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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.

Polyhydroxyalkanoates (PHAs) have a wide range of applicability due to their biodegradable and biocompatible characteristics. This makes them suitable for commercialization as an alternative to petroleum-based synthetic plastics. Solvents such as chloroform are reported to solubilize polyhydroxyalkanoates. With chloroform being hazardous for both health and the environment, this work attempts to replace this chlorinated solvent with green solvents like ionic liquids. In this study, poly-[(R)-3hydroxybutyrate] (PHB) was extracted from Halomonas hydrothermalis, and its solubility, stability, and film-forming ability were investigated in the presence of ammonium-based ionic liquids (ILs). Among the studied ILs, maximum solubility (3% w/v at 70 °C) along with chemical and structural stability of the polymer was observed in diethanol ammonium acetate (DA), while the lowest dissolution (0.4% w/v) was exhibited in 2-hydroxyethylammonium formate (HF). The molecular docking studies have established a critical role of the anions of the ILs in the dissolution process. Further, PHB dissolved in DA formed a film in the presence of gelatin (G). The recovered ILs were found to be soil compatible, and due to their high nitrogen content, they can be used as a fortifier for nitrogen-deficient seaweed-based liquid plant biostimulants making them suitable soil nutrients for agriculture applications.

The bacterial endophytes isolated from the halophyte Salicornia brachiata were explored for the antimicrobial potential to discover novel microbial inhibitors that combat multidrug resistance. Upon investigation, ethyl acetate extract of the endophyte Bacillus subtilis NPROOT3 displayed significant potency against Mycobacterium smegmatis MTCC6 as well as Mycobacterium tuberculosis H37Rv strain. Further investigation of ethyl acetate crude extract by repeated chromatographic separations followed by characterization using UV, HR-ESI-MS, MALDI-MS, MALDI-MS/MS, CD, and NMR spectroscopy yielded a series of five known siderophores, namely, SVK21 (1), bacillibactin C (2), bacillibactin B (3), tribenglthin A (4), and bacillibactin (5). A total of two out of five compounds, 4 (MIC 38.66 μM) and 5 (MIC 22.15 μM) exhibited significant inhibition against the strain M. smegmatis MTCC6 comparable with positive control rifampicin (MIC 12.15 μM). None of these five bacillibactin molecules are previously reported to exhibit bioactivity against Mycobacterium sp. Herein for the first time, all the compounds were screened for their antibacterial activities against a panel of bacterial pathogens of humans. Furthermore, the probable mechanism of action of bacillibactin compounds for their antimycobacterial activity is also discussed. The findings of this study open up a new chemotype for inhibition of the Mycobacterium sp. and other multidrug-resistant pathogens.

Among various protein-containing biomass wastes, waste animal wool, poultry feather, and human hair are considered one of the most important renewable sources of keratin. Animal wool and human hair are utilized for the production of several products. However, the substantial quantity of short fibers that are inappropriate for spinning and being unusable is thrown away as waste resulting in significant environmental issues in terms of their accumulation in water bodies resulting in obstruction of waterways and other related problems. Similarly, poultry wastes, especially waste chicken feathers (WCF) are dumped or burnt or used as low-value fertilizer in certain applications. The purpose of this research is to develop an efficient method that can extract the recoverable keratin from various wastes and effectively utilize the spent solvent in the extraction process. Herein suitability of an aqueous solution of quaternary ammonium hydroxide known as tetramethyl ammonium hydroxide (TMAOH, 25% w/w in water) to solubilize these protein wastes and extract keratin from them was investigated. The solvent could solubilize ca. 39-44% w/w of waste animal wool (WAW), 19-25% of waste human hair (WHH), and 55-60% of WCF. Crude keratin with ca. 19-20%, 35-37%, and 69-74% were isolated from WAW, WHH, and WCF, respectively. The chemical and structural stability of keratin thus isolated was established. The recovered TMAOH, insoluble WAW, and WCF were found to be nontoxic to soil microbes. The recovered TMAOH thus generated after isolation of keratin was used for green gram (Vigna radiata) seed treatment, and a substantial increase in the height (4-12%) and weight (9-58%) of the plants was observed. Treating biomass waste as a source of high-value compounds may minimize environmental impact by reducing the waste load.

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 broad-spectrum 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 1H- and 13C-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.

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