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  • 1
    Electronic Resource
    Electronic Resource
    Fermentation in cyanobacteria (1997)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology reviews 21 (1997), S. 0 
    Details
    ISSN: 1574-6976
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Although cyanobacteria are oxygenic phototrophic organisms, they often thrive in environments that become periodically anoxic. This is particularly the case in the dark when photosynthetic oxygen evolution does not take place. Whereas cyanobacteria generally utilize endogenous storage carbohydrate by aerobic respiration, they must use alternative ways for energy generation under dark anoxic conditions. This aspect of metabolism of cyanobacteria has received little attention but nevertheless in recent years a steadily increasing number of publications have reported the capacity of fermentation in cyanobacteria. This review summarizes these reports and gives a critical consideration of the energetics of dark fermentation in a number of species. There are a variety of different fermentation pathways in cyanobacteria. These include homo- and heterolactic acid fermentation, mixed acid fermentation and homoacetate fermentation. Products of fermentation include CO2, H2, formate, acetate, lactate and ethanol. In all species investigated, fermentation is constitutive. All enzymes of the fermentative pathways are present in photoautotrophically grown cells. Many cyanobacteria are also capable of using elemental sulfur as electron acceptor. In most cases it seems unlikely that sulfur respiration occurs. The main advantage of sulfur reduction seems to be the higher yield of ATP which can be achieved during fermentation. Besides oxygen and elemental sulfur no other electron acceptors for chemotrophic metabolism are known so far in cyanobacteria. Calculations show that the yield of ATP during fermentation, although it is low relative to aerobic respiration, exceeds the amount that is likely to be required for maintenance, which appears to be very low in these cyanobacteria. The possibility of a limited amount of biosynthesis during anaerobic dark metabolism is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6976.1997.tb00350.x
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  • 2
    Electronic Resource
    Electronic Resource
    Lactate dehydrogenase in the cyanobacterium Microcystis PCC7806 (1995)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 127 (1995), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The cyanobacterium Microcystis PCC7806 was found to possess an NAD-dependent lactate dehydrogenase (EC 1.1.1.27) which catalyzes the reduction of pyruvate to l-lactate. The enzyme required fructose 1,6-bisphosphate for activity and displayed positive cooperativity towards pyruvate. Lactate was not formed during fermentation by cell suspensions, possibly due to low intracellular concentrations of fructose 1,6-bisphosphate and/or pyruvate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1995.tb07448.x
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  • 3
    Electronic Resource
    Electronic Resource
    Fermentation in the unicellular cyanobacterium Microcystis PCC7806 (1994)
    Springer
    Archives of microbiology 162 (1994), S. 63-69 
    Details
    ISSN: 1432-072X
    Keywords: Survival ; Anaerobic metabolism ; Dark metabolism ; Glycogen ; Embden-Meyerhof-Parnas pathway ; Pyruvate:ferredoxin oxidoreductase ; Hydrogenase ; Alcohol dehydrogenase ; Acetate kinase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The cyanobacterium Microcystis PCC7806 fermented endogenously stored glycogen to ethanol, acetate, CO2, and H2 when incubated anaerobically in the dark. The switch from photoautotrophic to fermentative metabolism did not require de novo protein synthesis, and fermentation started immediately after cells had been transferred to dark anoxic conditions. From the molar ratios of the products and from enzyme activities in cell-free extracts, it was concluded that glucose derived from glycogen was degraded via the Embden-Meyerhof-Parnas pathway. In addition, CoA-dependent pyruvate:ferredoxin oxidoreductase, alcohol dehydrogenase, acetate kinase, and hydrogenase were present. The specific activities of these enzymes were sufficiently high to account for the rates of product formation by cell suspensions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00264374
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