Diatom Strains Research Articles

Resurrection of a diatom after 7000years from anoxic Baltic Sea sediment.

Dormancy is a widespread key life history trait observed across the tree of life. Many plankton species form dormant cell stages that accumulate in aquatic sediments and, under anoxic conditions, form chronological records of past species and population dynamics under changing environmental conditions. Here we report on the germination of a microscopic alga, the abundant marine diatom Skeletonema marinoi Sarno et Zigone, that had remained dormant for up to 6871 ± 140years in anoxic sediments of the Baltic Sea and resumed growth when exposed to oxygen and light. Resurrected diatom strains, representing cohorts from six different time points of the past 6871 ± 140years, are genetically differentiated, and fundamental physiological functions such as growth and photosynthesis have remained stable through time despite distinct environmental dynamics. Showing that resurrection and full functional recovery, in comparison to 3 ± 2years of dormancy, is possible after millennial resting, we emphasize the relevance of dormancy and living sediment archives. For the future, sediment archives, together with the resurrection approach, would offer a powerful tool to trace adaptive traits over millennia under distinct climatic conditions and elucidate the underlying mechanisms.

The queen scallop Aequipecten opercularis: A slow domoic acid depurator?

Domoic acid (DA) is a dangerous phycotoxin produced by several strains of diatoms of the genus Pseudo-nitzschia, and responsible for Amnesic Shellfish Poisoning (ASP) in humans. The increasingly intense ASP-outbreaks along the English Channel over the last three decades have forced persistent harvest closures of economically important and highly contaminated bivalve stocks exhibiting slow DA-depuration rates, like the king scallop Pecten maximus. Under this scenario, other pectinid species, such as the queen scallop Aequipecten opercularis have been empirically proposed as alternative resources to redress the high economic losses due to the banning of the exploitation of P. maximus. Nevertheless, the kinetics of DA depuration in A. opercularis have not been assessed so far, and its direct extraction after ASP-episodes could represent a serious threat to public health. Hence, the main objective of this work was to estimate the DA-depuration rate in the digestive gland (DG) of naturally contaminated scallops A. opercularis after a toxic Pseudo-nitzschia australis bloom subjected to experimental depuration in the laboratory for 30 days. This study also intended to go further in the knowledge about the anatomical distribution of DA in scallop tissues, and corroborate the implications of autophagy in DA-sequestration in the DG of this species as recently hypothesized. In the DG, the DA-depuration rate (0.018 day−1) suggested that even with toxin burdens as low as 40 mg⋅kg−1 in the DG, queen scallops may remain contaminated for about 70 days, thus longer under intensely contamination scenarios. The subcellular analyses corroborated DA-sequestration mainly through late-autophagy within residual bodies in the DG, without differences in the frequencies of anti-DA labeled residual bodies across the entire depuration process. These results revealed that A. opercularis cannot be considered a fast DA-depurator, and represent a baseline knowledge for decision-making about harvesting natural beds of queen scallops after toxic Pseudo-nitzschia blooms. The findings of this work also represent a cornerstone for further research to accelerate DA-depuration in this species.

Description of Two New Species of Stauroneis Ehrenberg (Naviculales, Bacillariophyceae) from the Russian Far East Using an Integrative Approach.

Stauroneis (Naviculales, Bacillariaceae) are widespread, mostly in fresh-water habitats, and account for 343 species. They are described mainly on the basis of morphology and morphometric traits. These characteristics vary during life cycles and may overlap between species, making their identification difficult. We isolated two strains of naviculoid diatoms and examined them using an integrative approach (phylogenetic, morphological, ultrastructural data, and life cycle). Phylogenetic analyses based on chloroplast rbcL gene data showed affinity of the new strains to the genus Stauroneis. Our algae share morphological features typical of Stauroneis but differ from similar species in minimal valve length measurements, valve apex shape, and minimal number of striae in 10 μm. Two strains are distinct from each other in maximal valve length and width, partially valve shape, the number of areolae in 10 μm, and cingulum structure. It was revealed that the strains reproduce via isogamy. Three species delimitation methods (ASAP, PTP, and GMYC) also confirmed that the two closely related new strains represent distinct species. Based on molecular data and phenotypic traits examined within the framework of an integrative approach, we describe two new isolates as Stauroneis urbani sp. nov. and Stauroneis edaphica sp. nov.

