Specific association between bacteria and buoyant Microcystis colonies compared with other bulk bacterial communities in the eutrophic Lake Taihu, China

Abstract

The diversity of buoyant Microcystis colony-associated, settling particle-associated and free-living freshwater bacteria in the eutrophic Lake Taihu in China was compared by the polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) of 16S rRNA genes and by clone library analysis. The cluster analysis of DGGE profiles revealed that the buoyant Microcystis colony associates collected in summer and winter were clustered together and were distinct from settling particle-associated and free-living bacteria. In contrast, the bacterial communities of the latter two populations collected in summer were clustered together and varied from those collected in winter. The diversity indices of the Microcystis-associated bacterial population were significantly lower than those of the other two bulk bacterial communities (P < 0.05). Clone library analysis revealed that no shared operational taxonomic units were found in the three populations. Phylogenetic analysis confirmed that buoyant Microcystis-associated bacteria were distinct from the other communities and that they were dominated by Alphaproteobacteria, Betaproteobacteria and Gammaproteobacteria. Proteobacteria, Bacteroidetes and Actinobacteria were prevalent in all three habitats. Other bacterial taxa such as Planctomycetes, Verrucomicrobia, Gemmatimonadetes and Acidobacteria were associated with settling particles and with the water column. Buoyant Microcystis colonies, settling particles and the water column in the eutrophic lake are thus inhabited by different bacterial flora. In addition, specific bacterial communities are associated with buoyant Microcystis colonies.

Bacterial Community Composition of Size-Fractioned Aggregates within the Phycosphere of Cyanobacterial Blooms in a Eutrophic Freshwater Lake

“…Proteobacteria was also abundant and dominated 08MCA with a relative abundance of 77%. Other studies have shown Proteobacteria as a significant fraction of bloom associated bacteria [9], [12], [13]. Alpha- , Beta- , Gamma- , and Deltaproteobacteria were all detected in all nine samples, but relative abundances varied.…”

“…Thus, all these communities were highly specialized, and as there were major differences among communities, we conclude that they were affected by the phycosphere conditions created by cyanobacteria. Others have also observed the selection of specific bacterial species within the Microcystis phycosphere by comparing Microcycstis -attached bacteria (phycosphere bacteria) with other microbial communities living in the same aquatic ecosystem [11], [13].…”

“…While the microbial community associated with cyanobacterial aggregates/colonies has been widely investigated in recent years [9]–[13], few studies investigated the complex interior structure in the phycosphere of cyanobacterial blooms. In eutrophic lakes and estuaries, cyanobacterial Microcystis colonies usually aggregate, and then form mucilaginous Microcystis blooms through coagulation of extracellular polymeric substances [14], moreover, cyanobacterial debris and other particle organic matter also was released from the Microcystis colonies.…”

“…In addition, the non-cyanobacterial community associated with blooms has been intensively studied by the application of various molecular methods, including polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) [13] and terminal restriction fragment length polymorphism (T-RFLP) [16]. Because Microcystis spp.…”

Experimental evidence for the role of heterotrophic bacteria in the formation of Microcystis colonies

“…Thus, taken together with these studies, we speculated that species-specific relationships might exist in colonial Microcystis formation and their bacteria. Shi et al (2012) also found a specific relationship between colonial Microcystis and their assoicated bacteria living in the mucilage. In addition, Parveen et al (2013) showed a clear distinction between Microcystis-attached and freeliving bacterial communities.…”