Escherichia coli is a Gram-negative, facultatively anaerobic, rod-shaped, coliform bacterium of the genus Escherichia that is commonly found in the lower intestine of warm-blooded organisms (endotherms). rpsM can be deleted, but null mutants grow slowly and express kanamycin resistance weakly, which may explain why a deletion was not isolated by Baba, leading to its misclassification as an essential gene.