methane production,four stages hydrolysis,acidogenesis,acetogenesis,methanogenesis

1. By sreeremya.s

2.  Over the years a number of methods have
been developed to grow strict anaerobes and
even obtain single colony isolates but none of
these methods utilized conventional petri
plates. The purpose of this study was to test
the possibility of anaerobic direct agar plating
of environmental samples for efficacy and to
determine if novel isolates could be obtained.

3.  Facultative anaerobes - can grow in the
presence or absence of oxygen
 Obtain energy by both respiration and
fermentation
 Oxygen not toxic, some use nitrate (NO3
-) or
sulphate (SO4
2-) as a terminal electron
acceptor under anaerobic conditions

4.  Obligate (strict) anaerobes - oxygen is toxic
to these organisms, do not use oxygen as
terminal electron acceptor
 Archaea such as methanogens and Bacteria,
e.g Clostridia, Bacteriodes etc. etc.

5.  Microaerophilic organisms - require low
levels of oxygen for growth, but cannot
tolerate the levels present in the atmosphere
 Aerotolerant Anaerobes: Metabolism is
anaerobic but they are unaffected by the
presence of oxygen.

7.  Oxygen is used by aerobic and facultatively
anaerobic organisms as its strong oxidising
ability makes it an excellent electron acceptor
 During the stepwise reduction of oxygen,
which takes place in respiration toxic and
highly reactive intermediates are produced
reactive oxygen species (ROS).

8.  Organisms that use O2 have developed defence
mechanisms to protect themselves from these
toxic forms of oxygen - enymes
 Catalase: H2O2 + H2O2 => 2H2O + O2
 Peroxidase: H2O2 + NADH + H+ => 2H2O +
NAD+
 Superoxide dismutase: O2
- + O2
- + 2H+
=> H2O2
+ O2

9.  Anaerobic environments (low reduction potential)
include:
 Sediments of lakes, rivers and oceans; bogs,
marshes, flooded soils, intestinal tract of
animals; oral cavity of animals, deep undrground
areas, e.g. oil packets and some aquifers
 Anaerobes also important in some infections,
e.g. C. tetanii and C. perfringens important in
deep puncture wound infections