Nitrifying Bacteria (Aerobic Bacteria)

 Hidden literally in the shadows of every successful aquaculture operation lies a reclusive bacterial clan whose lifestyle spans the extremes of bizarre and beautiful. Few humans will ever see these magnificent creatures, miniature residents of life's trailing edge, yet without their help your fish would be downright miserable if not altogether lifeless.

The group, collectively known as nitrifiers, actually includes two discrete microbial partners tied faithfully to a life of biochemical harmony. Together, they play a critical role in every earthly ecosystem, both aquatic and soil, scavenging potentially toxic nitrogen compounds from their surroundings, including: ammonia (NH3) and nitrite (NO2-). Linked in `bucket-brigade' fashion, this nitrifying family successively transforms these nitrogenous chemicals through a delicate set of biochemical oxidations, eventually producing a soluble nitrate (NO3-) end-product.

Given their subtle and minute nature, the role of nitrifying bacteria in these reactions escaped detection until late in the nineteenth century. However, mankind had long been fascinated with nitrifications's mineralized crystalline product (i.e., nitre or saltpeter). Over a period extending nearly two millenia, ancient philosophers, alchemical wizards, and modern chemists alike tried desperately to find this enigmatic crystal's true source, driven largely by the explosive discovery of gunpowder.

Oblivious to nitre's bacterial origin, let alone its true composition, this potent crystal seemingly coalesced from unseen atmospheric spirits, an earthly offspring magically impregnated with nature's thunderous `menstruum.' In fact, nitrogen's own name (a.k.a. nitre-genesis) bears witness to this original hypothesis, forever perpetuating the quaint legacy of nitre's supposed aerial origin.

Our current understanding of these bacteria has improved considerably, though, over the past century. Shortly after discovering its biochemical source, researchers identified two separate bacterial companions responsible for nitrification. Each partner critically depends on the other, and each finds nourishment in seemingly barren substrates. Both of these bacteria qualify as lithotrophic microbes (translated from Greek, `rock eaters'), feeding on chemicals which no other bacteria would possibly use as their primary energy source.

Aside from this particularly spartan diet, using chemicals often regarded as potential toxins, their intermediate and final products are similarly unusual. Perhaps most notably, the lead organism actually makes, and then reingests, a dangerous mutagenic substance (hydroxylamine, NH2OH) whose noxious character hardly seems commensurate with normally healthy metabolic activity.

Based on our overall perception of its unusual lifestyle, therefore, the conventional wisdom for nitrifiers provided in most textbooks describes a fragile, highly sensitive life form. However, evidence collected over the past few years strongly refutes this image. In fact, recent discoveries about these unusual microorganisms suggest a far different behavior, as robust, metabolically agile microorganisms.

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