Friends and foes: competition experiments reveal growth facilitation and interference between cyanobacteria and diatom strains in microbial mats

Friends and foes: competition experiments reveal growth facilitation and interference between cyanobacteria and diatom strains in microbial mats

Performance characteristics of marine diatoms Cylindrotheca sp. and Trieres chinensis under nutrient limitation and their potency as feedstock for biodiesel production

Microalgae-derived biodiesel is commonly studied and recently gained attention as a possible substitute feedstock for production of biodiesel. In this study, the potential of marine diatoms, Cylindrotheca sp. (FPU 0031) and T. chinensis (FPU 0030), for production of biodiesel was evaluated by investigating the effect of nutrient limitation (100, 75, 50, and 25 % Roschin medium) on growth behavior response, lipid productivity, and FAME profiles of the diatom strains. The total lipid yield increased under nutrient-limited culture condition. When the concentration of the nutrient was restricted to 50 %, the average lipid yield of Cylindrotheca sp. and T. chinensis were 19.32 and 21.72 % with lipid productivity of 73.46 and 68.19 mg L−1 day−1, respectively. Nutrient limitation resulted in a decrease in biomass yield and an increase in the lipid yield of the diatom strains. The properties of biodiesel generated by the two diatoms were assessed based on FAME profiles using empirical equations. Results showed that Cylindrotheca sp. and T. chinensis conforms to the biodiesel standards specifications set by EN 14214 and ASTM D6751. The predicted properties of biodiesel observed for Cylindrotheca sp. and T. chinensis were both ideal, e.g. good cold filter plugging points (−6.94 °C and − 2.16 °C), cetane numbers (65.57 and 75.29), cloud points (1.81 °C and 7.75 °C), pour points (1.60 °C and − 4.86 °C), and low kinematic viscosities (2.89 and 2.16 mm2 s−1), respectively. Thus, suggesting the potential use of these diatoms as feedstock for producing biodiesel with high-grade fuel characteristics.

A removable and cosmopolitan dsRNA Toti-like virus causes asymptomatic but productive infection in a model diatom strain

Diatoms contribute to 20 % of global primary productivity. Although some diatom viruses have been identified, the molecular mechanisms underlying their interactions with the host remain poorly understood. In this study, we report the discovery of an RNA molecule in the DNA extracts of the Phaeodactylum tricornutum strain Pt1, which possesses a well-annotated genome and has been used as a diatom model system since 1956. We confirmed this molecule to be a double-stranded linear RNA molecule and, through sequencing, demonstrated it to be a virus in the Totiviridae family that is prevalent among marine stramenopiles. We also detected this virus in Phaeodactylum tricornutum strain Pt3, which was collected in 1930s from a similar geographic location to Pt1, suggesting its prevalence within the region. By employing various inhibitors of the viral RNA-dependent RNA polymerase, we successfully generated a virus-free line isogenic to Pt1, establishing a model system to investigate the impact of RNA viruses on diatom physiology. The virus-free lines did not display obvious growth advantages or defects, indicating a tendency of the virus towards asymptomatic infection. Furthermore, we generated a robust antibody against the coat protein of this virus. By performing immunoprecipitation coupled with mass spectrometry, we found that translation-related proteins are enriched as potential interacting partners of the coat protein. Our results suggest that potential viral impacts in molecular research should be considered when Pt1 and Pt3 are used for studying translation-related processes. Additionally, our study unveiled a mode of asymptomatic but productive infection between viruses and marine algal hosts that differs from the commonly-reported virulent, lytic infections.

