Answer:
The hemoglobin molecule has four binding sites for oxygen molecules: the iron atoms in the four heme groups. Thus, each Hb tetramer can bind four oxygen molecules.
Regarding the order rhizobiales of the class Alphaproteobacteria, the genus that includes human pathogens is Brucella.
Rhizobiales are a type of Alphaproteobacteria, which are a type of Proteobacteria, which are Gram-negative bacteria.
Brucella is also a type of Gram-negative bacteria that can cause brucellosis, which is an infectious disease caused by eating unpasteurized milk or undercooked meat.
