Análise morfológica e molecular de cianobactérias isoladas de efluentes de uma mina de urânio desativada com ênfase em Aphanothece e sua capacidade de biossorção do 226Ra / Morphological and molecular analysis of cyanobacteria isolated from a deactivated uranium mine effuents with emphasis in Aphanothece and its 226Ra biosorption capacity

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Cyanobacteria are oxygenic photosynthetic microorganisms with wide metabolic and structural plasticity, which have biotechnological potential for exploration in metals biosorption and organic pollutants biodegradation. Due to its strong interactions with cations and a reliable supply of cheap biomass, cyanobacteria may be a promising biosorbent candidate for removing metals and radionuclides. In this way, in an attempt to find a cyanobacteria with this profile to remove 226Ra from a deactivated uranium mine effluents of the Ores Treatment Unit (UTM) belonging to the Nuclear Industries of Brazil (INB), Caldas, MG, twelve cyanobacterial strains were isolated from this environment. These strains were characterized morphologically as Aphanothece sp. CENA75, Rhabdoderma sp. CENA114, Synechococcus cf. lividus CENA79, Aphanocapsa cf. holsatica CENA80, Geitlerinema acutissimum CENA85, Pseudanabaena galeata CENA84, Pseudanabaena sp. CENA81, Leptolyngbya cf. tenerrima CENA76, Leptolyngbya sp. CENA83, Phormidium formosum CENA86, Phormidium violaceum CENA82 and Nostoc sp. CENA87. The molecular analysis of the isolates, based on the sequences of nearly complete 16S rRNA gene (1325 bp), was in agreement with the morphological analysis, with exception of Rhabdoderma sp. CENA114 and Phormidium violaceum CENA82 strains. The 16S rRNA sequences of these two strains showed low identities scores (<92%) with sequences from GenBank, which may represent novel cyanobacterial species. High percentages of identities (>96%) of 16S rRNA gene sequences were found between the remaining strains and of the GenBank. The phylogenetic tree of 16S rRNA sequences constructed using Neighbour-Joining method showed that unicellular strains of the orders Chroococcales and filamentous Oscillatoriales were polyphyletic, as reported earlier. The distribution and abundance of cyanobacterial population in the effluents of UTMINB were investigated by viable cells counting (most probable number, MPN) method. The MPN showed a cyanobacterial population range from 4.0 x 100 to ?2.4 x 108 cells?mL-1. The locations of the Pit Mine with pH 3.88 and the Plant System Treatment with pH 8.0 showed the lowest and highest MPN values, respectively. To identify harmful cyanobacterial isolates, an immunological test (ELISA) was carried out to detect microcystins, a hepatotoxin which cause human poisoning. Microcystins production was found in three isolates, Pseudanabaena galeata CENA84, Pseudanabaena sp. CENA81 and Leptolyngbya cf. tenerrima CENA76. This is a novel result since there is no report for both genera, Pseudanabaena and Leptolyngbya, as microcystin producers. Based on the obtained results, the Aphanothece CENA75 strain found in all UTM-INB effluents sampled, including in the Pit Mine location, which has an acidic pH (average of 3.88) and high level of uranium (5.68 mg?L-1) and radium, was selected for the 226Ra biosorption assays. The experiments performed in pH 3.5 and 5.0 showed that dried biomass of Aphanothece CENA75 behaves as a weakly acid resin. The ratio (final concentration/initial concentration) of 226Ra adsorption after 135 min in pH 3.5 and 5.0 was 0.86 and 0.82, respectively. These results showed that the dried biomass of Aphanothece CENA75 adsorbed low amount of 226Ra in both studied pH values. However, the increase of the radionuclide retention in pH 5.0 suggests that more adsorption may occur in pH above of this value.

ASSUNTO(S)

phylogeny radionuclideo. adsorption genes rnar 16s radionuclide filogenia cultura de microrganismos microorganisms culture 16s rrna genes adsorção

ACESSO AO ARTIGO

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