Browsing by Author "Liu, Tonghua"

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Effects of Growth Conditions on the Forms of Xenorhabdus nematophila: A Symbiotic Bacterium of the Entomopathogenic Steinernema carpocapsae
(Ingenta, 2019-06) Zhang, Fengqin; Makirita, Winisia E.; Wu, Lili; Yajie, Gou; Liu, Yong; Peng, Liuliang; Chacha, Musa; Mbega, Ernest; Li, Xiaolong; He, Nongyue; Liu, Tonghua
Xenorhabdus nematophila (X . nematophila) is a mutualistic gram negative bacterium, associated with the entomopathogenic nematodes of the genus Steinernema. The nematode-bacterial complexes increase the pathogen's ability to kill a wide range of host insect in 24–48 h after infestation, due to the complex toxins produced by the primary form of the X . nematophila bacteria. Recently, the application of primary bacterial in pest control and mass production of Steinernema carpocapsae nematode is increasing. However, the association of culture conditions on bacterial growth and its effects on the symbiotic relation and pathogenicity still needs to be explored. Based on the limited information regarding the influence of culture conditions for bacterial growth, this study explored the effect of pH, temperature and culture time on primary and secondary bacterial growth, as well as physiological and biochemical parameters. Results showed that the growth and metabolism of the primary bacteria depend on the growth conditions more than the secondary bacteria. The primary bacterial form was easily and completely transformed to the secondary form after growing for 72 h, showing morphological change from rod-shaped to granular shape. The bacterial growth was directly proportional to the increase in temperature, although the temperature of 25 °C was the optimum for the primary bacteria growth. The secondary bacterium was stable under all pH growing conditions tested, but the primary bacteria did not grow at pH value of 5.166. Thus, using pH differences, secondary bacteria can be purified from the primary bacterium. Also, both forms of the X. nematophila reacted positive on glucose test, indicating high affinity to glucose substrates. Therefore, this study presents the basic growth conditions required for the symbiotic bacteria for effective production of entomopathogenic nematode (Steinernema carpocapsae), although the effect of bacterial growth conditions on both the nematode survival and productions needs to be studied further.
Influence of Metal Oxides Nanoparticles on Pathogenicity of Steinernema carpocapsae Nematodes Against Lepidopteran Galleria mellonella
(American Scientific Publishers, 2020-03-01) Makirita, Winisia; Zhang, Fengqin; Mbega, Ernest; He, Nongyue; Li, Xiaolong; Chacha, Musa; Liu, Tonghua
Entomopathogenic nematodes (EPNs) have been cited as a safe and effective method for pest management. Their virulence against lepidopterans and other foliar pest has been demonstrated in the laboratory, but achieving field efficacy is challenged with environmental conditions such as desiccation and ultraviolet radiations. Nanoparticles (NPs) as UV-blocking agents have been reported to provide an alternative approach to enhance the EPNs efficacy. We screened the effect of ZnO, TiO2 and Fe3O4 NPs on survival and pathogenicity of EPNs, and determined whether the nanoparticles could provide protection to the EPNs at low concentrations when applied in direct sunlight. All nanoparticles had less influence on the survival of infective juveniles and did not deprive their pathogenic properties following prolonged exposure. The survival rate of nematodes decreased with increased concentrations, with no measurable difference between NPs. Moreover, the survival rate of nematodes exposed to UV radiation in different formulation decreased significantly with the increase in exposure time (p < 0.001). On the other side when EPNs in nanoparticles formulations were exposed to sunlight, their efficacy significantly improved by protecting nematodes from ultraviolet radiation when compared to the water-based formulation. Pathogenic efficacy after exposure to sunlight was in the order of ZnO > TiO2 > Fe3O4 > H2O, indicating the compatibility of nematodes and NPs, and the benefit of different NPs in EPNs formulations. General nanoparticles are novel ingredients that provide suitable protection of EPNs for management of foliar pests. However, the EPNs nanoparticles formulation under a specific agricultural system and climatic condition need to be established.
Molecular Mechanism and Changes of Antioxidant Enzyme in ZnO Nanoparticles Against Fungus.
(Ingenta Connect, 2020, 2019-04-01) Zhang, Fengqin; Liu, Xiongduo; Pentok, Myima; Sauli, Elingarami; He, Nongyue; Zen, Xiangli; Li, Xiaolong; Liu, Tonghua
Although zinc oxide nanoparticles are known as an effective antimicrobial agent, the mechanism for its antifungal activity has been assessed by only few studies. In this study, antifungal activity mechanism for ZnO via the change of physiology was explored. It was showed that the activities of SOD and CAT and the MDA content were increased significantly. The possible mechanisms were obtained that zinc oxide directly acts on the mycelium of to produce oxidative stress and destroy intracellular physiological balance. RNA-seq was then used to verify the conclusion obtained before, and obtained results suggested that the antifungal mechanism is attributed to oxidative stress and changes in membrane function.
Sustainable Crop Protection Using Nematodes (Steinernema Spp) as Biological Control Agents
(American Scientific Publishers, 2019-06-01) Makirita, Winisia E.; Myima, Pentok; Wu, Lili; Liu, Yong; Chacha, Musa; He, Nongyue; Li, Xiaolong; Zhang, Fengqin; Liu, Tonghua
Crop productions play an important role in food production, raw material production and income generation. Crop production is challenged by pest infestation with new outbreaks every now and then, reducing yield and increasing production cost. The use of biological control agent has been cited as the potential approach in pest management due to the high performing ability with limited effects on the environment and non-targeted organisms. Entomopathogenic nematode is one of the biological control agents used for management of insect pest and it is mostly used in many developed countries with increasing application interest in developing countries. Entomopathogenic formulations from steinernema species (spp) are commercially available, although shipping and stability have been the major challenge. Recently, more than 90 spp. have been isolated from different region and this shows the possibility of having more beneficial strains of steinernema in our surroundings. Research have determined the high performance of entomopathogenic nematode against local insect, this shows the importance of isolating local stain to manage the local pest. On other hands, the different materials have been proven to enhance the pathogenic effect and stability of the nematode when incorporated together and this opens more windows in identifying potential materials for entomopathogenic nematode formulation. Despites some few available challenges of entomopathogenic nematodes applications, it is gaining more attention in agricultural and forest industry due to its broad range of activities and this serves as a potential bio control agent. It is from this view, that this review discussed the potential of Steinernema spp. in crop protection and its performance.