Identification of promoter targets by Aureochrome 1a in the diatom Phaeodactylum tricornutum

Aureochromes (AUREOs) are unique blue light receptors and transcription factors found only in stramenopile algae. While each of the four AUREOs identified in the diatom Phaeodactylum tricornutum may have a specific function, PtAUREO1a has been shown to have a strong impact on overall gene regulation, when light changes from red to blue light conditions. Despite its significance, the molecular mechanism of PtAUREO1a is largely unexplored. To comprehend the overall process of gene regulation by PtAUREO1a, we conducted a series of in vitro and in vivo experiments, including pull-down assays, yeast one-hybrid experiments, and phenotypical characterization using recombinant PtAUREOs and diatom mutant lines expressing a modified PtAureo1a gene. We describe the distinct light absorption properties of four PtAUREOs and the formation of all combinations of their potential dimers. We demonstrate the capability of PtAUREO1a and 1b to activate the genes, diatom-specific cyclin 2, PtAureo1a, and PtAureo1c under both light and dark conditions. Using mutant lines expressing a modified PtAUREO1a protein with a considerably reduced light absorption, we found novel evidence that PtAUREO1a regulates the expression of PtLHCF15, which is essential for red light acclimation. Based on current knowledge, we present a working model of PtAUREO1a gene regulation properties.

Carbon and energy balance of biotechnological glycolate production from microalgae in a pre-industrial scale flat panel photobioreactor

Glycolate is produced by microalgae under photorespiratory conditions and has the potential for sustainable organic carbon production in biotechnology. This study explores the glycolate production balance in Chlamydomonas reinhardtii, using a custom-built 10-L flat panel bioreactor with sophisticated measurements of process factors such as nutrient supply, gassing, light absorption and mass balances. As a result, detailed information regarding carbon and energy balance is obtained to support techno-economic analyses. It is shown how nitrogen is a crucial element in the biotechnological process and monitoring nitrogen content is vital for optimum performance. Moreover, the suitable reactor design is advantageous to efficiently adjust the gas composition. The oxygen content has to be slightly above 30% to induce photorespiration while maintaining photosynthetic efficiency. The final volume productivity reached 27.7 mg of glycolate per litre per hour, thus, the total process capacity can be calculated to 13 tonnes of glycolate per hectare per annum. The exceptional volume productivity of both biomass and glycolate production is demonstrated, and consequently can achieve a yearly CO2 sequestration rate of 35 tonnes per hectare. Although the system shows such high productivity, there are still opportunities to enhance the achieved volume productivity and thus exploit the biotechnological potential of glycolate production from microalgae.

De novo retinoic acid receptor beta (RARB) variant associated with microphthalmia and dystonia

BACKGROUND

Definition of the individual genotypes that cause a Mendelian phenotype is of great importance both to clinical diagnostics and disease characterization. Heterozygous de novo gain-of-function missense variants in RARB are associated with syndromic microphthalmia 12 (MCOPS12), a developmental disorder characterized by eye malformations and variable involvement of other organs. A subset of patients were described with poorly delineated movement disorders. Additionally, RARB bi-allelic loss-of-function variants, inherited from asymptomatic heterozygous carrier parents, have been found in a recessive family with four MCOPS12-affected members.

PATIENT/METHODS

We used trio whole-exome sequencing to explore the molecular basis of disease in an individual with congenital eye abnormality and movement disorder. All patients with reported RARB variants were reviewed.

RESULTS

We report on identification of a heterozygous de novo RARB nonsense variant in a girl with microphthalmia and progressive generalized dystonia. Public database entries indicate that the de novo variant is recurrently present in clinically affected subjects but a literature report has not yet been available.

CONCLUSIONS

We provide the first detailed evidence for a role of dominant RARB truncating alterations in congenital eye-brain disease, expanding the spectrum of MCOPS12-associated mutations. Considered together with the published family with bi-allelic variants, the data suggest manifestation and non-manifestation of disease in relation to almost identical RARB loss-of-function variations, an apparent paradox that is seen in a growing number of human genetic conditions associated with both recessive and dominant inheritance patterns.

Meilensteine in der Algenbiotechnologie

Recent progress in algal biotechnology has identified new products based on their broad evolutionary origin. Novel metabolites were found for pharmacy, food industry, medicine e.g. tumor suppression and antibiotics. However, sustainable and economical algal production for crude oil replacement is limited by extremely low space time yields in photobioreactors. The consequences are a high energy burden for mass flow dependent processes and the need of space being in conflict with sustainable landscape management. New concepts using algae not as biomass producers but as living catalysts may open new options.

Prediction of Clinical Outcomes with Explainable Artificial Intelligence in Patients with Chronic Lymphocytic Leukemia

BACKGROUND

The International Prognostic Index (IPI) is applied to predict the outcome of chronic lymphocytic leukemia (CLL) with five prognostic factors, including genetic analysis. We investigated whether multiparameter flow cytometry (MPFC) data of CLL samples could predict the outcome by methods of explainable artificial intelligence (XAI). Further, XAI should explain the results based on distinctive cell populations in MPFC dot plots.

METHODS

We analyzed MPFC data from the peripheral blood of 157 patients with CLL. The ALPODS XAI algorithm was used to identify cell populations that were predictive of inferior outcomes (death, failure of first-line treatment). The diagnostic ability of each XAI population was evaluated with receiver operating characteristic (ROC) curves.

RESULTS

ALPODS defined 17 populations with higher ability than the CLL-IPI to classify clinical outcomes (ROC: area under curve (AUC) 0.95 vs. 0.78). The best single classifier was an XAI population consisting of CD4+ T cells (AUC 0.78; 95% CI 0.70-0.86; p < 0.0001). Patients with low CD4+ T cells had an inferior outcome. The addition of the CD4+ T-cell population enhanced the predictive ability of the CLL-IPI (AUC 0.83; 95% CI 0.77-0.90; p < 0.0001).

CONCLUSIONS

The ALPODS XAI algorithm detected highly predictive cell populations in CLL that may be able to refine conventional prognostic scores such as IPI.

[COVID-19: Collateral damage in head and neck oncology and preventive measures for future pandemics]

The start of the COVID-19 pandemic led to enormous challenges for global healthcare, as capacities and resources had to be made available quickly for the treatment of COVID-19 patients. As a result, restrictions had to be accepted, especially in the care of oncological patients. The collateral damage of these limitations inevitably also affects patients with head and neck cancer. This review article summarizes the development of tumor incidences during the pandemic, internationally developed guidelines for the care of patients with head and neck cancer and studies on the delay in oncological therapies and mortality. In addition, the effects on the mental health of the patients, the psychosocial consequences and ethical issues are examined. In perspective, preventive measures for such negative collateral effects in future pandemics are discussed using the example of a concept for application software (app)-based digital care for patients with head and neck cancer.

Isolation of fucoxanthin chlorophyll protein complexes of the centric diatom Thalassiosira pseudonana associated with the xanthophyll cycle enzyme diadinoxanthin de-epoxidase

In the present study, low concentrations of the very mild detergent n-dodecyl-α-d-maltoside in conjunction with sucrose gradient ultracentrifugation were used to prepare fucoxanthin chlorophyll protein (FCP) complexes of the centric diatom Thalassiosira pseudonana. Two main FCP fractions were observed in the sucrose gradients, one in the upper part and one at high sucrose concentrations in the lower part of the gradient. The first fraction was dominated by the 18 kDa FCP protein band in SDS-gels. Since this fraction also contained other protein bands, it was designated as fraction enriched in FCP-A complex. The second fraction contained mainly the 21 kDa FCP band, which is typical for the FCP-B complex. Determination of the lipid composition showed that both FCP fractions contained monogalactosyl diacylglycerol as the main lipid followed by the second galactolipid of the thylakoid membrane, namely digalactosyl diacylglycerol. The negatively charged lipids sulfoquinovosyl diacylglycerol and phosphatidyl glycerol were also present in both fractions in pronounced concentrations. With respect to the pigment composition, the fraction enriched in FCP-A contained a higher amount of the xanthophyll cycle pigments diadinoxanthin (DD) and diatoxanthin (Dt), whereas the FCP-B fraction was characterized by a lower ratio of xanthophyll cycle pigments to the light-harvesting pigment fucoxanthin. Protein analysis by mass spectrometry revealed that in both FCP fractions the xanthophyll cycle enzyme diadinoxanthin de-epoxidase (DDE) was present. In addition, the analysis showed an enrichment of DDE in the fraction enriched in FCP-A but only a very low amount of DDE in the FCP-B fraction. In-vitro de-epoxidation assays, employing the isolated FCP complexes, were characterized by an inefficient conversion of DD to Dt. However, in line with the heterogeneous DDE distribution, the fraction enriched in FCP-A showed a more pronounced DD de-epoxidation compared with the FCP-B.

