There is a particularly high interest to derive carotenoids such as β-carotene and lutein from higher plants and algae for the global market. It is well known that β-carotene can be overproduced in the green microalga Dunaliella salina in response to stressful light conditions. However, little is known about the effects of light quality on carotenoid metabolism, e.g., narrow spectrum red light. In this study, we present UPLC-UV-MS data from D. salina consistent with the pathway proposed for carotenoid metabolism in the green microalga Chlamydomonas reinhardtii. We have studied the effect of red light-emitting diode (LED) lighting on growth rate and biomass yield and identified the optimal photon flux for D. salina growth. We found that the major carotenoids changed in parallel to the chlorophyll b content and that red light photon stress alone at high level was not capable of upregulating carotenoid accumulation presumably due to serious photodamage. We have found that combining red LED (75 %) with blue LED (25 %) allowed growth at a higher total photon flux. Additional blue light instead of red light led to increased β-carotene and lutein accumulation, and the application of long-term iterative stress (adaptive laboratory evolution) yielded strains of D. salina with increased accumulation of carotenoids under combined blue and red light.Electronic supplementary materialThe online version of this article (doi:10.1007/s00253-012-4502-5) contains supplementary material, which is available to authorized users.

Bacteria are a major source of natural products that provide rich opportunities for both chemical and biological investigation. Although the vast majority of known bacterial metabolites derive from free-living organisms, increasing evidence supports the widespread existence of chemically prolific bacteria living in symbioses. A strategy based on bioinformatic prediction, symbiont cultivation, isotopic enrichment, and advanced analytics was used to characterize a unique polyketide, nosperin, from a lichen-associated Nostoc sp. cyanobacterium. The biosynthetic gene cluster and the structure of nosperin, determined from 30 μg of compound, are related to those of the pederin group previously known only from nonphotosynthetic bacteria associated with beetles and marine sponges. The presence of this natural product family in such highly dissimilar associations suggests that some bacterial metabolites may be specific to symbioses with eukaryotes and encourages exploration of other symbioses for drug discovery and better understanding of ecological interactions mediated by complex bacterial metabolites.biosynthesis | Peltigera membranacea | trans-acyltransferase polyketide synthase | 13 C nuclear magnetic resonance

Background Lichens, encompassing 20,000 known species, are symbioses between specialized fungi (mycobionts), mostly ascomycetes, and unicellular green algae or cyanobacteria (photobionts). Here we describe the first parallel genomic analysis of the mycobiont Cladonia grayi and of its green algal photobiont Asterochloris glomerata . We focus on genes/predicted proteins of potential symbiotic significance, sought by surveying proteins differentially activated during early stages of mycobiont and photobiont interaction in coculture, expanded or contracted protein families, and proteins with differential rates of evolution. Results A) In coculture, the fungus upregulated small secreted proteins, membrane transport proteins, signal transduction components, extracellular hydrolases and, notably, a ribitol transporter and an ammonium transporter, and the alga activated DNA metabolism, signal transduction, and expression of flagellar components. B) Expanded fungal protein families include heterokaryon incompatibility proteins, polyketide synthases, and a unique set of G-protein α subunit paralogs. Expanded algal protein families include carbohydrate active enzymes and a specific subclass of cytoplasmic carbonic anhydrases. The alga also appears to have acquired by horizontal gene transfer from prokaryotes novel archaeal ATPases and Desiccation-Related Proteins. Expanded in both symbionts are signal transduction components, ankyrin domain proteins and transcription factors involved in chromatin remodeling and stress responses. The fungal transportome is contracted, as are algal nitrate assimilation genes. C) In the mycobiont, slow-evolving proteins were enriched for components involved in protein translation, translocation and sorting. Conclusions The surveyed genes affect stress resistance, signaling, genome reprogramming, nutritional and structural interactions. The alga carries many genes likely transferred horizontally through viruses, yet we found no evidence of inter-symbiont gene transfer. The presence in the photobiont of meiosis-specific genes supports the notion that sexual reproduction occurs in Asterochloris while they are free-living, a phenomenon with implications for the adaptability of lichens and the persistent autonomy of the symbionts. The diversity of the genes affecting the symbiosis suggests that lichens evolved by accretion of many scattered regulatory and structural changes rather than through introduction of a few key innovations. This predicts that paths to lichenization were variable in different phyla, which is consistent with the emerging consensus that ascolichens could have had a few independent origins. Electronic supplementary material The online version of this article (10.1186/s12864-019-5629-x) contains supplementary material, which is available to authorized users.

