The presence of which type of bacteria can lead to musty odors in water systems?

The presence of iron bacteria in water systems is well known for causing musty odors. These bacteria are typically found in natural environments where iron is present, and they have the ability to oxidize iron compounds. As they metabolize, they produce byproducts that can lead to unpleasant odors, often described as musty or earthy.

Iron bacteria thrive in environments with sufficient iron and can form slimy deposits that affect water quality, appearance, and taste. Their presence is not only a nuisance due to odors but can also indicate issues in the water system that may require attention, as they can clog pipes and filters.

In contrast, pathogenic bacteria are associated with health risks and are not directly linked to musty odors. Sulfate-reducing bacteria are typically related to rotten egg smells due to hydrogen sulfide production. Nitrogen-fixing bacteria play a role in nutrient cycling in soil and water but lack the characteristics that produce musty odors. Therefore, iron bacteria is the correct answer in this context.