Combined Focused Next-Generation Sequencing Assays to Guide Precision Oncology in Solid Tumors: A Retrospective Analysis from an Institutional Molecular Tumor Board

BACKGROUND

Increasing knowledge of cancer biology and an expanding spectrum of molecularly targeted therapies provide the basis for precision oncology. Despite extensive gene diagnostics, previous reports indicate that less than 10% of patients benefit from this concept.

METHODS

We retrospectively analyzed all patients referred to our center's Molecular Tumor Board (MTB) from 2018 to 2021. Molecular testing by next-generation sequencing (NGS) included a 67-gene panel for the detection of short-sequence variants and copy-number alterations, a 53- or 137-gene fusion panel and an ultra-low-coverage whole-genome sequencing for the detection of additional copy-number alterations outside the panel's target regions. Immunohistochemistry for microsatellite instability and PD-L1 expression complemented NGS.

RESULTS

A total of 109 patients were referred to the MTB. In all, 78 patients received therapeutic proposals (70 based on NGS) and 33 were treated accordingly. Evaluable patients treated with MTB-recommended therapy (n = 30) had significantly longer progression-free survival than patients treated with other therapies (n = 17) (4.3 vs. 1.9 months, p = 0.0094). Seven patients treated with off-label regimens experienced major clinical benefits.

CONCLUSION

The combined focused sequencing assays detected targetable alterations in the majority of patients. Patient benefits appeared to lie in the same range as with large-scale sequencing approaches.

Ru/C-Catalyzed Hydrogenation of Aqueous Glycolic Acid from Microalgae - Influence of pH and Biologically Relevant Additives

Ethylene glycol (EG) is obtained by a novel, two‐step approach combining a biotechnological and a heterogeneously catalyzed step. First, microalgae are cultivated to photobiocatalytically yield glycolic acid (GA) by means of photosynthesis from CO₂ and water. GA is continuously excreted into the surrounding medium. In the second step, the GA‐containing algal medium is used as feedstock for catalytic reduction with H₂ to EG over a Ru/C catalyst. The present study focuses on the conversion of an authentic algae‐derived GA solution. After identification of the key characteristics of the algal medium (compared to pure aqueous GA), the influence of pH, numerous salt additives, pH buffers and other relevant organic molecules on the catalytic GA reduction was investigated. Nitrogen‐ and sulfur‐containing organic molecules can strongly inhibit the reaction. Moreover, pH adjustment by acidification is required, for which H₂SO₄ is found most suitable. In combination with a modification of the biotechnological process to mitigate the use of inhibitory compounds, and after acidifying the algal medium, over Ru/C a EG yield of up to 21 % even at non‐optimized reaction conditions was achieved.

Crossing and selection of Chlamydomonas reinhardtii strains for biotechnological glycolate production

Abstract

As an alternative to chemical building blocks derived from algal biomass, the excretion of glycolate has been proposed. This process has been observed in green algae such as Chlamydomonas reinhardtii as a product of the photorespiratory pathway. Photorespiration generally occurs at low CO₂ and high O₂ concentrations, through the key enzyme RubisCO initiating the pathway via oxygenation of 1.5-ribulose-bisphosphate. In wild-type strains, photorespiration is usually suppressed in favour of carboxylation due to the cellular carbon concentrating mechanisms (CCMs) controlling the internal CO₂ concentration. Additionally, newly produced glycolate is directly metabolized in the C2 cycle. Therefore, both the CCMs and the C2 cycle are the key elements which limit the glycolate production in wild-type cells. Using conventional crossing techniques, we have developed Chlamydomonas reinhardtii double mutants deficient in these two key pathways to direct carbon flux to glycolate excretion. Under aeration with ambient air, the double mutant D6 showed a significant and stable glycolate production when compared to the non-producing wild type. Interestingly, this mutant can act as a carbon sink by fixing atmospheric CO₂ into glycolate without requiring any additional CO₂ supply. Thus, the double-mutant strain D6 can be used as a photocatalyst to produce chemical building blocks and as a future platform for algal-based biotechnology.

Key Points

• Chlamydomonas reinhardtii cia5 gyd double mutants were developed by sexual crossing

• The double mutation eliminates the need for an inhibitor in glycolate production

• The strain D6 produces significant amounts of glycolate with ambient air only

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-11933-y.

Detection and differentiation of active and inactive isoforms of coagulation factors II, VII, IX, and X in prothrombin complex concentrate by mass spectrometry

PURPOSE

Prothrombin complex concentrates (PCCs) are plasma products containing a mixture of four inactive/proactive coagulation factors. The activated forms of human coagulation factors, like Thrombin (FIIa), Convertin (FVIIa), activated Christmas factor (FIXa) and the activated Stuart-Prower factor (FXa), are impurities in PCCs. Until now no valid assay exists to differentiate the non activated proform (inactive) from active coagulation factor isoforms in PCCs in one measurement. Therefore, the aim of this study was to establish a mass spectrometry (LC-MS/MS)-based assay to address this issue in the ready to use medicinal product.

METHODS

Bottom-up proteomics combining double digestion (Glu-C & Lys-C) and LC-MS/MS, was used to differentiate the inactive and active forms of the coagulation factors Prothrombin (FII), Proconvertin (FVII), Christmas factor (FIX) and the Stuart-Prower-factor (FX) in PCCs.

RESULTS AND CONCLUSIONS

A targeted pseudo-multiple reaction monitoring (pMRM-LC-MS/MS)-assay was developed for the specific detection of four different coagulation factors in PCCs. Proteotypic peptides for the inactive/active isoforms (zymogen) of the four coagulation factors were identified and validated by the investigation of six investigational and one commercially available PCCs. In conclusion, the semi-quantitative determination and the distinction between the active and the inactive isoform of the respective coagulation factors were possible in one liquid chromatography tandem mass spectrometry (LC-MS/MS) run.

Influence of the compatible solute sucrose on thylakoid membrane organization and violaxanthin de-epoxidation

The compatible solute sucrose reduces the efficiency of the enzymatic de-epoxidation of violaxanthin, probably by a direct effect on the protein parts of violaxanthin de-epoxidase which protrude from the lipid phase of the thylakoid membrane. The present study investigates the influence of the compatible solute sucrose on the violaxanthin cycle of higher plants in intact thylakoids and in in vitro enzyme assays with the isolated enzyme violaxanthin de-epoxidase at temperatures of 30 and 10 °C, respectively. In addition, the influence of sucrose on the lipid organization of thylakoid membranes and the MGDG phase in the in vitro assays is determined. The results show that sucrose leads to a pronounced inhibition of violaxanthin de-epoxidation both in intact thylakoid membranes and the enzyme assays. In general, the inhibition is similar at 30 and 10 °C. With respect to the lipid organization only minor changes can be seen in thylakoid membranes at 30 °C in the presence of sucrose. However, sucrose seems to stabilize the thylakoid membranes at lower temperatures and at 10 °C a comparable membrane organization to that at 30 °C can be observed, whereas control thylakoids show a significantly different membrane organization at the lower temperature. The MGDG phase in the in vitro assays is not substantially affected by the presence of sucrose or by changes of the temperature. We conclude that the presence of sucrose and the increased viscosity of the reaction buffers stabilize the protein part of the enzyme violaxanthin de-epoxidase, thereby decreasing the dynamic interactions between the catalytic site and the substrate violaxanthin. This indicates that sucrose interacts with those parts of the enzyme which are accessible at the membrane surface of the lipid phase of the thylakoid membrane or the MGDG phase of the in vitro enzyme assays.

