Which organism is indicated by the presence of a yellow pigment and positive nitrate reduction?

The presence of a yellow pigment and positive nitrate reduction is indicative of Pseudomonas aeruginosa. This organism is known for its ability to produce a variety of pigments, including pyocyanin, which can contribute to its characteristic blue-green color, but it can also produce yellow-green pigments under certain conditions. Additionally, Pseudomonas aeruginosa is capable of reducing nitrate to nitrite, demonstrating its versatility in utilizing different nitrogen sources, which is a key metabolic feature. This capability is commonly tested in laboratories and serves as an important identifying characteristic for this species.

The other organisms mentioned have different characteristics that do not align with both the yellow pigment production and the nitrate reduction feature specific to Pseudomonas aeruginosa. Thus, understanding these metabolic traits is essential for correctly identifying and distinguishing Pseudomonas aeruginosa in microbiological studies.