biofertilizers, and many cyanobacteria are potentially used as nitrogen fixer and
phosphate solubilizer (Rai 2006; Sahu et al. 2012).
Excessive use of nitrogen fertilizer is a major reason for soil acidification which
leads to soil deterioration. Plants generally uptake nitrogen in the form of ammonia,
but excessive use of ammonia-based nitrogen fertilizers such as ammonium nitrate,
ammonium sulphate, monoammonium phosphate, and diammonium phosphate than
adequate level increases the soil pH through the conversion of ammonia into nitric
acid (Wallace 1994). Instead of chemical fertilizers, nitrogen fixing microbes can be
employed to eliminate ammonia residues in soil. Generally, nitrogen fixers use
nitrogenase enzymes to fix atmospheric nitrogen into ammonia in soil. All
heterocystous and many non-heterocystous cyanobacteria are capable of fixing
atmospheric nitrogen. Anabaena and Nostoc sp. are the model organism for
heterocyst-based nitrogen fixing cyanobacteria (Kumar et al. 2010). Anabaena
azollae symbiotic relation is the most commonly known nitrogen fixing symbionts,
especially in irrigated rice fields.
Similarly, non-heterocystous cyanobacteria were also reported to fix nitrogen in
soil. The important nitrogen fixing genera are Gloeocapsa, Gloeothece, Cyanothece,
Synechococcus, Synechocystis, Lyngbya, Symploca, Oscillatoria and
Trichodesmium. Nitrogen fixation by non-heterocystous cyanobacteria under aerobic condition is an amazing fact as nitrogenase is irreversibly inhibited by oxygen,
non-heterocystous cyanobacteria utilize diverse mechanism to fix nitrogen, the
intracellular location of nitrogenase and the supply of ATP, reductant and carbon
skeletons to support N 2 fixation. Moreover, they fix during dark period (Gallon and
Stal 1992).
Apart from nitrogen fixation, under anaerobic condition, cyanobacteria also
reduce the free ammonia content in soil through denitrification and anaerobic
ammonia oxidation process (Chen et al. 2012). Moreover, over heterocyst
cyanobacteria are able to recognize the presence and absence of nitrogen source.
In the absence of nitrogen source like nitrate or ammonia, it forms heterocyst in
between 10 and 20 vegetative cells for nitrogen fixation. While in the presence of
ammonia or nitrate, it just forms a long filament containing stretch of hundred
photosynthetic vegetative cells (Kumar et al. 2010). Thereby, cyanobacteria could
perform the combined activity of diazotrophic bacteria and denitrifying bacteria,
hence relevantly replace the usage of ammonia fertilizers in farm lands.
Many reports have been made on mineral phosphate solubilization by
cyanobacteria. Phosphorus is highly essential for nitrogen fixation by cyanobacteria,
hence they generally withstand under excess phosphorus condition. Under phosphorus limitation condition, they undergo mineral phosphate solubilization. Common
mechanism involved in solubilization are organic acid production and enzyme
activity. Phosphate solubilization ability of two diazotrophic cyanobacteria,
Westiellopsis prolifica and Anabaena variabilis, was assessed, and it was found
that among many organic acids, phthalic acid plays the major role in phosphate
solubilization (Yandigeri et al. 2011). Anabaena was reported with phosphate
solubilization by using phosphatase enzyme under phosphorus-deficit condition
5 Cyanobacteria-Mediated Bioremediation of Problem Soils
145
phosphate solubilizer (Rai 2006; Sahu et al. 2012).
Excessive use of nitrogen fertilizer is a major reason for soil acidification which
leads to soil deterioration. Plants generally uptake nitrogen in the form of ammonia,
but excessive use of ammonia-based nitrogen fertilizers such as ammonium nitrate,
ammonium sulphate, monoammonium phosphate, and diammonium phosphate than
adequate level increases the soil pH through the conversion of ammonia into nitric
acid (Wallace 1994). Instead of chemical fertilizers, nitrogen fixing microbes can be
employed to eliminate ammonia residues in soil. Generally, nitrogen fixers use
nitrogenase enzymes to fix atmospheric nitrogen into ammonia in soil. All
heterocystous and many non-heterocystous cyanobacteria are capable of fixing
atmospheric nitrogen. Anabaena and Nostoc sp. are the model organism for
heterocyst-based nitrogen fixing cyanobacteria (Kumar et al. 2010). Anabaena
azollae symbiotic relation is the most commonly known nitrogen fixing symbionts,
especially in irrigated rice fields.
Similarly, non-heterocystous cyanobacteria were also reported to fix nitrogen in
soil. The important nitrogen fixing genera are Gloeocapsa, Gloeothece, Cyanothece,
Synechococcus, Synechocystis, Lyngbya, Symploca, Oscillatoria and
Trichodesmium. Nitrogen fixation by non-heterocystous cyanobacteria under aerobic condition is an amazing fact as nitrogenase is irreversibly inhibited by oxygen,
non-heterocystous cyanobacteria utilize diverse mechanism to fix nitrogen, the
intracellular location of nitrogenase and the supply of ATP, reductant and carbon
skeletons to support N 2 fixation. Moreover, they fix during dark period (Gallon and
Stal 1992).
Apart from nitrogen fixation, under anaerobic condition, cyanobacteria also
reduce the free ammonia content in soil through denitrification and anaerobic
ammonia oxidation process (Chen et al. 2012). Moreover, over heterocyst
cyanobacteria are able to recognize the presence and absence of nitrogen source.
In the absence of nitrogen source like nitrate or ammonia, it forms heterocyst in
between 10 and 20 vegetative cells for nitrogen fixation. While in the presence of
ammonia or nitrate, it just forms a long filament containing stretch of hundred
photosynthetic vegetative cells (Kumar et al. 2010). Thereby, cyanobacteria could
perform the combined activity of diazotrophic bacteria and denitrifying bacteria,
hence relevantly replace the usage of ammonia fertilizers in farm lands.
Many reports have been made on mineral phosphate solubilization by
cyanobacteria. Phosphorus is highly essential for nitrogen fixation by cyanobacteria,
hence they generally withstand under excess phosphorus condition. Under phosphorus limitation condition, they undergo mineral phosphate solubilization. Common
mechanism involved in solubilization are organic acid production and enzyme
activity. Phosphate solubilization ability of two diazotrophic cyanobacteria,
Westiellopsis prolifica and Anabaena variabilis, was assessed, and it was found
that among many organic acids, phthalic acid plays the major role in phosphate
solubilization (Yandigeri et al. 2011). Anabaena was reported with phosphate
solubilization by using phosphatase enzyme under phosphorus-deficit condition
5 Cyanobacteria-Mediated Bioremediation of Problem Soils
145