Autochthonous Dissolved Organic Matter Drives Bacterial Community Composition during a Bloom of Filamentous Cyanobacteria

Abstract

The dynamics of dissolved organic matter (DOM) and the succession of bacterial community composition (BCC) were investigated during bloom of filamentous cyanobacteria in a mesocosm experiment conducted in the western Gulf of Finland, the Baltic Sea. The effects of labile dissolved organic carbon (glucose), inorganic nutrients (N and P) and large zooplankton (> 100 µm) on the DOM pool, bacterial production and the composition of bacterial communities were analyzed over a period of 10 days. In addition, the bioavailability of dissolved organic carbon (DOC) and its turnover by heterotrophic bacteria (biomass and respiration) were investigated in three 1-week bacterial bioassays. Heterotrophic bacteria rapidly utilized about 25-55% of the DOC released from the plankton community, thus assuming it to be highly labile DOC. More than half of the accumulating net DOC pool was degraded over 7 days, thus assuming it to be labile. In average, labile autochthonous DOC was degraded with bacterial growth efficiency of 25%. A distinct succession of bacterial communities accompanied the supply of autochthonous DOM, with the most prominent responses occurring in a few single phylotypes of the Delta-and Gammaproteobacterial classes. About 40% of the variation in the relative shares of dominant bacterial classes could be explained by changes in the functional groups of autotrophs. Inorganic nutrient treatment proved beneficial to Deltaproteobacteria and increased bacterial production over that of other mesocosms.

Effects of zooplankton carcasses degradation on freshwater bacterial community composition and implications for carbon cycling

“…In many lakes with an ‘inverted’ biomass pyramid, zooplankton biomass is higher than phytoplankton biomass (Heathcote et al ., ). We suppose that the same pattern for dead biomass would indicate that zooplankton and not algal LOM, which is usually in the researcher's focus (Hoikkala et al ., ; Landa et al ., ), could be the major driver for bacterioplankton community composition in such ecosystems. In lakes with a ‘normal’ biomass pyramid, zooplankton may still play an important role for determining bacterial community composition in the occasional events of mass zooplankton mortality (Tang et al ., ).…”

Shifting Diatom—Dinoflagellate Dominance During Spring Bloom in the Baltic Sea and its Potential Effects on Biogeochemical Cycling

“…Only a part of the DOC from lysing cells is easily available for bacterial degradation, and in their review of different aquatic habitats, Søndergaard and Middelboe (1995) reported an average of 19% of the total dissolved organic carbon (DOC) pool to be labile in marine waters. However, higher percentages of 25-55% have been found in the Baltic Sea (Hoikkala et al, 2016), andHoikkala et al (2015) presented a conceptual model, where ∼50% of DOC produced by phytoplankton is rapidly degraded by bacteria. As the spring bloom depletes inorganic N sources in most of the sub basins of the Baltic Sea, autochthonous DON is an important component for primary and bacterial production (Korth et al, 2012).…”

Spatiotemporal patterns of N<sub>2</sub> fixation in coastal waters derived from rate measurements and remote sensing

“…The biomass of heterotrophic bacteria increased during the bloom of heterocystous cyanobacteria to levels (250 µg C L −1 ) that were appreciably higher than other coastal (Gulf of Finland and Archipelago Sea = 30-55 µg C L −1 ) or open areas of the Baltic Sea (Bothnian Sea ∼ 80 µg C L −1 ; Baltic Proper = 16-44 µg C L −1 ; Heinänen, 1991). It is likely that heterocystous cyanobacteria release dissolved organic matter which stimulates the growth of heterotrophic bacteria (Bertos-Fortis et al, 2016;Hoikkala et al, 2016;Berg et al, 2018;Berner et al, 2018). There is also evidence that non-N 2 -fixing cyanobacteria benefitted from the bloom of heterocystous cyanobacteria as indicated by higher abundance of Microcystis spp.…”