Isolation,characterisation of major secondary metabolites of the Himalayan Trichoderma koningii and their antifungal activity

Ethyl acetate extracts of two strains of Trichoderma koningii were evaluated for antifungal activity against soilborne pathogenic fungi, Rhizoctonia solani, Sclerotium rolfsii, Macrophomina phaseolina and Fusarium oxysporum by poisoned food technique. Secondary metabolites, namely δ-decanolactone, 6-pentyl-α-pyranone and 6-(4-oxopentyl)-2H-pyran-2-one were isolated from T. koningii (T-8) extract while palmitic acid, 6-pentyl-α-pyranone and stigmasterol were isolated from T. koningii (T-11) extract. Secondary metabolites were identified by ¹H NMR, ¹³C NMR and mass spectroscopic methods. These metabolites were evaluated for antifungal activity against the test pathogens 6-Pentyl-α-pyranone and 6-(4-oxopentyl)-2H-pyran-2-one exhibited excellent antifungal activity against S. rolfsii. The antifungal activity though slightly less was comparable to that of hexaconazole, a commercial fungicide.     

Microbial population index and community structure in saline–alkaline soil using gene targeted metagenomics

Population indices of bacteria and archaea were investigated from saline–alkaline soil and a possible microbe–environment pattern was established using gene targeted metagenomics. Clone libraries were constructed using 16S rRNA and functional gene(s) involved in carbon fixation (cbbL), nitrogen fixation (nifH), ammonia oxidation (amoA) and sulfur metabolism (apsA). Molecular phylogeny revealed the dominance of Actinobacteria, Firmicutes and Proteobacteria along with archaeal members of Halobacteraceae. The library consisted of novel bacterial (20%) and archaeal (38%) genera showing ≤95% similarity to previously retrieved sequences. Phylogenetic analysis indicated ability of inhabitant to survive in stress condition. The 16S rRNA gene libraries contained novel gene sequences and were distantly homologous with cultured bacteria. Functional gene libraries were found unique and most of the clones were distantly related to Proteobacteria, while clones of nifH gene library also showed homology with Cyanobacteria and Firmicutes. Quantitative real-time PCR exhibited that bacterial abundance was two orders of magnitude higher than archaeal. The gene(s) quantification indicated the size of the functional guilds harboring relevant key genes. The study provides insights on microbial ecology and different metabolic interactions occurring in saline–alkaline soil, possessing phylogenetically diverse groups of bacteria and archaea, which may be explored further for gene cataloging and metabolic profiling.     

Genome‐wide analysis of polymorphisms identified domestication‐associated long low‐diversity region carrying important rice grain size/weight quantitative trait loci

Rice grain size and weight are major determinants of grain quality and yield and so have been under rigorous selection since domestication. However, the genetic basis for contrasting grain size/weight trait among Indian germplasms and their association with domestication‐driven evolution is not well understood. In this study, two long (LGG) and two short grain (SGG) genotypes were resequenced. LGG (LGR and PB 1121) differentiated from SGG (Sonasal and Bindli) by 504 439 single nucleotide polymorphisms (SNPs) and 78 166 insertion‐and‐deletion polymorphisms. The LRK gene cluster was different and a truncation mutation in the LRK8 kinase domain was associated with LGG. Phylogeny with 3000 diverse rice accessions revealed that the four sequenced genotypes belonged to the japonica group and were at the edge of the clades indicating them to be the potential source of genetic diversity available in Indian rice germplasm. Six SNPs were significantly associated with grain size/weight and the top four of these could be validated in mapping a population, suggesting this study as a valuable resource for high‐throughput genotyping. A contiguous long low‐diversity region (LDR) of approximately 6 Mb carrying a major grain weight quantitative trait loci (harbouring OsTOR gene) was identified on Chromosome 5. This LDR was identified as an evolutionary important site with significant positive selection and multiple selection sweeps, and showed association with many domestication‐related traits, including grain size/weight. The aus population retained more allelic variations in the LDR than the japonica and indica populations, suggesting it to be one of the divergence loci. All the data and analyses can be accessed from the RiceSzWtBase database.     

