Final answer:
The class Betaproteobacteria does not include the genus Enterococcus; therefore, the correct answer to which genus is not part of the Betaproteobacteria class is d) Enterococcus.
Step-by-step explanation:
The class Betaproteobacteria includes a diverse group of bacteria, but it does not include the genus Enterococcus. The options listed in the student's question (Nitrosomonas, Bordetella, and Burkholderia) are all part of the Betaproteobacteria class, which is known for its wide range of metabolic strategies and environments for survival. Some genera, such as Neisseria, include species that are human pathogens like N. gonorrhoeae and N. meningitides. The Bordetella genus includes B. pertussis, the causative agent of whooping cough. The correct answer to the student's question is d) Enterococcus, which is not a genus within the Betaproteobacteria class.