Differences in the Formation Mechanism of Giant Colonies in Two Phaeocystis globosa Strains

Transcriptomics of Lactobacillus paracasei: metabolism patterns and cellular responses under high-density culture conditions

Lactobacillus paracasei has significant potential for development and application in the environmental field, particularly in addressing malodor pollution. This study aims to investigate the cellular response of L. paracasei B1 under high-density culture conditions. The selected strain has previously shown effective deodorizing and bacteriostatic abilities. Transcriptomics techniques are employed to dissect the nutrient metabolism pattern of L. paracasei B1 and its response mechanism under environmental stress. The study characterizes the functions of key differentially expressed genes during growth before and after optimizing the culture conditions. The optimization of fermentation culture conditions provides a suitable growth environment for L. paracasei B1, inducing an enhancement of its phosphotransferase system for sugar source uptake and maintaining high levels of glycolysis and pyruvate metabolism. Consequently, the strain is able to grow and multiply rapidly. Under acid stress conditions, glycolysis and pyruvate metabolism are inhibited, and L. paracasei B1 generates additional energy through aerobic respiration to meet the energy demand. The two-component system and quorum sensing play roles in the response and regulation of L. paracasei B1 to adverse environments. The strain mitigates oxygen stress damage through glutathione metabolism, cysteine and methionine metabolism, base excision repair, and purine and pyrimidine metabolism. Additionally, the strain enhances lysine synthesis, the alanine, aspartate, and glutamate metabolic pathways, and relies on the ABC transport system to accumulate amino acid-compatible solutes to counteract acid stress and osmotic stress during pH regulation. These findings establish a theoretical basis for the further development and application of L. paracasei B1 for its productive properties.

Morphological, molecular, and life cycle characteristics of Phaeocystis globosa Scherffel (Prymnesiophyceae) in the Southeast China Sea

Phaeocystis globosa blooms frequently occur in the Southeast China Sea and cause significant negative impacts on coastal ecology and mariculture. The P. globosa blooms in southeastern China are very different compared to those of European strains, suggesting that differences may exist in their morphological, phylogenetic, and life history traits. In this study, seven strains of P. globosa isolated from Southeast China Sea that were typical strains of algal blooms in the region, in addition to one strain from the Gulf of Mexico (CCMP629), were comprehensively evaluated to better understand region-specific differences of the species. Significant differences were not observed in the internal cell structures and other characteristics compared to those of European strains, while differences in cell surface structures were apparent. For example, small and large flagellated Chinese P. globosa cells exhibited two flagella with slightly unequal lengths and a short haptonema, the surfaces of small flagellated cells were not covered by scales, and colony cell diameters were smaller. 18S rRNA sequence phylogenetic analysis also revealed that P. globosa comprised a species complex with two ecotypes (warm- and cold-water types), of which the strains from the southeastern coast of China and CCMP629 belonged to the warm-water type. In addition, the life cycles and variable modes of P. globosa colony formation were evaluated in detail. The algal bloom may be due to the rapid colonies formation by budding and colony fragments. These results provide new insights into the life cycle of P. globosa and highlight the differences in morphological and phylogenetic relationships between strains from the southeast coast of China and those from coastal European regions.

Response mechanism of harmful algae Phaeocystis globosa to ocean warming and acidification

Simultaneous ocean warming and acidification will alter marine ecosystem structure and directly affect marine organisms. The alga Phaeocystis globosa commonly causes harmful algal blooms in coastal areas of eastern China. P. globosa often outcompetes other species due to its heterotypic life cycle, primarily including colonies and various types of solitary cells. However, little is known about the adaptive response of P. globosa to ocean warming and acidification. This study aimed to reveal the global molecular regulatory networks implicated in the response of P. globosa to simultaneous warming and acidification. After exposure to warming and acidification, the phosphatidylinositol (PI) and mitogen-activated protein kinase (MAPK) signaling pathways of P. globosa were activated to regulate other molecular pathways in the cell, while the light harvesting complex (LHC) genes were downregulated to decrease photosynthesis. Exposure to warming and acidification also altered the intracellular energy flow, with more energy allocated to the TCA cycle rather than to the biosynthesis of fatty acids and hemolytic substances. The upregulation of genes associated with glycosaminoglycan (GAG) degradation prevented the accumulation of polysaccharides, which led to a reduction in colony formation. Finally, the upregulation of the Mre11 and Rad50 genes in response to warming and acidification implied an increase in meiosis, which may be used by P. globosa to increase the number of solitary cells. The increase in genetic diversity through sexual reproduction may be a strategy of P. globosa that supports rapid response to complex environments. Thus, the life cycle of P. globosa underwent a transition from colonies to solitary cells in response to warming and acidification, suggesting that this species may be able to rapidly adapt to future climate changes through life cycle transitions.

