In this article, using 16S rRNA gene amplicon, culturomics, and plant co-inoculation assays, we show that the native pigeon pea symbionts such as Bradyrhizobium spp. are able to nodulate their host, despite being poor competitors for colonizing roots. Hence, in this system, the establishment of effective symbiosis seems decoupled from microbial competition on plant roots. Thus, the effort of finding suitable symbionts should focus not only on their N2-fixing potential but also on their ability to colonize. Increasing pigeon pea yield is a low-hanging fruit to reduce world hunger and degradation of the environment through the overuse of synthetic fertilizers.

Methylobacterium ajmalii sp. nov., Isolated From the International Space Station.

Four strains belonging to the family of Methylobacteriaceae were isolated from different locations on the International Space Station (ISS) across two consecutive flights. Of these, three were identified as Gram-negative, rod-shaped, catalase-positive, oxidase-positive, motile bacteria, designated as IF7SW-B2T, IIF1SW-B5, and IIF4SW-B5, whereas the fourth was identified as Methylorubrum rhodesianum. The sequence similarity of these three ISS strains, designated as IF7SW-B2T, IIF1SW-B5, and IIF4SW-B5, was <99.4% for 16S rRNA genes and <97.3% for gyrB gene, with the closest being Methylobacterium indicum SE2.11T. Furthermore, the multi-locus sequence analysis placed these three ISS strains in the same clade of M. indicum. The average nucleotide identity (ANI) values of these three ISS strains were <93% and digital DNA-DNA hybridization (dDDH) values were <46.4% with any described Methylobacterium species. Based on the ANI and dDDH analyses, these three ISS strains were considered as novel species belonging to the genus Methylobacterium. The three ISS strains showed 100% ANI similarity and dDDH values with each other, indicating that these three ISS strains, isolated during various flights and from different locations, belong to the same species. These three ISS strains were found to grow optimally at temperatures from 25 to 30°C, pH 6.0 to 8.0, and NaCl 0 to 1%. Phenotypically, these three ISS strains resemble M. aquaticum and M. terrae since they assimilate similar sugars as sole carbon substrate when compared to other Methylobacterium species. Fatty acid analysis showed that the major fatty acid produced by the ISS strains are C18 : 1-ω7c and C18 : 1-ω6c. The predominant quinone was ubiquinone 10, and the major polar lipids were diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, and an unidentified lipid. Therefore, based on genomic, phylogenetic, biochemical, and fatty acid analyses, strains IF7SW-B2T, IIF1SW-B5, and IIF4SW-B5, are assigned to a novel species within the genus Methylobacterium, and the name Methylobacterium ajmalii sp. nov. is proposed. The type strain is IF7SW-B2T (NRRL B-65601T and LMG 32165T).

New Class of Chitosanase from Bacillus amyloliquefaciens for the Generation of Chitooligosaccharides.

Chitooligosaccharides (COS) generated from either chitin (chitin oligosaccharides) or chitosan (chitosan oligosaccharides) have a wide range of applications in agriculture, medicine, and other fields. Here, we report the characterization of a chitosanase from Bacillus amyloliquefaciens (BamCsn) and the importance of a tryptophan (Trp), W204, for BamCsn activity. BamCsn hydrolyzed the chitosan polymer by an endo mode. It also hydrolyzed chitin oligosaccharides and interestingly exhibited transglycosylation activity on chitotetraose and chitopentaose. Mutation of W204, a nonconserved amino acid in chitosanases, to W204A abolished the hydrolytic activity of BamCsn, with a change in the structure that resulted in a decreased affinity for the substrate and impaired the catalytic ability. Phylogenetic analysis revealed that BamCsn could belong to a new class of chitosanases that showed unique properties like transglycosylation, cleavage of chitin oligosaccharides, and the presence of W204 residues, which is important for activity. Chitosanases belonging to the BamCsn class showed a high potential to generate COS from chitinous substrates.

Catalytic efficiency of a multi-domain transglycosylating chitinase from Enterobacter cloacae subsp. cloacae (EcChi2) is influenced by polycystic kidney disease domains.

