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The agricultural crops are often affected by the scarcity of fresh water. Seasonal drought is a major constraint on Northeast Indian agriculture. Almost 80% of the agricultural land in this region is acidic and facing severe drought during the winter period. Apart from classical breeding and transgenic approaches, the application of plant-growth-promoting bacteria (PGPB) is an alternative strategy for improving plant fitness under stressful conditions. The 1-aminocyclopropane-1-carboxylate (ACC) deaminase-producing PGPB offer drought stress tolerance by regulating plant ethylene levels. The aim of the present study was to evaluate the consortium effect of three ACC-deaminase producing rhizobacteria – Ochrobactrum pseudogrignonenseRJ12, Pseudomonas sp.RJ15 and Bacillus subtilisRJ46 on drought stress alleviation in Vigna mungo L. and Pisum sativum L. Consortium treatment significantly increase seed germination percentage, root length, shoot length, and dry weight of treated plants. An elevated production of reactive oxygen species scavenging enzymes and cellular osmolytes; higher leaf chlorophyll content; increase in relative water content and root recovery intension were observed after consortium treatment in comparison with the uninoculated plants under drought conditions. The consortium treatment decreased the ACC accumulation and down-regulated ACC-oxidase gene expression. This consortium could be an effective bio-formulator for crop health improvement in drought-affected acidic agricultural fields.

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Microorganisms associated with medicinal plants are of interest as the producers of important bioactive compounds. To date, the diversity of culturable endophytic actinomycetes associated with medicinal plants is in its initial phase of exploration. In this study, 42 endophytic actinomycetes were isolated from different organs of seven selected medicinal plants. The highest number of isolates (n = 22, 52.3%) of actinomycetes was isolated from roots, followed by stems (n = 9, 21.4%), leaves (n = 6, 14.2%), flowers (n = 3, 7.1%), and petioles (n = 2, 4.7%). The genus Streptomyces was the most dominant among the isolates (66.6%) in both the locations (Dampa TRF and Phawngpuii NP, Mizoram, India). From a total of 42 isolates, 22 isolates were selected for further studies based on their ability to inhibit one of the tested human bacterial or fungal pathogen. Selected isolates were identified based on 16S rRNA gene analysis and subsequently the isolates were grouped to four different genera; Streptomyces, Brevibacterium, Microbacterium, and Leifsonia. Antibiotic sensitivity assay was performed to understand the responsible antimicrobials present in the isolates showing the antimicrobial activities and revealed that the isolates were mostly resistant to penicillin G and ampicillin. Further, antimicrobial properties and antibiotic sensitivity assay in combination with the results of amplification of biosynthetic genes polyketide synthase (PKS-I) and non-ribosomal peptide synthetase (NRPS) showed that the endophytic actinomycetes associated with the selected medicinal plants have broad-spectrum antimicrobial activity. This is the first report of the isolation of Brevibacterium sp., Microbacterium sp., and Leifsonia xyli from endophytic environments of medicinal plants, Mirabilis jalapa and Clerodendrum colebrookianum. Our results emphasize that endophytic actinomycetes associated with medicinal plants are an unexplored resource for the discovery of biologically active compounds.

In this study, a total of 130 rhizobacteria was isolated from a saline infested zone of wheat rhizosphere, and screened for plant growth promoting (PGP) traits at higher salt (NaCl) concentrations (2, 4, 6, and 8%). The results revealed that 24 rhizobacterial isolates were tolerant at 8% NaCl. Although all the 24 salt tolerable isolates produced indole-3-acetic acid (IAA), while 10 isolates solubilized phosphorus, eight produced siderophore, and six produced gibberellin. However, only three isolates showed the production of 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Diversity was analyzed through 16S rDNA-RFLP, and of these isolates with three tetra cutter restriction enzymes (HaeIII, AluI, and MspI), the representative cluster groups were identified by 16S rDNA sequencing. Bacillus and Bacillus-derived genera were dominant which showed PGP attributes at 8% NaCl concentration. Out of 24 isolates, nitrogen fixing ability (nif H gene) was detected in the two isolates, SU18 (Arthrobacter sp.) and SU48.