PHYSIOLIGY OF METHANOGENIC BACTERIA PPTX

THERMOPHILES METABOLISM

1. Nidhi Sahni L-2010-BS-66-D Physiology of methanogenic bacteria

2. INTRODUCTION In 1776, Alessandro Volta ran some experiments on combustible air. On a little boat in Lake, he started to poke and stir the bottom of an area covered with reeds. Upon doing this, Volta noticed a lot of air emerging and decided to collect some in a large glass container. Upon analysis of the air he noted that it burned a beautiful blue flame. The discovery of methanogens helped produce the idea for the kingdom  Archaeobacteria , that would include methanogens , some extreme halophiles , and some extreme thermophilic sulfur-dependant organisms.

3. CELL STRUCTURE Rods and coccoid , seem to dominate the methanogens . Rod shaped sporulating : Methanobacillus , Rod shaped non sporulating : Methanobacterium Spherical arranged as sarcina : Methanosarcina Spherical not as sarcina : Methanococcus Plate shaped   Methanoplanus   Methanospirillum  that are long thin spirals   Methanosarcina  that are cluster of round cells Methanogens lack murein typical of bacteria ( eubacteria ), but some contain pseudomurein ,

4. ECOLOGY live in a wide range of environments; freshwater to hypersaline . Present in anoxic environment; aq. sediments of ponds, marshes, swamps, lakes and oceans; intestinal tract of human & animal, rumens of cattle and other ruminants Methanohalophilus contain the most halophilic methanogens , who share some similarities to the aerobic archaeobacteria Halobacterium ; since 16S and 23S rRNA sequence comparisons show a specific relationship between the two. In addition, they are the only methanogens to possess cytochromes which are found in halobacteria .

5. contd … Methanogenesis is greatly limited when the surrounding temperature is below 15 o C, but can still occur readily at temperatures near 100 o C Methanoculleus submarinus   is found at temperatures near 15 o C and   Methanococcus jannaschii , growing around 85 o C High temp tolerance due to : high G + C content reverse gyrase : produces positive supercoils in DNA that could render more tightly coiled DNA and greater stability pH optima near neutral Hydrogenotrophic methanogen was isolated from peat bogs and was able to grow at pH as low as 5 while still producing some methane down to pH 3.0 Methanohalophilus zhilinae , has been found in a hypersaline lake in Egypt which also has an optimum pH value of 9.2.

6. METABOLISM Unique among prokaryotes as they produce methane through anaerobic metabolism. About half the genera can metabolize formate , by first oxidizing it by formate dehydrogenase to H 2 + CO 2 , and then by reducing CO 2 to methane HCOOH=CO 2 + H 2 = CH 4 + H 2 O Also form methane from methanol, formate , methyl amine, acetate, valeric acid, isovaleric acid For example: Methanococcoides methylutens grows only on methylamines or methanol

7. Methanogens generally possess Cofactor F 420 Co enzyme M (2 mercapto -ethane sulphonic acid) Methanofuran ( Methanobacterium thermoautotrophicum ), named as carbon dioxide reduction factor (CRF) Methanopterin

8. Contd … 70 % or more of the methane formed is derived from acetate Common in landfills and sewage digesters Methanogens represent a microbial system that can be exploited to produce energy from waste materials. Large amounts of methane are produced during industrial sewage treatment processes, but the gas is usually wasted rather than trapped for recycling. Accumulation of compatible solutes, by uptake or de novo synthesis, enables bacteria to reduce the difference between osmotic potentials of the cell cytoplasm and the extracellular environment, occur in halophilic and halotolerant methanogenic archaebacteria

9. Contd …… Methanogens are a taxonomically and phylogenetically diverse group of microorganisms that all gain energy for growth from the reactions that lead to the production of methane. As a group, methanogens use a small number of compounds, H 2 or one-carbon atom compounds. This specialization makes methanogens dependent on other organisms for the supply of substrates in most anaerobic environments. Without methanogens , effective degradation of organic matter would cease due to the accumulation of nongaseous products of fermentation which have almost the same energy content as the original substrate.

10. The ability of methanogens to use H 2 plays a key regulatory role that controls the types of products made by fermentative bacteria and sets the thermodynamic conditions required for the degradation of fatty and aromatic acids. The favorable thermodynamics of H 2 use by methanogens allows them to metabolize H 2 to very low partial pressures.

11. Because of the large capacity for H 2 use by methanogens , H 2 concentrations are normally very low in well operated anaerobic digestors , even though large amounts of H 2 are produced. The ability of methanogens to maintain low levels of H 2 affects the types of products formed by fermentative bacteria and is essential for the degradation of fatty and aromatic acids by syntrophic associations.

12. Contd ….. Methanogenic reactions 4H 2 + HCO 3 - +H CH 4 + 3H 2 O Acetate + H 2 O CH 4 + HCO 3 - Syntrophic reactions without H 2 use by methanogens Lactate + 2H 2 O Acetate + HCO 3 - + H + + 2H 2 Ethanol + H 2 O Acetate + H + + 2H 2 Butyrate + 2H 2 O 2 Acetate + H + + 2H 2 Syntrophic reactions with H2 use by methanogens 2Lactate + 2H 2 O 2Acetate + HCO 3 - + H + +2H 2 2Ethanol + H 2 O 2Acetate + H + + 2H 2 2Butyrate + 2H 2 O 4Acetate+ H + +2H 2

13. EFFECT OF TEMPERATURE Methanogenic bacteria are more sensitive to changes in temperature than other organisms present in digesters. This is due to the faster growth rate of the other groups, such as the acetogens . Temperature variations can have adverse affects on mesophilic (35°C) digestion, or thermophilic (55°C) digestion. The temperature effect also depends significantly on the solids concentration of the fermentation. When high concentrations of organic loading were used (over 10%), the tolerance for changes of 5 - 10°C is much higher, and bacterial activity returns quickly when the temperature is raised again. Two distinct temperature regions for digestion have been noted: optimal digestion occurs at about 35°C ( mesophilic range) and 55°C ( thermophilic range), with decreased activity at around 45°C. This response to temperature may be due to effects on methanogenic bacteria, since these appear to exhibit similar optimal regions.

14. EFFECT OF pH Acetate and fatty acids produced during anaerobic digestion tend to lower the pH of digester liquor. However, the ion bicarbonate equilibrium of the carbon dioxide in the digester exerts substantial resistance to pH change. This resistance, known as buffer capacity, is quantified by the amount of strong acid (or alkali) added to the solution in order to bring about a change in pH. Thus the presence of bicarbonate helps prevent adverse effects on microorganisms ( methanogens ) which would result from low pH caused by excessive production of fatty acids during digestion. Proteins and other organic compounds, as well as bicarbonate, take a part in the buffering capacity and the resistance to changes in pH.

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