Mathew Jyothis

Plant growth promoting potential of endophytic bacteria isolated from Piper nigrum

Piper nigrum is an interesting plant to study the endophytic microbial factors affecting plant growth because of its unique features. Endophytic bacterial isolation from the plant resulted in the isolation of twelve bacterial isolates which were screened for various plant growth promoting properties like phosphate solubilization, ACC deaminase production, siderophore production etc. Interestingly, seven isolates were found to have IAA biosynthetic potential. Bacterial isolates with multiple plant growth promoting properties were studied for their growth promoting effect on Vigna radiata seedlings. This resulted in the identification of Klebsiella sp. (PnB 10) and Enterobacter sp. (PnB 11) as the isolates with excellent growth promoting properties. The results confirm promising applications of the endophytic bacterial isolates obtained in the study and also their possible growth promoting effect in P. nigrum.

Piperine production by endophytic fungus Colletotrichum gloeosporioides isolated from Piper nigrum

Many endophytic fungi have been reported with the biosynthetic potential to produce same or similar metabolites present in host plants. The adaptations that might have acquired by these fungi as a result of the long-term association with their host plants can be the possible basis of their biosynthetic potential. The bioactive compounds originated from endophytes are currently explored for their potential applications in pharmaceutical, agriculture and food industries. Piper nigrum, a plant of the Piperaceae is very remarkable because of the presence of the alkaloid piperine. Piperine has been reported to have broad bioactive properties ranging from antimicrobial, antidepressant, anti-inflammatory, antioxidative to anticancer activities. Interestingly, piperine also plays a vital role in increasing the bioavailability of many drugs which again is a promising property. The current study was carried out to identify piperine producing endophytic fungus from Piper nigrum L. By screening various endophytic fungi, the isolate which was identified as member of Colletotrichum gloeosporioides was found to have the ability to form piperine and was confirmed by HPLC and LCMS. Considering the broad bioactive potential of piperine, the piperine producing fungi identified in the study can expect to have much industrial potential.

Phenazine carboxylic acid production and rhizome protective effect of endophytic Pseudomonas aeruginosa isolated from Zingiber officinale

Abstract Ginger (Zingiber officinale) is cultivated commercially in most parts of the world especially in India for its culinary and medicinal applications. One of the major challenges that limit the yield of ginger is rhizome rot disease caused by organisms including Pythium myriotylum. A feasible ecofriendly method is yet to be devised to prevent the plant from this threatening disease. Recent studies on plant microbiome show the possibility of having endophytic organisms with plant protective characteristics associated with the plants. Because of the uniquely evolved underground nature of the ginger rhizome and its peculiar survival in soil for a long time, many interesting endophytic microbes with plant protective characters can be well expected from it. In the current study, previously isolated endophytic Pseudomonas aeruginosa from ginger was investigated in detail for its effect on Pythium myriotylum. The rhizome protective effect of the organism was also studied by co-inoculation studies, which confirmed that Pseudomonasaeruginosa has very potent inhibitory effect on Pythium myriotylum. On further studies, the active antifungal compound was identified as phenazine 1-carboxylic acid.

Effect of biofabricated gold nanoparticle-based antibiotic conjugates on minimum inhibitory concentration of bacterial isolates of clinical origin

Medical device related infections caused by coagulase-negative staphylococci (CoNS) are difficult to treat mainly because of the increased bacterial genetic tolerance to antibiotics and its notorious biofilm formation property which has been reported to be achieved through a wide range of mechanisms. Current study is the demonstration of persistent antibiotic delivering potential and broad spectrum of activity of nanoantibiotic combinations designed from gold nanoparticles in conjugation with known antimicrobial agents. Such formulations are of potential applications as surface engineering agents on medical devices to prevent device mediated infection caused by pathogens like CoNS. For this, highly stable gold nanoparticles fabricated by a Bacillus sp. were functionalized with ciprofloxacin, gentamycin, rifampicin, and vancomycin and these nanoparticle-antibiotic conjugates were studied for its effectiveness against selected CoNS like Staphylococcus epidermidis and Staphylococcus haemolyticus. Very interestingly, the designed conjugates were identified to have a profound antibacterial efficiency compared to pure antibiotic and AuNPs. Thus, the result of the study is with highly significant medical applications as the test organisms used are emerging opportunistic pathogens.