Bacteria Associated With Phaeocystis globosa and Their Influence on Colony Formation

Phaeocystis globosa (P. globosa) is one of the dominant algae during harmful algal blooms (HABs) in coastal regions of Southern China. P. globosa exhibits complex heteromorphic life cycles that could switch between solitary cells and colonies. The ecological success of P. globosa has been attributed to its colony formation, although underlying mechanisms remain unknown. Here, we investigated different bacterial communities associated with P. globosa colonies and their influence on colony formation of two P. globosa strains isolated from coastal waters of Guangxi (GX) and Shantou (ST). Eight operational taxonomic units (OTUs) were observed in ST co-cultures and were identified as biomarkers based on Linear discriminant analysis Effect Size (LEfSe) analysis, while seven biomarkers were identified in P. globosa GX co-cultures. Bacterial communities associated with the P. globosa GX were more diverse than those of the ST strain. The most dominant phylum in the two co-cultures was Proteobacteria, within which Marinobacter was the most abundant genus in both GX and ST co-cultures. Bacteroidota were only observed in the GX co-cultures and Planctomycetota were only observed in the ST co-cultures. Co-culture experiments revealed that P. globosa colony formation was not influenced by low and medium cell densities of Marinobacter sp. GS7, but was inhibited by high cell densities of Marinobacter sp. GS7. Overall, these results indicated that the associated bacteria are selected by different P. globosa strains, which may affect the colony formation and development of P. globosa.

Aureococcus anophagefferens (Pelagophyceae) genomes improve evaluation of nutrient acquisition strategies involved in brown tide dynamics

The pelagophyte Aureococcus anophagefferens causes harmful brown tide blooms in marine embayments on three continents. Aureococcus anophagefferens was the first harmful algal bloom species to have its genome sequenced, an advance that evidenced genes important for adaptation to environmental conditions that prevail during brown tides. To expand the genomic tools available for this species, genomes for four strains were assembled, including three newly sequenced strains and one assembled from publicly available data. These genomes ranged from 57.11 to 73.62 Mb, encoding 13,191-17,404 potential proteins. All strains shared ~90% of their encoded proteins as determined by homology searches and shared most functional orthologs as determined by KEGG, although each strain also possessed coding sequences with unique functions. Like the original reference genome, the genomes assembled in this study possessed genes hypothesized to be important in bloom proliferation, including genes involved in organic compound metabolism and growth at low light. Cross-strain informatics and culture experiments suggest that the utilization of purines is a potentially important source of organic nitrogen for brown tides. Analyses of metatranscriptomes from a brown tide event demonstrated that use of a single genome yielded a lower read mapping percentage (~30% of library reads) as compared to a database generated from all available genomes (~43%), suggesting novel information about bloom ecology can be gained from expanding genomic space. This work demonstrates the continued need to sequence ecologically relevant algae to understand the genomic potential and their ecology in the environment.

Pigment characterization of the giant colony-forming haptophyte Phaeocystis globosa in the Beibu Gulf reveals blooms of different origins

