Researchers studying the rigidity and flexibility of the cell envelope used chemotaxis to measure the ability of microbes to squeeze through tight spaces. E. coli, a gram-negative bacterium, was able to traverse narrower channels than B. subtilis, a gram-positive microbe, even though both cells are the same size when grown without restriction. E. coli has the more flexible cell envelope because. a. lipopolysaccharide has no charge. b. it has fewer flagella. c. it has only a single membrane. d. there is less structural carbohydrate. e. there are fewer protein receptors.