Rhizospheric microorganisms and arbuscular mycorrhiza in soil from a petrochemical waste landfarming system. / Microbiota RizosfÃrica e Micorriza Arbuscular em Solo de "Landfarming" de ResÃduos PetroquÃmicos.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

In the petroleum industrialization a great volume of different toxic residues is generated. Because of these waste environmental hazards they need to be adequately treated before final disposition in the environment. These wastes are usually treated by landfarming systems, but this technique has only relative success, since it doesn t completely remove all components especially those with high recalcitrancy and toxicity. It has been suggested that the use of plants coupled with landfarming can enhance the efficiency of the remediation process, as a result of the rhizospheric effects that stimulate degrader microorganisms and biochemical processes responsible for the dissipation of contaminants in soil. Plants effects on soil biochemical processes, microbial degraders and the arbuscular mycorrhizal fungi (AMF) need to be better studied. The aim of this study was to evaluate microbial density, activity and community structure, and occurrence of AMF in the rhizosphere of plants with frequent spontaneous occurrence (Bidens pilosa, Cyperus sp., Eclipta alba e Eleusine indica) in a landfarming soil for petrochemical waste treatament. Microbial density was stimulated by the presence of plants. In rhizospheric soils larger countings were observed (average 10 times larger) of total and anthracene degrader bacteria in relation to treatments without plants. Whereas density of total and anthracene degrader fungi plant stimulating effects were not generalized as found for bacteria. Plants effects were differentiated among species. Bidens pilosa and Eleusine indica were the most stimulatory ones. Soil actinomycetes exhibited high countings in all treatments independently of plants presence. When compared to other species, Brachiaria decumbens showed low microbial density in the rhizosphere. Plants had little influence on soil heterotrofic activity as evaluated by the fluorescein diacetate hydrolysis while the lypase activity was lightly higher in the soils with plants. The total polycyclic aromatic hydrocarbon concentration in soil was slightly higher in soil with plants. The occurrence of AMF was observed in all studied plants, being the colonization rates pretty high (greater than 40%), except in Cyperus sp. The spore density was enhanced by plants, especially in B. decumbens, in which 4.738 spores 50 mL soil-1 were found. Four AMF species were identified in this soil: Acaulospora morrowiae, Glomus intraradices, Paraglomus occultum e Archaeospora trappei. Considering this soil has a long history of landfarming with a heavy load of petroleum wastes, these AMF are adapted to high concentrations of petroleum pollutants. The DGGE analysis revealed existence of different bacterial communities in different treatments. It was found lower numbers of amplicons in rhizospheric soils and alteration in the dominant populations in the rhizosphere soil. The 16S rDNA partial sequencing analysis of bacterial isolates that grew in medium with anthracene allowed the identification of six different genera: Streptomyces, Nocardioides, Fulvimonas, Arthrobacter, Cellulomonas e Paracoccus. Four the identified genera belong to the actinomycetes. This suggests a great importance of this group of bacteria in the degradation of those compounds in soil. Among these genera, only Nocardioides and Cellulomonas, were already reported to be found in soils contaminated with petroleum hydrocarbons in Brazil. The isolation and identification of microorganisms capable to degrade PAHs are important for additional studies concerning degradation of these pollutants in soil. The results of this study indicate that plants modifies microbiological characteristics of petroleum wast landfarming soil favoring microbial populations more adapted to toxic compounds present in soil.

ASSUNTO(S)

micorrizas arbusculares degrader microorganisms 16s rdna sequencing microrganismos degradadores dgge rizosfera rhizosphere petrÃleo dgge enzimas do solo soil enzymes microbiologia agricola petroleum wastes arbuscular mycorrhiza seqÃenciamento do 16s rdna

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