Identification of two strains of Paenibacillus sp. as indole 3 acetic acid-producing rhizome-associated endophytic bacteria from Curcuma longa

Curcuma longa is well known for its use as spice and medicine. The remarkable feature of the plant is the presence of rhizome, which provides an interesting habitat for association by various groups of bacteria. Some of these associated endophytic bacteria can have growth-promoting effects. In the current study, two species of endophytic Paenibacillus has been identified from the rhizome as indole 3 acetic acid producers. These isolates can thus have potential growth-regulating effect in rhizomes.

Studies on Plant Growth Promoting Properties of Fruit-Associated Bacteria from Elettaria cardamomum and Molecular Analysis of ACC Deaminase Gene

Endophytic microorganisms have been reported to have diverse plant growth promoting mechanisms including phosphate solubilization, N2 fixation, production of phyto-hormones and ACC (1-aminocyclopropane-1-carboxylate) deaminase and antiphyto-pathogenic properties. Among these, ACC deaminase production is very important because of its regulatory effect on ethylene which is a stress hormone with precise role in the control of fruit development and ripening. However, distribution of these properties among various endophytic bacteria associated with fruit tissue and its genetic basis is least investigated. In the current study, 11 endophytic bacteria were isolated and identified from the fruit tissue of Elettaria cardamomum and were studied in detail for various plant growth promoting properties especially ACC deaminase activity using both culture-based and PCR-based methods. PCR-based screening identified the isolates EcB 2 (Pantoea sp.), EcB 7 (Polaromonas sp.), EcB 9 (Pseudomonas sp.), EcB 10 (Pseudomonas sp.) and EcB 11 (Ralstonia sp.) as positive for ACC deaminase. The PCR products were further subjected to sequence analysis which proved the similarity of the sequences identified in the study with ACC deaminase sequences reported from other sources. The detailed bioinformatic analysis of the sequence including homology-based modelling and molecular docking confirmed the sequences to have ACC deaminase activity. The docking of the modelled proteins was done using patch dock, and the detailed scrutiny of the protein ligand interaction revealed conservation of key amino acids like Lys51, Ser78, Tyr268 and Tyr294 which play important role in the enzyme activity. These suggest the possible regulatory effect of these isolates on fruit physiology.

Green synthesized silver nanoparticles by marine endophytic fungus Penicillium polonicum and its antibacterial efficacy against biofilm forming, multidrug-resistant Acinetobacter baumanii

Acinetobacter baumanii, a gram-negative, non-motile, encapsulated coccobacillus which causes infections worldwide. The objective of this study was to find a fungal strain that could be utilized to biosynthesize antibacterial silver nanoparticles (AgNPs) against Acinetobacter baumanii. The present investigation explains rapid and extracellular biosynthesis of silver nanoparticles by the algicolous endophytic fungus, Penicillium polonicum, isolated from the marine green alga Chetomorpha antennina. The obtained silver nanoparticles were characterized by UV-Vis spectroscopy, Raman spectroscopy, Fourier transformation infrared (FTIR), and Transmission electron microscopy (TEM). The SNPs showed a characteristic UV- visible peak at 430 nm with an average size of 10-15 nm. As evident from the FTIR and Raman spectra, possibly the protein components of fungal extract have caused the reduction of silver nitrate. Parametric optimization, including the concentration of AgNO3, ratio of cell filtrate and AgNO3, fungal biomass, reaction time, pH, and presence of light, was done for rapid AgNPs production. The antibacterial efficacy of AgNPs against multi-drug-resistant, biofilm-forming Acinetobacter baumanii, was evaluated by well diffusion assay. The Minimum inhibitory concentration (MIC) of AgNP was 15.62 μgml-1 and the minimum bactericidal concentration (MBC) was 31.24 μgml-1. Killing kinetic assay revealed complete killing of the bacterial cells within 6 h. Log reduction and percent survival of bacterial cells were analyzed from killing kinetic study. Bactericidal nature of synthesized nanoparticles was confirmed by fluorescent microscopical analysis. The effect of AgNPs on the ultrastructure of bacterial pathogen was evaluated by Transmission electron microscopy.

