Study of the microbial dynamics in the root environment of closed, hydroponic cultivation systems for tomato using phospholipid fatty acid profiles.

: A more basic understanding of the microbial dynamics of closed, hydroponic cultivation systems is needed. We therefore initiated a study of the microbial community inhabiting the root environment, using phospholipid fatty acid (PLFA) profiles, and started to examine whether changes in the microbial population structure would result from the introduction of selected isolates of plant growth-promoting rhizobacteria (PGPR). Tomato were cultured in deep-flow systems with circulating nutrient solution. Bacteria were sampled from tomato roots at three locations, longitudinally, in the gutters of a control system and in two systems inoculated with PGPR. In the beginning of the gutters the PLFA profiles were similar in all systems, whereas the profiles differed in the gutter ends (following the direction of flow). In the control system, and in a treatment inoculated with two Gram-negative and one Gram-positive PGPR strain, the relative proportion of PLFAs characteristic to Gram-positive bacteria was highest at the end of the gutter. In a treatment inoculated only with a Gram-negative PGPR strain, the relative proportion of PLFAs characteristic of Gram-negative bacteria was highest at the end of the gutter. The results indicate a complex situation with different micro-environments distributed along the root mat. It can also be concluded that PLFA profiles may be useful tools in the study of the microbiology of closed hydroponic plant cultivation systems.