CHARACTERIZATION OF THE BACTERIAL FLORA IN CIRCULATING NUTRIENT SOLUTIONS OF A HYDROPONIC SYSTEM WITH ROCKWOOL

Already 20 h after planting the tomatoes high populations of aerobic, heterotrophic bacteria (10⁵ – 10⁶ cfu/ml) were present in the circulating nutrient solutions. In contrast to this, control solution without plant contact showed only densities of 500 – 900 cfu/ml. During the 12 weeks of examinations no significant change in the organisms densities was detectable.

Identification of bacteria was achieved with the aid of the Microbial Identification System (MIS) using characteristic fatty acid methyl ester profiles. In addition the MicroLog-System (BIOLOG Inc.) was used for the identification of the bacterial isolates.

Members of the genus Pseudomonas represented with 40 % the major group of totally 160 bacterial strains isolated from the circulating nutrient solutions by a random process. The rest of the isolates were assigned to the genera Agrobacterium, Azospirillum, Comamonas, Enterobacter and Xanthomonas. Represented with less than 2 % were the genera Alcaligenes, Aureobacterium Cytophaga, Flavobacterium, Rhodococcus and Yersinia. 18 % of the populations examined could not be identified with certainty or could not be identified at all.

The cluster analysis included in the MIS-program-packet made it possible to characterize the observed populations further. Ten clusters were clearly distinguishable in the computer developed 2-D-plot, seven of which represented the most common bacterial genera.