Bacterial chitinases recruited multiple accessory domains for the conversion of recalcitrant polysaccharides to simple soluble sugars/amino sugars. Here, we report detailed properties of a multi-domain GH18 chitinase from Enterobacter cloacae subsp. cloacae (EcChi2) that preferred ß-chitin as substrate. EcChi2 exhibited transglycosylation (TG) activity on oligomeric substrates from DP4-DP6. The high amount of DP2 is indicative of exo mode activity of EcChi2. We generated EcChi2 variants (truncated and fusion chimeras) and elucidated the role of catalytic and accessory domains. The catalytic efficiency of truncated GH18 and fusion chimera of GH18+ChBD1-ChBD2 decreased to 22 and 17-fold, respectively, than EcChi2, and lost the hydrolytic activity on polymeric substrates, except colloidal chitin. On the other hand, the catalytic activity of truncated PKD1-GH18-PKD2 on polymeric and oligomeric substrates was similar to EcChi2, suggesting that PKD domains are essential for increasing the rate of hydrolysis. Moreover, the truncated ChBD1-ChBD2 and fusion PKD1 + PKD2 participated in chitin-binding.

Selection and mutational analyses of the substrate interacting residues of a chitinase from Enterobacter cloacae subsp. cloacae (EcChi2) to improve transglycosylation.

Transglycosylation (TG) by Enterobacter cloacae subsp. cloacae chitinase 2 (EcChi2) has been deciphered by site-directed mutagenesis. EcChi2 originally displayed feeble TG with chitin oligomer with a degree of polymerization (DP4), for a short duration. Based on the 3D modelling and molecular docking analyses, we altered the substrate interactions at the substrate-binding cleft, catalytic center, and catalytic groove of EcChi2 by mutational approach to improve TG. The mutation of W166A and T277A increased TG by EcChi2 and also affected its catalytic efficiency on the polymeric substrates. Whereas, R171A had a drastically decreased hydrolytic activity but, retained TG activity. In the increased hydrolytic activity of the T277A, altered interactions with the substrates played an indirect role in the catalysis. Mutation of the central Asp, in the conserved DxDxE motif, to Ala (D314A) and Asn (D314N) conversion yielded DP5-DP8 TG products. The quantifiable TG products (DP5 and DP6) increased to 8% (D314A) and 7% (D314N), resulting in a hyper-transglycosylating mutant. Mutation of W276A and W398A resulted in the loss of TG activity, indicating that the aromatic residues (W276 and W398) at +1 and +2 subsites are essential for the TG activity of EcChi2.

Efficient conversion of α-chitin by multi-modular chitinase from Chitiniphilus shinanonensis with KOH and KOH-urea pretreatment.

Enzymatic conversion of α-chitin to high-value chitooligosaccharides (COS) was up to 7.2 % by a slow-acting endo-chitinase (uni-modular) after KOH or KOH-urea pretreatment. Here, we report a better source for efficient conversion of α-chitin, with KOH/KOH-urea (20K2 or 20KU2) pretreatment, by a multi-modular chitinase (CsChiG) from Chitiniphilus shinanonensis. The CsChiG and its catalytic domain (Cat-CsChiG) converted 20KU2 substrate to soluble COS with an efficiency of 43.1 % and 11.8 %, respectively. Deletion of the chitin binding domain has reduced the conversion of untreated and colloidal chitin substrates by 4-5 folds, and for 20K2 and 20KU2 substrates it was only two folds decrease. A combination of KOH or KOH-urea pretreatment, followed by enzymatic hydrolysis with multi-modular chitinases, thus appears a promising approach to convert the abundantly available chitin to highly useful COS.

Functional and molecular characterization of plant growth promoting Bacillus isolates from tomato rhizosphere.