Phosphine-Stabilized Germasilenylidene: Source for a Silicon-Atom Transfer

A phosphine-stabilized germasilenylidene is synthesized following the pathway of SiCl₄ oxidative addition at a germylene-phosphine Lewis pair. Low-temperature reduction using {(^MesNacnac)Mg}₂ resulted in a chlorosilylene intermediate and finally a molecule exhibiting a Ge═Si: motif. Inside the chelating phosphine-germylene, a low-valent silicon atom is stabilized and was transferred to diazabutadiene to give N-heterocyclic silylenes. Because of the high reactivity of the phosphine-stabilized germasilenylidene, a reaction of two Ge═Si: units was found to yield a Si₂Ge₂-ring molecule exhibiting a germasilene substituted with a silylene.

Effect of Hypoxia on Proliferation and the Expression of the Genes HIF-1α and JMJD1A in Head and Neck Squamous Cell Carcinoma Cell Lines

BACKGROUND/AIM

The aim of the study was to investigate the effects of hypoxia on proliferation and the expression of HIF-1α (hypoxia-inducible factor 1 alpha) and JMJD1A (jumonji domain 1A) in head and neck squamous cell carcinoma (HNSCC).

MATERIALS AND METHODS

FaDu and HLaC78 cells were incubated for 1-24 h in hypoxia and normoxia. Cell proliferation, mRNA and protein levels of HIF-1α and JMJD1A were quantified by counting, PCR and western blot.

RESULTS

Hypoxia led to a constant decrease in cell proliferation. Short hypoxia resulted in an increase in HIF-1α mRNA levels. This effect was reversed after longer incubation. The western blot for HIF-1α showed a maximum accumulation after 3-6 h of hypoxia. In FaDu cells, the concentration of JMJD1A reached a peak after 6 h and decreased thereafter, whereas in HLaC78 cells, it presented a second peak after 48 h.

CONCLUSION

The transcription factors HIF-1α and JMJDA1 were confirmed as relevant hypoxia-dependent regulators of carcinogenesis in HNSCC.

Effects of iron limitation on carbon balance and photophysiology of the Antarctic diatom Chaetoceros cf. simplex

In the Southern Ocean (SO), iron (Fe) limitation strongly inhibits phytoplankton growth and generally decreases their primary productivity. Diatoms are a key component in the carbon (C) cycle, by taking up large amounts of anthropogenic CO2 through the biological carbon pump. In this study, we investigated the effects of Fe availability (no Fe and 4 nM FeCl3 addition) on the physiology of Chaetoceros cf. simplex, an ecologically relevant SO diatom. Our results are the first combining oxygen evolution and uptake rates with particulate organic carbon (POC) build up, pigments, photophysiological parameters and intracellular trace metal (TM) quotas in an Fe-deficient Antarctic diatom. Decreases in both oxygen evolution (through photosynthesis, P) and uptake (respiration, R) coincided with a lowered growth rate of Fe-deficient cells. In addition, cells displayed reduced electron transport rates (ETR) and chlorophyll a (Chla) content, resulting in reduced cellular POC formation. Interestingly, no differences were observed in non-photochemical quenching (NPQ) or in the ratio of gross photosynthesis to respiration (GP:R). Furthermore, TM quotas were measured, which represent an important and rarely quantified parameter in previous studies. Cellular quotas of manganese, zinc, cobalt and copper remained unchanged while Fe quotas of Fe-deficient cells were reduced by 60% compared with High Fe cells. Based on our data, Fe-deficient Chaetoceros cf. simplex cells were able to efficiently acclimate to low Fe conditions, reducing their intracellular Fe concentrations, the number of functional reaction centers of photosystem II (RCII) and photosynthetic rates, thus avoiding light absorption rather than dissipating the energy through NPQ. Our results demonstrate how Chaetoceros cf. simplex can adapt their physiology to lowered assimilatory metabolism by decreasing respiratory losses.

The Aureochrome Photoreceptor PtAUREO1a Is a Highly Effective Blue Light Switch in Diatoms

Aureochromes represent a unique type of blue light photoreceptors that possess a blue light sensing flavin-binding LOV-domain and a DNA-binding bZIP domain, thus being light-driven transcription factors. The diatom Phaeodactylum tricornutum, a member of the essential marine primary producers, possesses four aureochromes (PtAUREO1a, 1b, 1c, 2). Here we show a dramatic change in the global gene expression pattern of P. tricornutum wild-type cells after a shift from red to blue light. About 75% of the genes show significantly changed transcript levels already after 10 and 60 min of blue light exposure, which includes genes of major transcription factors as well as other photoreceptors. Very surprisingly, this light-induced regulation of gene expression is almost completely inhibited in independent PtAureo1a knockout lines. Such a massive and fast transcriptional change depending on one single photoreceptor is so far unprecedented. We conclude that PtAUREO1a plays a key role in diatoms upon blue light exposure.

•

Blue light induces a very fast transcriptional response in the diatom P. tricornutum

•

This strong response is almost completely inhibited when Aureochrome 1a is absent

•

The results imply a key role of PtAureo1a in blue light-induced responses in diatoms

Pre-purification of diatom pigment protein complexes provides insight into the heterogeneity of FCP complexes

BACKGROUND

Although our knowledge about diatom photosynthesis has made huge progress over the last years, many aspects about their photosynthetic apparatus are still enigmatic. According to published data, the spatial organization as well as the biochemical composition of diatom thylakoid membranes is significantly different from that of higher plants.

RESULTS

In this study the pigment protein complexes of the diatom Thalassiosira pseudonana were isolated by anion exchange chromatography. A step gradient was used for the elution process, yielding five well-separated pigment protein fractions which were characterized in detail. The isolation of photosystem (PS) core complex fractions, which contained fucoxanthin chlorophyll proteins (FCPs), enabled the differentiation between different FCP complexes: FCP complexes which were more closely associated with the PSI and PSII core complexes and FCP complexes which built-up the peripheral antenna. Analysis by mass spectrometry showed that the FCP complexes associated with the PSI and PSII core complexes contained various Lhcf proteins, including Lhcf1, Lhcf2, Lhcf4, Lhcf5, Lhcf6, Lhcf8 and Lhcf9 proteins, while the peripheral FCP complexes were exclusively composed of Lhcf8 and Lhcf9. Lhcr proteins, namely Lhcr1, Lhcr3 and Lhcr14, were identified in fractions containing subunits of the PSI core complex. Lhcx1, Lhcx2 and Lhcx5 proteins co-eluted with PSII protein subunits. The first fraction contained an additional Lhcx protein, Lhcx6_1, and was furthermore characterized by high concentrations of photoprotective xanthophyll cycle pigments.

CONCLUSION

The results of the present study corroborate existing data, like the observation of a PSI-specific antenna complex in diatoms composed of Lhcr proteins. They complement other data, like e.g. on the protein composition of the 21 kDa FCP band or the Lhcf composition of FCPa and FCPb complexes. They also provide interesting new information, like the presence of the enzyme diadinoxanthin de-epoxidase in the Lhcx-containing PSII fraction, which might be relevant for the process of non-photochemical quenching. Finally, the high negative charge of the main FCP fraction may play a role in the organization and structure of the native diatom thylakoid membrane. Thus, the results present an important contribution to our understanding of the complex nature of the diatom antenna system.

