Effects of organoclays on soil eubacterial community assessed by molecular approaches

The aim of this study was to evaluate the effects of the commercial organoclays, CLOISITE 30B, NANOFIL 804 and DELLITE 26C on soil eubacterial community. An enrichment test was carried out on Nutrient Broth containing the organoclay and the microorganisms previously isolated from soil. Four transfers were made, each after 7 days incubation. The molecular analyses on the eubacterial community were performed before treatment and 7 days after each transfer. DNA was extracted, amplified with eubacterial primers, finally analysed by amplified ribosomal DNA restriction analysis (ARDRA) and denaturing gradient gel electrophoresis (DGGE). The profiles of the samples treated with each organoclay showed the absence, the appearance and an increase in the intensity of some bands. These bands were excised from the gels, and the related microorganisms were identified by DNA sequencing, as Pseudomonas putida, Alcaligenes xylosoxidans, Pseudomonas monteilii and Pseudomonas aeruginosa. NAN804 treatment did not have any influence on soil eubacterial community, CLO30B had a slight toxic effect only on P. putida, instead the DEL26C treatment had a stronger toxic effect on P. putida and a slight toxic effect on P. monteilii. Finally, all the tested organoclays stimulated the growth of both A. xylosoxidans and P. aeruginosa.