Prioritizing Tiger Conservation through Landscape Genetics and Habitat Linkages

Even with global support for tiger (Panthera tigris) conservation their survival is threatened by poaching, habitat loss and isolation. Currently about 3,000 wild tigers persist in small fragmented populations within seven percent of their historic range. Identifying and securing habitat linkages that connect source populations for maintaining landscape-level gene flow is an important long-term conservation strategy for endangered carnivores. However, habitat corridors that link regional tiger populations are often lost to development projects due to lack of objective evidence on their importance. Here, we use individual based genetic analysis in combination with landscape permeability models to identify and prioritize movement corridors across seven tiger populations within the Central Indian Landscape. By using a panel of 11 microsatellites we identified 169 individual tigers from 587 scat and 17 tissue samples. We detected four genetic clusters within Central India with limited gene flow among three of them. Bayesian and likelihood analyses identified 17 tigers as having recent immigrant ancestry. Spatially explicit tiger occupancy obtained from extensive landscape-scale surveys across 76,913 km² of forest habitat was found to be only 21,290 km². After accounting for detection bias, the covariates that best explained tiger occupancy were large, remote, dense forest patches; large ungulate abundance, and low human footprint. We used tiger occupancy probability to parameterize habitat permeability for modeling habitat linkages using least-cost and circuit theory pathway analyses. Pairwise genetic differences (F _ST) between populations were better explained by modeled linkage costs (r>0.5, p<0.05) compared to Euclidean distances, which was in consonance with observed habitat fragmentation. The results of our study highlight that many corridors may still be functional as there is evidence of contemporary migration. Conservation efforts should provide legal status to corridors, use smart green infrastructure to mitigate development impacts, and restore habitats where connectivity has been lost.     

Characterization of metabolically active developmental stage of Aspergillus niger cells immobilized in polyacrylamide gel

Summary The in-situ development of Aspergillus niger entrapped in polyacrylamide gel from spores and the gel surface characteristics were studied during the repeated shake flask batch citric acid fermentation. A marked increase in the rate of citric acid production was observed with the periodic replacement of culture with fresh media at an interval of 6 days reducing the fermentation time nearly to half. The metabolically active A. niger cells for citric acid production were characterized by the appearance of thick and bulbous hyphae scattered in and on the gel surface.     

Mutants of initiator tRNA that function both as initiators and elongators

We describe the effect of mutations in the acceptor stem of Escherichia coli initiator tRNA on its function in vivo. The acceptor stem mutations were coupled to mutations in the anticodon sequence from CAU----CUA to allow functional studies on the mutant tRNAs in initiation and in elongation in vivo. We show that, with one exception, there is a good correlation between the kinetic parameters for formylation of the mutant tRNAs in vitro (preceding paper, Lee, C.P., Seong, B. L., and RajBhandary, U.L. (1991) J. Biol. Chem. 266, 18012-18017) and their activity in initiation in vivo. These results suggest an important role for formylation of initiator tRNA in its function in initiation, at least when it is aminoacylated with glutamine as is the case with the mutant tRNAs used here. Mutant tRNAs that have a base pair between nucleotides 1 and 72 at the top of the acceptor stem function as elongators, as analyzed by their ability to suppress an amber mutation in the E. coli beta-galactosidase gene. One of these mutants is also quite active in initiation. Thus, activities of a tRNA in initiation and elongation steps of protein synthesis are not mutually exclusive. Using a mRNA with two in frame UAG codons, we show that this mutant tRNA can both initiate protein synthesis from the upstream UAG and suppress the down-stream UAG. We discuss the potential use of tRNAs with such "dual" functions in tightly regulated expression of genes for proteins in E. coli.     

Role of methionine and formylation of initiator tRNA in initiation of protein synthesis in Escherichia coli.

We showed recently that a mutant of Escherichia coli initiator tRNA with a CAU-->CUA anticodon sequence change can initiate protein synthesis from UAG by using formylglutamine instead of formylmethionine. We further showed that coupling of the anticodon sequence change to mutations in the acceptor stem that reduced Vmax/Km(app) in formylation of the tRNAs in vitro significantly reduced their activity in initiation in vivo. In this work, we have screened an E. coli genomic DNA library in a multicopy vector carrying one of the mutant tRNA genes and have found that the gene for E. coli methionyl-tRNA synthetase (MetRS) rescues, partially, the initiation defect of the mutant tRNA. For other mutant tRNAs, we have examined the effect of overproduction of MetRS on their activities in initiation and their aminoacylation and formylation in vivo. Some but not all of the tRNA mutants can be rescued. Those that cannot be rescued are extremely poor substrates for MetRS or the formylating enzyme. Overproduction of MetRS also significantly increases the initiation activity of a tRNA mutant which can otherwise be aminoacylated with glutamine and fully formylated in vivo. We interpret these results as follows. (i) Mutant initiator tRNAs that are poor substrates for MetRS are aminoacylated in part with methionine when MetRS is overproduced. (ii) Mutant tRNAs aminoacylated with methionine are better substrates for the formylating enzyme in vivo than mutant tRNAs aminoacylated with glutamine. (iii) Mutant tRNAs carrying formylmethionine are significantly more active in initiation than those carrying formylglutamine. Consequently, a subset of mutant tRNAs which are defective in formylation and therefore inactive in initiation when they are aminoacylated with glutamine become partially active when MetRS is overproduced.     

Glucose oxidase immobilized electrode for potentiometric estimation of glucose

Glucose oxidase has been immobilized onto a thin platinum strip, by co-crosslinking with bovine serum albumin and glutaraldehyde. The retention of redox characteristics of glucose oxidase has been verified by cyclic voltammetry. The activity of the immobilized enzyme reduces to a quarter of its value when the enzyme is in solution but improves when coimmobilized with 1 urea. The potentiometric response builds up and remains stable after 100 s. It is sensitive to the thickness of the immobilizing matrix, pH and temperature. An improvement in the performance of the electrode has been achieved by coimmobilizing 2 urea and metal ions such as Mg²⁺ and Mn²⁺. The presence of Cu has been proved to be detrimental. The electrode has been calibrated in the 0.1–5.0 mM glucose concentration range. It gives a stable response for more than 50 independent assays and can be stored for 60 days without significant loss of function.     

Raffinose family oligosaccharides (RFOs): role in seed vigor and longevity

Seed vigor and longevity are important agronomic attributes, as they are essentially associated with crop yield and thus the global economy. Seed longevity is a measure of seed viability and the most essential property in gene bank management since it affects regeneration of seed recycling. Reduced seed life or storability is a serious issue in seed storage since germplasm conservation and agricultural enhancement initiatives rely on it. The irreversible and ongoing process of seed deterioration comprises a complex gene regulatory network and altered metabolism that results in membrane damage, DNA integrity loss, mitochondrial dysregulation, protein damage, and disrupted antioxidative machinery. Carbohydrates and/or sugars, primarily raffinose family oligosaccharides (RFOs), have emerged as feasible components for boosting or increasing seed vigor and longevity in recent years. RFOs are known to perform diverse functions in plants, including abiotic and biotic stress tolerance, besides being involved in regulating seed germination, desiccation tolerance, vigor, and longevity. We emphasized and analyzed the potential impact of RFOs on seed vigor and longevity in this review. Here, we comprehensively reviewed the molecular mechanisms involved in seed longevity, RFO metabolism, and how RFO content is critical and linked with seed vigor and longevity. Further molecular basis, biotechnological approaches, and CRISPR/Cas applications have been discussed briefly for the improvement of seed attributes and ultimately crop production. Likewise, we suggest advancements, challenges, and future possibilities in this area.