Interaction of head and neck squamous cell carcinoma cells and mesenchymal stem cells under hypoxia and normoxia

Mesenchymal stem cells (MSCs) exhibit strong tropism towards tumor tissue. While MSCs generally surround tumors, they can also infiltrate tumors and thereby influence their proliferation. Interactions between MSCs and tumor cells are usually tested under normoxia, but the majority of solid tumors, including head and neck squamous cell carcinoma (HNSCC), are also characterized by hypoxic areas. Hence, the present study aimed to assess the interaction between MSCs and tumor cells under hypoxic conditions. MSCs were cultivated under normoxia and hypoxia, and conditioned media were used to cultivate the HNSCC cell line FaDu. The cell cycle distribution and viability of MSCs and the proliferation of FaDu cells were analyzed under normoxia and hypoxia, and changes in cytokine levels in the conditioned media were evaluated. No cell cycle changes were observed for MSCs after 24 h of cultivation under hypoxia, but the cell viability had declined. Hypoxia also led to a decrease in the proliferation of FaDu cells; however, FaDu cells proliferated faster after 48 h under hypoxia compared with normoxic conditions. This effect was reversed after incubation under normoxia for 72 h and hypoxia for 72 h. While these changes constituted a trend, these differences were not statistically significant. A cytokine assay showed an increase in interleukin (IL)-6 in the hypoxic medium. Overall, the results indicated that there was an interaction between MSCs and tumor cells. The presence or absence of oxygen seemed to influence the functionality of MSCs and their protumorigenic properties, in which IL-6 was identified as a potential mediator. Since MSCs are a component of the tumor stroma, further in vitro and in vivo studies are needed to investigate this interaction in order to develop novel approaches for tumor therapy.

Tipifarnib in recurrent, metastatic HRAS-mutant salivary gland cancer

BACKGROUND

To the authors' knowledge, there are no approved therapies for recurrent, metastatic (R/M) salivary gland carcinoma (SGC), but molecularly targeted therapies warrant ongoing investigation. In the current study, the authors have reported on the efficacy of tipifarnib in patients with aggressive HRAS-mutant, R/M SGC.

METHODS

The current prospective, nonrandomized, multicenter, international cohort study involved 8 centers and was conducted from May 2015 to June 2019. The median follow-up was 22 months (range, 6-55 months). Subjects with HRAS-mutant R/M SGC (any histology) and disease progression within the last 6 months were enrolled. Tipifarnib was dosed orally twice daily. The authors determined the objective response rate using Response Evaluation Criteria in Solid Tumors (version 1.1), duration of response, and molecular predictors of response.

RESULTS

A total of 13 patients with R/M SGC were enrolled; all had received prior systemic therapy (1-3 regimens). One objective response was observed; an additional 7 of 12 evaluable patients (58%) had stable disease as their best response with a median duration of 9 months (range, 3-14 months). Five of 7 patients had >10% tumor regression and 6 of 7 had stable disease lasting >6 months. Q61R was the most frequent activating HRAS mutation noted (7 of 13 patients; 54%), but gene variant and allele frequency did not correlate with outcomes. The median progression-free survival was 7 months (95% confidence interval, 5.9-10.1 months), and the median overall survival was 18 months (95% confidence interval, 9.6-22.4 months) with approximately 58.6% of patients alive at 1 year. Survival was similar regardless of HRAS mutant variant or co-occurring PIK3CA alterations. No participant discontinued treatment because of toxicity.

CONCLUSIONS

Tipifarnib resulted in modest clinical activity with a promising disease control rate among patients with HRAS-mutant, R/M SGC who developed disease progression within the last 6 months.

The fluid-mosaic membrane theory in the context of photosynthetic membranes: Is the thylakoid membrane more like a mixed crystal or like a fluid?

Since the publication of the fluid-mosaic membrane theory by Singer and Nicolson in 1972 generations of scientists have adopted this fascinating concept for all biological membranes. Assuming the membrane as a fluid implies that the components embedded in the lipid bilayer can freely diffuse like swimmers in a water body. During the detailed biochemical analysis of the thylakoid protein components of chloroplasts from higher plants and algae, in the '80 s and '90 s it became clear that photosynthetic membranes are not homogeneous either in the vertical or the lateral directions. The lateral heterogeneity became obvious by the differentiation of grana and stroma thylakoids, but also the margins have been identified with a highly specific protein pattern. Further refinement of the fluid mosaic model was needed to take into account the presence of non-bilayer lipids, which are the most abundant lipids in all energy-converting membranes, and the polymorphism of lipid phases, which has also been documented in thylakoid membranes. These observations lead to the question, how mobile the components are in the lipid phase and how this ordering is made and maintained and how these features might be correlated with the non-bilayer propensity of the membrane lipids. Assuming instead of free diffusion, a "controlled neighborhood" replaced the model of fluidity by the model of a "mixed crystal structure". In this review we describe why basic photosynthetic regulation mechanisms depend on arrays of crystal-like lipid-protein macro-assemblies. The mechanisms which define the ordering in macrodomains are still not completely clear, but some recent experiments give an idea how this fascinating order is produced, adopted and maintained. We use the operation of the xanthophyll cycle as a rather well understood model challenging and complementing the standard Singer-Nicolson model via assigning special roles to non-bilayer lipids and non-lamellar lipid phases in the structure and function of thylakoid membranes.

Determination of CD43 and CD200 surface expression improves accuracy of B-cell lymphoma immunophenotyping

BACKGROUND

The Matutes score (MS) was proposed to differentiate chronic lymphocytic leukemia (CLL) from other B-cell non-Hodgkin lymphomas (B-NHLs). However, ambiguous immunophenotypes are common and remain a diagnostic challenge. Therefore, we evaluated the diagnostic benefit of measuring CD200 and CD43 expression together with the standard MS antigens.

METHODS

138 lymphoma patient samples and a validation cohort of 138 additive samples were classified according to the standard MS and further assigned with one or two additional points, for high CD200 and/or CD43 expression levels. The "classical" MS and the "Matutes score-extended" (MS-e) were categorized as high (4-5/6-7), intermediate (2-3/4-5), and low (0-1/0-3). Samples were reclassified into the MS-e with focus on ambiguous cases with an intermediate "classical" MS.

RESULTS

A total of 35 of 138 (25.4%) patient samples were assigned to the intermediate MS group and confirmed by histopathological reports as CLL (14/40.0%) and B-NHLs other than CLL (21/60%). MS-e analysis identified 13 of 14 (92.9%) of CLL cases (MS-e 4-5) and 18/21 (85.7%) non-CLL cases (MS-e ≤ 3) correctly. Overall, the sensitivity of the CLL diagnosis was significantly increased by application of MS-e compared to the "classical" MS (98.8% vs. 82.7%; p = 0.0009), while specificity of both methods was almost equal (94.7% vs. 98.3%; p = 0.4795). Of note, sole measurement of CD43 and CD200 on B-cells sufficiently differentiated CLL from non-CLL with a test accuracy superior to the "classical" MS (F1 score 96.2 vs. 93.6).

CONCLUSION

CD200 and CD43 have a high informative value in diagnostic immunophenotyping and facilitate the separation of CLL from other B-NHLs particularly in ambiguous cases.

