The detrimental effects of synthetic fungicides have increased the emphasis for biological control as an effective and safe sustainable alternative method. In the present work, a potent rhizospheric actinobacterium MR14 showed broad spectrum antifungal and plant growth promoting activities indicating the potential to fulfill the need. Phylogenetic analysis confirmed that the isolate could be assigned as new species of the Streptomyces , coded as Streptomyces sp. MR14. It formed clade with Streptomyces daghestanicus but with very low bootstrap value (14%). The MR14 supernatant showed potent antagonistic activity against 13 different tested fungal phytopathogens. The most and least sensitive fungal phytopathogens were found to be Pyricularia oryzae and Fusarium oxysporum with inhibition zones of 31 mm and 11 mm, respectively. The antifungal metabolites produced by strain MR14 were thermostable, photostable, and remained active at extreme acidic and neutral pH. In pot experiments, the Streptomyces sp. MR14 cells, supernatant and extract significantly suppressed Fusarium wilt caused by Fusarium moniliforme in tomato plants. Various growth parameters such as shoot and root lengths, and plant fresh and dry weights were significantly enhanced by 19.65 to 321.62% over the pathogen infested plants only. The treatment with culture cells/supernatant/extract in the rhizosphere soil also reduced the microbial count as compared to control. In addition, the strain also possessed plant growth promoting potential which was indicated by the increase in various agronomic traits from 3.64 to 116.88%. This study provided a scientific validation that the new rhizobacterium Streptomyces sp. MR14 could be further developed as bioformulation, exhibiting biocontrol and plant growth promoting capabilities.

Biocontrol agents and their bioactive metabolites provide one of the best alternatives to decrease the use of chemical pesticides. In light of this, the present investigation reports the biocontrol potential of Streptomyces hydrogenans DH16 and its metabolites towards Alternaria brassicicola, causal agent of black leaf spot and damping off of seedlings of crucifers. In vitro antibiosis of strain against pathogen revealed complete suppression of mycelial growth of pathogen, grown in potato dextrose broth supplemented with culture supernatant (20% v/v) of S. hydrogenans DH16. Microscopic examination of the fungal growth showed severe morphological abnormalities in the mycelium caused by antifungal metabolites. In vivo studies showed the efficacy of streptomycete cells and culture supernatant as seed dressings to control damping off of Raphanus sativus seedlings. Treatment of pathogen infested seeds with culture supernatant (10%) and streptomycete cells significantly improved seed germination (75–80%) and vigor index (1167–1538). Furthermore, potential of cells and culture supernatant as foliar treatment to control black leaf spot was also evaluated. Clearly visible symptoms of disease were observed in the control plants with 66.81% disease incidence and retarded growth of root system. However, disease incidence reduced to 6.78 and 1.47% in plants treated with antagonist and its metabolites, respectively. Additionally, treatment of seeds and plants with streptomycete stimulated various growth traits of plants over uninoculated control plants in the absence of pathogen challenge. These results indicate that S. hydrogenans and its culture metabolites can be developed as biofungicides as seed dressings to control seed borne pathogens, and as sprays to control black leaf spot of crucifers.

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BackgroundDestructive impacts of insecticides on non targeted populations necessitate the development of an eco friendly pest control method. Streptomyces spp. are rich source of bioactive secondary metabolites which may provide valuable alternatives to chemical insect-control agents as they can be less toxic and readily biodegradable. Because of its potent biocontrol attributes, ethyl acetate extract of Streptomyces hydrogenans DH16, a soil isolate, was tested to assess its anti-insect potential against polyphagous noctuid, Spodoptera litura.ResultsThe secondary metabolites in the ethyl acetate extract of S. hydrogenans DH16 exhibited larvicidal and growth inhibitory activities. The results indicated that highest concentration of 1600 μg/ml was significantly effective as 70% larval, 66.66% prepupal and 100% pupal mortality was noticed. The metabolites also prolonged the larval developmental period. The LC50 and LC90 values were 1337.384 and 2070.516 μg/ml, respectively for the insect. Negative effects of S. hydrogenans were also observed on development of the insect. Significant decline in adult emergence, adult longevity, fecundity and % hatching was recorded at higher concentrations along with morphological abnormalities as compared to control. Significant decrease in relative growth and consumption rate, efficiency of ingested and digested food and increase in approximate digestibility in larvae reared on diet supplemented with ethyl acetate extract accounts for the toxic as well as anti-nutritive nature of extract.ConclusionSecondary metabolites in the fermentation broth from S. hydrogenans were toxic to the larvae at higher concentrations whereas lower concentrations significantly reduced the reproductive potential of S. litura. Therefore, these metabolites show considerable potential for incorporation in pest management programmes as new biopesticidal formulation.