The giant colony-forming haptophyte Phaeocystis globosa has caused several large-scale blooms in the Beibu Gulf since 2011, but the distribution and dynamics of the blooms remained largely unknown. In this study, colonies of P. globosa, as well as membrane-concentrated phytoplankton samples, were collected during eight cruises from September 2016 to August 2017 in the Beibu Gulf. Pigments were analyzed by high performance liquid chromatography coupled with a diode-array detector (HPLC-DAD). The pigment 19'-hexanoyloxyfucoxanthin (hex-fuco), generally considered as a diagnostic pigment for Phaeocystis, was not detected in P. globosa colonies in Beibu Gulf, whereas 19'-butanoyloxyfucoxanthin (but-fuco) was found in all colony samples. Moreover, but-fuco in membrane-concentrated phytoplankton samples exhibited a similar distribution pattern to that of P. globosa colonies, suggesting that but-fuco provided the diagnostic pigment for bloom-forming P. globosa in the Beibu Gulf. Based on the distribution of but-fuco in different water masses in the region prior to the formation of intensive blooms, it's suggested that P. globosa blooms in the Beibu Gulf could originate from two different sources. IMPORTANCE Phaeocystis globosa has formed intensive blooms in the South China Sea and even around the world, causing huge social economic losses and environmental damage. However, little is known about the formation mechanism and dynamics of P. globosa blooms. 19'-hexanoyloxyfucoxanthin (hex-fuco) is often used as the pigment proxy to estimate Phaeocystis biomass, while this is challenged by the giant colony-forming P. globosa in the Beibu Gulf which only containing 19'-butanoyloxyfucoxanthin (but-fuco) but not hex-fuco. Using but-fuco as a diagnostic pigment, we traced two different origins of P. globosa bloom in Beibu Gulf. This study clarified the development process of P. globosa blooms in the Beibu Gulf, which provided a basis for the early monitoring and prevention of the bloom.

Research on the biology and ecology of the harmful algal bloom species Phaeocystis globosa in China: Progresses in the last 20 years

Chinese researchers have made substantial progresses in research on the harmful algal bloom (HAB) species Phaeocystis globosa since the first P. globosa bloom outbreak in the Chinese coastal waters in 1997. However, as many results, especially the earlier ones, were published in non-English literature, much of the research on P. globosa biology, ecology, and biogeochemistry made by Chinese researchers have been unknown to colleagues from other countries. We review current knowledge on taxonomy, morphology, genetics, physiology, survival strategies and mitigation of P. globosa gained by Chinese researchers from the past two decades. P. globosa is the only Phaeocystis species that causes blooms in the Chinese waters, although other Phaeocystis species including P. jahnii and P. cordata have been detected in Chinese coastal regions. P. globosa has a complex life history with at least two morphotypes including a haploid flagellate and a diploid colonial cell. Colonial P. globosa blooms typically occur in winter after a diatom bloom in coastal waters of the South China Sea. P. globosa in Chinese coastal waters usually has extremely large colonial sizes, up to 3 cm in diameter, an order of magnitude greater than that observed in European coastal waters. The development of giant colonies is associated with enhanced sinking rate, limited nutrient diffusion, as well as decreased stability of colonies. The Chinese P. globosa strains also showed strong genetic diversity and physiological plasticity, being able to grow and develop into colonies at higher temperature and irradiance relative to that in European waters. High genetic diversity of P. globosa was revealed by developing high-resolution and high-specificity molecular markers including Phaeocystis globosa chloroplast 1 (pgcp1). Due to the severe impact of P. globosa on ecology and economy, much effort has been made to mitigate P. globosa blooms including the application of modified clays. Overall, P. globosa in the Chinese waters demonstrate unique genetic, phenotypical and physiological features that differ from P. globosa in other ocean regions. Further studies are needed to explore how environmental factors trigger the occurrence of P. globosa blooms and ascertain the impact of P. globosa blooms on the environment.

The effect of Ditylum brightwellii (Bacillariophyceae) on colony development of bloom forming species Phaeocystis globosa (Prymnesiophyceae) under nutrient-replete condition

To improve our knowledge of the factors regulating Phaeocystis globosa colony formation, the effects of the diatom Ditylum brightwellii on P. globosa colony development were investigated using co-culture and cell-free filtrate approaches. The co-culture experiments showed the moderate abundance of D. brightwellii significantly increased the number and size of colonies, whereas a dramatically decreased effect from high abundance of D. brightwellii. The low abundance of D. brightwellii promoted early formation of P. globosa colony. The cell-free filtrate experiments indicated that culture-filtrates from the exponential phase of D. brightwellii were stimulatory for P. globosa colony formation with more and bigger colonies formed, whereas an inhibitory effect from its senescence phase filtrates. D. brightwellii may influence P. globosa colony formation by regulating the growth of P. globosa solitary cells. Our results suggest that D. brightwellii influences P. globosa colony development, but its effects vary according to its concentrations and growth phases.