Agronomic application of olive mill wastewaters with rock phosphate increase the 10Me18:0 fatty acid marker of actinomycetes and change rhizosphere microbial functional groups under long-term field conditions

The objectives of this study were to determine the long-term effects of agronomic application of olive mill wastewaters (OMW) with rock phosphate (RP) in a field of olive trees on the soil microbial community structures. Ester-linked fatty acid methyl ester (EL-FAME) profiles were used for characterizing the numerically dominant portion of soil microbial communities. EL-FAME analysis showed significant shifts of specific groups of fatty acids after application of OMW with RP. In particular, the FAME 10Me18:0 indicative of actinomycetes increased and the FAME 18:1ω9 and 18:2ω6 commonly found in fungi decreased. The soil microbial cells reacted to the addition of OWM and RP with an increase in the percentage of cy17:0 and cy19:0 cyclopropane fatty acids. Other changes in FAME composition included the increase of saturated/unsaturated ratio. It seems that alterations of fatty acid composition, after agronomic application of OMW and RP, are responsible for the substantial maintenance of cell membrane integrity, physiological functions and growth.