Abstract：The intestinal tract of a vertebrate is a complex ecosystem that often harbors a complex assemblages of bacterial community. During the intestinal microbiota and the host, the microbial community has become an integral component of the host. Among its many important functions, the intestinal microbiota can convert feedstuffs into microbial biomass and fermentation end products that can be utilized by the animal host. The composition of the intestinal bacterial community is determined in part by dietary preferences and host life histories. The eel (Anguilla anguilla) is the major culture species in China, feeding with dough feed largely based on eel feed is a common practice. α-starch is an important component of eel feed ingredients. In order to study the eel intestine bacteria utilization of α-starch and in vitro metabolic characteristics, the α-amylase producing abilities of strains isolated from eel intestine. The results indicated that there were α-amylase producing strains in eel intestine. It showed that the microbial communinty colonized in the eel intestinal tract may played an important role in the nutrient digestion and absorption. 4 α-amylase producing strains were isolated, which accounted for 12.9% of the total strains populations in the eel intestinal tracts. Among them, the strain MJ18 had the highest ability to utilize α-strach. The study was designed to identify strain MJ18 by morphology and molecular methods. Strain MJ18 shared following characteristcs: Gram negative, 1.2 μm×2 μm in size, short rod, flagellum, motile. The result of sequencing the 16S rRNA gene revealed that strain MJ18 homology higher than 99% with Edwardsiella tarda strain KC570942.1. According to the characteristics of morphological features and 16S rRNA sequences analysis, the strain MJ18 was identified as Edwardsiella tard. Kinetic studies showed that the michaelis constant of α-amylase (Km) was 4.64 mg/mL, and maximum velocity (Vmax) was 45.45 mg/(min·mL). Biolog-AN system with 95 kinds of carbon source was used to exploit the metabolism feature of strain MJ18. The changes of absorbance values of strain MJ18 in 95 kinds of carbon sources were determined in different time. Results showed that strain MJ18 utilized carbon sources selectively, and the number of positive wells was 9 kinds. Dextrin, maltotriose and pyruvic acid were the principal intermediates in α-starch metabolism. The 3 cabon sources utilization ratio were more than 3%, which were higher than other carbon sources. Further analyses showed average well color development (AWCD) values were at satationary phase after 96 h cultivation. Significant differences in different sole carbon utilization characterized as AWCD value were found. The nucleotides utilization capacity was the highest, followed by organic acid and carbohydrates, and the lowest at amino acides. With the extension of the culture time, the utilization of carbohydrates, organic acid and nucleotides at strain MJ18 improved, but the utilization of amino acides did not change. This study screened and identified a α-amylase producing strain MJ18 which was isolated from the intestinal tracts of eel, which can provide new insights into potential contribution of intestine bacteria to α-starch metabolism in eel.
