Journal of Phycology最新文献

Delta-6 fatty acid desaturases, which play key roles in the biosynthesis of polyunsaturated fatty acids (PUFAs), are membrane-associated enzymes that present significant challenges for isolation and purification, complicating their structural characterization. Here we report the identification and structure-function analysis of a novel Δ6 fatty acid desaturase (PmD6) from the marine alga Prorocentrum micans with substrate preference to α-linolenic acid (18:3n-3). Structural modeling revealed a mushroom-like structure of PmD6 formed by four transmembrane α-helices as a stem and three cytoplasmic domains as a cap. Structural alignment identified several key residues positioned around the substrate tunnel and catalytic center in PmD6. Functional analysis of these residues by site-directed mutagenesis showed that Tyr226, Trp235, Phe345, and Ser349, facing the middle region of the substrate tunnel of PmD6, played critical roles in defining the structure for acceptance of substrates. Thr200, Leu391, and Met389, surrounding the end of the substrate tunnel, had roles in interaction with the methyl end of substrates. Asp255, close to a metal iron in the catalytic center, was essential for catalytic reaction by supporting the regional structure. These results have provided mechanistic insights into the structure-function relationship of membrane-bound front-end fatty acid desaturases.

Over 400 cyanobacterial genera have been described up to the present. Since the Cambridge Rules (https://www.iapt-taxon.org/historic/1935.htm: Rendle 1935), a type species (generitype) must be specified at the time of description for a new genus to be validly described. Even though we have entered a time in which sequencing has become practical and widespread, the basic molecular characterization (e.g., 16S rRNA gene sequence) of most cyanobacterial generitypes is still lacking. About 15 cyanobacterial genera were originally described from Scandinavia. Following a field excursion in which the type or syntype localities for the type species of these genera were visited and sampled, we succeeded in finding three type species from their type or syntype localities: Capsosira brebissonii, Stigonema mamillosum, and Paracapsa siderophila. Epitypes for all three generitypes are herein established. Cells or filaments of C. brebissonii and S. mamillosum were isolated and used for single-cell/filament PCR amplification of the 16S rRNA gene and subsequent cloning and sequencing of the PCR amplicons. This allows a firm establishment of reference sequences of these two genera, to which morphologically similar taxa can now be compared. Stigonema and Capsosira are shown herein to be sister to Aetokthonos hydrillicola, a cyanobacterium known to cause avian vacuolar myelinopathy in birds, including bald eagles.

Cyanobacteria exhibit a vast diversity from polar to tropical environments. Though much work has been done on elucidating their biodiversity, knowledge on the occurrence, diversity and toxicity of benthic cyanobacteria is limited when compared to the planktonic forms. Integrating molecular techniques with ecological and morphological analyses has become essential in untangling cyanobacterial diversity, particularly for benthic taxa such as the cryptic "Lyngbya." Molecular markers such as the 16S rRNA gene and whole genome sequencing have significantly improved the taxonomy of cyanobacteria. Building on these advancements, this study characterizes benthic cyanobacterial isolates from various locations in Florida, USA, and Orange Walk, Belize, resulting in the identification of a novel genus, Floridanema, and four new species (F. aerugineum, F. evergladense, F. flaviceps, and F. fluviatile). This new genus commonly occurs in canals, ponds, lakes and rivers. By integrating ecological, morphological, and genomic analyses, this study provides support for the family Aerosakkonemataceae and the establishment of the order Aerosakkonematales. The LC-MS data revealed that Floridanema strains do not produce microcystins, nodularin-R, or anabaenopeptins.

The composition and abundance of crustose coralline algae (CCA) have been documented in the Xinfeng algal reef (XAR). Eight CCA species were identified, including four in Phymatolithon (P. margoundulatum, P. taiwanense, P. variabile, and Phymatolithon sp.) and four only identified to the genus level (Chamberlainium sp. and three Dawsoniolithon spp.). Chamberlainium sp. was the most abundant species, while the three species of Dawsoniolithon were rarely observed. The CCA coverage varied from 18% ± 15% to 27% ± 21% in spring seasons of 2021-2024, but there were no significant differences. Based on carbon-14 dating, the CCA sediments in the XAR were estimated to be 5850-5990 years old. These CCA sediments were primarily composed of two paleo-CCA species, resembling modern Chamberlainium sp. and Dawsoniolithon sp. 1. However, the modern species of Phymatolithon, which are widespread and abundant in the algal reefs of northwestern Taiwan, were not observed in the CCA sediments. It is unclear whether their absence was due to fragile thalli after their death or their lack of occurrence, and this requires further investigation. The paleoenvironmental data and biogenic sediment composition analysis suggests that the XAR started to develop ~6000 years ago when the sea surface temperature began to decrease and seawater turbidity increased due to rainfall. Additional CCA sediment samples from this algal reef are needed to fully understand the historical changes in the paleo-environments in the XAR.

Chlorophyll (Chl) f was reported as the fifth Chl in oxygenic photoautotrophs. Chlorophyll f production expanded the utilization of photosynthetically active radiation into the far-red light (FR) region in some cyanobacterial genera. In this study, 11 filamentous cyanobacterial strains were isolated from FR-enriched habitats, including hydrophyte, moss, shady stone, shallow ditch, and microbial mat across Central and Southern China. Polyphasic analysis classified them into the same genus of Leptodesmis and further recognized them as four new species, including Leptodesmis atroviridis sp. nov., Leptodesmis fuscus sp. nov., Leptodesmis olivacea sp. nov., and Leptodesmis undulata sp. nov. These cyanobacteria had absorption peaks beyond 700 nm due to Chl f production and red-shifted phycobiliprotein complexes under FR conditions. All but L. undulata produced phycoerythrin and showed varying degrees of a reddish-brown to dark green color under white light conditions. However, the phycoerythrin contents were sharply decreased under FR conditions, and these three Leptodesmis species appeared green. In summary, the Leptodesmis genus contains diverse species with the capacity to synthesize Chl f and is likely a ubiquitous group of Chl f-producing cyanobacteria.