Effects of temperature and salinity on respiratory losses and the ratio of photosynthesis to respiration in representative Antarctic phytoplankton species

The Southern Ocean (SO) is a net sink for atmospheric CO₂ whereby the photosynthetic activity of phytoplankton and sequestration of organic carbon (biological pump) plays an important role. Global climate change will tremendously influence the dynamics of environmental conditions for the phytoplankton community, and the phytoplankton will have to acclimate to a combination of changes of e.g. water temperature, salinity, pH, and nutrient supply. The efficiency of the biological pump is not only determined by the photosynthetic activity but also by the extent of respiratory carbon losses of phytoplankton cells. Thus, the present study investigated the effect of different temperature and salinity combinations on the ratio of gross photosynthesis to respiration (rGP/R) in two representative phytoplankton species of the SO. In the comparison of phytoplankton grown at 1 and 4°C the rGP/R decreased from 11.5 to 7.7 in Chaetoceros sp., from 9.1 to 3.2 in Phaeocystis antarctica strain 109, and from 12.4 to 7.0 in P. antarctica strain 764, respectively. The decrease of rGP/R was primarily dependent on temperature whereas salinity was only of minor importance. Moreover, the different rGP/R at 1 and 4°C were caused by changes of temperature-dependent respiration rates but were independent of changes of photosynthetic rates. For further interpretation, net primary production (NPP) was calculated for different seasonal conditions in the SO with specific combinations of irradiance, temperature, and salinity. Whereas, maximum photosynthetic rates significantly correlated with calculated NPP under experimental ‘Spring’, ‘Summer’, and ‘Autumn’ conditions, there was no correlation between rGP/R and the respective values of NPP. The study revealed species-specific differences in the acclimation to temperature and salinity changes that could be linked to their different original habitats.

Development and In-House Validation of an LC–MS and LC–MS/MS Assay for the Determination of Food Fraud for Different Fish Species

Background: Fish and fish products are one of the most important food sources of high commercial interest. The global food trade and the associated risks are constantly presenting new challenges to consumer protection and public authorities, which, among other things, demand state-of-the-art analytical methods to ensure food authenticity. Objective: The establishment of MS-based strategies plays a decisive role alongside the (further) development of ELISA- or DNA-oriented methods. Methods: In the present work, therefore, the development and in-house validation of an LC–MS and LC–MS/MS-based assay for authenticity testing of certain fish species is described. Results: Based on the execution of a validated bottom-up LC–electrospray–MS and MS/MS assay and multivariate analysis, the commercially available species Lutjanus malabaricus (red snapper) and Sebastes spp. (redfish) are distinguished from each other, whereas an additional 68 samples [nine additional marine species such as pangasius (Pangasianodon hypophthalmus), salmon (Salmo salar), turbot (Scophthalmus maximus), plaice (Pleuronectes platessa), sole (Solea solea), lemon sole (Glyptocephalus cynoglossus), halibut (Reinhardtius hypoglossoides), red salmon (Oncorhynchus nerka), and great scallop (Pecten jacobaeus)] served as blinded negative controls to ensure the specificity of the assay. Conclusions and Highlights: A promising LC–MS and LC–MSMS based assay has been developed that could enable the detection of fish fraud at the protein level in the future.

Development and In-House Validation of an LC-MS and LC-MS/MS Assay for the Determination of Food Fraud for Different Fish Species

Background: Fish and fish products are one of the most important food sources of high commercial interest. The global food trade and the associated risks are constantly presenting new challenges to consumer protection and public authorities, which, among other things, demand state-of-the-art analytical methods to ensure food authenticity. Objective: The establishment of MS-based strategies plays a decisive role alongside the (further) development of ELISA- or DNA-oriented methods. Methods: In the present work, therefore, the development and in-house validation of an LC-MS and LC-MS/MS-based assay for authenticity testing of certain fish species is described. Results: Based on the execution of a validated bottom-up LC-electrospray-MS and MS/MS assay and multivariate analysis, the commercially available species Lutjanus malabaricus (red snapper) and Sebastes spp. (redfish) are distinguished from each other, whereas an additional 68 samples [nine additional marine species such as pangasius (Pangasianodon hypophthalmus), salmon (Salmo salar), turbot (Scophthalmus maximus), plaice (Pleuronectes platessa), sole (Solea solea), lemon sole (Glyptocephalus cynoglossus), halibut (Reinhardtius hypoglossoides), red salmon (Oncorhynchus nerka), and great scallop (Pecten jacobaeus)] served as blinded negative controls to ensure the specificity of the assay. Conclusions and Highlights: A promising LC-MS and LC-MSMS based assay has been developed that could enable the detection of fish fraud at the protein level in the future.

Glycolate from microalgae: an efficient carbon source for biotechnological applications

Glycolate is produced in autotrophic cells under high temperatures and C_i -limitation via oxygenation of ribulose-1,5-bisphosphate. In unicellular algae, glycolate is lost via excretion or metabolized via the C₂ cycle by consuming reductants, ATP and CO₂ emission (photorespiration). Therefore, photorespiration is an inhibitory process for biomass production. However, cells can be manipulated in a way that they become glycolate-producing 'cell factories', when the ratio carboxylation/oxygenation is 2. If under these conditions the C₂ cycle is blocked, glycolate excretion becomes the only pathway of photosynthetic carbon flow. The study aims to proof the biotechnological applicability of algal-based glycolate excretion as a new biotechnological platform. It is shown that cells of Chlamydomonas can be cultivated under specific conditions to establish a constant and long-term stable glycolate excretion during the light phase. The cultures achieved a high efficiency of 82% of assimilated carbon transferred into glycolate biosynthesis without losses of function in cell vitality. Moreover, the glycolate accumulation in the medium is high enough to be directly used for microbial fermentation but does not show toxic effects to the glycolate-producing cells.

Carbon dots, a powerful non-toxic support for bioimaging by fluorescence nanoscopy and eradication of bacteria by photothermia

Carbon Dots (CDs) are innovative materials which have potential applications in many fields, including nanomedicine, energy and catalysis. Here CDs were produced by the alkali-assisted ultrasonic route and characterized by several techniques to determine their composition and properties. Fluorescence nanoscopy using single-molecule localization microscopy shows that they have very good photophysical properties and a remarkable blinking behaviour at 405 nm. Moreover, these CDs are a safe material, non-toxic towards different cell lines (cancer and non-cancer cells) even at very high concentration, reflecting an excellent biocompatibility. Photothermia, i.e. their heating capacity under laser irradiation, was evaluated at two wavelengths and at several power densities. The resulting temperature increment was high (5 < ΔT < 45 °C) and appropriate for biomedical applications. Bioimaging and photothermia were then performed on E. coli, a Gram(-) bacterium, incubated with CDs. Remarkably, by photothermia at 680 nm (0.3, 1 and 1.9 W cm^-2) or 808 nm (1.9 W cm^-2), CDs are able to eradicate bacteria in their exponential and stationary phases. Images obtained by 3D super-resolution microscopy clearly show the different CD distributions in surviving bacteria after mild photothermal treatment. These results confirm that CDs are multifunctional materials with a wide range of biomedical applications.

Low number of intrafollicular T cells may predict favourable response to rituximab-based immuno-chemotherapy in advanced follicular lymphoma: a secondary analysis of a randomized clinical trial

Background

First-line rituximab therapy together with chemotherapy is the standard care for patients with advanced follicular B-cell lymphoma, as rituximab together with chemotherapy prolongs progression-free and overall survival (Herold et al. 2007; Marcus et al. 2005). However, as not all patient subgroups benefit from combined immuno-chemotherapy, we asked whether the microenvironment may predict benefit from rituximab-based therapy.

Design

To address this question, we performed a retrospective immunohistochemical analysis on pathological specimens of 18 patients recruited into a randomized clinical trial, where patients with advanced follicular lymphoma were randomized into either chemotherapy or immuno-chemotherapy with rituximab (Herold et al. 2007).

Results

We show here that rituximab exerts beneficial effects, especially in the subgroup of follicular lymphoma patients with low intrafollicular CD3, CD5, CD8, and ZAP70 and high CD56 and CD68 expression.

Conclusion

Rituximab may overcome immune-dormancy in follicular lymphoma in cases with lower intrafollicular T-cell numbers and higher CD56 and CD68 cell counts. As this was a retrospective analysis on a small subgroup of patients, these data need to be corroborated in larger clinical trials.

Electronic supplementary material

The online version of this article (10.1007/s00432-019-02961-9) contains supplementary material, which is available to authorized users.

