How Communities of Marine Stramenopiles Varied with Environmental and Biological Variables in the Subtropical Northwestern Pacific Ocean.

MArine STramenopiles (MASTs) have been recognized as parts of heterotrophic protists and contribute substantially to protist abundances in the ocean. However, little is known about their spatiotemporal variations with respect to environmental and biological factors. The objectives of this study are to use canonical correspondence analysis to investigate how MASTs communities are shaped by environmental variables, and co-occurrence networks to examine their potential interactions with prokaryotic communities. Our dataset came from the southern East China Sea (sECS) in the subtropical northwestern Pacific, and involved 14 cruises along a coastal-oceanic transect, each of which sampled surface water from 4 to 7 stations. MASTs communities were revealed by metabarcoding of 18S rDNA V4 region. Most notably, MAST-9 had a high representation in warm waters in terms of read number and diversity. Subclades of MAST-9C and -9D showed slightly different niches, with MAST-9D dominating in more coastal waters where concentrations of nitrite and Synechococcus were higher. MAST-1C was a common component of colder water during spring. Overall, canonical correspondence analysis showed that MASTs communities were significantly influenced by temperature, nitrite and Synechococcus concentrations. The co-occurrence networks showed that certain other minor prokaryotic taxa can influence MAST communities. This study provides insight into how MASTs communities varied with environmental and biological variables.

Evaluation of the Relationship Between the 18S rRNA/rDNA Ratio and Population Growth in the Marine Diatom Skeletonema tropicum via the Application of an Exogenous Nucleic Acid Standard.

Ribosomal RNA (rRNA) has been regarded as a proxy for metabolic activity and population growth in microbes, but the limitations and assumptions of this approach should be better defined, particularly in eukaryotic microalgae. In this study, the 18S rRNA/rDNA ratio of a marine diatom, Skeletonema tropicum, was examined in batch and semi-continuous cultures subjected to low nitrogen and phosphorus treatments at a temperature of 20 °C. In the semi-continuous cultures, the measured 18S rRNA/rDNA ratio ranged from 4.0 × 102 to 5.0 × 103 , and the logarithmic form of this ratio increased linearly with the population growth rate under both low nitrogen and low phosphorus conditions. In batch cultures grown under low nitrogen or low phosphorus conditions, log (rRNA/rDNA) also increased linearly with growth rate when the latter ranged between -0.4 and 1.5 day-1 . The 18S rRNA/rDNA ratios of Skeletonema sampled from in the southern East China Sea were substantially lower than measured from laboratory cultures. Among the field samples, ratios obtained at a coastal station were higher than those obtained farther offshore. These results imply higher growth rate at the coastal station, but the influences of other factors, such as cell size and temperature, cannot be ruled out.

The impact of flooding from the Minjiang River on the succession of harmful algal blooms (HABs) caused by diatoms in China's offshore waters.

This study examines diatom assemblages in the Matsu Archipelago, an area influenced by Minjiang River runoff. It focuses on harmful algal blooms (HABs) that occurred between August 2021 and July 2022. Utilizing 18S rRNA metabarcoding and microscopic analysis, we observed a significant diatom bloom during early summer runoff, peaking at 5 × 105 cells L-1. The research reveals dynamic community changes during the runoff season, with dominant genera including Pseudo-nitzschia, Chaetoceros, and Skeletonema. Skeletonema cell density correlated with NO3 levels, Chaetoceros had a slight PO4 affinity, and Pseudo-nitzschia showed a negative correlation with Skeletonema. Pseudo-nitzschia, which prefers high light and pH conditions, had notably high concentrations in the flood season and in the autumn. In both, it was dominated by potential toxin-producing species - P. multistriata and P. pungens during the flooding, and P. cuspidate in the autumn. These findings highlight the intricate relationship between diatom dynamics and environmental factors, providing essential insights for managing HABs, especially Pseudo-nitzschia species, amidst environmental changes.

Distinctive microbial community and genome structure in coastal seawater from a human-made port and nearby offshore island in northern Taiwan facing the Northwestern Pacific Ocean.

Pollution in human-made fishing ports caused by petroleum from boats, dead fish, toxic chemicals, and effluent poses a challenge to the organisms in seawater. To decipher the impact of pollution on the microbiome, we collected surface water from a fishing port and a nearby offshore island in northern Taiwan facing the Northwestern Pacific Ocean. By employing 16S rRNA gene amplicon sequencing and whole-genome shotgun sequencing, we discovered that Rhodobacteraceae, Vibrionaceae, and Oceanospirillaceae emerged as the dominant species in the fishing port, where we found many genes harboring the functions of antibiotic resistance (ansamycin, nitroimidazole, and aminocoumarin), metal tolerance (copper, chromium, iron and multimetal), virulence factors (chemotaxis, flagella, T3SS1), carbohydrate metabolism (biofilm formation and remodeling of bacterial cell walls), nitrogen metabolism (denitrification, N2 fixation, and ammonium assimilation), and ABC transporters (phosphate, lipopolysaccharide, and branched-chain amino acids). The dominant bacteria at the nearby offshore island (Alteromonadaceae, Cryomorphaceae, Flavobacteriaceae, Litoricolaceae, and Rhodobacteraceae) were partly similar to those in the South China Sea and the East China Sea. Furthermore, we inferred that the microbial community network of the cooccurrence of dominant bacteria on the offshore island was connected to dominant bacteria in the fishing port by mutual exclusion. By examining the assembled microbial genomes collected from the coastal seawater of the fishing port, we revealed four genomic islands containing large gene-containing sequences, including phage integrase, DNA invertase, restriction enzyme, DNA gyrase inhibitor, and antitoxin HigA-1. In this study, we provided clues for the possibility of genomic islands as the units of horizontal transfer and as the tools of microbes for facilitating adaptation in a human-made port environment.