esson. 2020. Faster nitrogen cycling and more fungal and root biomass in cold ecosystems under experimental warming: a meta-analysis. Ecology 101(2):Abstract. Warming can alter the biogeochemistry and ecology of soils. These alterations can be particularly large in high northern latitude ecosystems, which are experiencing the most intense warming globally. In this meta-analysis, we investigated global trends in how experimental warming is altering the biogeochemistry of the most common limiting nutrient for biological processes in cold ecosystems of high northern latitudes (>50°): nitrogen (N). For comparison, we also analyzed cold ecosystems at intermediate and high southern latitudes. In addition, we examined N-relevant genes and enzymes, and the abundance of belowground organisms. Together, our findings suggest that warming in cold ecosystems increases N mineralization rates and N 2 O emissions and does not affect N fixation, at least not in a consistent way across biomes and conditions. Changes in belowground N fluxes caused by warming lead to an accumulation of N in the forms of dissolved organic and root N. These changes seem to be more closely linked to increases in enzyme activity that target relatively labile N sources, than to changes in the abundance of N-relevant genes (e.g., amoA and nosZ). Finally, our analysis suggests that warming in cold ecosystems leads to an increase in plant roots, fungi, and (likely in an indirect way) fungivores, and does not affect the abundance of archaea, bacteria, or bacterivores. In summary, our findings highlight global trends in the ways warming is altering the biogeochemistry and ecology of soils in cold ecosystems, and provide information that can be valuable for prediction of changes and for management of such ecosystems.

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In past decades, environmental nitrogen fixation has been attributed almost exclusively to the action of enzymes in the wellstudied molybdenum-dependent nitrogen fixation system. However, recent evidence has shown that nitrogen fixation by alternative pathways may be more frequent than previously suspected. In this study, the nitrogen fixation systems employed by lichen-symbiotic cyanobacteria were examined to determine whether their diazotrophy can be attributed, in part, to an alternative pathway. The mining of metagenomic data (generated through pyrosequencing) and PCR assays were used to determine which nitrogen-fixation systems are present in cyanobacteria from the genus Nostoc associated with four samples from different geographical regions, representing different lichen-forming fungal species in the genus Peltigera. A metatranscriptomic sequence library from an additional specimen was examined to determine which genes associated with N 2 fixation are transcriptionally expressed. Results indicated that both the standard molybdenum-dependent system and an alternative vanadium-dependent system are present and actively transcribed in the lichen symbiosis. This study shows for the first time that an alternative system is utilized by cyanobacteria associated with fungi. The ability of lichen-associated cyanobacteria to switch between pathways could allow them to colonize a wider array of environments, including habitats characterized by low temperature and trace metal (e.g. molybdenum) availability. We discuss the implications of these findings for environmental studies that incorporate acetylenereduction assay data.

Polyketides are a group of natural products that have gained much interest due to their use as antibiotics, cholesterol lowering agents, immunosuppressors, and as other drugs. Many organisms that naturally produce polyketides are difficult to cultivate and only produce these metabolites in small amounts. It is therefore of general interest to transfer polyketide synthase (PKS) genes from their natural sources into heterologous hosts that can over-produce the corresponding polyketides. In this study we demonstrate the heterologous expression of 6-methylsalicylic acid synthase (6-MSAS), naturally produced by Penicillium patulum, in the yeast Saccharomyces cerevisiae. In order to activate the PKS a 4'-phosphopantetheinyl transferase (PPTase) is required. We therefore co-expressed PPTases encoded by either sfp from Bacillus subtilis or by npgA from Aspergillus nidulans. The different strains were grown in batch cultures. Growth and product concentration were measured and kinetic parameters were calculated. It was shown that both PPTases could be efficiently used for activation of PKS's in yeast as good yields of 6-MSA were obtained with both enzymes.

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