The present study is the first report of isolation and characterization of endophytic actinobacteria from cactus (Opuntia ficus-indica). A total of 179 morphologically distinct endophytic actinobacterial isolates were purified from the roots of two different genetic accessions of cactus. All these isolates were screened for their plant growth promotion traits namely growth on N-free medium, P-solubilization, siderophore production, ACC deaminase activity and IAA production. A majority of the endophytic actinobacterial isolates (85%) exhibited the potential for plant growth promotion under in vitro conditions. Ten among the isolates were selected based on their multi-PGP traits and were identified as Streptomyces sp. based on the 16S rRNA gene sequencing and phylogenetic analysis. Plant growth promoting potential of these selected endophytic Streptomyces was studied in wheat seedlings. All these selected isolates significantly enhanced the growth parameters like seedling length and rootlets number compared to the uninoculated control. The wheat seeds inoculated with Streptomyces tuirus VL-70-IX exhibited maximum number of rootlets (6.33) compared to uninoculated control (3.67). The inoculation of endophytic actinobacteria Streptomyces pseudogriseolus VL-70-XII caused maximum seedling length (20.53 cm) and root length (8.26 cm) while the inoculation of S. radiopugnans HV-VIII resulted in highest shoot length (12.33 cm). These endophytic actinobacteria isolated from the roots of cactus accessions showed potential PGP traits. This work lays foundation for characterization and selection of endophytic actinobacteria from the under-exploited, drought tolerant species such as cactus with potential cross-compatibility for the improvement of plant growth of field crops especially under abiotic stress conditions..
Xylanases are glycosyl hydrolases that catalyze the hydrolysis of internal beta-1,4 glycosidic bonds of xylan, the major hemi-cellulose component of the plant cell wall. Enzymes such as xylanases are used considerably in industries. Their industrial usage is especially attractive since they can replace some of the environmental pollutants. We have earlier isolated a family 11-xylanase gene from Bacillus subtilis-AK1, which is active at high temperature as well as at alkaline pH. In order to understand the factors liable for the adaptation of this enzyme, three dimensional model of B. subtilis-AK1 xylanase has now been obtained by homology modeling. Modeling was carried out using Molecular Operating Environment (MOE) software developed by Chemical Computing Group Inc., running on Pentium IV workstation. The model showed that B. subtilis-AK1 xylanase having molecular weight around 20 kDa contains in its fold an alpha-helix and two beta-sheets packed against each other forming a beta-sandwich. The conserved active site amino acids E78R, Y80L were mutated in this novel B. subtilis-AK1 strain, but the protein folding and the function was maintained with high thermal stability. Several minor modifications appeared to be responsible for the increased thermo stability of AK1. Docking studies of the substrate xylan with -AK1 shows the possibility of the Arg 78 acting as the nucleophile instead of Glu 78.
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