Growth study under combined effects of temperature, pH and salinity and transcriptome analysis revealed adaptations of Aspergillus terreus NTOU4989 to the extreme conditions at Kueishan Island Hydrothermal Vent Field, Taiwan.

A high diversity of fungi was discovered on various substrates collected at the marine shallow-water Kueishan Island Hydrothermal Vent Field, Taiwan, using culture and metabarcoding methods but whether these fungi can grow and play an active role in such an extreme environment is unknown. We investigated the combined effects of different salinity, temperature and pH on growth of ten fungi (in the genera Aspergillus, Penicillium, Fodinomyces, Microascus, Trichoderma, Verticillium) isolated from the sediment and the vent crab Xenograpsus testudinatus. The growth responses of the tested fungi could be referred to three groups: (1) wide pH, salinity and temperature ranges, (2) salinity-dependent and temperature-sensitive, and (3) temperature-tolerant. Aspergillus terreus NTOU4989 was the only fungus which showed growth at 45 °C, pH 3 and 30 ‰ salinity, and might be active near the vents. We also carried out a transcriptome analysis to understand the molecular adaptations of A. terreus NTOU4989 under these extreme conditions. Data revealed that stress-related genes were differentially expressed at high temperature (45 °C); for instance, mannitol biosynthetic genes were up-regulated while glutathione S-transferase and amino acid oxidase genes down-regulated in response to high temperature. On the other hand, hydrogen ion transmembrane transport genes and phenylalanine ammonia lyase were up-regulated while pH-response transcription factor was down-regulated at pH 3, a relative acidic environment. However, genes related to salt tolerance, such as glycerol lipid metabolism and mitogen-activated protein kinase, were up-regulated in both conditions, possibly related to maintaining water homeostasis. The results of this study revealed the genetic evidence of adaptation in A. terreus NTOU4989 to changes of environmental conditions.

Identification of Microalgae by Laser Desorption/Ionization Mass Spectrometry Coupled with Multiple Nanomatrices.

In this study, we demonstrate a simple method to identify microalgae by surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using three different substrates: HgSe, HgTe, and HgTeSe nanostructures. The fragmentation/ionization processes of complex molecules in algae varied according to the heat absorption and transfer efficiency of the nanostructured matrices (NMs). Therefore, the mass spectra obtained for microalgae showed different patterns of m/z values for different NMs. The spectra contained both significant and nonsignificant peaks. Constructing a Venn diagram with the significant peaks obtained for algae when using HgSe, HgTe, and HgTeSe NMs in m/z ratio range 100-1000, a unique relationship among the three sets of values was obtained. This unique relationship of sets is different for each species of microalgae. Therefore, by observing the particular relationship of sets, we successfully identified different algae such as Isochrysis galbana, Emiliania huxleyi, Thalassiosira weissflogii, Nannochloris sp., Skeletonema cf. costatum, and Tetraselmis chui. This simple and cost-effective SALDI-MS analysis method coupled with multi-nanomaterials as substrates may be extended to identify other microalgae and microorganisms in real samples. Graphical Abstract Identification of microalgae by surface-assisted laser desorption/ionization mass spectrometry coupled with three different mercury-based nanosubstrates.

Identification and characterization of an extracellular alkaline phosphatase in the marine diatom Phaeodactylum tricornutum.

In phosphorus-deficient conditions, Phaeodactylum tricornutum releases an alkaline phosphatase (PtAPase) to the medium that is readily detectable by activity staining. Nucleic acid and amino acid sequence of this alkaline phosphatase (APase) was identified by performing proteomic analysis and database searches. Sequence alignment suggests that PtAPase belongs to the PhoA family, and it possesses key residues at the Escherichia coli PhoA active site. Quantitative PCR results indicate that the induction of APase mRNA transcription is very sensitive to phosphorus availability and population growth. The molecular mass of native PtAPase (148 kDa) determined by gel filtration chromatography indicates that PtAPase, like most PhoA, is homodimeric. Zn and Mg ions are essential cofactors for most PhoA enzymes; however, PtAPase activity did not require Zn ions. In fact, 5 mM Zn²âº, Mo²âº, Co²âº, Cd²âº, or Cu²âº inhibited its enzymatic activity, whereas 5 mM Mn²âº, Mg²âº, or Ca²âº enhanced its enzymatic activity. The responses of PtAPase to divalent metal ions were different from those of most PhoAs, but were similar to the PhoA in a marine bacterium, Cobetia marina. Phylogenetic analysis shows that homologs of PhoA are also present in other diatom species, and that they clustered in a unique branch away from other PhoA members. PtAPase may represent a novel class of PhoA that helps diatoms to survive in the ocean. Quantification of the PtAPase mRNA may help monitor the physiological condition of diatoms in natural environments and artificial bioreactors.