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Dinoflagellates, including harmful algal bloom species, are known to co-exist with and rely upon bacteria but how the microbiome changes with the physiologies of the cognate dinoflagellates is poorly understood. Here, we used 16S rRNA gene meta-barcoding to characterize the bacterial community in the cultures of Gambierdiscus balechii, a ciguatoxin-producing benthic dinoflagellate, under different nitrogen (N)-nutrient conditions and at different ciguatoxin-producing growth. The high-throughput sequencing of a total of 12 libraries generated 926,438 reads which were classified into 16 phyla. We observed a shift of the G. balechii-associated microbiome from N-replete to low-N conditions and from the early (low toxin) to the late exponential (high toxin) growth stage. Common across these conditions were species from families Rhodobacteraceae and Flavobacteriaceae. Species abundant in the low-N condition mainly included Planctomyces, Ekhidna, and Lactobacillus. Dominant or highly abundant microbial taxa in the high toxin-producing stage (N-replete, late exponential stage) were Oceanococcus and Marinoscillum. Under this condition, one Rhizobiales bacterium, Oricola, also increased in relative abundance. Our study documents the high diversity and dynamics of the G. balechii-associated microbiome, and identifies condition-specific sub-communities: the core (constitutive) microbiome that stably co-exists with G. balechii, the bacterial lineages that are responsive to N-nutrient variations, and species whose abundances are correlated with toxin content of the dinoflagellate. These findings demonstrate that particular bacterial groups are responsive to N-nutrient or toxicity changes of G. balechii and thus will be useful for further investigations on the associated microbiome’s interactions with benthic dinoflagellates and functions in the course of benthic harmful algae blooms.

Catalytic chain transfer emulsion polymerization (CCTP) and subsequent chain extension via reversible addition− fragmentation chain transfer (RAFT) were used to synthesize amphiphilic macromonomers (MM), in the form of polymer latexes. The macromonomers consisted of two blocks whose first was a random copolymer of methacrylic acid and methyl methacrylate, at 35:65 mol:mol, while the second block was n-butyl methacrylate P[(MAA-co-MMA)-block-PBMA]. The block copolymer colloids were disintegrated and micellized upon addition of ammonia. The resulting nanosized polymer dispersions were used as reactive surfactants in the emulsion polymerization of n-butyl methacrylate. For this, a dual stage slow−fast monomer feed profile was used. The final polymer latexes were in the sub-100 nm range for the particle diameter at 30% w/w total polymer content. The emphasis of the work is to discuss and find an explanation for the observed particle size distributions in the three consecutive emulsion polymerization steps. The particle size distribution of the ω-unsaturated macromonomer latex synthesized by CCTP emulsion polymerization was found to be much broader than expected. This discrepancy is attributed to an extended particle nucleation period. The chain extension step in the macromonomer latex preparation showed considerable secondary nucleation. The presence of water-soluble macromonomer species from the CCTP emulsion polymerization step assured that control of chain growth persisted. The use of the amphiphilic macromonomers as reactive surfactants in the form of a nanosized aggregate seed dispersion showed that the average particle diameter could be tuned and that the molecular weight distributions could be regulated, when monomer starved conditions were used in the emulsion polymerizations.

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