The Role Of Gut Bacteria In Tenebrio Molitor Larvae In The Digestion And Utilization Of Protein

As an economic insect, Tenebrio molitor is a promising supplier of high quality protein for human in the future. Besides, it is an important model insect in biological experiment. In this study, the composition and distribution of bacteria associated with T. molitor larvae guts were investigated using both culture-dependent and culture-independent denaturing gradient gel electrophoresis (DGGE) methods. We also investigated the potential role of gut bacteria in the protein utilization in T. molitor larvae.Eight strains (BGH, GD, ZKNR, SCH, BYZZ, PRO, BYP, LBTR) in five genera, Weissella, Lactococcus, Rahnella, Cronobacter and Enterococcus, were isolated using nutrient agar. All these strains were present in the posterior midgut and hindgut. The strains with milk-clotting activity in selective casein-plates assay were sequenced and identified as species of genera Weissella and Lactococcus, and those with proteolytic activity as Rahnella and Cronobacter, implying that they may be involved in protein utilization. But none of these strains showed cellulolytic activity. In DGGE experiment, nineteen isolated bands belonging to nine taxa (Spiroplasma, Lactococcus, Lactobacillus, Bacillus, an uncultured Bacillaceae, Clostridium, Enterobacter, Pantoea and an uncultured Clostridium) were extracted and identified from DGGE gels. These species could be assigned to three phyla Tenericutes, Firmicutes and Proteobacteria. According to the DGGE analysis, the bacterial communities of the four gut regions exhibited some differences, with the hindgut showing the highest level of band abundance and diversity; the hindgut bacterial communities were different in random individuals. More interestingly, the genus Spiroplasma, generally regarded as pathogen or male-killing bacteria in insect, had a high abundance in the gut environment, its potential role is worthy of a further study.We chose antibiotic treatment to eliminate the gut bacteria of T. molitor. The results showed that the proteolytic activity and insect weight were similar after treatment, chymosin activity was much higher. The protein content was higher (not obvious), and the protein composition in PAGE exhibited differences. We could therefore conclude that the gut bacteria may play a role in the protein utilization or nutrition utilization but it needs further study on how this process works.