The rhizosphere offers a quintessential habitat for the microbial communities and facilitates a variety of plant-microbe interactions. Members of the genus Bacillus constitute an important group of plant growth promoting rhizobacteria (PGPR), which improve growth and yield of crops. In a total of 60 bacterial isolates from the tomato rhizosphere, 7 isolates were selected based on distinct morphological characteristics and designated as tomato rhizosphere (TRS) isolates with a number suffixed viz., TRS-1, 2, 3, 4, 5, 7, and TRS-8. All the seven isolates were Gram positive, with in vitro plant growth promoting (PGP) traits like phosphate and zinc solubilization, and also produced indoleacetic acid (IAA), phytase, siderophore, hydrogen cyanide (HCN), and 1-aminocyclopropane-1-carboxylate (ACC) deaminase, besides being antagonistic to other microbes and formed biofilm. The seven isolates belonged to the genus Bacillus as per the 16S rDNA sequence analysis. Phylogenetic tree grouped the isolates into four groups, while BOX-PCR fingerprinting allowed further differentiation of the seven isolates. The PGP activity of the isolates was measured on tomato seedlings in plant tissue culture and greenhouse assays. A significant increase in root colonization was observed over 15 days with all the isolates. Greenhouse experiments with these isolates indicated an overall increase in the growth of tomato plants, over 60 days. Isolates TRS-7 and TRS-8 were best plant growth promoters among the seven isolates, with a potential as inoculants to increase tomato productivity.

Chitinase-E from Chitiniphilus shinanonensis generates chitobiose from chitin flakes.

Enzymatic deconstruction of chitin to chitobiose is of significant interest in view of its various biological applications. Here we report detailed insights into the chitin degradation by chitinase-E from a chitinolytic bacterium Chitiniphilus shinanonensis (CsChiE). CsChiE was optimally active at 50 °C in 50 mM sodium phosphate pH-7.0. It showed a kcat and overall catalytic efficiency (Kcat/Km) as 3.9 × 103 s-1 and 0.6 × 103 s-1 mg-1 mL, respectively, on colloidal chitin (CC). CsChiE efficiently hydrolyzed crystalline polymers like α-, ß- and CC and released chitobiose as the predominant product (11.3 mM on CC). Further, CsChiE displayed substantial activity towards the unmilled crab shell chitin waste (chitin-flakes) and generated chitobiose. Activity studies on chitooligosaccharides revealed that CsChiE produced chitobiose as the major product. Our results indicate that the multi-modular CsChiE is a non-processive exo-chitinase which is more suitable to generate chitobiose from a variety of chitinous substrates including unprocessed chitin-flakes.

Pretreatment with KOH and KOH-urea enhanced hydrolysis of α-chitin by an endo-chitinase from Enterobacter cloacae subsp. cloacae.

Chitin is the second most abundant and renewable polysaccharide, next to cellulose. Hydrolysis of abundant and highly crystalline α-chitin, pretreated with KOH and KOH-urea aqueous solutions, by a single modular endo-chitinase from Enterobacter cloacae subsp. cloacae (EcChi1) was investigated. The hydrolysis of untreated α-chitin and colloidal chitin by EcChi1 produced N-acetylglucosamine and N, N'-diacetylchitobiose, whereas, hydrolysis of treated substrates generated N, N', N''-triacetylchitotriose, in addition to N-acetylglucosamine and N, N'-diacetylchitobiose. The total amount of chitooligosaccharides (COS) generated by EcChi1 from pretreated substrates was 10 to 25-fold higher compared to untreated α-chitin at 24 h (depending on the solvent type and state of substrate). EcChi1 released higher amount of DP1 and DP2 products on treated α-chitin, with a fold change of 45 and 18, respectively. Treatment of α-chitin with KOH/KOH-urea is, therefore, a promising approach for an efficient conversion of rich source of chitin to soluble COS by chitinases like EcChi1.

Truncated domains of human serum albumin improves the binding efficiency of uremic toxins: A surface plasmon resonance and computational approach.

Albumin binding is the major cause for the toxicity of protein bound uremic toxins (PBUTs) in uremic patients. Albumin binding property is exploited to address this issue, as some of the extracorporeal dialysis systems use albumin as dialysate. In this line, a detailed study about binding of PBUTs to human serum albumin (HSA) and its domains gives valuable information. The focus of this work emphasizes the mechanism of binding of HSA and its domains with a few selected PBUTs such as hippuric acid (HA), indole acetic acid (IAA) and melatonin. The HSA domains (D2, D3 and D2-3) were expressed in Pichia pastoris and purified by using Albupure matrix. The binding of the expressed domains and HSA, with PBUTs, was measured using surface plasmon resonance and analyzed. All the three domains have significant affinity towards PBUTs, while D3 had greater affinity for all the three selected PBUTs. Docking studies showed that the basic amino acid, lysine, was forming hydrogen bond with PUBTs inorder to stabile these complex. This study would be having therapeutic importance for preparing the extracorporeal dialysis systems, in combination of different domains of HSA to remove the PBUTs.

