5 Fluorescent Pseudomonads …
115
5.12 Influence of Amino Acids, Organic Acids, and Sugars
on Growth, Fluorescence, and Siderophore Production
The organic substrates in the rhizosphere lead to greater growth and activity of the
microorganisms around the roots. The influence of amino acids, organic acids, and
six sugars, commonly encountered in root exudates showed siderophore production,
plant growth promotion, and disease suppression. Among the eight amino acids
tested (L-alanine, D-L-arginine, L-glutamine. L-lysine, D-methionine, D-L-proline,
D-L-serine, L-tyrosine) for growth of the organisms, amino acids (methionine and
serine) did not support the growth of any of the organisms and thus were not an
energy source for these bacteria (Dileep et al. 1998).
Among the rest six amino acids, three (L-alanine, D-L-proline, and L-tyrosine)
supported both growth and fluorescence. Six organic acids screened were L-aspartic
acid, citric acid, D or L-glutamic acid, L (+) lactic acid, D-maleic acid, and succinic
acid that supported growth curtailing fluorescence and not supported siderophore
production. Arabinoses among several sugars not supported growth and it supported
only growth (not fluorescence) of the rest two organisms. It is interesting to note that
in the presence of sugars (except glucose) the siderophore production was arrested
(Dileep et al. 1998). Thus, sugars do not support siderophore production. But keeping
in view the ubiquity of glucose, it does not affect much in nature (Table 5.3).
5.13 Siderophores as Iron Storage Compounds
Although siderophores were identified and confirmed as iron transporting agents,
there is evidence that they may have further intracellular functions. Several spectroscopic studies confirmed the possible involvement siderophores on iron storage
(Kraemer et al. 2006). Recent research on the occurrence of siderophores in P.
aeruginosa has indicated well-known hydroxamate type Siderophores. Uptake of
iron-mediated by siderophores is energy-dependent and requires the specific interaction with siderophores is transport systems in the cytoplasmic membranes. Iron from
siderophores is transported to the cellular metabolism by a reductive removal, which
is not operating in the corresponding aluminum, chromium, or gallium complexes
(Römheld and Marschner 1986). Transport studies using various hydroxamate type
siderophores revealed that the absolute configuration of the metal center, the number,
and kind of irons surrounding N-acetyl residues and the overall structure of the
various hydroxamate families. Besides the function in iron chelation and transport,
the third function in iron storage has recently been confirmed by the hydroxamate
siderophores.
115
5.12 Influence of Amino Acids, Organic Acids, and Sugars
on Growth, Fluorescence, and Siderophore Production
The organic substrates in the rhizosphere lead to greater growth and activity of the
microorganisms around the roots. The influence of amino acids, organic acids, and
six sugars, commonly encountered in root exudates showed siderophore production,
plant growth promotion, and disease suppression. Among the eight amino acids
tested (L-alanine, D-L-arginine, L-glutamine. L-lysine, D-methionine, D-L-proline,
D-L-serine, L-tyrosine) for growth of the organisms, amino acids (methionine and
serine) did not support the growth of any of the organisms and thus were not an
energy source for these bacteria (Dileep et al. 1998).
Among the rest six amino acids, three (L-alanine, D-L-proline, and L-tyrosine)
supported both growth and fluorescence. Six organic acids screened were L-aspartic
acid, citric acid, D or L-glutamic acid, L (+) lactic acid, D-maleic acid, and succinic
acid that supported growth curtailing fluorescence and not supported siderophore
production. Arabinoses among several sugars not supported growth and it supported
only growth (not fluorescence) of the rest two organisms. It is interesting to note that
in the presence of sugars (except glucose) the siderophore production was arrested
(Dileep et al. 1998). Thus, sugars do not support siderophore production. But keeping
in view the ubiquity of glucose, it does not affect much in nature (Table 5.3).
5.13 Siderophores as Iron Storage Compounds
Although siderophores were identified and confirmed as iron transporting agents,
there is evidence that they may have further intracellular functions. Several spectroscopic studies confirmed the possible involvement siderophores on iron storage
(Kraemer et al. 2006). Recent research on the occurrence of siderophores in P.
aeruginosa has indicated well-known hydroxamate type Siderophores. Uptake of
iron-mediated by siderophores is energy-dependent and requires the specific interaction with siderophores is transport systems in the cytoplasmic membranes. Iron from
siderophores is transported to the cellular metabolism by a reductive removal, which
is not operating in the corresponding aluminum, chromium, or gallium complexes
(Römheld and Marschner 1986). Transport studies using various hydroxamate type
siderophores revealed that the absolute configuration of the metal center, the number,
and kind of irons surrounding N-acetyl residues and the overall structure of the
various hydroxamate families. Besides the function in iron chelation and transport,
the third function in iron storage has recently been confirmed by the hydroxamate
siderophores.