Green bacteria - are phylogenetic isolated group photosyntetic microorganisms. The peculiarity of the structure of their cells is the presence of special vesicles - so-called chlorosom containing bacteriochlorofils and carotenoids. These microorganisms can not use water as a donor of electrons to form molecular oxygen during photosynthesis. Electrons required for reduction of assimilation CO2, green bacteria are recovered from the sulfur compounds with low redox potential.
Ecological niche of green bacteria is low. Well known types of green bacteria - a common aquatic organisms that occur in anoxic, was lit areas of lakes or coastal sediments. In some ecosystems, these organisms play a key role in the transformation of sulfur compounds and carbon. They are adapted to low light intensity. Compared with other phototrophic bacteria, green bacteria can lives in the lowest layers of water in oxygen-anoxic ecosystems.
Representatives of various genera and species of green bacteria differ in morphology of cells, method of movement, ability to form gas vacuoles and pigment structure of the complexes. For most other signs, including metabolism, structure photosyntetic apparats and phylogeny, these families differ significantly. Each of the two most studied families of green bacteria (
Representatives of the green sulfur bacteria family
In the evolution of autotrophic organisms formed several ways to assimilate CO2, each of which is characterized by biochemical reactions that require the appropriate enzymes and reduction equivalents [9, 11]. The most common mechanism for CO2 assimilation is Calvin cycle, which was found in most plants, algae and most famous groups of autotrophic prokaryotes. In green bacteria described two alternative ways of assimilation of CO2. Revers cycle of tricarboxylic acids (RTAC) in green sulfur bacteria, first proposed by Evans in 1966. In 1989, Holo described 3-hidroksypropionat way that is characteristic of green non sulfur bacteria.
Larsen, using washed cells of
Green sulfur bacteria can use some organic compounds (sugars, amino acids and organic acids). However, adding these compounds to the environment leads only to a slight stimulation of growth of culture in the presence of CO2 and is to ensure that they are used only as additional sources of carbon . In any case they are electron donors or major source of carbon. The use of these substances only if there among CO2 and H2S.
In the cells of
They make possible (RTAC), in which two molecules of CO2 formed a molecule of acetyl - CoA (Fig. 1).
First, revers tricarboxylic acid cycle (RTAC) considered an additional mechanism for better functioning of rehabilitation Calvin cycle of the genus
The study of restorative (RTAC) can explain the inability of green sulfur bacteria photoheterotroph. Simultaneously with the operation of the mechanism fixation of CO2 cycle intermediates also provide cells needed organic matter for the synthesis of fatty acids (from acetyl-CoA), amino acids (from pyruvate, α-ketoglutarat acid) and carbohydrates (with pyruvate). However, since the activity of α-ketoglutaratdehidrohenaz not found in species of the genus
Recovery (RTAC) provides fixation of CO2, to be based on restorative carboxylation reaction of organic acids. Fixation of carbon dioxide occurs in three enzymatic reactions, two of which occur with photochemically reduced ferredoksyn, and one - the same way formed provided with (H+). As a result of a turnover cycle of four molecules of CO2 and 10 [H+] using the energy of three molecules of ATP synthesized molecule oxaloacetat acid is the end product cycle.
Described as "short" version of the cycle, in which 2 molecules of CO2 are fixed using for their restoration 8 [H+] and the energy of ATP. The final product in this case is acetyl-CoA, which is used to build components of cells. Addition of acetate in the culture medium promotes the accumulation of biomass and stimulates the formation of reserve polysacharides in the cells of green sulfur bacteria. Representatives of the family
Larsen and collaborators found that the bacteria
Larsen found that washed suspensions of cells
Found that in cells
To detect sugars that accumulate in cells of
It follows that the sugar is reduced
It was found that light intensity plays an important role in CO2 assimilation in
On the intensity of photosynthesis reveals a significant influence of mineral nutrition of bacteria We shows the influence of different sources nitrogen and phosphorus supply of glucose in the cells
Simultaneous limitation of growth of culture nitrogen and phosphorus accompanied by increase in glucose in the cells. Her level of these compounds for the deficit grew by about 60%. Separately salts of nitrogen and phosphorus showed much less effect In these experiments investigated how bacteria use glucose under various conditions of cultivation. This used washed cells were incubated under light and dark. When incubation of cells at the light in the presence of CO2 and H2S levels of glucose in the cells practically did not change while under these conditions in the dark glucose concetration in the cells decreased about 2.5 times.