A transglycosylating chitinase from Chitiniphilus shinanonensis (CsChiL) hydrolyzes chitin in a processive manner.

Chitin, mostly extracted from shrimp waste, is the second most abundant biopolysaccharide, next only to cellulose. Enzymatic conversion of chitin into useful bioactive molecules such as chitooligosaccharides (COS) has potential biotechnological applications. The current study describes the characterization of a single modular GH18 chitinase from Chitiniphilus shinanonensis (CsChiL). CsChiL was optimally active at 50 °C in sodium citrate buffer, pH 6.0 and active over a broad pH range (6-10). In addition to hydrolysis, CsChiL displayed chitobiase and transglycosylation activities on COS with degree of polymerization (DP) 2 and 4-6, respectively. CsChiL hydrolyzed chitin polymers (α, ß, and colloidal chitin) in a processive manner. Molecular dynamics simulations and residue-wise binding energy contributions provided structural insights and molecular basis of inherent transglycosylation activity by CsChiL. Overall, CsChiL could be useful in generation of COS from the chitin obtained from shrimp waste with potential applications in agriculture and food industries.

Opportunities, Challenges and Directions in Science and Technology for Tackling COVID-19.

The ongoing global crisis due to Coronavirus disease-2019 (COVID-19) pandemic has caused an enormous socioeconomic burden. A novel coronavirus causing severe acute respiratory syndrome (SARS-CoV-2) that evolved from a virus infecting bats is responsible for COVID-19, first reported in the Chinese city of Wuhan. In the absence of any specific scientifically proven and clinically tested drug or vaccine against SARS-CoV-2, the virus is wreaking havoc across the world, claiming more than 2,50,000 lives in less than 5 months, and posed a global health emergency. The scientific community is relentlessly working on the design and testing of vaccines and antiviral drugs against the novel coronavirus, several of which have reached advanced stages of testing and are undergoing clinical trials. Here we discuss the recent advances and developments in understanding the etiology and epidemiology of the COVID-19 pandemic, the factors influencing the disease transmission, and the countermeasures adopted to combat and stop further spread of the disease.

Metabolites in the root exudates of groundnut change during interaction with plant growth promoting rhizobacteria in a strain-specific manner.

Plant growth promoting rhizobacteria (PGPR) are extensively used as biofertilizers to improve the soil nutrition for a variety of crop plants. The plant-PGPR interaction, with special reference to chemical signalling molecules is not understood clearly, unlike other beneficial plant-microbe interactions. Chemo-attraction of a PGPR from soil microbial pool towards a plant could be dependent on some of the molecules in the plant root exudates (REs), similar to the beneficial association of legume-rhizobia. In this study, a few functional properties of PGPR like growth, chemotaxis, and biofilm formation by two PGPR strains viz., Bacillus sonorensis RS4 and Pseudomonas aeruginosa RP2 were assessed in the presence of groundnut REs. Functional properties of both the strains were significantly influenced by the REs in a strain-dependent manner. Metabolite profiling of the REs from PGPR-bacterized (RS4 or RP2) and non-bacterized seedlings was performed with GC-MS/MS after 12 and 24 days of growth. A total of 75 metabolites were detected in groundnut REs. Threonine and glyoxylic oxime acid were detected in RP2-bacterized REs, while serine, pentanoic acid, glucopyranoside, tartaric acid, and 2-pyrrolidinone were detected in REs of seedlings bacterized with RP2 and RS4. The results suggested that the PGPR induced distinct variations in the REs. Identification of the interaction-specific metabolites will be useful to develop effective PGPR based bio-formulations for better PGPR colonization and improving crop yields.