Antarctic benthic diatoms after 10 months of dark exposure: consequences for photosynthesis and cellular integrity.

Antarctic algae are exposed to prolonged periods of extreme darkness due to polar night, and coverage by ice and snow can extend such dark conditions to up to 10 months. A major group of microalgae in benthic habitats of Antarctica are diatoms, which are key primary producers in these regions. However, the effects of extremely prolonged dark exposure on their photosynthesis, cellular ultrastructure, and cell integrity remain unknown. Here we show that five strains of Antarctic benthic diatoms exhibit an active photosynthetic apparatus despite 10 months of dark-exposure. This was shown by a steady effective quantum yield of photosystem II (Y[II]) upon light exposure for up to 2.5 months, suggesting that Antarctic diatoms do not rely on metabolically inactive resting cells to survive prolonged darkness. While limnic strains performed better than their marine counterparts, Y(II) recovery to values commonly observed in diatoms occurred after 4-5 months of light exposure in all strains, suggesting long recovering times. Dark exposure for 10 months dramatically reduced the chloroplast ultrastructure, thylakoid stacking, and led to a higher proportion of cells with compromised membranes than in light-adapted cells. However, photosynthetic oxygen production was readily measurable after darkness and strong photoinhibition only occurred at high light levels (>800 µmol photons m-2 s-1). Our data suggest that Antarctic benthic diatoms are well adapted to long dark periods. However, prolonged darkness for several months followed by only few months of light and another dark period may prevent them to regain their full photosynthetic potential due to long recovery times, which might compromise long-term population survival.

Continuous reproduction of planktonic foraminifera in laboratory culture.

Planktonic foraminifera were long considered obligate sexual outbreeders but recent observations have shown that nonspinose species can reproduce by multiple fission. The frequency of multiple fission appears low but the survival rate of the offspring is high and specimens approaching fission can be distinguished. We made use of this observation and established a culturing protocol aimed at enhancing the detection and frequency of fission. Using this protocol, we selectively cultured specimens of Neogloboquadrina pachyderma and raised the frequency of reproduction by fission in culture from 3% in randomly selected specimens to almost 60%. By feeding the resulting offspring different strains of live diatoms, we obtained a thriving offspring population and during the subsequent 6 months of culturing, we observed two more successive generations produced by fission. This provides evidence that in nonspinose species of planktonic foraminifera, reproduction by multiple fission is likely clonal and corresponds to the schizont phase known from benthic foraminifera. We subsequently tested if a similar culturing strategy could be applied to Globigerinita glutinata, representing a different clade of planktonic foraminifera, and we were indeed able to obtain offspring via multiple fission in this species. This work opens new avenues for laboratory-based experimental work with planktonic foraminifera.

Hydraulic retention time governed the micro/nanostructures of titanium-incorporated diatoms and their photocatalytic activity

Titanium-incorporated diatoms are promising biomaterials to photodegrade micropollutants such as pharmaceuticals and personal care products (PPCPs). Hydraulic retention time (HRT) is a key parameter for diatom cultivation and the incorporation of titanium into diatom frustules. This study assessed how HRT governs the micro/nanostructures, titania (TiO2) content and distribution, and the photocatalytic activity of titanium-incorporated diatom frustules. We cultivated a diatom strain Stephanodiscus hantzschii using a feed solution containing titanium(IV) in membrane bioreactors (MBRs) at a solids retention time (SRT) of 10 d and staged HRTs from 24 to 12 and to 6 h. The decrease in HRT reduced the porosity of diatom frustules but increased their silicon and titania contents. When the HRT decreased from 24 to 12 and to 6 h, the specific surface areas of the diatom decreased from 37.65 ± 3.19 to 31.53 ± 3.71 and to 18.43 ± 2.69 m2·g−1 frustules, while the titanium (Ti) contents increased from 53 ± 14 to 71 ± 9 and to 85 ± 13 mg Ti·g−1 frustules. The increase in the influent flow rates of the MBRs with decreasing HRTs likely enhanced nutrient diffusion inside the diatom valve pores, facilitating the uptake and incorporation of silicon and titanium. The titanium-incorporated frustules were effective in removing two representative PPCPs, bisphenol A (BPA) and N,N-diethyl-meta-toluamide (DEET), from water. As photocatalytic activity depends on the amount of titanium, decreasing the HRT substantially increased the photocatalytic activity of the titanium-incorporated frustules. In batch tests under ultraviolet light, frustules from the diatom cultivated at HRTs of 24, 12, and 6 h had the pseudo-first-order removal (mainly through photodegradation) rate constants of BPA of 0.376, 0.456, and 0.683 h−1, respectively. Under the same experimental condition, the pseudo-first-order removal rate constants of DEET by the frustules cultivated at HRTs of 24, 12, and 6 h increased from 0.270 to 0.330 and to 0.480 h−1.

