Abstract: 【Aim】 This study aims to assay the effect of lactic acid bacteria on the developmental duration of fruit flies, and to further exploit their molecular mechanisms of growth stimulation of fruit flies. 【Methods】 Lactic acid bacteria were isolated from D. melanogaster using lactic acidic bacteria-selective medium MRS and identified by Gram staining, biochemical and 16S rRNA gene techniques. The symbiotic relationship was assayed by in vivo colonization and generation transfer experiments. The growth promoting effect of lactic acid bacteria on D. melanogaster was assessed in germ-free and gnotobiotic model. The expression levels of prothoracicotropic hormone gene (PTTH) and insulin-like receptor gene (InR) were examined using real-time PCR. The glucose concentration in haemolymph was examined using commercial kit with spetrometry. 【Results】 The isolated bacterium from D. melanogaster was identified as Lactobacillus plantarum strain FY1 (GenBank accesson no.: KY038178), which could colonize in the guts of flies with a mount of 10⁴ CFU/gut and be transferred from the parental generation to their offspring. L. plantarum FY1 decreased the pH value of culture media to 5.2 in vitro, and shortened the egg-to-puparium duration of D. melanogaster from 20.0 d to 6.9 d and the egg-to-adult duration from 30.0 d to 10.7 d, respectively, resulting in 2-fold growth rate of flies compared with that of germ-free siblings. Real-time PCR result revealed that L. plantarum FY1 significantly stimulated the expression peak of PTTH gene in advance, while decreased the expression level of InR gene in D. melanogaster, and reduced the glucose concentration in haemolymph from 5.1 mg/mL to 2.7 mg/mL. 【Conclusion】 L. plantarum is a type of commensal bacteria of D. melanogaster, and might promote the growth and development of the host via insulin signal pathway.

Key words: Lactobacillus plantarum, Drosophila melanogaster, commensal bacteria, in vivo colonization, gut