Muthuswamy Anandaraj

Phosphate solubilizing bacteria isolated from the rhizosphere soil and its growth promotion on black pepper (Piper nigrum L.) cuttings

Bacterial isolates from the rhizosphere soil and root cuttings of bush black pepper (Piper nigrum L.) (pepper raised by laterals) exhibiting high phosphate solubilizing ability in-vitro is described in this paper. Microbial phosphorus solubilization (MPS) trait was analyzed by determining the P solubilization efficiency E (E = Diameter of bacterial growth/Diameter of clearing zone×100). The highest P solubilization efficiency was demonstrated by the isolate PB-21 followed by the isolate PB-16: which was identified as Pseudomonas sp. All isolates under study released inorganic phosphate from tricalcium phosphate (TCP) indicating the potential of these strains to release soluble inorganic phosphates from fixed phosphate sources for plant uptake. The isolate PIAR6-2 was able to solubilize 20.01% of P and also fix atmospheric nitrogen, which was later identified as the nitrogen fixing Azospirillum sp. Greenhouse trials using two systems; viz; Soil:Terracare (composted coir pith) and Sand:Soil:FYM with three experimental sets such as rock phosphate (RP as an external P source), PSB isolate in combination with VAM and PSB isolate alone, all against their respective control sets showed very clearly the growth promoting activity of phosphate solubilizing bacteria. Field studies were also carried out using these isolates and some promising results were obtained. Further studies are required to analyze these strains to confirm its plant growth promoting properties. The in-vitro analyses and greenhouse studies of these bacteria reflect their potentiality as efficient P solubilizer in black pepper growing soils.

Isolation, characterization, and evaluation of multi-trait plant growth promoting rhizobacteria for their growth promoting and disease suppressing effects on ginger

In this study, 100 PGPR strains isolated from different varieties of ginger (Zingiber officinale Rosc.) were first characterized for their morphological, biochemical, and nutrient mobilization traits in vitro. The PGPR were also screened in vitro for inhibition of Pythium myriotylum causing soft rot in ginger. Results revealed that only five PGPR showed >70% suppression of P. myriotylum. These 5 PGPR viz., GRB (Ginger rhizobacteria) 25--Burkholderia cepacia, GRB35--Bacillus amyloliquefaciens; GRB58--Serratia marcescens; GRB68--S. marcescens; GRB91--Pseudomonas aeruginosa were used for further growth promotion and biocontrol studies in the green house and field. The green house study revealed that GRB35 (B. amyloliquefaciens) and GRB68 (S. marcescens) registered markedly higher sprouting (96.3%) and lower disease incidence (48.1%) and greater rhizome yield (365.6 g pot(-1) and 384.4 g pot(-1), respectively), while control registered the lowest sprouting (66%), maximum soft rot incidence (100%) and lowest rhizome yield (134.4 g pot(-1)). In the field experiments also, GRB68 (S. marcescens) and GRB35 (B. amyloliquefaciens) registered the greatest sprouting (80% each), markedly lower soft rot incidence (5.2% and 7.3%, respectively) and higher yield (5.0 and 4.3 kg(3)m(-2), respectively) compared to chemicals like Streptomycin sulphate (73.0%, 18.5% and 2.3 kg(3)m(-2), respectively), Metalaxyl-Mancozeb (73.0%, 14.0% and 3.8 kg(3)m(-2), respectively) and control (73.0%, 25.1% and 2.2 kg 3m(-2), respectively). Overall, the results suggested that for growth promotion and management of soft rot disease in ginger, GRB35 B. amyloliquefaciens and GRB68 S. marcescens could be good alternatives to chemical measures. Since, the latter has been reported to be an opportunistic human pathogen, we recommend the use of B. amyloliquefaciens for integration into nutrient and disease management schedules for ginger cultivation.

