Part 3. Microbe-Host interactions. In 2008 Turnbaugh et al. explored the relatio

Question

Part 3. Microbe-Host interactions. In 2008 Turnbaugh et al. explored the relationship between the gut microbiota and diet-induced obesity. The researchers colonized WT lean germ free mice with the same microbiotas, but restricted one roup of mice to a low fat plant-based polysaccaride diet (CHO) and restricted the other to ah?ghtat artihydat"ich (Western Diet). 6. Describe and interpret the data shown below. Do these results make sense to you based on everything you've learned so far in class? As you interpret the data, consider the fact that when compared to Firmicutes, Bacteroidetes species contain more types of genes that encode polysaccharide specific enzymes and transports. ? Firmicutes Bacteroidetes 1001 3 4o CHO Western 40 20 Western CHO

Explanation / Answer

The study as done by Turnbaugh et al. in 2008 shows that the germ-free mice indicate the structure and operations of the gut microbiota. Colonization of adult germ-free animals with a distal gut microbiota was fed a low-fat polysaccharide-rich diet produces a marked increase in body fat content within 10–14 days.

A significantly higher relative abundance of Firmicutes and a significantly lower relative abundance of the Bacteroidetes was seen in the Western diet-associated cecal community (Figure A). The overall diversity of the Western diet microbiota dropped prominently, due to a bloom in a single class of the Firmicutes-the Mollicutes.

To directly test whether the DIO-associated gut microbial community possesses functional attributes that could increase the host adiposity to a greater degree than a CHO diet-associated gut microbial community, researchers have transplanted the cecal microbiota as harvested from obese, conventionally-raised wild-type donors who had been on the Western diet for ?8 weeks since the cecal microbiota from lean CHO-fed controls, to 8- to 9-week-old germ-free CHO-fed recipients (n = 1 donor and 4 to 5 recipients/treatment group/experiment; n = 3 independent experiments, including one CHO-fed control group described in Turnbaugh et al., 2006). All the recipients were maintained on a CHO diet (16% of kcal from fat, 61% from carbohydrates of which 2% are from fructose, glucose, lactose, maltose, and sucrose combined), and sacrificed 14 days after receiving the microbiota transplant. Mice colonized with a DIO-associated microbiota exhibited a significantly greater percentage increase in body fat as defined bdual-energygy X-ray absorptiometry (DEXA) than mice who had been gavaged with a microbiota from CHO-fed donors (43.0 ± 7.1 versus 24.8 ± 4.9 percentage increase; p < 0.05, Student's t test based on the combined data from all three experiments) (Figure B). Importantly, there were no statistically significant differences in chow consumption (14.5 ± 0.3 versus 14.7 ± 0.8 kcal/d) or initial weight (22.9 ± 0.3 versus 23.8 ± 0.7g) between recipients of the obese and lean cecal microbiotas.

A. The relative abundance (% of total 16S rRNA gene sequences) of the Firmicutes and Bacteroidetes divisions in the distal gut microbiota of the conventional, wild-type C57BL/6J mice were fed a standard low-fat, high-polysaccharide chow diet (CHO; n = 5) or a high-fat/high-sugar diet (Western diet; n = 5).

B. Microbiota transplantation experiments have revealed that the DIO community has an increased capacity to promote host fat deposition. Total body fat was measured using dual-energy X-ray absorptiometry (DEXA) before and after a two-week colonization of adult germ-free CHO-fed C57BL/6J wild-type mice with a cecal microbiota harvested from mice maintained on CHO or Western diet (n = 14 mice/treatment group). Mean values ± SEM are shown. Asterisks in panels (A)–(D) indicate that the differences are statistically significant (Student's t test, p < 0.05) after using the Bonferroni correction to limit false positives.

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