Insight into Andrographis paniculata associated bacterial endomicrobiome and assessment of culturable bacterial endophytes for enhancement of industrially important andrographolide content

Andrographis paniculata is a common medicinal plant used worldwide for its preventive and curative properties. However, no information exists about the A. paniculata associated bacterial endophytes and their potential relationship with the plant-bioactive substances. In this study, we investigated the bacterial endophytic diversity of A. paniculata root and shoot tissues using culture-based and culture-independent high-throughput sequencing methods. The culture-independent analyses unveiled the presence of 465 operational taxonomic units (OTU's) and 232 genera, respectively in the samples. Further, downstream categorization of OTU's revealed the dominance of Proteobacteria, Firmicutes, Actinobacteria and Bacteriodetes phylum members, with Bacillus being the most prevalent endophytic genera in the root, while Pseudomonas dominated the shoot tissues. A total of 39 bacterial endophytes from the roots, stems, leaves, and seeds of A. paniculata were isolated by a culture-dependent investigation whose subsequent examination using 16S rRNA gene sequencing confirmed a similar pattern of the dominance of the Bacillus and Pseudomonas genera. When all the isolates were further screened for their plant growth promotion activity, Micrococcus luteus (ASd6) significantly enhanced the biomass and andrographolide content by 68.01% and 44.16%, respectively. Taken together, the information captured through metagenomics and culture-dependent approach reveals some promising bacterial endophytes which could be employed in field for growth promotion and in planta secondary metabolite enhancement studies in near future.