Photocalorespirometry (Photo-CR): A Novel Method for Access to Photosynthetic Energy Conversion Efficiency

One key parameter for assessing the CO₂ fixation in aquatic ecosystems but also for the productivity of photobioreactors is the energy conversion efficiency (PE) by the photosynthetic apparatus. PE strictly depends on a range of different fluctuating environmental conditions and is therefore highly variable. PE is the result of complex metabolic control. At the moment PE can only be determined indirectly. Furthermore, the currently available techniques either capture only short time processes, thus reflecting only parts of the photosynthetic engine, or quantify the total process but only with limited time resolution. To close this gap, we suggest for the first time the direct measurement of the fixed energy combined with respirometry, called photocalorespirometry (Photo-CR). The proof of the principle of Photo-CR was established with the microalga Chlamydomonas reinhardtii. The simultaneous measurement of oxygen production and energy fixation provides an calorespirometric ratio of -(437.9 ± 0.7) kJ mol^-1 under low light conditions. The elevated calorespirometric ratio under high light conditions provides an indication of photo-protective mechanisms. The Photo-CR delivers the PE in real time, depending on the light intensity. Energetic differences less than 0.14% at radiation densities of up to 800 μE m^-2 s^-1 can be quantified. Other photosynthetic growth parameters (e.g. the specific growth rate of 0.071 h^-1, the cell specific energy conservation of 30.9 ± 1.3 pW cell^-1 at 150 µE m^-2 s^-1 and the number of photons (86.8) required to fix one molecule of CO₂) can easily be derived from the Photo-CR data.

Monitoring cellular C:N ratio in phytoplankton by means of FTIR-spectroscopy

Statistical growth rate modelling can be applied in a variety of ecological and biotechnological applications. Such models are frequently based on Monod or Droop equations and, especially for the latter, require reliable determination of model input parameters such as C:N quotas. Besides growth rate modelling, a C:N quota quantification can be useful for monitoring and interpretation of physiological acclimation to abiotic and biotic disturbances (e.g., nutrient limitations). However, as high throughput C:N quota determination is difficult to perform, alternatives need to be established. Fourier-transformed infrared (FTIR) spectroscopy is used to analyze a variety of biochemical, chemical, and physiological parameters in phytoplankton. Hence, a quantification of the C:N quota should also be feasible. Therefore, using FTIR spectroscopy, six phytoplankton species from among different phylogenetic groups have been analyzed to determine the effect of nutrient limitation on C:N quota patterns. The typical species-specific response to increasing nitrogen limitation was an increase in the C:N quota. Irrespective of this species specificity, we were able to develop a reliable multi-species C:N quota prediction model based on FTIR spectroscopy using the partial least square regression (PLSR) algorithm. Our data demonstrate that the PLSR approach is more robust in C:N quota quantification (R²  = 0.93) than linear correlation of C:N quota versus growth rate (R² ranges from 0.74 to 0.86) or biochemical information based on FTIR spectra (R² ranges from 0.82 to 0.89). This accurate prediction of C:N values may support high throughput measurements in a broad range of future approaches.

15N photo-CIDNP MAS NMR on both photosystems and magnetic field-dependent 13C photo-CIDNP MAS NMR in photosystem II of the diatom Phaeodactylum tricornutum

Diatoms contribute about 20-25% to the global marine productivity and are successful autotrophic players in all aquatic ecosystems, which raises the question whether this performance is caused by differences in their photosynthetic apparatus. Photo-CIDNP MAS NMR presents a unique tool to obtain insights into the reaction centres of photosystems (PS), by selective enhancement of NMR signals from both, the electron donor and the primary electron acceptor molecules. Here, we present the first observation of the solid-state photo-CIDNP effect in the pennate diatoms. In comparison to plant PSs, similar spectral patterns have been observed for PS I at 9.4 T and PS II at 4.7 T in the PSs of Phaeodactylum tricornutum. Studies at different magnetic fields reveal a surprising sign change of the ¹³C photo-CIDNP MAS NMR signals indicating an alternative arrangement of cofactors which allows to quench the Chl a donor triplet state in contrast to the situation in plant PS II. This unusual quenching mechanism is related to a carotenoid molecule in close vicinity to the Chl a donor. In addition to the photo-CIDNP MAS NMR signals arising from the donor and the primary electron acceptor cofactors, a complete set of signals of the imidazole ring ligating to the magnesium of Chl a can be observed.

Quantitative macromolecular patterns in phytoplankton communities resolved at the taxonomical level by single-cell Synchrotron FTIR-spectroscopy

BACKGROUND

Technical limitations regarding bulk analysis of phytoplankton biomass limit our comprehension of carbon fluxes in natural populations and, therefore, of carbon, nutrients and energy cycling in aquatic ecosystems. In this study, we took advantage of Synchrotron FTIR micro-spectroscopy and the partial least square regression (PLSr) algorithm to simultaneously quantify the protein, lipid and carbohydrate content at the single-cell level in a mock phytoplankton community (composed by a cyanobacterium, a green-alga and a diatom) grown at two temperatures (15 °C and 25 °C).

RESULTS

The PLSr models generated to quantify cell macromolecules presented high quality fit (R² ≥ 0.90) and low error of prediction (RMSEP 2-6% of dry weight). The regression coefficients revealed that the prediction of each macromolecule was not exclusively dependent on spectral features corresponding to that compound, but rather on all major macromolecular pools, reflecting adjustments in the overall cell carbon balance. The single-cell analysis, studied by means of Kernel density estimators, showed that the modes of density distribution of macromolecules were different at 15 °C and 25 °C. However, a substantial proportion of cells was biochemically identical at the two temperatures because of population heterogeneity.

CONCLUSIONS

The spectroscopic approach presented in this study allows the quantification of macromolecules in single phytoplankton cells. This method showed that population heterogeneity most likely ensures a backup of non-acclimated cells that may rapidly exploit new favourable niches. This finding may have important consequences for the ecology of phytoplankton populations and shows that the "average cell" concept might substantially limit our comprehension of population dynamics and biogeochemical cycles in aquatic ecosystems.

Outcome of non-mold effective anti-fungal prophylaxis in patients at high-risk for invasive fungal infections after allogenic stem cell transplantation

Patients who develop severe graft-versus-host disease (GvHD) after allogeneic stem cell transplantation (alloSCT) have a higher risk for invasive fungal infection (IFI). At our center, fluconazole prophylaxis is standard and upfront mold-effective prophylaxis performed only in patients with specific risk constellations. A total of 290 patients undergoing alloSCT between May 2002 and August 2011 were analyzed. Patients were regarded as high-risk if they suffered from acute GvHD II-IV° or extensive chronic GvHD. The 2-year incidence of an IFI after alloSCT was 8.97% (26/290) in the entire cohort and 7.78% (7/90) in the high-risk group. Mortality due to IFI was 3.85% (1/26) without including a high-risk patient. In the multivariate analysis a pre-transplant fungal infection was the only significant risk factor for developing an IFI after alloSCT (HR = 5.298; p = .001). A fluconazole prophylaxis in patients with GvHD after alloSCT is feasible in facilities with HEPA filtration and high awareness of clinical signs for IFI.

Electron balancing under different sink conditions reveals positive effects on photon efficiency and metabolic activity of Synechocystis sp. PCC 6803

BACKGROUND

Cyanobacteria are ideal model organisms to exploit photosynthetically derived electrons or fixed carbon for the biotechnological synthesis of high value compounds and energy carriers. Much effort is spent on the rational design of heterologous pathways to produce value-added chemicals. Much less focus is drawn on the basic physiological responses and potentials of phototrophs to deal with natural or artificial electron and carbon sinks. However, an understanding of how electron sinks influence or regulate cellular physiology is essential for the efficient application of phototrophic organisms in an industrial setting, i.e., to achieve high productivities and product yields.