Comparison of the Transcriptomes of Ginger (Zingiber officinale Rosc.) and Mango Ginger (Curcuma amada Roxb.) in Response to the Bacterial Wilt Infection

Bacterial wilt in ginger (Zingiber officinale Rosc.) caused by Ralstonia solanacearum is one of the most important production constraints in tropical, sub-tropical and warm temperature regions of the world. Lack of resistant genotype adds constraints to the crop management. However, mango ginger (Curcuma amada Roxb.), which is resistant to R. solanacearum, is a potential donor, if the exact mechanism of resistance is understood. To identify genes involved in resistance to R. solanacearum, we have sequenced the transcriptome from wilt-sensitive ginger and wilt-resistant mango ginger using Illumina sequencing technology. A total of 26387032 and 22268804 paired-end reads were obtained after quality filtering for C. amada and Z. officinale, respectively. A total of 36359 and 32312 assembled transcript sequences were obtained from both the species. The functions of the unigenes cover a diverse set of molecular functions and biological processes, among which we identified a large number of genes associated with resistance to stresses and response to biotic stimuli. Large scale expression profiling showed that many of the disease resistance related genes were expressed more in C. amada. Comparative analysis also identified genes belonging to different pathways of plant defense against biotic stresses that are differentially expressed in either ginger or mango ginger. The identification of many defense related genes differentially expressed provides many insights to the resistance mechanism to R. solanacearum and for studying potential pathways involved in responses to pathogen. Also, several candidate genes that may underline the difference in resistance to R. solanacearum between ginger and mango ginger were identified. Finally, we have developed a web resource, ginger transcriptome database, which provides public access to the data. Our study is among the first to demonstrate the use of Illumina short read sequencing for de novo transcriptome assembly and comparison in non-model species of Zingiberaceae.

Endophytic actinobacteria: Diversity, secondary metabolism and mechanisms to unsilence biosynthetic gene clusters

Abstract Endophytic actinobacteria, which reside in the inner tissues of host plants, are gaining serious attention due to their capacity to produce a plethora of secondary metabolites (e.g. antibiotics) possessing a wide variety of biological activity with diverse functions. This review encompasses the recent reports on endophytic actinobacterial species diversity, in planta habitats and mechanisms underlying their mode of entry into plants. Besides, their metabolic potential, novel bioactive compounds they produce and mechanisms to unravel their hidden metabolic repertoire by activation of cryptic or silent biosynthetic gene clusters (BGCs) for eliciting novel secondary metabolite production are discussed. The study also reviews the classical conservative techniques (chemical/biological/physical elicitation, co-culturing) as well as modern microbiology tools (e.g. next generation sequencing) that are being gainfully employed to uncover the vast hidden scaffolds for novel secondary metabolites produced by these endophytes, which would subsequently herald a revolution in drug engineering. The potential role of these endophytes in the agro-environment as promising biological candidates for inhibition of phytopathogens and the way forward to thoroughly exploit this unique microbial community by inducing expression of cryptic BGCs for encoding unseen products with novel therapeutic properties are also discussed.

Trichoderma harzianum MTCC 5179 impacts the population and functional dynamics of microbial community in the rhizosphere of black pepper (Piper nigrum L.)

Employing Illumina Hiseq whole genome metagenome sequencing approach, we studied the impact of Trichoderma harzianum on altering the microbial community and its functional dynamics in the rhizhosphere soil of black pepper (Piper nigrum L.). The metagenomic datasets from the rhizosphere with (treatment) and without (control) T. harzianum inoculation were annotated using dual approach, i.e., stand alone and MG-RAST. The probiotic application of T. harzianum in the rhizhosphere soil of black pepper impacted the population dynamics of rhizosphere bacteria, archae, eukaryote as reflected through the selective recruitment of bacteria [Acidobacteriaceae bacterium (p = 1.24e−12), Candidatus koribacter versatilis (p = 2.66e−10)] and fungi [(Fusarium oxysporum (p = 0.013), Talaromyces stipitatus (p = 0.219) and Pestalotiopsis fici (p = 0.443)] in terms of abundance in population and bacterial chemotaxis (p = 0.012), iron metabolism (p = 2.97e−5) with the reduction in abundance for pathogenicity islands (p = 7.30e−3), phages and prophages (p = 7.30e−3) with regard to functional abundance. Interestingly, it was found that the enriched functional metagenomic signatures on phytoremediation such as benzoate transport and degradation (p = 2.34e−4), and degradation of heterocyclic aromatic compounds (p = 3.59e−13) in the treatment influenced the rhizosphere micro ecosystem favoring growth and health of pepper plant. The population dynamics and functional richness of rhizosphere ecosystem in black pepper influenced by the treatment with T. harzianum provides the ecological importance of T. harzianum in the cultivation of black pepper.