CHEMOTACTIC RESPONSE TO AMINO-ACIDS OF FLUORESCENT PSEUDOMONADS ISOLATED FROM SPINACH ROOTS GROWN IN SOILS WITH DIFFERENT SALINITY LEVELS

Chemotactic response to amino acids of fluorescent pseudomonads isolat ed from spinach roots grown in a low-salinity soil (LR-group) and its corresponding high-salinity soil (HR-group) was investigated. Furtherm ore, the amount and composition of amino acids in the root exudate und er low-and high-salinity conditions mere investigated. All the isolate s examined showed a chemotactic response exclusively to the amino acid fraction, while most of them did not respond to the sugar and the org anic acid fractions. Based on these results, the chemotactic response to 20 amino acids of randomly selected 48 isolates, of which 12 isolat es each belongs to the LR- and HR-groups of both Pseudomonas putida an d P. fluorescens, was investigated. The results showed that the spectr um of chemotaxis to 20 amino acids of the H-group of each species was markedly different from that of the corresponding L-group. Also, the a mino acid composition of the root exudate in the high-salinity culture solution significantly differed from that in the low-salinity culture solution. The total amount of amino acids from the high-salinity solu tion was 2.83 mu mol g(-1) fresh roots, which was as small as 42% of t hat from the low-salinity culture solution. These results indicated th at high salinity of soil may exert an effect on root colonization by f luorescent pseudomonads not only directly through the effect in the ba cterial chemotaxis but also indirectly through the modification of the root exudation of amino acids qualitatively and quantitatively.