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