Which of the following statements about citrate-positive organisms is correct?

Citrate-positive organisms, such as certain species of bacteria, demonstrate a unique ability to utilize citrate as their sole carbon source under aerobic or anaerobic conditions. This means that these organisms can grow in environments where citrate is abundant while lacking other carbon sources. The correct answer highlights that they can release calcium, which is associated with metabolic processes involving citrate.

In some instances, bacteria can metabolize citrate, producing various end products, including calcium ions, which may be released into the environment. This capability plays a significant role in their ecological niche, especially in environments like the human gut or in soil microbiomes, where nutrient cycling is critical.

The other options do not accurately describe citrate-positive organisms. While they effectively utilize citrate, they do not specifically use it as a source of calcium or act as a type of beta-lactamase, which is related to antibiotic resistance. Additionally, they are not known for releasing oxygen, a characteristic more associated with photosynthetic organisms or certain aerobic processes.