RESULTS

The physiological responses of the cyanobacterium Synechocystis sp. PCC 6803 to electron sink variation were investigated in a systematic and quantitative manner. A variation in electron demand was achieved by providing two N sources with different degrees of reduction. By additionally varying light and CO₂ availabilities, steady state conditions with strongly differing source-sink ratios were established. Balancing absorbed photons and electrons used for different metabolic processes revealed physiological responses to sink/source ratio variation. Surprisingly, an additional electron sink under light and thus energy limitation was found not to hamper growth, but was compensated by improved photosynthetic efficiency and activity. In the absence of carbon and light limitation, an increase in electron demand even stimulated carbon assimilation and growth.

CONCLUSION

The metabolism of Synechocystis sp. PCC 6803 is highly flexible regarding the compensation of additional electron demands. Under light limitation, photosynthesis obviously does not necessarily run at its maximal capacity, possibly for the sake of robustness. Increased electron demands can even boost photosynthetic activity and growth.

Contrast-Enhanced Ultrasound in Pulmonary Lymphoma: A Small Pilot Study

Here, we describe the appearance and pattern of pulmonary lymphoma on B-mode imaging and with contrast-enhanced ultrasound (CEUS). From July 2009 to December 2015, 6 patients with histologically or cytologically confirmed lymphoma of the lung were examined by B-mode imaging, followed by CEUS. A retrospective analysis of the imaging data was performed with respect to the time to enhancement, pulmonary artery (PA) and bronchial artery, echogenicity (hypoechoic, isoechoic, or hyperechoic), and homogeneity (homogeneous or inhomogeneous) of the contrast enhancement. On B-mode imaging, all 6 pulmonary lymphoma lesions were hypoechoic. Five cases had PA enhancement, and 1 case had bronchial artery enhancement on CEUS imaging. Strikingly, all 6 patients had isoechoic arterial contrast enhancement. In the parenchymal phase, 3 of the lymphoma lesions showed hypoechoic contrast enhancement, and 3 showed isoechoic enhancement. Pulmonary lymphomas are hypoechoic on B-mode imaging. With CEUS, all patients had predominant PA contrast enhancement in the arterial phase with variable parenchymal contrast enhancement. Thus, definite differentiation from other malignant or benign pulmonary lesions cannot be achieved by CEUS.

The artificial humic substance HS1500 does not inhibit photosynthesis of the green alga Desmodesmus armatus in vivo but interacts with the photosynthetic apparatus of isolated spinach thylakoids in vitro

Humic substances (HSs) can influence the growth and composition of freshwater phytoplankton assemblage. Since HSs contain many phenolic and quinonic moieties and cause growth reductions in eco-physiological field experiments, HSs are considered photosystem II herbicides. To test this specific mode of action in vivo and in vitro, respectively, we used intact cells of the green alga Desmodesmus armatus, as well as thylakoids isolated from spinach (Spinacia oleracea) as a model system for the green algal chloroplast. Photosynthetic electron transport was measured as oxygen evolution and variable chlorophyll fluorescence. The in vivo effect of the artificial humic substance HS1500 on algae consisted of no impact on photosynthesis-irradiance curves of intact green algae compared to untreated controls. In contrast, addition of HS1500 to isolated thylakoids resulted in light-induced oxygen consumption (Mehler reaction) as an in vitro effect. Fluorescence induction kinetics of HS-treated thylakoids revealed a large static quenching effect of HS1500, but no inhibitory effect on electron transport. For the case of intact algal cells, we conclude that the highly hydrophilic and rather large molecules of HS1500 are not taken up in effective quantities and, therefore, cannot interfere with photosynthesis. The in vitro tests show that HS1500 has no inhibitory effect on photosystem II but operates as a weak, oxygen-consuming Hill acceptor at photosystem I. Hence, the results indicate that eco-physiological field experiments should focus more strongly on effects of HSs on extracellular features, such as reducing and red-shifting the underwater light field or influencing nutrient availability by cation exchange within the plankton network.

Cell Wall Structure of Coccoid Green Algae as an Important Trade-Off Between Biotic Interference Mechanisms and Multidimensional Cell Growth

Coccoid green algae can be divided in two groups based on their cell wall structure. One group has a highly chemical resistant cell wall (HR-cell wall) containing algaenan. The other group is more susceptible to chemicals (LR-cell wall – Low resistant cell wall). Algaenan is considered as important molecule to explain cell wall resistance. Interestingly, cell wall types (LR- and HR-cell wall) are not in accordance with the taxonomic classes Chlorophyceae and Trebouxiophyceae, which makes it even more interesting to consider the ecological function. It was already shown that algaenan helps to protect against virus, bacterial and fungal attack, but in this study we show for the first time that green algae with different cell wall properties show different sensitivity against interference competition with the cyanobacterium Microcystis aeruginosa. Based on previous work with co-cultures of M. aeruginosa and two green algae (Acutodesmus obliquus and Oocystis marssonii) differing in their cell wall structure, it was shown that M. aeruginosa could impair only the growth of the green algae if they belong to the LR-cell wall type. In this study it was shown that the sensitivity to biotic interference mechanism shows a more general pattern within coccoid green algae species depending on cell wall structure.

Towards an understanding of the molecular regulation of carbon allocation in diatoms: the interaction of energy and carbon allocation

In microalgae, the photosynthesis-driven CO₂ assimilation delivers cell building blocks that are used in different biosynthetic pathways. Little is known about how the cell regulates the subsequent carbon allocation to, for example, cell growth or for storage. However, knowledge about these regulatory mechanisms is of high biotechnological and ecological importance. In diatoms, the situation becomes even more complex because, as a consequence of their secondary endosymbiotic origin, the compartmentation of the pathways for the primary metabolic routes is different from green algae. Therefore, the mechanisms to manipulate the carbon allocation pattern cannot be adopted from the green lineage. This review describes the general pathways of cellular energy distribution from light absorption towards the final allocation of carbon into macromolecules and summarizes the current knowledge of diatom-specific allocation patterns. We further describe the (limited) knowledge of regulatory mechanisms of carbon partitioning between lipids, carbohydrates and proteins in diatoms. We present solutions to overcome the problems that hinder the identification of regulatory elements of carbon metabolism.This article is part of the themed issue 'The peculiar carbon metabolism in diatoms'.

Phytoplankton growth rate modelling: can spectroscopic cell chemotyping be superior to physiological predictors?

Climate change has a strong impact on phytoplankton communities and water quality. However, the development of robust techniques to assess phytoplankton growth is still in progress. In this study, the growth rate of phytoplankton cells grown at different temperatures was modelled based on conventional physiological traits (e.g. chlorophyll, carbon and photosynthetic parameters) using the partial least square regression (PLSR) algorithm and compared with a new approach combining Fourier transform infrared-spectroscopy and PLSR. In this second model, it is assumed that the macromolecular composition of phytoplankton cells represents an intracellular marker for growth. The models have comparable high predictive power (R² > 0.8) and low error in predicting new observations. Interestingly, not all of the predictors present the same weight in the modelling of growth rate. A set of specific parameters, such as non-photochemical fluorescence quenching (NPQ) and the quantum yield of carbon production in the first model, and lipid, protein and carbohydrate contents for the second one, strongly covary with cell growth rate regardless of the taxonomic position of the phytoplankton species investigated. This reflects a set of specific physiological adjustments covarying with growth rate, conserved among taxonomically distant algal species that might be used as guidelines for the improvement of modern primary production models. The high predictive power of both sets of cellular traits for growth rate is of great importance for applied phycological studies. Our approach may find application as a quality control tool for the monitoring of phytoplankton populations in natural communities or in photobioreactors.

An optimized protocol for the preparation of oxygen-evolving thylakoid membranes from Cyclotella meneghiniana provides a tool for the investigation of diatom plastidic electron transport

BACKGROUND

The preparation of functional thylakoid membranes from diatoms with a silica cell wall is still a largely unsolved challenge. Therefore, an optimized protocol for the isolation of oxygen evolving thylakoid membranes of the centric diatom Cyclotella meneghiniana has been developed. The buffer used for the disruption of the cells was supplemented with polyethylene glycol based on its stabilizing effect on plastidic membranes. Disruption of the silica cell walls was performed in a French Pressure cell and subsequent linear sorbitol density gradient centrifugation was used to isolate the thylakoid membrane fraction.