Comparison of different small-scale cultivation methods towards the valorization of a marine benthic diatom strain for lipid production

Marine benthic diatoms have the capacity to produce quality biomass and bioactive compounds for various commercial applications. Amphora sp. NCC169 is one of such species that have high-value lipid production. However, mass-production of Amphora sp. NCC169 in traditional suspension photobioreactor is challenged by its sensitivity to stirring and turbulence. The aim of this study is to compare the biomass and lipid productivity of Amphora sp. NCC169 cultures between a Fernbach flask and a low-maintenance, laboratory-scale culture system adapted from previously described vertically oriented porous substrate bioreactor (PSBR) designs. Results revealed that cells in the PSBR could achieve significantly higher biomass productivity (Pbiomass = 0.51 ± 0.05 g·m−2·day−1) and lipid productivity (Plipid = 0.10 ± 0.03 g·m−2·day−1) than those in Fernbach flasks after 20 days of cultivation (Pbiomass = 0.29 ± 0.01 g m−2 day−1; Plipid = 0.07 ± 0.01 g·m−2·day−1). Cellular photosynthetic efficiency remained favorable in both culture conditions (Fv/Fm > 0.5) for the duration of the experiments.

Cooperative motility, force generation and mechanosensing in a foraging non-photosynthetic diatom.

Diatoms are ancestrally photosynthetic microalgae. However, some underwent a major evolutionary transition, losing photosynthesis to become obligate heterotrophs. The molecular and physiological basis for this transition is unclear. Here, we isolate and characterize new strains of non-photosynthetic diatoms from the coastal waters of Singapore. These diatoms occupy diverse ecological niches and display glucose-mediated catabolite repression, a classical feature of bacterial and fungal heterotrophs. Live-cell imaging reveals deposition of secreted extracellular polymeric substance (EPS). Diatoms moving on pre-existing EPS trails (runners) move faster than those laying new trails (blazers). This leads to cell-to-cell coupling where runners can push blazers to make them move faster. Calibrated micropipettes measure substantial single-cell pushing forces, which are consistent with high-order myosin motor cooperativity. Collisions that impede forward motion induce reversal, revealing navigation-related force sensing. Together, these data identify aspects of metabolism and motility that are likely to promote and underpin diatom heterotrophy.

Luticola tenera sp. nov. (Diadesmidaceae, Naviculales)-A New Diatom from the Soil of the State Nature Reserve "Bastak" (Jewish Autonomous Region, Russia).

