The Antibacterial, Antitumor Activities, and Bioactive Constituents’ Identification of Alectra sessiliflora Bacterial Endophytes

Exploration of Klebsiella aerogenes derived secondary metabolites and their antibacterial activities against multidrug-resistant bacteria

As the effectiveness of current treatments against the development of antimicrobial resistance is declining, new strategies are required. A great source of novel secondary metabolites with therapeutics effects are the endophytic bacteria present in medicinal plants. In this study, Klebsiella aerogenes (an endophytic bacteria belonging to the Enterobacteriaceae family) was isolated from Kalanchoe blossfeldiana (a medicinal plant". The bacterial secondary metabolites were identified using GC-MS techniques. Furthermore, the antibacterial potentials were investigated against multi-drug resistance (MDR) Salmonella typhi and Staphylococcus aureus. The GC-MS chromatogram of K. aerogenes secondary metabolites extract displayed total of 36 compounds. Ethyl acetate extracts of K. aerogenes, showed mean zone of growth inhibition of 15.00 ± 1.00 against S. typhi and 7.00 ± 1.00mm against S. aureus, respectively. The extract demonstrated significant antibacterial effectiveness against S. typhi and moderate antibacterial efficacy against S. aureus, with minimum inhibitory concentration (MIC) values ranging from 0.089 to 0.39 mg/mL. The time-kill kinetics profile of the ethyl acetate extract against S. typhi revealed a decrease in the number of viable cells during the initial 5, 6, and 24 hours. Conversely, there was a sudden increase in viable cells up to 6 hours for S. aureus. The identified secondary metabolite with high percentage than others, benzeneethanamine exhibited favorable interactions (-7.2 kcal/mol) with the penicillin-binding protein (PBP2a) of S. aureus and (-7.5 kcal/mol) osmoporin (OmpC) of S. typhi, indicating its potential as a candidate for drug development against these MDR bacteria. This study reported for the first time, bacterial endophytes associated with K. blossfeldiana with antibacterial activities.

Isolation, identification, and biological characterization of bacterial endophytes isolated from Gunnera perpensa L

In the present study, eleven endophytic bacterial strains, Herbaspirillum sp. (GP-SGM1, GP-SGM2, GP-SGM3, and GP-SGM11), Pseudomonas sp. (GP-SGM4, GP-SGM5), Novosphingobium sp. GP-SGM6, Chryseobacterium sp. GP-SGM7, Labedella sp. GP-SGM8, Brevibacterium sp. GP-SGM9, and Pseudomonas sp. GP-SGM10, were isolated from the rhizomes of Gunnera perpensa L. The growth kinetics, assessed through maximum growth rates (μmax) and optical density (OD) values, revealed that GP-SGM7 exhibited highest μmax values of 0.33 ± 0.01 hours (h)-1 with an OD of 4.20 ± 0.04. In contrast, GP-SGM11 exhibited the lowest μmax of 0.12 ± 0.05 h-1 and the smallest OD of 1.50 ± 0.00. In addition, the endophyte crude extracts were tested for antibacterial activity against five pathogenic strains using the disk diffusion method, with GP-SGM7 crude extracts exhibiting promising antibacterial activity against Klebsiella pneumoniae and Staphylococcus aureus. Antioxidant activity was determined by DPPH (2, 2-diphenyl-1-picrylhydrazyl) and FRAP (ferric reducing antioxidant power) assays. The crude extracts of GP-SGM1, GP-SGM7, GP-SGM9, and GP-SGM10 were the most effective at scavenging DPPH radicals, with GP-SGM7 also exhibiting a high FRAP value of 0.54 ± 0.01. These findings emphasize the therapeutic potential of endophytic bacteria from G. perpensa L. in addressing skin-related issues, including bacterial infections and free radicals.

Functional Characterization and Localization of Plant-Growth Promoting Bacteria Grown Under Stressful Conditions

Various bacterial species are associated with plant roots. However, symbiotic and free-living plant growth-promoting bacteria (PGPB) can only help plants to grow and develop under normal and stressful conditions. Several biochemical and in vitro assays were previously designed to differentiate between the PGPB and other plant-associated bacterial strains. This chapter describes and summarizes some of these assays and proposes a strategy to screen for PGPB. To determine the involvement of the PGPB in abiotic stress tolerance, assays for the ability to produce 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, ammonium, gibberellic acid (GA), indole acetic acid (IAA), and microbial volatile organic compounds (mVOCs) are described in this chapter. Additionally, assays to show the capacity to solubilize micronutrients such as potassium, phosphorus, and zinc by bacteria were also summarized in this chapter. To determine the contribution of the PGPB in biotic stress tolerance in plants, Fe-siderophore, hydrogen cyanide, and antibiotic and antifungal metabolites production assays were described. Moreover, assays to investigate the growth-promotion activities of a bacterium strain on plants, using the gnotobiotic root elongation, in vitro, and pots assays, were explained. Finally, an assay for the localization of endophytic bacterium in plant tissues was also presented in this chapter. Although the assays described in this chapter can give evidence of the nature of the mechanism behind the PGPB actions, other unknown growth-promoting means are yet to decipher, and until then, new methodologies will be developed.