RESULTS

Spectroscopic characterization of the thylakoids by absorption and 77 K fluorescence spectroscopy showed that the photosynthetic pigment protein complexes in the isolated thylakoid membranes were intact. This was supported by oxygen evolution measurements which demonstrated high electron transport rates in the presence of the artificial electron acceptor DCQB. High photosynthetic activity of photosystem II was corroborated by the results of fast fluorescence induction measurements. In addition to PSII and linear electron transport, indications for a chlororespiratory electron transport were observed in the isolated thylakoid membranes. Photosynthetic electron transport also resulted in the establishment of a proton gradient as evidenced by the quenching of 9-amino-acridine fluorescence. Because of their ability to build-up a light-driven proton gradient, de-epoxidation of diadinoxanthin to diatoxanthin and diatoxanthin-dependent non-photochemical quenching of chlorophyll fluorescence could be observed for the first time in isolated thylakoid membranes of diatoms. However, the ∆pH, diadinoxanthin de-epoxidation and diatoxanthin-dependent NPQ were weak compared to intact diatom cells or isolated thylakoids of higher plants.

CONCLUSIONS

The present protocol resulted in thylakoids with a high electron transport capacity. These thylakoids can thus be used for experiments addressing various aspects of the photosynthetic electron transport by, e.g., employing artificial electron donors and acceptors which do not penetrate the diatom cell wall. In addition, the present isolation protocol yields diatom thylakoids with the potential for xanthophyll cycle and non-photochemical quenching measurements. However, the preparation has to be further refined before these important topics can be addressed systematically.

Functional proteomics of light-harvesting complex proteins under varying light-conditions in diatoms

Comparative proteome analysis of subcellular compartments like thylakoid membranes and their associated supercomplexes can deliver important in-vivo information on the molecular basis of physiological functions which go far beyond to that what can be learnt from transcriptional-based gene expression studies. For instance, the finding that light intensity influences mainly the relative stoichiometry of subunits could be obtained only by high resolution proteome analysis. The high sensitivity of LC-ESI-MS/MS based proteome analysis allows the determination of proteins in very small subfractions along with their non-labeled semi quantitative analysis. This provides insights in the protein-protein interactions of supercomplexes that are the operative units in intact cells. Here, we have focused on functional proteome approaches for the identification of microalgal light-harvesting complex proteins in chloroplasts and the eyespot in general and in detail for those of diatoms that are exposed to varying light conditions.

An update on aureochromes: Phylogeny - mechanism - function

Light is important for algae, as it warrants metabolic independence via photosynthesis. In addition to the absorption of light by the photosystems, algae possess a variety of specific photoreceptors that allow the quantification of the light fluxes as well as the assessment of light qualities. About a decade ago, aureochromes have been described in the xanthophyte alga Vaucheria frigida. These proteins represent a new type of blue light photoreceptor as they possess both a light-oxygen-voltage (LOV) domain for light reception as well as a basic region leucine zipper (bZIP) domain for DNA binding, indicating that they represent light-driven transcription factors. Aureochromes so far have been detected only in a single group of algae, photosynthetic stramenopiles, but not in any other prokaryotic or eukaryotic organisms. Recent biophysical work on aureochromes in the absence and the presence of DNA revealed the mechanism of allosteric communication between the sensor and effector domains despite their unusual inversed arrangement. Different molecular models have been proposed to describe the effect of light on DNA binding. Functional characterization of mutants of the diatom Phaeodactylum tricornutum, in which the aureochrome genes have been silenced or deleted, indicate that different aureochromes may have different functions, being involved in central processes like light acclimation and regulation of the cell cycle.

PtAUREO1a and PtAUREO1b knockout mutants of the diatom Phaeodactylum tricornutum are blocked in photoacclimation to blue light

Aureochromes are blue light receptors specifically found in photosynthetic Stramenopiles (algae). Four different Aureochromes have been identified in the marine diatom Phaeodactylum tricornutum (PtAUREO 1a, 1b, 1c, and 2). Since blue light is necessary for high light acclimation in diatoms, it has been hypothesized that Aureochromes might play an important role in the light acclimation capacity of diatoms. This hypothesis was supported by an RNAi knockdown line of PtAUREO1a, which showed a phenotype different from wild type cells when grown in either blue or red light. Here, we show for the first time the phenotype and the photoacclimation reaction of TALEN-mediated knockout mutants of PtAUREO1a and PtAUREO1b, clearly proving the necessity of Aureochromes for light acclimation under blue light. However, both mutants do also show specific differences in their respective phenotypes. Hence, PtAUREO1a and 1b are not functionally redundant in photoacclimation to blue light, and their specific contribution needs to be clarified further.

A Fateful Meeting of Two Phytoplankton Species-Chemical vs. Cell-Cell-Interactions in Co-Cultures of the Green Algae Oocystis marsonii and the Cyanobacterium Microcystis aeruginosa

Massive growth of single species of cyanobacteria is a common phenomenon in many eutrophicated waters worldwide. Allelopathic growth control of phytoplankton species is one suggested mechanism, but still controversially discussed. The fact that the synthesis of biological active compounds requires high energy costs and carbon investment for a single cell in contrast to high dilution rates in natural systems questions the universal validity of allelopathic mechanisms, even more as high concentrations of allelopathic substances are often needed in several experiments to cause biological effects. In this study, it was tested, if growth inhibition is induced by chemical signaling alone or via direct cell-cell interaction. As a test system, we used a co-culture of the green algae Oocystis marsonii (Trebouxiophyceae) with the cyanobacterium Microcystis aeruginosa which is known to strongly reduce the growth of the green algal competitor. In this study, direct co-culturing as well as membrane-separated growth chambers were used to test for chemical and contact-mediated interactions. In the membrane-separated chambers, both species can be co-cultivated and a membrane allows the exchange of metabolites. Growth of O. marsonii was only affected in the direct co-cultivation situation, where direct cell-to-cell contact was possible. During direct co-cultivation, deviating cellular traits, namely cell cycle pattern and large cell-aggregate formation of both species, could be detected. These data strongly support the hypothesis of a direct cell-cell-contact necessary for allelopathic growth control in this model system. Such direct contact would allow targeting allelopathic metabolites directly towards the competitor and thereby minimizing dilution effects.

Influence of thylakoid membrane lipids on the structure of aggregated light-harvesting complexes of the diatom Thalassiosira pseudonana and the green alga Mantoniella squamata

The study investigated the effect of the thylakoid membrane lipids monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulphoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG) on the structure of two algal light-harvesting complexes (LHCs). In contrast to higher plants whose thylakoid membranes are characterized by an enrichment of the neutral galactolipids MGDG and DGDG, both the green alga Mantoniella squamata and the centric diatom Thalassiosira pseudonana contain membranes with a high content of the negatively charged lipids SQDG and PG. The algal thylakoids do not show the typical grana-stroma differentiation of higher plants but a regular arrangement. To analyze the effect of the membrane lipids, the fucoxanthin chlorophyll protein (FCP) complex of T. pseudonana and the LHC of M. squamata (MLHC) were prepared by successive cation precipitation using Triton X-100 as detergent. With this method, it is possible to isolate LHCs with a reduced amount of associated lipids in an aggregated state. The results from 77 K fluorescence and photon correlation spectroscopy show that neither the neutral galactolipids nor the negatively charged lipids are able to significantly alter the aggregation state of the FCP or the MLHC. This is in contrast to higher plants where SQDG and PG lead to a strong disaggregation of the LHCII whereas MGDG and DGDG induce the formation of large macroaggregates. The results indicate that LHCs which are integrated into thylakoid membranes with a high amount of negatively charged lipids and a regular arrangement are less sensitive to lipid-induced structural alterations than their counterparts in membranes enriched in neutral lipids with a grana-stroma differentiation.