Nitric Oxide Induces Flowering in the Duckweed Lemna aequinoctialis Welw. (Syn. L. paucicostata Hegelm.) Under Noninductive Conditions

Nitric oxide (NO) plays diverse roles in the growth and development of plants and in their responses to various abiotic and biotic stresses. It has also been reported to repress flowering in Arabidopsis thaliana. In the present study, NO donors sodium nitroprusside (SNP), S-nitroso-N-acetyl penicillamine (SNAP), and 3-morpholinosydnonimine (SIN-1) induced flowering in Lemna aequinoctialis 6746 (a short-day strain) and in L. aequinoctialis LP₆ (a photoperiod-insensitive strain) under noninductive conditions. Nitrate and nitrite, two stable metabolites of NO, did not induce flowering. On the other hand, cyanide donors potassium ferricyanide {K₃[Fe(CN)₆]} and potassium cyanide (KCN) induced flowering in both strains under noninductive conditions. The flowering induced under a 8-h daily photoperiod regime in the short-day strain L. aequinoctialis 6746 was inhibited by NO and cyanide donors. Vegetative multiplication of both strains was adversely affected by NO and cyanide donors, irrespective of the photoperiod conditions. The observed effects of NO donors on flowering were substantially negated by NO scavengers c-PTIO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide] and methylene blue. This confirmed the role of NO in induction of flowering. The inductive effect of CN⁻ also appeared to be partly mediated through NO as NO scavengers partially negated the effect of CN⁻.     

Occurrence of unique three-celled megagametophyte and single fertilization in an aquatic angiosperm-Dalzellia zeylanica (Podostemaceae-Tristichoideae)

Angiosperms are characterized by the occurrence of double fertilization. However, Podostemaceae is considered an exception with the presence of only single fertilization (syngamy) though two male gametes are formed conventionally. To determine the cause for the failure of double fertilization in Dalzellia zeylanica (Gardn.) Wight, we closely tracked the movement of the male gametes from the time of pollen tube initiation to the time of entry into the megagametophyte to affect fertilization. We report for the first time, the presence of a novel type of three-nucleate/three-celled mature megagametophyte consisting of two synergids and an egg cell in D. zeylanica. Therefore, of the two male gametes formed in this plant, one fuses with the egg cell resulting in syngamy, whereas the other male gamete eventually degenerates due to the absence of its partner i.e. single polar nucleus of the central cell that degenerates prior to the entry of the pollen tube into the synergid. The present work not only highlights the highly reduced nature of megagametophyte but also the occurrence of single fertilization resulting in sperm selection in D. zeylanica.     

Purification and characterization of Plasmodium yoelii adenosine deaminase

Plasmodium lacks the de novo pathway for purine biosynthesis and relies exclusively on the salvage pathway. Adenosine deaminase (ADA), first enzyme of the pathway, was purified and characterized from Plasmodium yoelii, a rodent malarial species, using ion exchange and gel exclusion chromatography. The purified enzyme is a 41 kDa monomer. The enzyme showed K_m values of 41 μM and 34 μM for adenosine and 2′-deoxyadenosine, respectively. Erythro-9-(2-hydroxy-3-nonyl) adenine competitively inhibited P. yoelii ADA with K_i value of 0.5 μM. The enzyme was inhibited by DEPC and protein denaturing agents, urea and GdmCl. Purine analogues significantly inhibited ADA activity. Inhibition by p-chloromercuribenzoate (pCMB) and N-ethylmaleimide (NEM) indicated the presence of functional –SH groups. Tryptophan fluorescence maxima of ADA shifted from 339 nm to 357 nm in presence of GdmCl. Refolding studies showed that higher GdmCl concentration irreversibly denatured the purified ADA. Fluorescence quenchers (KI and acrylamide) quenched the ADA fluorescence intensity to the varied degree. The observed differences in kinetic properties of P. yoelii ADA as compared to the erythrocyte enzyme may facilitate in designing specific inhibitors against ADA.     

