Associação de bactérias à cápsula de Anabaena spiroides (Cyanobacteria) em cultura

Abstract

The cyanobacterium Anabaena spiroides, a cosmopolitan species occurring in eutrophic environments as in Barra Bonita reservoir, is covered by a thick polysaccharide capsule that provides a microenvironment for association of bacterial communities. The aims of this study were: to identify bacteria attached to A. spiroides capsule to evaluate interspecific relationships among bacteria communities and A. spiroides, considering bacteria selectivity and succession dynamics of attached bacteria; as well as the effect of bacterial inoculum (1.2 µm filtered water from Barra Bonita reservoir) on cyanobacterial growth. For this purpose, density, production, biomass and diversity of bacteria attached to cyanobacteria capsules and free-living bacteria were determined in two replicate cultures of A. spiroides inoculated with bacteria from Barra Bonita reservoir. The diversity was verified by the number of bands obtained through separation of PCR amplification products of 16S rDNA from free-living and attached bacterial communities using Denaturing Gradient Gel Electrophoresis (DGGE). Bacteria attached to the capsule were identified by sequencing the fragment of 16S rDNA. A set of cultures were performed to evaluate cyanobacterial growth as affected by Barra Bonita filtered water. A. spiroides cultures without Barra Bonita inoculum were used as control. The results showed that bacterial density, biomass and total production were higher for free-living bacteria, but no significant difference was obtained between attached and free-living bacteria regarding production per cell. The diversity was lower for the attached bacteria than free-living ones. Three strains of attached bacteria present in A. spiroides inoculum, identified as one Acidobacteria and two Alphaproteobacteria, remained up to the beginning of exponential growth phase. At the senescence phase these bacteria were replaced by four strains identified as one Deltaproteobacteria, one Betaproteobacteria, one Bacilli (Firmicutes) and one unidentified strain. This research demonstrated that there were selectivity and succession in the bacterial community attached to A. spiroides, and that the addition of the filtered water from Barra Bonita inoculum accelerates the death of cyanobacterium cultures