Algae control via nitrogen removal — Which organism has been used to oxidize ammonia and thereby help prevent algal growth in water systems?

Introduction / Context:
Algal blooms in aquatic systems are often fueled by available nitrogen (and phosphorus). Biological nitrification can convert ammonia, a form readily assimilated by algae, into nitrate, which can be further removed by denitrification or reduced in bioavailability, helping control algal growth.

Given Data / Assumptions:

• Ammonia-oxidizing bacteria (AOB) convert NH3/NH4+ to nitrite (NO2−).
• Nitrite-oxidizing bacteria (NOB) convert NO2− to NO3−.
• Denitrifiers reduce nitrate to gaseous nitrogen under anoxic conditions.

Concept / Approach:
Nitrosomonas europaea is a model AOB used in biofilters and nitrification reactors. By oxidizing ammonia, it reduces the pool of algal-available nitrogen in the form most stimulatory for growth, forming part of an integrated nutrient management strategy in water treatment.

Step-by-Step Solution:

Verification / Alternative check:
Engineering texts on aquaculture and drinking water biofiltration cite Nitrosomonas-based biofilters for ammonia control and consequent algae suppression.

Why Other Options Are Wrong:

• Hypomicrobium and Micrococcus denitrificans: employed for denitrification, not ammonia oxidation.
• Anabaena (cyanobacteria): fixes nitrogen and can contribute to blooms rather than prevent them.

Common Pitfalls:
Confusing nitrification (aerobic) with denitrification (anoxic); each step involves different organisms and goals in nutrient control.

Final Answer:
Nitrosomonas europaea (ammonia-oxidizing bacterium)