| Gut microbes play an important role in human health. Evidences indicated that gut microbes could be regulated by diets and out-of-balance of gut microbes could be a reason of various diseases. It was suggested that functional food components could influence human health by modulating gut microbes. Thus it's of great value to research the relationship between functional food components and gut microbes.Just like human or mice, C.elegans gut could also provide a settled place for microorganism. In laboratory culture conditions, it's convenient to feed C.elegans monoxenie or several given bacteria without interference of others. Gut microbes are so complex that lots of them still cannot be cultured in vitro. Whereas, C.elegans provides a nice intestinal environment for the growth of mammalian gut microbes and the complexity of gut microbes can be sustained by fecal microbiota transplantation. So far, there were no studies found to introduce the gut microbes from mammals to C.elegans.This study aimed to establish a new method by using C.elegans to reflect the connections between certain food components and gut microbes effectively and rapidly. Besides, a relationship was established among diets, gut microbes and host health, which provided a new approach to study the effects of gut microbes.In this study, second generation sequencing technology was used to detect and analyze the diversity and composition of C.elegans intestinal microbes after feeding on murine fecal microflora as well as the given fecal microflora to determine the feasibility of fecal transplantation across the two systems. Then, taking n-3 PUFAs and n-6 PUFAs as examples, the different effects of them on the gut microbes in C.elegans-microbes system were compared. Furthermore, microbial communities altered by diets with different contents of n-3 PUFAs and n-6 PUFAs were used to observe their impacts on the lifespan of C.elegans. The main conclusions are as follows:(1)Exogenous microbes can survive in C.elegans intestineEscherichia coli BL21 expressing GFP was used to study the efficiency of C.elegans uptake and the maintain time of exogenous bacteria. The results showed that the gut of most of the C.elegans was full of bacteria after feeding for an hour. After stopping feeding for two hours, bacteria could still be found in the gut of the C.elegans and most of them located in the posterior. These results provided a basis for introducing the fecal microflora from mice into C.elegans through free-feeding and confirm the time course for C.elegans uptake. Meanwhile, the method to separate intestinal microbes and surface microbes was studied so that the interference of microbes from surface could be excluded during metagenomic analysis.(2)The nematode-gut microbes system was established by nematodes taking in fresh mice fecal microbiota freely.Based on the verification of specific genus introduction through PCR using specific primers, second sequencing technique was used to analyze gut microbes of C.elegans under standard culture(GMSC), fecal microbes from mice(FM), gut microbes of C.elegans fed fecal microbes from mice for 24 hours(GMFM). Gut microbes of C.elegans under standard culture was mainly occupied by Proteobacteria. Compared to initial fecal microbes from mice, GMFM had the similar composition and proportion at phylum. And at genus, FM and GMFM had similar types of dominant bacteria communities while these communities occupied different ratio. The C.elegans gut microbes and its surrounding microbes in liquid culture as time went by were analyzed. The results showed that C.elegans formed a distinct community from its surroundings, which meant microflora had an enriched process. As time went by, the ratio of Bacteroidetes decreased while the ratio of Proteobacteria increased. At genus, genus belonging to Firmicutes stayed a stable proportion while many kinds of genus belonging to Proteobacteria appeared.(3)The different influences of n-3 PUFAs and n-6 PUFAs on the gut microbes of C.elegansAccording to the results above, C.elegans were fed with fresh FM and at the same time n-3 PUFAs and n-6 PUFAs were added respectively. After culturing for 24 hours, the samples were collected and sequencing was performed to analyze the gut microbes of C.elegans. Compared to negative control, n-3 PUFAs amplified the bacteria communities while adding of n-6 PUFAs showed no difference in amplification. In the aspect of composition and distribution, the ratio of Bacteroidetes and Firmicutes increased in both n-3 PUFAs and n-6 PUFAs groups. N-3 PUFAs decreased the ratio of Proteobacteria remarkably compared to the negative control. N-6 PUFAs increased the ratio of Lactobacillus significantly.(4)Fecal microbes from mice with n-3 PUFAs rich diets extended the lifespan of C.elegansC.elegans provides a good organism model to explore the impact of microorganism on the hosts. In the paper, lifespan was chosen as an index to determine the influences of microflora altered by various diets on the health. C.elegans lived on microflora altered by n-3PUFAs-rich diets lived longer than the other, which indicated microflora altered by various diets could affect health of the host.In this study, we explored the feasibility of introducing mammalian gut microbes into C.elegans for screening the impacts of functional food components on gut microbes for the first time. Most of the dominant bacterial communities from mice could be introduced to C.elegans and showed a dynamic diversity. The C.elegans gut microbes could be response to the supplement of PUFAs. N-3 PUFAs differed from n-6 PUFAs on the aspect of acting on gut microbes. We also found that gut microbes modulated by n-3 PUFAs could extend lifespan of C. elegans compared to the ones modulated by n-6 PUFAs. This discovery provided a new way to study the impact of diets on heath by modulation of the gut microbes as well as an evidence for benefits of n-3 PUFAs on health. |
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