Nature Wonders 3

Nature's Wonders 3


By Jim E. Quarles
Part 3


About three billion years ago, when life was just beginning to establish itself and evolve here on earth, ammonia was one of the most common molecules in our atmosphere and oceans. Once primitive plant life began producing oxygen, Nitrosomonas type bacteria undoubtedly began to flourish. While plants converted light through the process of photosynthesis into energy they required for survival, Nitrosomonas type bacteria developed metabolic pathways to exploit the energy released by combining ammonia and oxygen.


Fortunately for us, a lot has changed over this long period of time. As the result of the efforts of Nitrosomonas and other bacteria, ammonia is no longer a principle constituent of our planet's air and water. But Nitrosomonas bacteria rely on ammonia as their only food source. This has become a limited resource for these bacteria under the present conditions of our air and water.

To survive in such limited conditions with such scarce and unpredictable sources of ammonia, modern day Nitrosomonas have all developed a critical life sustaining adaptation. They have evolved the ability to become dormant. When starved of ammonia for prolonged period of time, Nitrosomonas began to conserve energy by shutting down the thousands of metabolic pathways, which characterize their active state.

By the time complete dormancy is achieved, there is only one critical activity which remains functional. That activity remaining functional is the ability to detect high concentration of ammonia coming into contact with the outer cell membrane. Under certain conditions, when a sufficiently high concentration of ammonia is detected over a sufficiently long period of time, the ability to transport this ammonia across the cell membrane also becomes reactivated.


Entering the dormant state is a major commitment. A significant expenditure of time and energy is required to systematically shut down enzymatic activity in the prescribed sequence to ensure long term survival. Significant amounts of time and energy are also required to reactivate these metabolic pathways. The dormant Nitrosomonas cannot afford to be frivolous in its decision to reactivate. If a newly detected source of ammonia is transient or short lived, a premature or rash commitment to reactivate could prove deadly. If the ammonia source would disappear to soon, the organism could be left without enough resources or time to return to the dormant state and would die.


Laboratory experiments have demonstrated just how conservative this reactivation response mechanism is. Dormant Nitrosomonas have been exposed to various concentrations of ammonia. The length of time required before reactivation begins was then measured. The ideal concentration required to obtain reactivation in the shortest period of time is in the area of two hundred parts per million (200 PPM). But even at this incredibly high concentration the organisms still require a time lag of two to three days before reactivation begins.

With the weak concentrations found in new aquariums this time will be expanded to ten days or even weeks in some cases.

Even when reactivation begins, the commitment is not total. Factors other than the availability of ammonia influence the rate at which metabolic activity is restored. When dormant, Nitrosomonas assume a free-floating form. The ability to move passively with the water currents increases the likelihood that they will stumble upon a new ammonia source. When reactivation begins the Nitrosomonas will attempt to become 'fixed' and adhere to a solid object. Even a new food source, which provides a high ammonia concentration, is of little value if the organism is soon to be swept away from it by the currents and left to starve.

A commitment to resume full metabolic activity, therefore, is not made until the organism adheres to a suitable solid object in ammonia rich waters.


Even small numbers of free floating Nitrosomonas will multiply in numbers and a new tank will cycle, establishing its own biological filtration system. Unfortunately this process seems to take forever. While many species of bacteria can reproduce and double their numbers every 20 minutes, the Nitrosomonas require at least 24 to 36 hours under ideal laboratory conditions to double their numbers.


Under ideal conditions, Nitrosomonas can survive in its dormant state for up to about three years but a significant percent of the organisms will began to die off, however, after more than one year. As with most adaptations for survival there are trade-offs. While the ability to become dormant has helped insure Nitrosomonas survival, it has not come without a price. As metabolic processes are shut down, so too are almost all the organism's protective mechanisms. While an active cell can respond to and withstand numerous environmental insults a dormant Nitrosomonas cell is left extremely vulnerable.

Chemical insults to dormant Nitrosomonas cells are of even greater significance to the aquarist. Nitrosomonas cells like most other aquatic organisms, are beasts adapted to an environment with very high water quality. (A change in concentration of almost any chemical beyond the level normally found in their natural unpolluted environment, is toxic). Waste products (except ammonia) from other organisms, water conditioning agents, and drugs are most common chemical insults of significance to the aquarist.

Different strains of Nitrosomonas exhibit extreme Variations with respect to their ability to survive temperature abuse. The outer cell membrane of these organisms is composed primarily of lipids (fat). When exposed to high temperatures, this proactive cell coating will actually melt and the organism will die. All strains will die if the liquid culture is frozen solid. Unlike most bacteria, Nitrosomonas cannot survive any drying or freeze-drying process. Even the liquid nitrogen freezing process is unsuccessful.

In a new aquarium, Nitrosomonas as well as other bacterial reproduction is often manifested in a bacterial bloom with the obvious turbidity or cloudiness developing in the water. Although unsightly, this cloudiness is harmless to other aquarium inhabitants and is actually a good sign, demonstrating a healthy environment required for the bacterial populations. This cloudiness will generally disappear within a few days.


While active Nitrosomonas require oxygen, they require much less oxygen then is generally believed. The natural environment for these bacteria is beneath the surface of the sediments at the bottom of the oceans or body of freshwater. This environment is not characterized with an abundance of dissolved oxygen. While the Nitrosomonas can tolerate oxygen depletion they cannot tolerate the waste products of anaerobic bacteria such as hydrogen sulfide. Even a one hour interruptions of air flow to an under gravel filter, for example, can provide enough time for lethal levels of these waste products to accumulate. Many aquarium additives are drugs that are toxic to both dormant and active cells.

Continued in final part

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