Diatoms inhabit different aquatic and non-aquatic environments, including soils. The naviculoid genus Luticola is widespread in various habitats and accounts for 264 species that are only based on morphological and morphometric characteristics. These parameters can greatly vary during the life cycle, making the species very similar to each other and complicating their unambiguous identification. During a study on soil algal diversity in the Russian Far East (Jewish Autonomous Region), we isolated a strain of naviculoid diatom and examined it using an integrative approach (phylogenetic, morphological, ultrastructural data, and life cycle). Phylogenetic analyses, based on chloroplast rbcL gene data, showed affinity of the new strain with the genus Luticola. Our alga shares morphological features typical of the genus members but differs from them by having valves with a larger width and hook-shaped external proximal raphe ends deflected to the side opposite the stigma. It was revealed that the strain reproduces via two types of sexual reproduction-isogamy and cis-anisogamy. Based on these phenotypic traits, we described the new isolate as Luticola tenera sp. nov.

Isolation and cultivation of freshwater diatom <italic>Nitzschia palea</italic> HY1 for increasing biomass and fucoxanthin production

Diatoms, a type of microalgae distributed worldwide, have been identified as potential sources of biomass, lipids, and high-value compounds. While marine diatoms have been extensively studied, the potential of freshwater diatoms still needs to be explored. In this study, a novel strain of freshwater diatom was isolated from the Jungnangcheon stream located in Seoul, Republic of Korea (37°33'08.0" N, 127°02'40.0" E). This newly isolated strain was classified through phylogenetic analysis, and its morphology was investigated using light and electron microscopy; it was named Nitzschia palea HY1. N. palea HY1 grown in freshwater media (FDM) produced higher biomass (0.68 g L<sup>-1</sup>) and fucoxanthin production (9.19 mg L<sup>-1</sup>) than in conventional diatom media. Furthermore, increasing the bicarbonate concentration from 2 to 10 mM enhanced the maximum biomass and fucoxanthin production in FDM by 2.7 fold and 1.5 fold, respectively. Remarkably, the introduction of aeration to the modified FDM (MFDM) led to a substantial increase in the maximum biomass and fucoxanthin production of N. palea HY1, exhibiting 3.8-fold and 4.1-fold enhancement, respectively, compared to FDM alone. These findings suggest that optimizing the cultivation of N. palea HY1 using MFDM could provide an alternative to marine sources for fucoxanthin production.

Lipid degradation and photosynthetic traits after prolonged darkness in four Antarctic benthic diatoms, including the newly described species Planothidium wetzelii sp. nov.

In polar regions, the microphytobenthos has important ecological functions in shallow-water habitats, such as on top of coastal sediments. This community is dominated by benthic diatoms, which contribute significantly to primary production and biogeochemical cycling while also being an important component of polar food webs. Polar diatoms are able to cope with markedly changing light conditions and prolonged periods of darkness during the polar night in Antarctica. However, the underlying mechanisms are poorly understood. In this study, five strains of Antarctic benthic diatoms were isolated in the field, and the resulting unialgal cultures were identified as four distinct species, of which one is described as a new species, Planothidium wetzelii sp. nov. All four species were thoroughly examined using physiological, cell biological, and biochemical methods over a fully controlled dark period of 3 months. The results showed that the utilization of storage lipids is one of the key mechanisms in Antarctic benthic diatoms to survive the polar night, although different fatty acids were involved in the investigated taxa. In all tested species, the storage lipid content declined significantly, along with an ultrastructurally observable degradation of the chloroplasts. Surprisingly, photosynthetic performance did not change significantly despite chloroplasts decreasing in thylakoid membranes and an increased number of plastoglobules. Thus, a combination of biochemical and cell biological mechanisms allows Antarctic benthic diatoms to survive the polar night.

Nutritional profile, bioactive compounds, and antioxidant activity of microalgal strain, Amphora sp., isolated from the Cape coastal waters, South Africa

