Heterocystous cyanobacteria

Figure 10.8 Increase in average total nitrogen concentration (mmol m-2) in the upper 20 m of the water column relative to the average concentration at depths of 25 and 30 m, compared to biomass (mmol m-2) of heterocystous cyanobacteria in the top 20 m (Station BY31) in the Lansort Deep region of the Baltic Sea—from 1994 to 1998. (Modified from Larsson et al., 2001.)...

Fig. 1. Energy metabolism in heterocystous cyanobacteria (refer to Shi et al. for details)...

Wasmimd, N., Voss, M., and Lochte, K. (2001). Evidence of nitrogen fixation by non-heterocystous cyanobacteria in the Baltic sea and re-calculation of a budget of nitrogen fixation. Mar. Ecol. Prog. Ser. 214, 1-14. 

Saino, T., and Hattori, A. (1982). Aerobic nitrogen fixation by the marine non-heterocystous cyanobacteria Trichodesmium Oscillatoria) spp. Its protective mechanism against oxygen. Mar. Biol. 70, 251-254. 

Staal, M., et al. (2003). Temperature excludes N2-fixing heterocystous cyanobacteria in the tropical oceans. Nature 425, 504-507. 

Most heterocystous cyanobacteria dominate brackish and freshwater environments where they occur in the plankton and the benthos as free-Hving cells and are seldom found in the open ocean. Few report Richelia and Calothrix as free-living (Gomez et al., 2005 White et al., 2007), thus both are the exception and have made their successful transition to the open ocean as symbionts. 

Nitrogen-fixing, heterocystous cyanobacteria such as Anabaena cylindrica can also liberate hydrogen and oxygen simultaneously under anaerobic, nitrogen-deficient conditions (Benemann and Weare, 1974). A. cylindrica does... 

PHOTOBIOLOGICAL HYDROGEN PRODUCTION AND NITROGENASE ACTIVITY IN SOME HETEROCYSTOUS CYANOBACTERIA... 

B. Heterocystous Cyanobacteria Production of a reduced substrate in the vegetative cells which is transported to the heterocyst where it is oxidized and hydrogen is released using the nitrogenase or hydrogenase enzymes as the catalyst. 

FIGURE 15.8 Annual course of concentrations of DIN, PO4, and biomass (wet weight) of heterocystous cyanobacteria in the upper mixed layer, as well as nitrogen fixation rates in the euphotic zone at station 271 in 2001, (after Wasmund et al., 2005b, coiTected). 

Estuaries and eutrophic coastal waters provide a striking contrast with this behavior. With only a few exceptions anywhere in the world, nitrogen fixation by planktonic, heterocystic cyanobacteria is immeasurably low in mesotrophic and eutrophic coastal marine systems, even when they are quite nitrogen limited (Doremus, 1982 Fogg, 1987 Howarth et al, 1988b Paerl, 1990 Howarth and Marino, 1990, 1998). This major difference in the behavior between lakes and estuaries allows nitrogen limitation to continue in estuaries (Howarth, 1988 Vitousek and Howarth, 1991). 

Many cyanobacteria can fix atmospheric nitrogen and dominate the microbial phototrophic population in environments where the supply of combined nitrogen is limiting. Until recently, heterocystous cyanobacteria were the only cyanobacteria known to fix nitrogen. Non-heterocystous cyanobacteria (e.g., Gloeothece, Plectonema, etc.) able to synthesize nitrogenase have since been recognized. 

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