The micro-ecological feature of colonies is a potential strategy for Phaeocystis globosa bloom formation.

Phaeocystis globosa is among the dominant microalgae associated with harmful algal blooms. P. globosa has a polymorphic life cycle and its ecological success has been attributed to algal colony formation, however, few studies have assessed differences in microbial communities and their functional profiles between intra- and extra-colonies during P. globosa blooms. To address this, environmental and metagenomics tools were used to conduct a time-series analysis of the bacterial composition and metabolic characteristics of intra- and extra-colonies during a natural P. globosa bloom. The results show that bacterial composition, biodiversity, and network interactions differed significantly between intra- and extra-colonies. Dominant extra-colonial bacteria were Bacteroidia and Saccharimonadis, while dominant intra-colonial bacteria included Alphaproteobacteria and Gammaproteobacteria. Despite the lower richness and diversity observed in the intra-colonial bacterial community, relative to extra-colonies, the complexity and interconnectedness of the intra-colonial networks were higher. Regarding bacterial function, more functional genes were enriched in substance metabolism (polysaccharides, iron element and dimethylsulfoniopropionate) and signal communication (quorum sensing, indoleacetic acid-IAA) pathways in intra- than in extra-colonies. Conceptual model construction showed that microbial cooperative synthesis of ammonium, vitamin B12, IAA, and siderophores were strongly related to the P. globosa bloom, particularly in the intra-colonial environment. Overall, our data highlight the differences in bacterial structure and functions within and outside the colony during P. globosa blooms. These findings represent fundamental information indicating that phenotypic heterogeneity is a selective strategy that improves microbial population competitiveness and environmental adaptation, benefiting P. globosa bloom formation and persistence.

Colony formation of Phaeocystis globosa: A case study of evolutionary strategy for competitive adaptation.

Some algae possess a multi-morphic life cycle, either in the form of free-living solitary cells or colonies which constantly occur in algal blooms. Though colony formation seems to consume extra energy and materials, many algae tend to outbreak in form of colonies. Here, we hypothesized that colony formation is a selected evolutionary strategy to improve population competitiveness and environmental adaptation. To test the hypothesis, different sizes of colonies and solitary cells in a natural bloom of Phaeocystis globosa were investigated. The large colony showed a relatively low oxidant stress level, a nutrient trap effect, and high nutrient use efficiency. The colonial nitrogen and phosphorus concentrations were about 5-10 times higher than solitary cell phycosphere and cellular nutrient allocation decreased with the enlargement of the colonial diameter following the economies of scale law. These features provide the colony with monopolistic competence and could function as an evolutionary strategy for competitive adaptation.

Optimizing the growth of Haematococcus pluvialis based on a novel microbubble-driven photobioreactor.

Haematococcus pluvialis, the richest bioresource for natural astaxanthin, encounters a challenge of achieving high growth rate when it comes to mass biomass production. Based on the substrate consumption model and Redfield ratio, rapid algae growth benefits from a proper carbon supply. However, the conventional cultivation schemes with limited carbon dioxide (CO2) supply and inefficient carbon mass transfer could have constrained the carbon capture and growing ability of H. pluvialis. We hypothesize that optimal H. pluvialis growth improvement may be achieved by efficient CO2 supply. Here, in this study, we first identified the carbon consumption of H. pluvialis during exponential growth. Then, a novel microbubble-driven photobioreactor (MDPBR) was designed to satisfy the carbon demand. The novel microbubble photobioreactor improves the CO2 supply by reducing bubble size, significantly elevating the CO2 mass transfer. With only 0.05 L min-1 of gas flow rate, higher cell growth rate (0.49 d-1) has been achieved in MDPBR.

High irradiance compensated with CO2 enhances the efficiency of Haematococcus lacustris growth.

Haematococcus lacustris (H. lacustris), a promising source for astaxanthin production, is a light-sensitive microalga that is prone to sluggish growth when subjected to high levels of irradiance. A challenge in H. lacustris culture is to find a way to efficiently use illumination to maintain vigorous growth and harvest dense biomass, which is essential for further exploiting the potential for astaxanthin production. Previous studies have shown that in addition to illumination, carbon supply in culture is a key limitation for algae growth. Here, we investigated a combined culture approach involving high light intensity (110 µmol m-2s-1) and injection of a 1% (v/v) CO2 air-gas mixture which provided an effective method for H. lacustris culture to achieve both a high growth rate and high cell density. The cell number in the group with high light exposure combined with CO2 enrichment was increased almost four-fold compared with a high light group (110 µmol m-2s-1 without CO2 injection). Additional experiments suggested a possible mechanism in which elevated CO2 increases the electron sink capacity, thus alleviating photoinhibition and oxidative damage. The scaled-up photobioreactor demonstrated much better performance, with growth rates improved by 50-350 %, providing further evidence that this new method can improve algal cell production. Overall, our work provides an efficient way for H. lacustris culture and manufacture, with potential industrial applications.