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作 者 ：肖海峰,焦加国,胡锋,李辉信*

期 刊 ：生态学报 2010年 30卷 24期 页码：7101~7105

关键词：Caenorhabditis elegans；Pseudomonas sp；取食偏好性；

Keywords:Caenorhabditis elegans, Pseudomonas sp, feeding preference,

摘 要 ：通过设置平板培养试验，以模式种线虫 Caenorhabditis elegans 为材料，观察了食细菌线虫的取食行为。结果表明：C. elegans 在取食细菌时对原位土壤中分离的一种Pseudomonas sp细菌存在最大的取食偏好性。这种取食偏好性表现在大部分C. elegans 在24 h内都直接朝Pseudomonas sp迁移，说明C. elegans能通过某种机制识别Pseudomonas sp。距离迁移试验及C. elegans迁移率表明它可能是通过辨别细菌所发出的气味识别它喜欢的食物。C. elegans的繁殖率跟其取食的偏好性是相关的，在迁移率较高的细菌培养基中线虫表现出更高的繁殖率。结果还表明：相对于G+细菌而言， C. elegans 偏好取食G-细菌。为进一步了解土壤生态系统中食细菌线虫与细菌群落结构间相互关系提供了帮助。

Abstract:Bacterial feeding nematodes are the most abundant and extensively distributed faunas in soils. Previous studies demonstrated that they exhibit pronounced preference when they feed on their food. This feeding preference on soil microorganisms could alter the microbial community structure and subsequently soil ecological processes. However, there were few studies reported on how the bacterial feeding nematodes distinguish between their foods. In this study, we set a plate culture experiment with Caenorhabditis elegans (C.elegans) as material to observe the feeding behavior of the bacterial feeding nematode and we explored three issues. First, do feeding preference exist when C.elegans feed on their food? Second, the possible mechanisms that bacterial feeding nematodes use to identify their food. Third, discuss the interactions between feeding preference and nematodes‘reproduction rate. Four strains of bacteria were coated as the food to allow the C.elegans to select naturally. Among them Bacillus subtilis and Escherichia coli (E. coli) were preserved in the laboratory, while Bacillus sp. and Pseudomonas sp. were isolated from the soil. 100 individuals of C. elegans were inoculated in the middle of the plate, and the migratory behavior was observed dynamically at the 1st, 2nd, 4th and the 24th hours. Results showed that, C. elegans exhibit feeding preference of Pseudomonas sp. which was isolated from the soil in situ. Most C.elegans exhibit feeding preference within a 24 hours period through a direct movement toward Pseudomonas sp., indicating that the nematodes could identify the food which they like through some mechanisms. In order to better understand the mechanisms of nematodes feeding behavior, we placed C.elegans within different distance (2cm，4cm, 6cm) from the food (E. coli) to observe their migratory behavior. Results showed that, farther away from the food source, fewer C.elegans could find the food. In addition, previous studies confirmed that one of C. elegans’ most robust behaviors is olfactory chemo-taxis towards food-associated odors, which is an innate behavior that is highly reproducible among animals. Based on these clues, it is reasonable to speculate that the most possible mechanism of nematodes feeding preference is that the nematodes can identify their food by their olfactory. After natural selection for 24h, the plates were incubated in 28℃ for 10d. After that, the C.elegans was isolated and the numbers were calculated. The result showed that the reproductive rate of C. elegans was associated with their feeding preference, the higher migration led to the higher reproductive rate. The four strains of bacteria include 2 gram-positive bacteria (G+) and 2 gram-negative bacteria (G-). Overall, our results suggested that the C. elegans preferred G+ rather than G- due to the thinner cell wall of Gram-negative bacteria,thus, G- bacteria are digested more easily than G+. Our study provided a reasonable explanation of bacterial feeding nematodes alter microbial community structure. The C.elegans was chosen as a sample of bacterivoral nematode for this study. The results provided some results for us to better understand the interactions between bacterial-feeding nematodes and bacterial community structure in soil ecosystems.

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