Microalgae represent a potential source of renewable nutrition, and there is growing global interest in algae-based dietary supplements. However, the selection of suitable and indigenous microalgae species is a fundamental requirement in developing value-added bioactive compounds in the food industry. The proximate composition, fatty acids, amino acids, and mineral profile, as well as bioactive compounds and antioxidant activity of an unexplored diatom strain, Amphora sp. WCA23.2, isolated from the Cape coastal waters, South Africa, were evaluated as a potential nutraceutical. The Amphora sp. WCA23.2 biomass had 44.2% ash, 28% carbohydrates, 15% protein, and 4% lipids. The fatty acid profile revealed that the diatom accumulates a significant amount of omega-7-monounsaturated fatty acid palmitoleic acid (24.50 mg/g), while the amino acid profile demonstrated that it contained all the nine essential amino acids. The antioxidant activities of the diatom extracts showed that the methanolic extract displayed the highest DPPH radical scavenging activity (1.90±0.11 mg GAE/g dry weight (DW)) and the lowest IC50 in all the antioxidant indices evaluated. These results suggest that Amphora sp. WCA23.2 biomass and its extracts can be utilized as a potential source of ingredients and nutraceuticals in food systems for humans.

Comparison between p-distance and single-locus species delimitation models for delineating reproductively tested strains of pennate diatoms (Bacillariophyceae) using cox1, rbcL and ITS.

Several automated molecular methods have emerged for distinguishing eukaryote species based on DNA sequence data. However, there are knowledge gaps around which of these single-locus methods is more accurate for the identification of microalgal species, such as the highly diverse and ecologically relevant diatoms. We applied genetic divergence, Automatic Barcode Gap Discovery for primary species delimitation (ABGD), Assemble Species by Automatic Partitioning (ASAP), Statistical Parsimony Network Analysis (SPNA), Generalized Mixed Yule Coalescent (GMYC) and Poisson Tree Processes (PTP) using partial cox1, rbcL, 5.8S + ITS2, ITS1 + 5.8S + ITS2 markers to delineate species and compare to published polyphasic identification data (morphological features, phylogeny and sexual reproductive isolation) to test the resolution of these methods. ASAP, ABGD, SPNA and PTP models resolved species of Eunotia, Seminavis, Nitzschia, Sellaphora and Pseudo-nitzschia corresponding to previous polyphasic identification, including reproductive isolation studies. In most cases, these models identified diatom species in similar ways, regardless of sequence fragment length. GMYC model presented smallest number of results that agreed with previous published identification. Following the recommendations for proper use of each model presented in the present study, these models can be useful tools to identify cryptic or closely related species of diatoms, even when the datasets have relatively few sequences.

A novel effective bio-originated methylene blue adsorbent: the porous biosilica from three marine diatom strains of Nanofrustulum spp. (Bacillariophyta)

In the present paper, for the first time the ability of the porous biosilica originated from three marine diatom strains of ‘Nanofrustulum spp.’ viz. N. wachnickianum (SZCZCH193), N. shiloi (SZCZM1342), N. cf. shiloi (SZCZP1809), to eliminate MB from aqueous solutions was investigated. The highest biomass was achieved under silicate enrichment for N. wachnickianum and N. shiloi (0.98 g L−1 DW and 0.93 g L−1 DW respectively), and under 15 °C for N. cf. shiloi (2.2 g L−1 DW). The siliceous skeletons of the strains were purified with hydrogen peroxide and characterized by SEM, EDS, the N2 adsorption/desorption, XRD, TGA, and ATR-FTIR. The porous biosilica (20 mg DW) obtained from the strains i.e. SZCZCH193, SZCZM1342, SZCZP1809, showed efficiency in 77.6%, 96.8%, and 98.1% of 14 mg L−1 MB removal under pH 7 for 180 min, and the maximum adsorption capacity was calculated as 8.39, 19.02, and 15.17 mg g−1, respectively. Additionally, it was possible to increase the MB removal efficiency in alkaline (pH = 11) conditions up to 99.08% for SZCZP1809 after 120 min. Modelling revealed that the adsorption of MB follows Pseudo-first order, Bangham’s pore diffusion and Sips isotherm models.