The invasive seaweed Rugulopteryx okamurae, native to East Asia, is spreading rapidly along the western Mediterranean and southern Portugal, severely affecting coastal biodiversity, ecosystem structure, and economic sectors such as fisheries and tourism. This study examined the nutrient uptake kinetics of R. okamurae, including ammonium, nitrate, urea, amino acids, and phosphate, and their role in nitrogen and phosphorus budgets based on laboratory growth rates. R. okamurae demonstrated the highest uptake for ammonium (V_max = 57.95 μmol · g^-1 DW · h^-1), followed by urea (7.74 μmol · g^-1 DW · h^-1), nitrate (5.37 μmol · g^-1 DW · h^-1), and amino acids (3.71 μmol · g^-1 DW · h^-1). The species showed higher uptake affinity for urea (α = 1.8), which accounted for 70% of nitrogen uptake. Phosphate uptake was low, and total nitrogen uptake exceeded growth requirements. These findings suggest that R. okamurae relies on organic nitrogen (urea) and may guide toward effective management strategies to mitigate its spread in coastal ecosystems.

Dissolved organic carbon (DOC) released by macroalgae is an intrinsic component of the coastal ocean carbon cycle, yet knowledge of how future ocean warming may influence this is limited. Temperature is one of the primary abiotic regulators of macroalgal physiology, but there is minimal understanding of how it influences the magnitude and mechanisms of DOC release. To investigate this, we examined the effect of a range of temperatures on DOC release rates and physiological traits of Ecklonia radiata, the most abundant and widespread kelp in Australia that represents a potentially significant contribution to coastal ocean carbon cycling. Juvenile sporophytes were incubated at eight temperatures (4–28°C) for 14 days, after which time, DOC concentrations and physiological traits (growth, photosynthesis, respiration, F_v/F_m, photosynthetic pigment content, and carbon, and nitrogen content) were analyzed using thermal performance curves (TPCs) or regression analyses. Thermal optima were 15.63°C for growth and 25.84°C for photosynthesis, highlighting vulnerability to future ocean warming. Dissolved organic carbon concentrations increased when the temperature was above ~22°C, being greatest at the highest temperature tested (28°C), which was likely driven by photosynthetic overflow and thermal stress. Mean F_v/F_m, total chlorophyll, and total fucoxanthin content were lowest at 28°C. The C:N ratio of blades increased linearly with temperature from 23.9 ± 1.30 at 4°C to 33.0 ± 1.22 at 28°C. We demonstrate increased DOC release by E. radiata under elevated seawater temperatures and discuss potential implications for coastal carbon cycling under future ocean warming given the complex and uncertain fate of macroalgal DOC in the marine environment.

Biological invasions are a major threat for many aquatic ecosystems. In contrast to higher plants and animals, microbial invasions are less obvious and more difficult to detect. One of the most prominent microbial invaders is the cyanobacterium Raphidiopsis raciborskii. To better understand the environmental conditions favoring its invasion success, we studied invasion under three different temperature regimes (one constant and two variable) in experimental plankton communities by invader addition experiments. To account for intraspecific variation, we tested four different strains of R. raciborskii and the mixture of them. Invasion success of R. raciborskii was higher under constant temperature conditions than under fluctuations suggesting that the resident species responded faster to the environmental changes than the invaders. We observed a clear strain-specific effect, demonstrating that strain identity is an important determinant of invasion success. The interaction of temperature fluctuations and strain identity indicates that, among the tested strains, the response to the temperature regimes varied. The mixture of all four strains did not perform better than the best single strain showing no sign of a positive genetic diversity effect. In our experiment, environmental fluctuations did not widen a window of opportunity for the invasion of R. raciborskii.

The Asian brown macroalga Rugulopteryx okamurae has invaded the oligotrophic areas of Mediterranean coasts since 2015, with drastic impacts on environmental conditions and socioeconomic activities in coastal areas in Europe. Therefore, it is intriguing how this species is able to grow and expand at the observed rates. In this context, the physiological responses of R. okamurae to changing nutrient concentrations and temperature were analyzed. Two experiments were conducted, evaluating six combinations of nitrate and phosphate concentrations and their potential interaction with temperature. Nutrient uptake efficiency (NUE) and rates (NUR), photosynthetic responses, growth rates, and biomass composition were evaluated. Photosynthesis parameters, soluble proteins, and $N{O}_3^{-}$ -NUR increased with increasing N:P ratio; however, $P{O}_4^{3-}$ -NUR was very similar in all treatments. The species showed high capacity for nitrate assimilation, which was rapidly modulated by its external concentration and temperature (more than 90% of NO₃-NUE after 5 days in treatments with N:P rations of 5, 10, 16, 25, and 40 N to 1 P). Consequently, N-nutrients were removed from the water by R. okamurae and likely stored inside the cells. This process will allow the alga to maintain high growth rates if thalli are moved to oligotrophic areas, favoring its spreading to many marine environments. Additionally, fucoxanthin was the predominant carotenoid in this species, although its content was lower than in other brown macroalgae species (mean value of 0.51 ± 0.05 mg · g^-1 DW). However, since a huge amount of R. okamurae is observed recurrently on beaches, the use of this biomass might be proposed to compensate partially for its impacts.