RESUMO
Entomopathogenic nematodes (EPNs) of the families Steinernematidae and Heterorhabditidae have a symbiotic association with bacteria which makes them virulent against insects. EPNs have been mass produced using in vivo and in vitro methods, including both solid and liquid fermentation. This study assessed the effect of nematode inoculum age on the production of Steinernema feltiae in liquid, solid and biphasic processes. Several physical parameters were also assessed: the effect of medium viscosity, flask size and aeration speed on the recovery and yield of infective juveniles (IJs). Inoculum age treatments included inoculum liquid cultures that were 7, 14, 21 and 28 days old. Nematodes from the same inoculum were added to one liquid medium (liquid culture), one solid medium with bacteria previously grown in sponge (solid culture) and a variation of the solid medium (a biphasic culture), in which the bacteria were first grown in liquid and, then, soaked into the sponges, with the purpose of providing a more homogeneous bacterial culture before nematode inoculation. Experiments were conducted in Erlenmeyer flasks. Eight treatments were established involving combinations of three variables: two media (with and without 0.2% agar), two flask sizes (250 and 150 ml) and two agitation speeds (180 and 280 rpm). The study showed increases in nematode yield for liquid cultures, but not for solid or biphasic cultures, with the advance of the inoculum age up to 28 days of growth. Furthermore, the addition of 0.2% agar to the liquid medium and increasing the aeration rate by using larger flasks with higher agitation speed may increase nematode recovery and final yield. The experiments were conducted using shake flasks but the results may also be applicable for bioreactors.
Assuntos
Insetos/parasitologia , Rabditídios/crescimento & desenvolvimento , Animais , Meios de Cultura/química , Meios de Cultura/metabolismo , Rabditídios/metabolismo , Rabditídios/microbiologia , Xenorhabdus/crescimento & desenvolvimento , Xenorhabdus/metabolismo , Xenorhabdus/fisiologiaRESUMO
The submerged culture of the entomopathogenic nematode Steinernema carpocapsae and its symbiotic bacterium, Xenorhabdus nematophila, was carried out in orbitally agitated bottles using a culture medium containing whey (in grams per litre: 500 whey, 20 yeast extract, 10 dried egg yolk-food grade, 3 sodium chloride, 37 corn oil-food grade). Maximum total viable nematode concentrations of 198,333ml(-1) were achieved within fermentations of 24 days with 64% of the nematode population within the infective juvenile stage (IJ) (126,666ml(-1)) at the end. The kinetics of the bioprocess was well modelled using the four-parameter Sigmoidal model and the corresponding maximum specific rates of nematode production (0.47 day(-1)), carbohydrates consumption (0.0008g(carbohydrates)g(nematodes)(-1)day(-1)) and nitrogen consumption (4.44g(nitrogen)g(nematodes)(-1)day(-1)) are first proposed. Besides, X. nematophila appears to have the capacity of lactose hydrolysis.
Assuntos
Meios de Cultura/metabolismo , Proteínas do Leite/metabolismo , Nematoides/crescimento & desenvolvimento , Rabditídios/crescimento & desenvolvimento , Xenorhabdus/crescimento & desenvolvimento , Animais , Técnicas Bacteriológicas/métodos , Biomassa , Carboidratos/química , Técnicas de Cocultura/métodos , Meios de Cultura/química , Fermentação , Cinética , Lactose/química , Lactose/metabolismo , Proteínas do Leite/química , Nematoides/metabolismo , Nematoides/microbiologia , Nitrogênio/química , Rabditídios/metabolismo , Rabditídios/microbiologia , Simbiose , Proteínas do Soro do Leite , Xenorhabdus/isolamento & purificação , Xenorhabdus/metabolismoRESUMO
This article presents the evolution of culture broth rheological properties during monoxenic cultures of Steinernema carpocapsae in cylindrical bottles agitated orbitally. Rheological properties were evaluated in simple-shear flow conditions and were well-modeled by the Ostwald-de Waele model. Rheological properties varied from slightly dilatant, n = 1.2 (-), to moderately pseudoplastic flow behavior, n = 0.6 (-). Nematode concentrations increased from 750 +/- 190 to 130 900 +/- 6900 nematodes/mL, and the apparent viscosity (eta(a)) evolved from 4.5 +/- 0.7 to 46.6 +/- 3.2 mPa.s during the fermentations. Rheological behavior did not appear to be strongly influenced by nematode number and/or its stage of development; however, the release of substances from the decomposition of nematode cadavers appeared to be of great importance. Among the different developmental stages of the nematodes, only juveniles of the first stage (J1) were highly susceptible to the shearing conditions tested (shear stress, tau(r)()(theta), from 0.9 to 3.5 Pa during periods of 80-100 min), resulting in the viability loss of 85% of J1 nematodes.