Obviously, in the dark using glucose as an energy source, turning towards Embdena-Meyerhof-Parnas. The level of intracellular glucose is reduced and the conditions of incubation of cells at the light in the environment without hydrogen sulfide, indicating that the use of glucose under these conditions as the sole source of renewable equivalents. In the dark, without glucose hydrogen sulfide is the only source of energy. Thus, the glucose formed by cells plays an important role in the life of cell
2. Isolation, identification and patterns of accumulation poliglucose
C. limicola IMB- K-8
Nature poliglucose formed in the cells of
Comparative analysis of selected polisaharide and glycogen company "Sigma" showed that the resulting sample shows identical chemical and physical properties: white crystalline powder soluble in water, not soluble alcohol, hydrolyzed in acidic medium to form glucose. Infrared spectroscopy etylaceton extract the studied sample and glycogen "Sigma" has shown that these substances are characterized by the presence of identical functional groups, O-H bonds (the interval 3608 - 3056 cm-1), revealed specific absorption in the carbonyl group (1656 cm- 1),- CH2-group (2932 cm-1), and -C-O-H groups (1048 cm-1) and others, indicating the identity of the investigated sample of bovine liver glycogen (the drug company "Sigma") (Fig. 3.) Therefore, we first selected polisacharide of cells
The laws of accumulation and utilization of glycogen
Only adding to the environment pyruvate and acetate stimulated the growth of glycogen content in cells of
The results obtained give grounds to assert that
So when the concentration of CO2 in the atmosphere 60mM observed maximum cell growth and increased by 50% the level of glycogen. A slight reduction of carbon dioxide in the environment (20%) accompanied by a reduction in biomass, while increasing the level of glycogen in the cells by about 30%. Further reduction of CO2 was accompanied by decrease in the intensity of photosynthesis. Increase in glycogen levels in cells with the shortage of carbon dioxide in the atmosphere, apparently, can be explained by inhibition of pyruvate carboxylation reaction and its conversion in to oksaloatsetat and then using it in a constructive metabolism. Note that formed in the process of photosynthesis annoxy carbohydrates not allocated to the environment and stockpiled exclusively in the cell. As evidenced by a negative test for glucose and other sugars is reduced before and after hydrolysis of culture broth. To find ways of further use of glycogen in these experiments, free cells of
These results are consistent with data Sirevag, under which the cells incubated with
Under the conditions of incubation, washed cells
In addition to the family
Found that one of the key enzymes - piruvatsyntaza that catalyzes the formation of pyruvate from acetyl-CoA and CO2 detects activity in
Holo and Grace in 1987 found that in autotrophic conditions is inhibiting the tricarboxylic acid cycle and gliocsilate shunt, and in the cells is a new metabolic pathways in which acetyl-CoA is an intermediate product. Later Holo found that in autotrophic conditions
Hidrokspropionat role as intermediate in the fixation of CO2 was investigated Fuchs and Staff in experiments using 13C. The relative amount of 13C after growth
For a final check of the cycle Strauss and Fuchs had enzymatic studies and showed that the cells of green bacteria is nonsulfur activity of all enzymes required for assimilation cycle 3-hidroksypropionat reduction of carbon dioxide. In this cycle acetyl - CoA in malonil - CoA and then, reducing turns through 3-hidroksypropionat to propionil - CoA.
Thus, in green bacteria nonsulfur
Thus, green bacteria families
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