Biofilm production, swimming and swarming motility ofarsenic resistant rhizospheric bacterias strains in the presence of the metalloid

MARIANA CRISTIANI, ANA L WEVAR OLLER, MELINA A TALANO, ELIZABETH AGOSTINI

Rosario

Congreso; IX SAMIGE 2013; 2013

Arsenic (As) is a highly toxic metalloid widely distributed in the environment, including farming soils, where agricultural production can be adversely affected. Beneficial rhizospheric bacterial communities can colonize plant roots and can also alter metals and metalloids ioavailability in soil. Thus, the process of root colonization could be appropriate for enhancing metal bioremediation. Two important bacterial traits involved in plant root colonization are motility (swimming and swarming) and biofilm production. Swimming is considered a movement of individual cells, while swarming is a group migration movement. Regarding biofilm production, it has been described that toxic metals/metalloids can be absorbed on the biofilm extracellular matrix. However, little is known about the effect of As in motility and biofilm production of As-resistant rhizospheric bacterial. The aim of the study was to detect changes in both bacterial traits under different concentrations of the metalloid. Swimming and swarming of six rhizospheric arsenite (As+3) resistant bacterial strains (Enterobacter sp. AW1, Pseudomonas sp. AW2, Rhodococcus sp. AW3, Pseudomonas sp. AW4, Pseudomonas sp. AW5, Pseudomonas sp. AW6) were analyzed in 1/10 diluted YEM medium plates containing 0.3-0.7% (w/v) agar and supplemented with 50, 500 and 5000 mM As+3. Biofilm production was determined for AW4 and AW5 strains by a spectrophotometric uantitative test using violet crystal in the presence of 25 μM, 50 μM and 20 mM As+3. Results showed that the presence of As+3 modified both types of motility patterns in a species-dependent manner. At increasing As+3 concentrations, strain AW2 increased swimming whereas AW5 decreased swimming in the same conditions. In the other strains, swimming did not show a definite trend when exposed to As+3. Regarding swarming, AW2 had the greatest motility halo (70 mm approximately) and its motility increased at low concentrations of the metalloid, but it decreased at concentrations higher than 500 mM As+3, similarly to AW3. Biofilm production was also affected by the presence of the metalloid. At 25 to 50 mM As+3, AW4 showed a decreasing biofilm production trend, while an opposite effect was observed in AW5. For 20 mM As+3 both strains notably decreased biofilm production, however AW4 produced less biofilm than AW5. Thus, at low concentrations of As+3, the effect seems to be species-specific, while at high concentrations, biofilm formation is inhibited, possibly by a notorius decrease of bacterial growth. In conclusion, the analyzed bacterial traits involved in rhizosphere colonization are affected by the presence of As+3 in a species-dependent manner and further studies are required to clearly understand these changes and their effects for improving As bioremediation.