Plastid-localized xanthorhodopsin increases diatom biomass and ecosystem productivity in iron-limited surface oceans.

Microbial rhodopsins are photoreceptor proteins that convert light into biological signals or energy. Proteins of the xanthorhodopsin family are common in eukaryotic photosynthetic plankton including diatoms. However, their biological role in these organisms remains elusive. Here we report on a xanthorhodopsin variant (FcR1) isolated from the polar diatom Fragilariopsis cylindrus. Applying a combination of biophysical, biochemical and reverse genetics approaches, we demonstrate that FcR1 is a plastid-localized proton pump which binds the chromophore retinal and is activated by green light. Enhanced growth of a Thalassiora pseudonana gain-of-function mutant expressing FcR1 under iron limitation shows that the xanthorhodopsin proton pump supports growth when chlorophyll-based photosynthesis is iron-limited. The abundance of xanthorhodopsin transcripts in natural diatom communities of the surface oceans is anticorrelated with the availability of dissolved iron. Thus, we propose that these proton pumps convey a fitness advantage in regions where phytoplankton growth is limited by the availability of dissolved iron.

The diatom Fragilariopsis cylindrus: A model alga to understand cold-adapted life.

Diatoms are significant primary producers especially in cold, turbulent, and nutrient-rich surface oceans. Hence, they are abundant in polar oceans, but also underpin most of the polar food webs and related biogeochemical cycles. The cold-adapted pennate diatom Fragilariopsis cylindrus is considered a keystone species in polar oceans and sea ice because it can thrive under different environmental conditions if temperatures are low. In this perspective paper, we provide insights into the latest molecular work that has been done on F. cylindrus and discuss its role as a model alga to understand cold-adapted life.

Ubiquity of the neurotoxin ß-N-methylamino-L-alanine and its isomers confirmed by two different mass spectrometric methods in diverse marine mollusks.

In recent years, the neurotoxin ß-N-methylamino-L-alanine (BMAA) has been reported in some marine mollusk species. To further discover BMAA in marine animals, a total of 59 samples belonging to 3 phyla, 22 families, and 43 species, were collected from Dalian, Rongcheng, and Zhoushan cities, China, in April 2017. All samples were quantified by a hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS) analysis of underivatized extract, and ten samples were also analyzed by a liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) analysis using a precolumn AQC (6-aminoquinolyl-N-hydroxysuccinimidyl carbamate)-derivatization method. Results indicated that 48 mollusk samples contained BMAA with concentrations above the limit of detection (0.31 µg g-1 wet weight), and the isomers of BMAA, ß-amino-N-methylalanine (BAMA) and 2,4-diaminobutyric acid (DAB) were universally present in most samples. However, N-(2-aminoethyl) glycine (AEG) was not found in any sample. Comparison of both analytical methods showed that BMAA and BAMA were not completely separated by the HILIC column although they still could be identified by specific transitions. In contrast the C18 column provided good separation for the AQC-derivatives of BMAA and all of its isomers. Development of analytical methods and stable isotope tracing of BMAA should be carried out in the future.

New Typical Vector of Neurotoxin ß-N-Methylamino-l-Alanine (BMAA) in the Marine Benthic Ecosystem.

The neurotoxin ß-N-methylamino-l-alanine (BMAA) has been identified as an environmental factor triggering neurodegenerative diseases such as Amyotrophic Lateral Sclerosis (ALS) and Alzheimer's disease (AD). We investigated the possible vectors of BMAA and its isomers 2,4-diaminobutyric acid (DAB) and N-2(aminoethyl)glycine (AEG) in marine mollusks collected from the Chinese coast. Sixty-eight samples of marine mollusks were collected along the Chinese coast in 2016, and were analyzed by an HILIC-MS/MS (hydrophilic interaction liquid chromatography with tandem quadrupole mass spectrometer) method without derivatization. BMAA was detected in a total of five samples from three species: Neverita didyma, Solen strictus, and Mytilus coruscus. The top three concentrations of free-form BMAA (0.99~3.97 µg·g-1 wet weight) were detected in N. didyma. DAB was universally detected in most of the mollusk samples (53/68) with no species-specific or regional differences (0.051~2.65 µg·g-1 wet weight). No AEG was detected in any mollusk samples tested here. The results indicate that the gastropod N. didyma might be an important vector of the neurotoxin BMAA in the Chinese marine ecosystem. The neurotoxin DAB was universally present in marine bivalve and gastropod mollusks. Since N. didyma is consumed by humans, we suggest that the origin and risk of BMAA and DAB toxins in the marine ecosystem should be further investigated in the future.