Overcoming the production limitations of Photorhabdus temperata ssp. temperata strain K122 bioinsecticides in low-cost medium

Abstract

For low-cost production of Photorhabdus temperata ssp. temperata strain K122 bioinsecticide, a cheap complex medium was optimized. Diluted seawater was used as the source of micronutrients, especially sodium chloride, involved in the improvement of cell density, culturability and oral toxicity of the bacterium P. temperata against Ephestia kuehniella larvae. Thus, the new formulated medium was composed only of 10 g/l of soya bean meal, used as the carbon and nitrogen main source, mixed in sevenfold diluted seawater. At such conditions, several limitations of P. temperata bioinsecticide productions were shown to be overcome. The appearance of variants small colony polymorphism was completely avoided. Thus, the strain K122 was maintained at the primary form even after prolonged incubation. Moreover, the viable but nonculturable state was partially overcome, since the ability of P. temperata cells to form colonies on the solid medium was prolonged until 78 h of incubation. In addition, when cultured in the complex medium, P. temperata cells were produced at high cell density of 12 × 10(8) cells/ml and exhibited 81.48% improvement of oral toxicity compared to those produced in the optimized medium. With such medium, the large-scale bioinsecticides production into 3-l fully controlled fermenter improved the total cell counts, CFU counts and oral toxicity by 20, 5.81 and 16.73%, respectively. This should contribute to a significant reduction of production cost of highly potent P. temperata strain K122 cells, useful as a bioinsecticide.

Development of a Cost-effective Medium for Photorhabdus Temperata Bioinsecticide Production From Wastewater and Exploration of Performance Kinetic

“…a). The enhancement of P. temperata toxin synthesis through NaCl addition was demonstrated by Jallouli et al (2011). Indeed, an improvement of 81.4 and 42.22 % of P. temperata oral toxicity in CM and OM, respectively was obtained when NaCl was added beyond 2 g/l.…”

“…Similarly, previous studies reported that addition of sodium chloride at 5 g/l to OM and CM doubles biomass production of the strain K122 of P. temperata. NaCl was demonstrated to be a stimulator of growth of the strain K122 by increasing nutrients assimilation (Jallouli et al 2011). In addition, Jallouli et al (2012) demonstrated that biomass production increased with the increase in inoculum size.…”

“…Enhancement of P. temperata cells production is achieved essentially by adding sodium chloride at 5 g/l. Indeed, at such concentration NaCl doubled biomass production, increased culturability and biological activity in both studied media (Jallouli et al 2011). Moreover, maintaining glucose at 4 g/l in the OM increased significantly P. temperata biomass production ((Jallouli et al 2012).…”

“…However, in this medium, low P. temperata biomass production and oral toxicity, against the Mediterranean flour moth E. kuehniella were obtained, which were of 4×10 8 cells/mL and 42 %, respectively (Keskes et al 2020). Improvement of P. temperata biomass production was well studied in two media: the optimized medium (OM) based on glucose and yeast extract (Jallouli et al 2008) and the complex medium (CM) based on soya bean meal (Jallouli et al 2011), but it was never reported in wastewater. Enhancement of P. temperata cells production is achieved essentially by adding sodium chloride at 5 g/l.…”

Potential of Photorhabdus temperata K122 bioinsecticide in protecting wheat flour against Ephestia kuehniella

“…Indeed, oral toxicity, assessed as the growth inhibition of E. kuehniella larvae fed with P. temperata K122 at 4 Â 10 8 cells/ml, was 27%, when cultured in the optimized medium (OM) (Jallouli et al, 2008). Several studies have been already carried out to improve toxicity of P. temperata K122 by avoiding Vsm polymorphism (Jallouli et al, 2008) and addition of sodium chloride at 5 g/l (Jallouli et al, 2011). Improvement could be achieved also by control of the dissolved oxygen concentration during the fermentation process using the OM or the complex medium.…”