Anaerobic organism

Anaerobic (from the Greek prefix ( ἀν ) " no, no " and aer ( ἀήρ ) "air" ): life without oxygen ( dioxygen O2). Creatures that do not use oxygen for their metabolism or even inhibited or killed by him are known as anaerobes or anaerobic.

Properties

Organisms that can grow ( under anoxic conditions ) only in an oxygen-free habitat are called obligate anaerobes. Organisms that can grow both under anoxic conditions but also under oxic conditions ( in the presence of oxygen) are referred to as facultative anaerobic. Anaerobic organisms that have only one anaerobic metabolism, so O2 can not use, but can also live in the presence of oxygen are called aero -tolerant.

Habitats in which no oxygen is present are called anoxic, in earlier parlance as anaerobic ( contrast: oxic, oxygen containing, formerly aerobic).

Anaerobic respiration

In the oxidative energy metabolism are used instead of O2 alternative oxidizing agent ( electron acceptor ). Alternative electron acceptors are frequently used are: nitrate, ferric iron ions ( Fe3 ), tetravalent manganese ions ( Mn4 ), sulfate, sulfur, fumarate and carbon dioxide ( CO2). These redox reactions are known as anaerobic respiration.

In the table, types of anaerobic respiration are listed, which are widespread in the environment ( for comparison is the aerobic respiration with it). The order of the breathing processes took place after opportunity after the standard redox potential of the Elektronenakzeptorpaars in volts at a pH value of 7 The actual pH values ​​may vary (eg acetogenesis ).

Fermentation

Rather than anaerobic respiration, but as referred to fermentation processes in which no external fuel is used as a terminal electron acceptor. Fermentation organisms are mainly:

• Lactic acid bacteria ( lactic fermentation )
• Yeasts (alcoholic fermentation)
• Virtually all aerobes dominate under anoxic conditions, the lactic acid fermentation: anaerobic metabolism ( see also in humans Anaerobic threshold)

Symbioses

Some Turbellaria, annelids and Enter Opara Sites like tapeworms harbor anaerobic bacteria and can live through this symbiosis even under anoxic conditions.

Identification

The behavior of microorganisms to oxygen, their identification as aerobes, anaerobes, facultative anaerobes Aero -tolerant or can be determined by culture in an oxygen concentration gradient. It is cultivated them in a Gelnährmedium, located in a one-sided sealed glass tube (test tube, culture tube ) and can penetrate by diffusion into the oxygen only from the upper, open end. In this way, an oxygen concentration gradient formed from high oxygen concentration above and low oxygen concentration below. The microorganisms are distributed in a very small amount evenly Gelnährmedium in which they are localized and can not move. There, where the microorganisms are under suitable conditions in terms of oxygen concentration, they multiply and you can after a certain time detect a growth with the naked eye. The zone in which growth shows is an indicator of the behavior of the microorganisms to oxygen, as is evident from the picture.

Culture of anaerobic microorganisms

Anaerobic, inter alia, in the cultivation of microorganisms of importance. Shall be cultivated over O2 -sensitive microorganisms or are facultative anaerobic microorganisms are cultured under anoxic conditions, it is necessary to exclude from the cultural O2. This so-called Anaerobentechniken be used. An example is the culture in an anaerobic chamber: This is achieved with a gas atmosphere of 10 vol - % H2 10 vol - % CO2 80 vol - % N2 anoxic conditions, which make it possible to cultivate anaerobic microorganisms.