Macroalgal blooms favor heterotrophic diazotrophic bacteria in nitrogen-rich and phosphorus-limited coastal surface waters in the Yellow Sea

Abstract

a b s t r a c tMacroalgal blooms may lead to dramatic changes in physicochemical variables and biogeochemical cycling in affected waters. However, little is known about the effects of macroalgal blooms on marine bacteria, especially those functioning in nutrient cycles. We measured environmental factors and investigated bacterial diazotrophs in two niches, surface waters that were covered (CC) and non-covered (CF) with massive macroalgal canopies of Ulva prolifera, in the Yellow Sea in the summer of 2011 using real-time PCR and clone library analysis of nifH genes. We found that heterotrophic diazotrophs (Gammaproteobacteria) dominated the communities and were mostly represented by Vibrio-related phylotypes in both CC and CF. Desulfovibrio-related phylotypes were only detected in CC. There were significant differences in community composition in these two environments (p < 0.001) and a much higher abundance of nifH in CC (4.55 Â 10 6 copies l À1) than in CF (2.49 Â 10 6 copies l À1). The nifH copy number was inversely related to concentrations of ammonium and dissolved inorganic nitrogen and to the stoichiometric ratios of N:P and N:Si. This indicates that macroalgal blooms significantly affect diazotrophic abundance and community composition and that vibrios and Desulfovibrio-related heterotrophic diazotrophs adapt well to the (N-rich but P-limited) environment during blooming. Potential ecological and microbiological mechanisms behind this scenario are discussed.

Diversity of Ulvan and Cellulose Depolymerizing Bacteria Associated With the Green Macroalgae Ulva Spp

“…Data indicated that the organisms predominantly belonged to phylum Proteobacteria and class Gammaproteobacteria while only a single organism belonging to phylum Bacteroidetes and class Flavobacteria was identified. Zhang X, et al 21 have observed that Gammaproteobacteria are the dominant class in environments where algal blooms occur and are represented mostly by Vibrios. Results of the current study are in agreement to this observation, with 35% of the positive organisms and 80% of identified organisms belonging to genus Vibrio.…”

Identification of Metallophores and Organic Ligands in the Chemosphere of the Marine Macroalga Ulva (Chlorophyta) and at Land-Sea Interfaces

“…Indeed, the fast growing Ulva might face risk of nitrogen and iron limitations in eutrophic waters, which may also affect its microbiome directly, which is, vice versa, essential for Ulva's proper growth, development and morphogenesis. It was shown recently that macroalgae blooms favor heterotrophic diazotrophic bacteria even in nitrogen-rich coastal surface waters, due potentially to the fast uptake of nitrogen by Ulva (Zhang et al, 2015). Given the role of trace metals in the production of Mo-, V-, and/or Fe-dependent nitrogenases, green tides may, thus, trigger metallophore production to increase the bioavailability of trace elements.…”

Seagrass (Zostera marina) Colonization Promotes the Accumulation of Diazotrophic Bacteria and Alters the Relative Abundances of Specific Bacterial Lineages Involved in Benthic Carbon and Sulfur Cycling

“…The resulting plasmids were transformed into Escherichia coli DH5␣ competent cells (Tiangen). The cloned plasmid inserts were amplified directly from the cells using M13 vector-specific primers (21). Approximately 100 clones in each library were randomly selected and sequenced (Sangon Biotech, China).…”

“…171 bp) of the bacterial 16S rRNA genes (27). The qPCR assay was based on the fluorescence intensity of the SYBR green dye and performed as previously described (21). Briefly, the 20-l reaction solution contained the reagents in the SYBR green PCR/carboxy-X-rhodamine qPCR kit (Thermo), 0.4 M each primer, and 10 ng of template DNA.…”