Antibacterial activity of autochthonous bacteria isolated from Anabas testudineus (Bloch, 1792) and it's in vitro probiotic characterization

Antimicrobial potentials of bacteria isolated from Anabas testudineus have been evaluated through in vitro antagonistic activity against potent fish pathogens. The cellular components and filtered culture medium were effective against six fish pathogens. Altogether 110 strains were isolated from the fish gut, out of which 10 strains were selected through well diffusion method. From them, a strain HGA8B having cumulative maximum score was selected as candidate probiotic. The whole-cell product, heat-killed whole-cell product, Ethyl acetate extract, and the filtered broth were exhibited bactericidal activity against the tested pathogens. In addition, the isolated bacterium was capable of producing extracellular enzymes important for the digestion of food materials and was capable of growth in fish mucus from Oreochromis niloticus. The strain tolerated bile juice secreted by the host and effectively produced biofilm. Analysis of 16S rDNA sequence revealed that isolated strain HGA8B was Bacillus sp. (MF351637). Furthermore, intraperitoneal injection of the bacterium did not induce any pathological signs, symptoms or mortalities in Oreochromis niloticus and revealed the safety of this bacterium as a candidate probiotic in aquaculture.

Antibacterial activity and probiotic characterization of autochthonous Paenibacillus polymyxa isolated from Anabas testudineus (Bloch, 1792)

Microbial fish pathogens are prevalent in aquaculture. Control of bacterial fish pathogens is important and bio control of pathogenic bacteria is a novel field of study. The aim of this study was to evaluate the antagonistic activity of bacteria isolated from Anabas testudineus against potent fish pathogens. The cellular components/preparations and filtered cell free culture supernatants were effective against six fish pathogens. Altogether 110 strains were isolated from fish proximal and distal intestine, out of which 10 strains were selected through well diffusion method. From them a strain HGA4C having prominent antimicrobial activity was selected as candidate probiotic strain. The whole-cell product, heat-killed whole-cell product and the filtered broth were exhibited bactericidal activity against the tested pathogens. Among them cell free culture supernatant showed maximum inhibition. In addition, isolated candidate probiotic bacterium was capable of producing extracellular enzymes important for the digestion of food ingredients and was effectively grown in fish mucus obtained from Oreochromis niloticus. The strain tolerated gradient of bile juice secreted by the host and effectively produced biofilm. Analysis of 16S rDNA sequence revealed that isolated strain HGA4C was Paenibacillus polymyxa (MF457398.1). Furthermore intraperitoneal injection of the bacterium did not induce any pathological anomalies or mortalities in Oreochromis niloticus and disclosed the safety of this bacterium as a candidate probiotic in aquaculture.

Efficient visible light induced synthesis of silver nanoparticles by Penicillium polonicum ARA 10 isolated from Chetomorpha antennina and its antibacterial efficacy against Salmonella enterica serovar Typhimurium

The green synthesis of silver nanoparticles (AgNPs) using biological systems such as fungi has evolved to become an important area of nanobiotechnology. Herein, we report for the first time the light-induced extracellular synthesis of silver nanoparticles using algicolous endophytic fungus Penicillium polonicum ARA 10, isolated from the marine green alga Chetomorpha antennina. Parametric optimization, including the concentration of AgNO3, fungal biomass, ratio of cell filtrate and AgNO3, pH, reaction time and presence of light, was done for rapid AgNPs production. The obtained silver nanoparticles (AgNPs) were characterized by UV-Visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy and Transmission electron microscopy (HRTEM-EDAX). The AgNPs showed a characteristic UV-visible peak at 430 nm with an average size of 10-15 nm. The NH stretches in FTIR indicate the presence of protein molecules. The Raman vibrational bands suggest that the molecules responsible for the reduction and stability of AgNPs were extracellular proteins produced by P.polonicum. Antibacterial evaluation of AgNPs against the major foodborne bacterial pathogen Salmonella enterica serovar Typhimurium MTCC 1251, was assessed by well diffusion, Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assay. Killing kinetic studies revealed complete killing of the bacterial cells within 4 h and the bactericidal nature of synthesized nanoparticles was confirmed by fluorescent microscopy and scanning electron microscopy. Furthermore, the bactericidal studies with Transmission electron microscopy (TEM) at different time intervals explored the presence of AgNPs in the cell wall of S.Typhimurium at about 30 min and the complete bacterial lysis was found at 24 h. The current research opens an insight into the green synthesis of AgNPs and the mechanism of bacterial lysis by direct damage to the cell wall.