Removal of the Basic and Diazo Dyes from Aqueous Solution by the Frustules of Halamphora cf. salinicola (Bacillariophyta)

Industrial wastes with hazardous dyes serve as a major source of water pollution, which is considered to have an enormous impact on public health. In this study, an eco-friendly adsorbent, the porous siliceous frustules extracted from the diatom species Halamphora cf. salinicola, grown under laboratory conditions, has been identified. The porous architecture and negative surface charge under a pH of 7, provided by the various functional groups via Si–O, N–H, and O–H on these surfaces, revealed by SEM, the N2 adsorption/desorption isotherm, Zeta-potential measurement, and ATR-FTIR, respectively, made the frustules an efficient mean of removal of the diazo and basic dyes from the aqueous solutions, 74.9%, 94.02%, and 99.81% against Congo Red (CR), Crystal Violet (CV), and Malachite Green (MG), respectively. The maximum adsorption capacities were calculated from isotherms, as follows: 13.04 mg g−1, 41.97 mg g−1, and 33.19 mg g−1 against CR, CV, and MG, respectively. Kinetic and isotherm models showed a higher correlation to Pore diffusion and Sips models for CR, and Pseudo-Second Order and Freundlich models for CV and MG. Therefore, the cleaned frustules of the thermal spring-originated diatom strain Halamphora cf. salinicola could be used as a novel adsorbent of a biological origin against anionic and basic dyes.

New report of Halamphora subtropica (Bacillariophyta) from the Strait of Malacca and its growth and biochemical characterisation under nutrient deprivation

A symmetrical bi-raphid pennate diatom isolated from tropical coastal waters in the Strait of Malacca was identified as Halamphora subtropica, which is significant given that the distribution of this species was until now limited to subtropical waters in western Atlantic Ocean and western Pacific Ocean, hence its etymology. To assess its potential as biodiesel feedstock, the alga was cultivated, and its growth and biochemical composition compared under nutrient replete and nutrient (N, P, Si) deprived conditions. The growth of H. subtropica was more suppressed under N- conditions but was less affected under P- and/or Si- conditions. The highest biomass and lipid productivity of 19.7 ± 0.8 and 4.0 ± 0.4 mg L−1 day −1 respectively, were achieved under nutrient replete condition followed by P- and Si- conditions. Cells grown in nutrient-deprived media contain higher monounsaturated fatty acids while higher polyunsaturated fatty acids were observed in the complete medium. Palmitic acid, palmitoleic acid and stearic acid accounted for over 60% of the total fatty acids. The strain used in this study showed comparable values of biomass productivity, lipid productivity and lipid content (≈30% dw) to diatom strains reported previously, suggesting that H. subtropica may be considered as a candidate for biofuel feedstock. These results contribute additional evidence on the potential of using tropical marine diatom strains as feedstock for biofuel, given that existing literature tend to focus on subtropical or temperate strains.

Characterization of oil body-associated proteins obtained from oil bodies with different sizes in oleaginous diatom Fistulifera solaris

Oil body-associated proteins from the oleaginous diatom Fistulifera solaris were identified by proteomic analysis of oil bodies of various sizes (small, middle, and large) by time-dependent culturing upon nutrient-starvation at 36, 96 and 168h. This diatom strain has the capability to accumulate neutral lipids and triacylglycerol. Liquid chromatography-tandem mass spectrometry analysis revealed 662 proteins in all oil body sizes. Among these, 132 proteins were predicted to be localized to the endoplasmic reticulum. Seventeen proteins that exhibited a positive correlation with gene expression and the oil body size were selected as novel candidates for oil body-associated proteins. Among the 17 protein candidates, two proteins encoded by fso:g8246 and fso:g10200 were confirmed to be localized on the surface of the oil body and endoplasmic reticulum. A protein encoded by fso:g2514, which is involved in sterol biosynthesis, was also identified. This protein was likely to localize to mitochondria; however, inhibitor assays suggested that it might play a role in lipid degradation. Our work provides new insights into the proteomics of microalgae and provides a valuable strategy for boosting lipid productivity in microalgae.