In the present study, an actinobacterium strain, possessing antagonistic activity against different fungal phytopathogens viz. Colletotrichum acutatum, Cladosporium herbarum, Alternaria brassicicola, Exserohilum sp., Alternaria mali, Colletotrichum gleospoiroides, Alternaria alternata, Cercospora sp., Fusarium oxysporum f.sp. dianthi and Fusarium moniliformae, was isolated from soil and identified as Streptomyces hydrogenans DH16. Application of culture supernatant (5%)/cells (10(7)  cfu ml(-1) ), 2 h post inoculation with A. brassicicola (10(5)  spores ml(-1) ), resulted in 85.95 and 93.75% suppression of black leaf spot of Raphanus sativus, respectively on detached leaves. Whereas cells/culture supernatant (above 5%) completely suppressed the disease incidence when co inoculated with fungal pathogen. The crude extract containing antifungal components was completely stable at 70 °C for 1 h retaining 90 and 67.67% activity after boiling (for 1 h) and autoclaving (121 °C for 30 min), respectively. No loss in activity was observed when treated with proteinase K and on exposure to sun and UV light and found to be active over a wide range of pH (2 to 14). Bioautography of the solvent extract against test phytopathogens revealed the presence of three active components. Ethyl acetate extract of DH16 also demonstrated insecticidal activity against Spodoptera litura, causing 40% larval mortality and extension of larval period. In addition, it produced 30 µg ml(-1) of Indole Acetic Acid (IAA) in a medium containing tryptophan which promoted lateral root formation in Vigna radiata (green gram). These results indicate that Streptomyces hydrogenans holds the potential to be used as antifungal, insecticidal, and plant growth promoting agent.

The present work demonstrated the nematicidal potential of Streptomyces hydrogenans strain DH16 (a strain with strong antagonism against fungal phytopathogens and insect pest) against Meloidogyne incognita. The culture supernatant and solvent extract significantly inhibited egg hatching (almost 100%) along with J2 mortality of more than 95% after 96h. The nematicidal activity of 10-(2,2-dimethyl-cyclohexyl)-6,9-dihydroxy-4,9-dimethyl-dec-2-enoic acid methyl ester (SH2; a new antifungal compound) purified from this streptomycete was also evaluated using different concentrations. The juvenile mortality of the nematode increased with increasing concentration and exposure time and reached the maximum (95%) after 96h at concentration of 100μg/ml. After 160h of incubation, egg hatch of 16% was observed at concentration of 100μg/ml as compared to control where 100% egg hatching was achieved. However, at the highest concentration of the compound (200μg/ml), 100% J2 mortality and 0% egg hatching were observed after 72 and 160h of incubation, respectively. In vivo pot experiments further revealed the nematicidal potential of S. hydrogenans where soil drenching with its culture supernatant and cells effectively controlled root galls, egg masses in nematode infested tomato plants and at the same time promoted the growth of tomato plants. Additionally, in the absence of nematodes, soil drenching with culture supernatant and cells significantly enhanced the various agronomic traits of plants as compared to control plants. Thus, the outcomes of the current study endorse the potential of S. hydrogenans strain DH16 and its metabolites to be developed as safe nematicidal and plant growth promoting agents.

Detection of pathogenic microbes as well as antibiotic residues in food animals, especially in chicken, has become a matter of food security worldwide. The association of various pathogenic bacteria in different diseases and selective pressure induced by accumulated antibiotic residue to develop antibiotic resistance is also emerging as the threat to human health. These challenges have made the containment of pathogenic bacteria and early detection of antibiotic residue highly crucial for robust and precise detection. However, the traditional culture-based approaches are well-comprehended for identifying microbes. Nevertheless, because they are inadequate, time-consuming and laborious, these conventional methods are not predominantly used. Therefore, it has become essential to explore alternatives for the easy and robust detection of pathogenic microbes and antibiotic residue in the food source. Presently, different monitoring, as well as detection techniques like PCR-based, assay (nucleic acid)-based, enzyme-linked immunosorbent assays (ELISA)-based, aptamer-based, biosensor-based, matrix-assisted laser desorption/ionization-time of flight mass spectrometry-based and electronic nose-based methods, have been developed for detecting the presence of bacterial contaminants and antibiotic residues. The current review intends to summarize the different techniques and underline the potential of every method used for the detection of bacterial pathogens and antibiotic residue in chicken meat.