Assessment of the microbial status in closed hydroponic system using phospholipid fatty acid analysis

Phospholipid fatty acid analysis (PLFA) was evaluated as a tool for discrimination of the microbial composition of the rhizosphere of hydroponically grown plants in a closed hydroponic greenhouse system and in a small scale climate chamber system. Root tissue was sampled and the microflora was separated from the roots and washed repeatedly by spinning and resuspension. The final suspension was frozen at -80 degreesC before lyophilization. PLFAs were isolated by split-phase extraction and step-wise lipid separation and identified by gas chromatography. The PLFA profiles of tomato roots grown in a closed hydroponic deep flow system could be separated depending on the sampling site in the gutter and the bacterization treatment the roots had been exposed to. The sensitivity of the method was further assessed in laboratory experiments in a climate chamber, where differences with respect to plant species, cultivars, plant age and seed treatment with genetically closely related bacterial isolates were studied. The results show that PLFA analysis may separate the root microflora of tomato plants differing in age and of different plant species and different seed bacterization treatments. Also a combined provocation of bacterized and non-bacterized plants with Pythium ultimum showed a clear discrimination of the root microflora in the different treatments on the basis of PLFAs of the root microflora community.