Long-term and seasonal changes in nutrients, phytoplankton biomass, and dissolved oxygen in deep bay, Hong Kong

Deep Bay is a semienclosed bay that receives sewage from Shenzhen, a fast-growing city in China. NH 4 is the main N component of the sewage (>50% of total N) in the inner bay, and a twofold increase in NH 4 and PO 4 concentrations is attributed to increased sewage loading over the 21-year period (1986-2006). During this time series, the maximum annual average NH 4 and PO 4 concentrations exceeded 500 and 39 μM, respectively. The inner bay (Stns DM1 and DM2) has a long residence time and very high nutrient loads and yet much lower phytoplankton biomass (chlorophyll (Chl) 2 mg L -1) than expected. Because it is shallow (̃2 m), phytoplankton growth is likely limited by light due to mixing and suspended sediments, as well as by ammonium toxicity, and biomass accumulation is reduced by grazing, which may reduce the occurrence of hypoxia. Since nutrients were not limiting in the inner bay, the significant long-term increase in Chl a (0. 52-0. 57 μg L -1 year -1) was attributed to climatic effects in which the significant increase in rainfall (11 mm year -1) decreased salinity, increased stratification, and improved water stability. The outer bay (DM3 to DM5) has a high flushing rate (0. 2 day -1), is deeper (3 to 5 m), and has summer stratification, yet there are few large algal blooms and hypoxic events since dilution by the Pearl River discharge in summer, and the invasion of coastal water in winter is likely greater than the phytoplankton growth rate. A significant long-term increase in NO 3 (0. 45-0. 94 μM year -1) occurred in the outer bay, but no increasing trend was observed for SiO 4 or PO 4, and these long-term trends in NO 3, PO 4, and SiO 4 in the outer bay agreed with those long-term trends in the Pearl River discharge. Dissolved inorganic nitrogen (DIN) has approximately doubled from 35-62 to 68-107 μM in the outer bay during the last two decades, and consequently DIN to PO 4 molar ratios have also increased over twofold since there was no change in PO 4. The rapid increase in salinity and DO and the decrease in nutrients and suspended solids from the inner to the outer bay suggest that the sewage effluent from the inner bay is rapidly diluted and appears to have a limited effect on the phytoplankton of the adjacent waters beyond Deep Bay. Therefore, physical processes play a key role in reducing the risk of algal blooms and hypoxic events in Deep Bay. © 2009 Coastal and Estuarine Research Federation.published_or_final_versionSpringer Open Choice, 01 Dec 201

Discovery of Nuclear-Encoded Genes for the Neurotoxin Saxitoxin in Dinoflagellates

Saxitoxin is a potent neurotoxin that occurs in aquatic environments worldwide. Ingestion of vector species can lead to paralytic shellfish poisoning, a severe human illness that may lead to paralysis and death. In freshwaters, the toxin is produced by prokaryotic cyanobacteria; in marine waters, it is associated with eukaryotic dinoflagellates. However, several studies suggest that saxitoxin is not produced by dinoflagellates themselves, but by co-cultured bacteria. Here, we show that genes required for saxitoxin synthesis are encoded in the nuclear genomes of dinoflagellates. We sequenced >1.2×106 mRNA transcripts from the two saxitoxin-producing dinoflagellate strains Alexandrium fundyense CCMP1719 and A. minutum CCMP113 using high-throughput sequencing technology. In addition, we used in silico transcriptome analyses, RACE, qPCR and conventional PCR coupled with Sanger sequencing. These approaches successfully identified genes required for saxitoxin-synthesis in the two transcriptomes. We focused on sxtA, the unique starting gene of saxitoxin synthesis, and show that the dinoflagellate transcripts of sxtA have the same domain structure as the cyanobacterial sxtA genes. But, in contrast to the bacterial homologs, the dinoflagellate transcripts are monocistronic, have a higher GC content, occur in multiple copies, contain typical dinoflagellate spliced-leader sequences and eukaryotic polyA-tails. Further, we investigated 28 saxitoxin-producing and non-producing dinoflagellate strains from six different genera for the presence of genomic sxtA homologs. Our results show very good agreement between the presence of sxtA and saxitoxin-synthesis, except in three strains of A. tamarense, for which we amplified sxtA, but did not detect the toxin. Our work opens for possibilities to develop molecular tools to detect saxitoxin-producing dinoflagellates in the environment

Loss of C2orf69 defines a fatal autoinflammatory syndrome in humans and zebrafish that evokes a glycogen-storage-associated mitochondriopathy