Wastewater utilization for poly-β-hydroxybutyrate production by the cyanobacterium Aulosira fertilissima in a recirculatory aquaculture system

Intensive aquaculture releases large quantities of nutrients into aquatic bodies, which can lead to eutrophication. The objective of this study was the development of a biological recirculatory wastewater treatment system with a diazotrophic cyanobacterium, Aulosira fertilissima, and simultaneous production of valuable product in the form of poly-β-hydroxybutyrate (PHB). To investigate this possible synergy, batch scale tests were conducted under a recirculatory aquaculture system in fiber-reinforced plastic tanks enhanced by several manageable parameters (e.g., sedimentation, inoculum size, depth, turbulence, and light intensity), an adequate combination of which showed better productivity. The dissolved-oxygen level increased in the range of 3.2 to 6.9 mg liter⁻¹ during the culture period. Nutrients such as ammonia, nitrite, and phosphate decreased to as low as zero within 15 days of incubation, indicating the system''s bioremediation capability while yielding valuable cyanobacterial biomass for PHB production. Maximum PHB accumulation in A. fertilissima was found in sedimented fish pond discharge at 20-cm culture depth with stirring and an initial inoculum size of 80 mg dry cell weight (dcw) liter⁻¹. Under optimized conditions, the PHB yield was boosted to 92, 89, and 80 g m⁻², respectively for the summer, rainy, and winter seasons. Extrapolation of the result showed that a hectare of A. fertilissima cultivation in fish pond discharge would give an annual harvest of ∼17 tons dry biomass, consisting of 14 tons of PHB with material properties comparable to those of the bacterial polymer, with simultaneous treatment of 32,640 m³ water discharge.     

High‐Performance Hydrogen Evolution by Ru Single Atoms and Nitrided‐Ru Nanoparticles Implanted on N‐Doped Graphitic Sheet

The most efficient electrocatalyst for the hydrogen evolution reaction (HER) is a Pt‐based catalyst, but its high cost and nonperfect efficiency hinder wide‐ranging industrial/technological applications. Here, an electrocatalyst of both ruthenium (Ru) single atoms (SAs) and N‐doped‐graphitic(G_N)‐shell‐covered nitrided‐Ru nanoparticles (NPs) (having a Ru‐N_x shell) embedded on melamine‐derived G_N matrix { 1 : [Ru(SA)+Ru(NP)@RuN_x@G_N]/G_N}, which exhibits superior HER activity in both acidic and basic media, is presented. In 0.5 m H₂SO₄/1 m KOH solutions, 1 shows diminutive “negative overpotentials” (?η = |η| = 10/7 mV at 10 mA cm^?2, lowest ever) and high exchange current densities (4.70/1.96 mA cm^?2). The remarkable HER performance is attributed to the near‐zero free energies for hydrogen adsorption/desorption on Ru(SAs) and the increased conductivity of melamine‐derived G_N sheets by the presence of nitrided‐Ru(NPs). The nitridation process forming nitrided‐Ru(NPs), which are imperfectly covered by a G_N shell, allows superb long‐term operation durability. The catalyst splits water into molecular oxygen and hydrogen at 1.50/1.40 V (in 0.1 m HClO₄/1 m KOH), demonstrating its potential as a ready‐to‐use, highly effective energy device for industrial applications.     

Overexpression of citrate operon in Herbaspirillum seropedicae Z67 enhances organic acid secretion,mineral phosphate solubilization and growth promotion of Oryza sativa

Background and aims

Herbaspirillum seropedicae Z67, nitrogen fixing endophyte, significantly promotes the growth of cereals. Organic acid secreting nitrogen fixing rhizobacteria have better plant growth promotion abilities due to mineral phosphate solubilization.

Method

Plasmids pAB7, pJNK3 and pJNK4 containing Escherichia coli cs (gltA), NADH insensitive cs (gltA1), and citrate operon consisting of gltA1 gene along with Salmonella typhimurium Na⁺ dependent citrate transporter (citC) gene under constitutive lac promoter were constructed in broad host range plasmid pUCPM18-Km^r. The plasmid transformants of H. seropedicae Z67 were obtained by electroporation.

Results

Hs (pAB7) and Hs (pJNK3) had increased CS activity but citric acid secretion was not significant. Hs (pJNK3) secreted 45 mM acetic acid while Hs (pJNK4) secreted 2.7 mM citric and 51 mM acetic acids. Hs (pJNK3) and Hs (pJNK4) released 80 μM and 110 μM amount of P from rock phosphate, respectively, in buffered medium under both aerobic and micro aerobic conditions. These transformants showed better plant growth promoting factors. Upon inoculation to rice plants (Gujarat – 17), increase of Fresh weight, Dry weight N, P and K content was observed.

Conclusion

Thus the study demonstrates that artificial citrate operon in H. seropedicae Z67 enhances phosphate solubilization and plant growth promotion abilities.