A novel bioconversion approach of Tunisian wastewater to low-cost Photorhabdus temperata bioinsecticide is presented in this study. Our results showed that when cultured on the food industry wastewater (WS4), P. temperata cells exhibited oral toxicity of about 42%, which is the same as those cultured in complex medium (CM), used as control. Moreover, variants small colony polymorphism (Vsm) of the strain K122 was completely avoided after a prolonged incubation. However, viable but non-culturable (VBNC) state was enhanced with the maximum colony-forming units (CFU) count of 9 × 10⁶ cells/mL obtained after 48 h of incubation in the WS4. According to flow cytometry analysis, almost 100% of P. temperata cells were viable until 48 h of incubation. The appearance of propidium iodide (PI) positively stained cells was observed after a prolonged incubation with a maximum of 17% of damaged cells in WS1. In order to follow the progress of P. temperata fermentation process carried out in industrial wastewater, we established for the first time, the mathematical relationship between total cell counts, CFU counts and oral toxicity of P. temperata strain K122. Indeed, irrespective of the medium used, the relationship between CFU count and total cell count followed a power law. Additionally, when plotting CFU count, or total cell count against toxicity, a semi-log linear relationship was obtained. Our results proved the efficiency of this bioconversion approach to produce bioinsecticide based on the entomopathogenic bacterium P. temperata, with practical benefits in terms of cost production and wastewater management.

中文翻译：

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通过突尼斯工业废水的生物转化，寻求一种新的生物防治方法来生产温带光生物杀虫剂

这项研究提出了一种新的突尼斯废水生物转化为低成本的温带光生物杀虫剂的方法。我们的结果表明，当在食品工业废水（WS4）上培养时，温带假单胞菌细胞表现出约42％的口服毒性，与用作对照的复杂培养基（CM）中的毒性相同。此外，长时间孵育后，完全避免了菌株K122的变异小菌落多态性（Vsm）。但是， 在WS4中孵育48小时后，获得的最大菌落形成单位（CFU）数量达到9×10 ⁶细胞/ mL，从而增强了存活但不可培养（VBNC）的状态。根据流式细胞仪分析，几乎100％的温带假单胞菌细胞存活直至孵育48小时。与WS1中最多有17％的受损细胞长时间孵育后，观察到了碘化丙啶（PI）阳性染色的细胞的出现。为了跟踪工业废水中温带假单胞菌发酵工艺的进展，我们首次建立了温带假单胞菌总细胞数，CFU数与口服毒性之间的数学关系。菌株K122。实际上，无论使用哪种培养基，CFU计数与总细胞计数之间的关系均遵循幂律。此外，绘制CFU计数或总细胞数与毒性的关系图时，获得了半对数线性关系。我们的结果证明了这种生物转化方法生产基于昆虫致病菌温带假单胞菌的生物杀虫剂的效率，在成本生产和废水管理方面具有实际优势。