Bacteria from aggregates at least half a millimeter in diameter survived three years of exposure to space, and were capable of repairing the genetic damage they suffered so, that bacteria could survive space long enough to make the trip between Mars and Earth. Facultative anaerobes show better growth in the presence of oxygen but will also grow without it. Although aerotolerant anaerobes do not perform aerobic respiration, they can grow in the presence of oxygen. Most aerotolerant anaerobes test negative for the enzyme catalase. Anaerobic bacteria thrive in oxygen depleted environments. They feed on waste water nutrients and release the foul sulfur-containing odors so commonly associated with sewage. This is primarily due to the incomplete “digestion” of the waste water food source.

The extremophilic bacterium Deinococcus radiodurans withstands the drastic influence of outer space: galactic cosmic and solar UV radiation, extreme vacuum, temperature fluctuations, desiccation, freezing, and microgravity. Anaerobes, on the other hand, cannot grow in the presence of oxygen. Oxygen is toxic for them, and they must therefore depend on other substances as electron acceptors. Facultative anaerobes show better growth in the presence of oxygen but will also grow without it. Although aerotolerant anaerobes do not perform aerobic respiration, they can grow in the presence of oxygen. Most aerotolerant anaerobes test negative for the enzyme catalase. Bacteria can be anaerobic or aerobic. Aerobic means involving oxygen the bacteria that take up oxygen for their cellular activities, anaerobic bacteria can survive without oxygen. Bacteria that require oxygen to grow are called obligate aerobic bacteria. In most cases, these bacteria require oxygen to grow because their methods of energy production and respiration depend on the transfer of electrons to oxygen, which is the final electron acceptor in the electron transport reaction. Well, facultative anaerobes may grow better in aerobic conditions based on the ATP yield. This is because aerobic respiration yields 36/38 ATP molecules as against 2 ATP molecules generated in fermentation. In contrast to obligate anaerobes, facultative anaerobes do aerobic cellular respiration when oxygen is available but are also capable of surviving off of fermentation. As a result, facultative anaerobes can survive with or without oxygen i.e. in aerobic environments or in anaerobic environments. Anaerobic means an environment without oxygen. Bacteria can be classified based on how they use oxygen. Obligate aerobes are obligated to use oxygen, meaning they have to have oxygen in the environment in order to survive. Obligate anaerobes do not require oxygen, and many cannot even live in the presence of oxygen. Aerobic bacteria live in normal air containing 21% oxygen. However, when aerobic bacteria is engulfed in clusters of oxygen composed of 100% pure oxygen and is continually bombarded with electron shots, it quickly dies. Four species of bacteria three of them previously unknown to science have been discovered onboard the International Space Station (ISS), begging questions about how they got there, and how they have managed to survive.

Environmental bacteria can be grouped into three categories: aerobes, facultative and anaerobes.

Some bacteria, such a nitrifiers, are strict aerobes; they need oxygen to grow.

Oxygen can be toxic to strict anaerobes.

In between are facultative bacteria.

It is important to keep in mind the size of the microbes and the environment in which they are found. For instance, even in an apparently oxygenated environment, conditions within floc can be very different. The floc inhibits free movement of gases and nutrients.

Facultative bacteria have a preferential choice of electron receptors. First is oxygen.

When or where this is depleted, nitrate can be used; nitrate is converted to nitrogen gas. Additions of nitrate can used in sewers and leach fields to help biodegradation. The nitrogen gas produced can help break up compaction in leach fields to improve percolation. Nitrate is also useful, because high concentrations can be added to flow downstream in sewers where oxygen cannot easily be added. Nitrate keeps the redox potential above -150mv.

If / when the redox potential drops below this value, bacteria can use sulfate as the electron receptor. This is usually undesirable as the sulfate is converted to sulfide (H2S), which is highly toxic and has a rotten egg smell. When the H2S exits the water in sewers, it reacts with oxygen in the air to form sulfuric acid (H2S04). Entire sewers and pump houses can be damaged or destroyed by crown corrosion. Good management requires keeping sewer infrastructure free of grease and sludge accumulations.

Dr Karl F Ehrlich thank you for your contribution to the discussion

Facultative anaerobes can change their metabolic processes depending on the presence of oxygen, using the more efficient process of cellular respiration in the presence of oxygen and the less efficient process of fermentation in the absence of oxygen. Anaerobic bacteria thrive in oxygen depleted environments. They feed on waste water nutrients and release the foul sulfur-containing odors so commonly associated with sewage. This is primarily due to the incomplete “digestion” of the waste water food source. When food goes bad and starts to become pungent, it is most often due to the growth of spoilage microbes such as bacteria, yeasts and mold. Odors can come from two sources: chemicals that are released from the food as the microbes decompose it, or chemicals produced directly by the microbes themselves. Anaerobic bacteria are germs that can survive and grow where there is no oxygen. For example, it can thrive in human tissue that is injured and does not have oxygen-rich blood flowing to it. Infections like tetanus and gangrene are caused by anaerobic bacteria. Obligate anaerobes, which live only in the absence of oxygen, do not possess the defenses that make aerobic life possible and therefore cannot survive in air. The excited singlet oxygen molecule is very reactive. Therefore, superoxide must be removed for the cells to survive in the presence of oxygen. Panspermia is only a possibility if at least some bacteria that can survive prolonged exposure to the harsh conditions of outer space, including airlessness, extreme temperatures, and radiation. After serving as a home away from home for astronauts over the last 20 years, the International Space Station has become the host for unique bacterial inhabitants and these microbes could prove useful. Four strains of bacteria, three of which were previously unknown to science, have been found on the space station. Organisms that can grow in the absence of oxygen are referred to as anaerobes, with several different categories existing. The facultative anaerobes are the most versatile, being able to grow in the presence or absence of oxygen by switching their metabolism to match their environment. Under aerobic conditions, oxygen acts as the final electron acceptor for the electron transport chain located in the plasma membrane of prokaryotes. Bacteria use this process to generate ATP, the energy source for most cellular processes.