No abstract

Natural melanin with many interesting properties has potential applications in cosmetics, drug delivery, semiconductors, etc. However, conventional production methods are not efficient, resulting in its high cost (350−650 USD g −1 ), which has been a bottleneck for its efficient commercial utilization. To explore a faster extraction method with a higher yield, a melanin-producing endophytic bacterium was isolated from the halophyte Salicornia brachiata and further identified as Bacillus subtilis 4NP-BL by phylogenetic analysis of 16S rRNA gene sequences. The maximum melanin yield of up to 1.5 g dry wt L −1 of production media was obtained through central composite design (CCD). The isolated melanin belonged to the eumelanin class with an irregular structure on the basis of elemental analysis, UV−vis, Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), and NMR studies. Furthermore, purified melanin displayed antioxidant activity and antimicrobial activity against pathogens Xanthomonas campestris and Alteromonas macleodii. Thus, this study further suggests a probable role of endophytes that produce melanin in aiding host plant protection from environmental stress and other pathogens.

Untapped natural habitats like halophytes, marsh land, and marine environment are suitable arena for chemical ecology between plants and microbes having environmental impact. Endophytes constitute an ecofriendly option for the promotion of plant growth and to serve as sustainable resources of novel bioactive natural products. The present study focusing on biodiversity of bacterial endophytes from Salicornia brachiata, led to isolation of around 350 bacterial endophytes. Phylogenetic analysis of 63 endophytes revealed 13 genera with 29 different species, belonging to 3 major groups: Firmicutes, Proteobacteria and Actinobacteria. 30% isolates belonging to various genera demonstrated broadspectrum antibacterial and antifungal activities against a panel of human, plant, and aquatic infectious agents. An endophytic isolate Bacillus amyloliquefaciens 5NPA-1, exhibited strong in-vitro antibacterial activity against human pathogen S. aureus and phytopathogen X. campestris. Investigation through LC-MS/MS-based molecular networking and bioactivity-guided purification led to the identification of three bioactive compounds belonging to lipopeptide class on the basis of 1 H-and 13 C-NMR and MS analysis. To our knowledge, this is the first report studying bacterial endophytic biodiversity of Salicornia brachiata and isolation of bioactive compounds from its endophyte. Overall, the present study provides insights into the diversity of endophytes associated with the plants from the extreme environment as rich source of metabolites with remarkable agricultural applications and therapeutic properties.