Which of the following is not patentable?

The selected answer highlights that bacteria are not considered patentable subject matter in a specific context. Under U.S. patent law, particularly as it relates to the implications of the Supreme Court's decisions and the guidelines outlined in the Manual of Patent Examining Procedure (MPEP), certain categories of natural products, including naturally occurring bacteria, are typically deemed not patentable.

While genetically modified organisms, hybrid plants, and new plant varieties can be patentable if they meet the requirements of novelty, non-obviousness, and usefulness, naturally occurring bacteria present a more complex issue. In many cases, if the bacteria are genetically modified to exhibit new characteristics or utility, they may be eligible for patent protection. However, the fundamental existence of a naturally occurring bacterium does not qualify for a patent, as they are considered a product of nature, which is a key principle in patent examination.

By contrast, the other options involve organisms or varieties that are often considered modified or invented, allowing for patent claims to be valid as they have undergone a transformation or represent a new creation by human intervention.