Summary Human C2orf69 is an evolutionarily conserved gene whose function is unknown. Here, we report eight unrelated families from which 20 children presented with a fatal syndrome consisting of severe autoinflammation and progredient leukoencephalopathy with recurrent seizures; 12 of these subjects, whose DNA was available, segregated homozygous loss-of-function C2orf69 variants. C2ORF69 bears homology to esterase enzymes, and orthologs can be found in most eukaryotic genomes, including that of unicellular phytoplankton. We found that endogenous C2ORF69 (1) is loosely bound to mitochondria, (2) affects mitochondrial membrane potential and oxidative respiration in cultured neurons, and (3) controls the levels of the glycogen branching enzyme 1 (GBE1) consistent with a glycogen-storage-associated mitochondriopathy. We show that CRISPR-Cas9-mediated inactivation of zebrafish C2orf69 results in lethality by 8 months of age due to spontaneous epileptic seizures, which is preceded by persistent brain inflammation. Collectively, our results delineate an autoinflammatory Mendelian disorder of C2orf69 deficiency that disrupts the development/homeostasis of the immune and central nervous systems

Production of C2 toxin by Alexandrium tamarense CI01 using different culture methods

The dinoflagellate Alexandrium tamarense CI01 was grown in three types of cultures: batch culture, semi-continuous culture and temporary culture, to investigate the effects of different culture methods on cell growth and the productivity of C2 toxin (C2, a paralytic shellfish toxin). In the batch cultures, cells grew in three phases: a short lag phase, an exponential phase with a specific growth rate (mu) of 0.78 day(-1) and a relatively long stationary phase. The maximum toxin productivity was 1.2 mumol L-1 or 77 fmol cell(-1) in 9 days. In the semi-continuous cultures, cells grew in response to the dilution cycles, with mu values being 0.64, 0.32 and 0.35 day(-1) for one-day, two-day and three-day cycles, respectively. The toxin yield was about one half of that of the batch cultures. A "temporary" culture method was used to maintain the metabolically active cells removed from the semi-continuous cultures, in a nutrient-depleted condition, to achieve a high toxin productivity of 1.0 mumol L-1 in 4 days. Thus, the semi-continuous culture method provided an efficient means to generate amounts of metabolically active algal cells. The temporary culture offered an effective way to produce C2. The highest yields of C2 were obtained in 3-4 days when the temporary cultures were aerated

Nutrient limitation in Hong Kong waters inferred from comparison of nutrient ratios, bioassays and 33P turnover times

There is a need to determine the spatial and temporal dynamics of nutrient limitation to decide which nutrients should be removed during sewage treatment in Hong Kong. We compared 3 methods to assess potential or actual nutrient limitation. Ambient nutrient ratios were calculated, and nutrient enrichment bioassays were conducted, along with 33P turnover times. Comparison of nutrient ratios and bioassays demonstrated that the ambient inorganic nutrient ratios, based on the Redfield Si:N:P ratio of 16:16:1, were a rapid and effective method that could be used to predict the potentially limiting nutrient of phytoplankton biomass, except in eastern waters in summer, since the DIN:PO 4 uptake ratio was occasionally below the Redfield ratio. The agreement between nutrient limitation indices of growth rate and biomass yield suggested that phytoplankton biomass and growth rate were P-limited in southern waters, with more stable conditions during summer. In contrast, a lack of agreement between these indicators showed that phytoplankton growth in potentially P-limited cases in western waters and Victoria Harbour was controlled by physical processes (e.g. strong hydrodynamic mixing and dilution). The limiting factor for phytoplankton growth varied spatially and temporally. In summer, there was a change from physical processes (e.g. the rapid dilution and possible light limitation due to strong turbulent mixing) in hydrodynamically active western waters and Victoria Harbour to P limitation, or N + P co-limitation, in southern and eastern waters with more stable conditions. In winter, phytoplankton growth was regulated by strong wind-induced vertical mixing. Hence, different seasonal sewage treatment strategies should be considered for nutrient removal. © Inter-Research 2009.published_or_final_versio

Geographical distribution of red and green Noctiluca scintillans

The dinoflagellate Noctiluca scintillans is one of the most important and abundant red tide organisms and it is distributed world-wide. It occurs in two forms. Red Noctiluca is heterotrophic and fills the role of one of the microzooplankton grazers in the foodweb. In contrast, green Noctiluca contains a photosynthetic symbiont Pedinomonas noctilucae (a prasinophyte), but it also feeds on other plankton when the food supply is abundant. In this review, we document the global distribution of these two forms and include the first maps of their global distribution. Red Noctiluca occurs widely in the temperate to sub-tropical coastal regions of the world. It occurs over a wide temperature range of about 10°C to 25°C and at higher salinities (generally not in estuaries). It is particularly abundant in high productivity areas such as upwelling or eutrophic areas where diatoms dominate since they are its preferred food source. Green Noctiluca is much more restricted to a temperature range of 25°C–30°C and mainly occurs in tropical waters of Southeast Asia, Bay of Bengal (east coast of India), in the eastern, western and northern Arabian Sea, the Red Sea, and recently it has become very abundant in the Gulf of Oman. Red and green Noctiluca do overlap in their distribution in the eastern, northern and western Arabian Sea with a seasonal shift from green Noctiluca in the cooler winter convective mixing, higher productivity season, to red Noctiluca in the more oligotrophic warmer summer season