Effect of the hydrocarbons contamination on the microbiological resilence of soils.

PESSACQ JORGE; BIANCHINI FLAVIA E.; TERADA CLAUDIA; MORELLI IRMA S.; DEL PANNO MARÍA T.

Torremolinos

Conferencia; IV International Conference on Environmental, Industrial and Applied Microbiology (BioMicroWorld2011); 2011

Different bacterial species that inhabit the soil environment can form a robust community and provide to the soil the capacity of perform a range of ecological functions when stressed by climatic fluxes and anthropogenic inputs. However, how these communities respond to changes in the environment and what makes them stable in the presence of potential stressors have not always been clear. There are different opinions about whether hydrocarbons pollution reduces the microbial diversity, and therefore produces less resilience of soil microbial communities. To investigate the incidence of previous history of hydrocarbon contamination from the soils on the capacity of response of soil microbial communities’, two places near petrochemical industrial area were sampled: petrochemical industry site S1 (THC 232.37 mg-1 dry soil) and petrochemical industry site S2 (THC 414.77 mg-1 dry soil). Also, a thirst place, outside the contaminated area was studied and considered as control, P. The Shannon-Weaver diversity index (H), determined from DGGE profiles, showed similar levels of diversity among the bacterial communities of the different sampled soils. Three different stressed were imposed to the sampled soils, in microcosms systems. To evaluate the response to Cd contamination two different concentration of CdSO4 were applied 140 and 400mg Cd kg-1 dry soil. The saline stress was provoked by the addition of 2.18 meq NaCl /100gdry soil and 7.79 meq NaCl/100 g dry soils. The acid stress was provoked by adjustment of the soil pH to 4.5 or 5.5 with dilute HCl (1mM). Following imposition of the treatments, all soil microcosms were incubated at 26±2 ºC and 70% WHC for two weeks. This time was chosen to allow sufficient equilibration of the microbial communities after imposition of each stress treatment and for decomposition of organic C released from microorganisms killed by the treatments. The activity of different enzymes, heterotrophic bacteria count (R2-agar) and the physiological diversity estimated by Biolog EcoPlate (average well colour development AWCD), were determined before and after the stresses were applied. Different response patterns were observed by principal components analysis (PCA), in relation with the previous pollution history from the soils. Three enzymatic activities (dehydrogenase, phosphatase and urease) and the AWCD were able to highlight the different behavior among the four microcosms after the stresses. Only saline stress provoked a negative impact on the dehydrogenase activity in P microcosms, reducing their resilience. The Cd contamination and the acid stress reduced the dehydrogenase activity in S1 microcosms. The most contaminated microcosms, S2, showed the lowest enzymatic activities and surprisingly, the acid stress stimulated its dehydrogenase activity and AWCD values. Any changes were observed in heterotrophic bacteria count of P microcosms after the stresses were applied. A significantly decrease in heterotrophic bacteria count was observed in S2 microcosms by effect of acid stress (pH 4 and pH5). Only the acid stress at pH 4 provokes a decrease in heterotrophic bacteria population in S1 microcosms. The different history of hydrocarbon contamination of soils was not evidenced into the bacterial community diversity; however different resilience patterns were demonstrated.