Diversity of Culturable Bacteria from Endemic Medicinal Plants of the Highlands of the Province of Parinacota, Chile

Endemic medicinal plants that grow at altitudes in northern Chile have been traditionally used for therapeutic applications by Aymara doctors. Several studies have analyzed the biological properties of these plants for therapeutic purposes. The aim was to characterize at molecular and biochemical levels the bacteria that live in the rhizosphere and roots from endemic medicinal plants that grow between 3681-5104 m.a.s.l. in the province of Parinacota. Thirty-nine bacteria were isolated from nine medicinal plants under our laboratory conditions. These bacteria were characterized by Gram stain, hydrolase production, plant-growth promotion, anti-fungal and antibacterial activities, and 16S rDNA sequencing. A phylogenetic study revealed the presence of three major phyla, Actinomycetota (46.2%), Bacillota (43.6%), and Pseudomonadota (10.3%). The rhizobacteria strains associated with the Aymara medicinal plant exhibited several interesting biological activities, such as hydrolytic enzymes, plant-growth-promoting traits, and antibacterial and antifungal properties, indicating their potential for developing new bio-based products for agricultural or clinical applications. These results are promising and highlight the need to point toward the search for explanations of the bio-molecular basis of the therapeutic effects of medicinal plants.

GC Analysis, Anticancer, and Antibacterial Activities of Secondary Bioactive Compounds from Endosymbiotic Bacteria of Pomegranate Aphid and Its Predator and Protector

Bacterial secondary metabolites are a valuable source of various molecules that have antibacterial and anticancer activity. In this study, ten endosymbiotic bacteria of aphids, aphid predators and ants were isolated. Bacterial strains were identified according to the 16S rRNA gene. Ethyl acetate fractions of methanol extract (EA-ME) were prepared from each isolated bacterium and tested for their antibacterial activities using the disk diffusion method. The EA-ME of three bacterial species, Planococcus sp., Klebsiella aerogenes, Enterococcus avium, from the pomegranate aphids Aphis punicae, Chrysoperia carnea, and Tapinoma magnum, respectively, exhibited elevated antibacterial activity against one or several of the five pathogenic bacteria tested. The inhibition zones ranged from 10.00 ± 0.13 to 20.00 ± 1.11 mm, with minimum inhibitory concentration (MIC) values ranging from 0.156 mg/mL to 1.25 mg/mL. The most notable antibacterial activity was found in the EA-ME of K. aerogenes against Klebsiella pneumonia and Escherichia coli, with an MIC value of 0.156 mg/mL. The cytotoxic activity of EA-ME was dependent on the cell line tested. The most significant cytotoxicity effect was observed for extracts of K. aerogenes and E. avium, at 12.5 µg/mL, against the epithelial cells of lung carcinoma (A549), with a cell reduction of 79.4% and 67.2%, respectively. For the EA-ME of K. aerogenes and Pantoea agglomerans at 12.5 µg/mL, 69.4% and 67.8% cell reduction were observed against human colon cancer (Hct116), respectively. Gas chromatography-mass spectrometry (GC-MS) analysis of three EA-ME revealed the presence of several bioactive secondary metabolites that have been reported previously to possess antibacterial and anticancer properties. To the best of our knowledge, this is the first study to examine the biological activities of endosymbiotic bacteria in aphids, aphid predators and ants. The promising data presented in this study may pave the way for alternative drugs to overcome the continued emergence of multidrug-resistant bacteria, and find alternative drugs to conventional cancer therapies.

Lysinibacilli: A Biological Factories Intended for Bio-Insecticidal, Bio-Control, and Bioremediation Activities

Microbes are ubiquitous in the biosphere, and their therapeutic and ecological potential is not much more explored and still needs to be explored more. The bacilli are a heterogeneous group of Gram-negative and Gram-positive bacteria. Lysinibacillus are dominantly found as motile, spore-forming, Gram-positive bacilli belonging to phylum Firmicutes and the family Bacillaceae. Lysinibacillus species initially came into light due to their insecticidal and larvicidal properties. Bacillus thuringiensis, a well-known insecticidal Lysinibacillus, can control many insect vectors, including a malarial vector and another, a Plasmodium vector that transmits infectious microbes in humans. Now its potential in the environment as a piece of green machinery for remediation of heavy metal is used. Moreover, some species of Lysinibacillus have antimicrobial potential due to the bacteriocin, peptide antibiotics, and other therapeutic molecules. Thus, this review will explore the biological disease control abilities, food preservative, therapeutic, plant growth-promoting, bioremediation, and entomopathogenic potentials of the genus Lysinibacillus.

Endophytes and their potential in biotic stress management and crop production

Biotic stress is caused by harmful microbes that prevent plants from growing normally and also having numerous negative effects on agriculture crops globally. Many biotic factors such as bacteria, fungi, virus, weeds, insects, and nematodes are the major constrains of stress that tends to increase the reactive oxygen species that affect the physiological and molecular functioning of plants and also led to the decrease in crop productivity. Bacterial and fungal endophytes are the solution to overcome the tasks faced with conventional farming, and these are environment friendly microbial commodities that colonize in plant tissues without causing any damage. Endophytes play an important role in host fitness, uptake of nutrients, synthesis of phytohormone and diminish the injury triggered by pathogens via antibiosis, production of lytic enzymes, secondary metabolites, and hormone activation. They are also reported to help plants in coping with biotic stress, improving crops and soil health, respectively. Therefore, usage of endophytes as biofertilizers and biocontrol agent have developed an eco-friendly substitute to destructive chemicals for plant development and also in mitigation of biotic stress. Thus, this review highlighted the potential role of endophytes as biofertilizers, biocontrol agent, and in mitigation of biotic stress for maintenance of plant development and soil health for sustainable agriculture.