The correct answer is "most of the sequences from infected individuals belonged to the phylum proteobacteria".
It has been shown that there are significant differences between the microbiome of H. pylori-negative individuals (people who were not infected by the bacterium H. pylori) and H. pylori-positive individuals (people whose stomachs were infected with this bacterium).
More specifically, the H. pylori individuals had a highly diverse gastric microbiota, which was comprised of five different phyla of microorganisms: Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes, and Fusobacteria.
On the other hand, the H. pylori individuals had a much less diverse gastric microbiota. This is because the bacterium H. pylori accounted for 72-97% of the microbes in the stomach of the infected individuals. Given that H. pylori belongs to the phylum of Proteobacteria, most of the sequences of the infected individuals belonged to the phylum of Proteobacteria.
