Algal biotechnology

Asparagopsis Genus: What We Really Know About Its Biological Activities and Chemical Composition

Although the genus Asparagopsis includes only two taxonomically accepted species, the published literature is unanimous about the invasive nature of this genus in different regions of the globe, and about the availability of large amounts of biomass for which it is important to find a commercial application. This review shows that extracts from Asparagospsis species have already been evaluated for antioxidant, antibacterial, antifungal, antiviral, antifouling, cytotoxic, antimethanogenic and enzyme-inhibitory activity. However, the tables presented herein show, with few exceptions, that the activity level displayed is generally low when compared with positive controls. Studies involving pure compounds being identified in Asparagopsis species are rare. The chemical compositions of most of the evaluated extracts are unknown. At best, the families of the compounds present are suggested. This review also shows that the volatile halogenated compounds, fatty acids and sterols that are biosynthesized by the Asparagopsis species are relatively well known. Many other non-volatile metabolites (halogen compounds, flavonoids, other phenolic compounds) seem to be produced by these species, but their chemical structures and properties haven’been investigated. This shows how much remains to be investigated regarding the secondary-metabolite composition of these species, suggesting further studies following more targeted methodologies.

Enhancement of Lipid Productivity and Self-flocculation by Cocultivating Monoraphidium sp. FXY-10 and Heveochlorella sp. Yu Under Mixotrophic Mode

To maintain high microalgae lipid productivity and flocculation efficiency simultaneously and reduce the production cost of microalgae lipids, Monoraphidium sp. FXY-10 with high lipid-producing capacity and Heveochlorella sp. Yu with strong self-flocculation ability were cocultivated and studied. Cocultivated microalgae lipid productivity and flocculation efficiency were increased to 203.8 mg L^-1 day^-1 and 70.55%, respectively, which is potentially related to the excessive competitive depletion of nitrogen sources and the upregulation of correlative key genes in lipid anabolic metabolism. Under cocultivation conditions, microalgae cells could enter the stationary phase 2 days earlier than that under monocultivation conditions, thus reducing the culture time. Relative expression of the accD, ME, and rbcL genes was upregulated to varying degrees, and the enzyme activities of ACCase, ME, and RuBisCO were also significantly increased compared with those in monocultivation. Moreover, fatty acid composition showed that microalgae lipids in cocultivation exhibited potential as a feedstock for biodiesel.

Identification and Characterization of a 25 kDa Protein That Is Indispensable for the Efficient Saccharification of Eisenia bicyclis in the Digestive Fluid of Aplysia kurodai

The digestive fluid of the sea hare Aplysia kurodai can liberate approximately 2.5 mg of glucose from 10 mg of dried Eisenia bicyclis powder. Although laminaran, a major storage polysaccharide in E. bicyclis, is easily digested to glucose by the synergistic action of the 110 and 210 kDa A. kurodai β-glucosidases (BGLs), glucose is not liberated from E. bicyclis by direct incubation with these BGLs. To clarify this discrepancy, we searched for an Eisenia hydrolysis enhancing protein (EHEP) in the digestive fluid of A. kurodai. A novel 25 kDa protein that enhances E. bicyclis saccharification by β-glucosidases was purified to a homogeneous state from the digestive fluid of A. kurodai, and its cDNA was cloned from total cDNAs reverse-transcribed from hepatopancreas total RNA. The E. bicyclis extract strongly inhibited BGLs, suggesting some compound within this brown alga functioned as a feeding deterrent. However, when E. bicyclis was incubated with BGLs in the presence of EHEP, glucose production was markedly increased. As E. bicyclis is rich in phlorotannin, which are only found in brown algae, our study suggested that these compounds are the main BGL inhibitors in E. bicyclis extract. EHEP protects BGLs from phlorotannin inhibition by binding to phlorotannins and forming an insoluble complex with phloroglucinol and phlorotannins. These findings indicated that EHEP plays a key role in the saccharification of brown seaweeds containing phlorotannins in the digestive fluid of A. kurodai. This is the first report of EHEP as a phlorotannin-binding protein that protects BGLs from inhibition.

Microbial communities mediating algal detritus turnover under anaerobic conditions

BACKGROUND

Algae encompass a wide array of photosynthetic organisms that are ubiquitously distributed in aquatic and terrestrial habitats. Algal species often bloom in aquatic ecosystems, providing a significant autochthonous carbon input to the deeper anoxic layers in stratified water bodies. In addition, various algal species have been touted as promising candidates for anaerobic biogas production from biomass. Surprisingly, in spite of its ecological and economic relevance, the microbial community involved in algal detritus turnover under anaerobic conditions remains largely unexplored.

RESULTS

Here, we characterized the microbial communities mediating the degradation of Chlorella vulgaris (Chlorophyta), Chara sp. strain IWP1 (Charophyceae), and kelp Ascophyllum nodosum (phylum Phaeophyceae), using sediments from an anaerobic spring (Zodlteone spring, OK; ZDT), sludge from a secondary digester in a local wastewater treatment plant (Stillwater, OK; WWT), and deeper anoxic layers from a seasonally stratified lake (Grand Lake O' the Cherokees, OK; GL) as inoculum sources. Within all enrichments, the majority of algal biomass was metabolized within 13-16 weeks, and the process was accompanied by an increase in cell numbers and a decrease in community diversity. Community surveys based on the V4 region of the 16S rRNA gene identified different lineages belonging to the phyla Bacteroidetes, Proteobacteria (alpha, delta, gamma, and epsilon classes), Spirochaetes, and Firmicutes that were selectively abundant under various substrate and inoculum conditions. Within all kelp enrichments, the microbial communities structures at the conclusion of the experiment were highly similar regardless of the enrichment source, and were dominated by the genus Clostridium, or family Veillonellaceae within the Firmicutes. In all other enrichments the final microbial community was dependent on the inoculum source, rather than the type of algae utilized as substrate. Lineages enriched included the uncultured groups VadinBC27 and WCHB1-69 within the Bacteroidetes, genus Spirochaeta and the uncultured group SHA-4 within Spirochaetes, Ruminococcaceae, Lachnospiraceae, Yongiibacter, Geosporobacter, and Acidaminobacter within the Firmicutes, and genera Kluyvera, Pantoea, Edwardsiella and Aeromonas, and Buttiauxella within the Gamma-Proteobaceteria order Enterobacteriales.

CONCLUSIONS

Our results represent the first systematic survey of microbial communities mediating turnover of algal biomass under anaerobic conditions, and highlights the diversity of lineages putatively involved in the degradation process.

Seasonal variation in Laminaria digitata and its impact on biochemical conversion routes to biofuels

Laminaria digitata is a highly prevalent kelp growing off the coast of the UK but has rarely been considered as a source of biomass to date. This study shows it can be used as a feedstock in both ethanol fermentation and anaerobic digestion for methane production. The study optimised several parameters in the fermentation of L. digitata and investigated the suitability of the macroalgae through the year using samples harvested every month. For both methane and ethanol production, minimum yields were seen in material harvested in March when the carbohydrates laminarin and mannitol were lowest. July material contained the highest combined laminarin and mannitol content and maximum yields of 167 mL ethanol and 0.219 m(3) kg(-1)L. digitata.

Modelling of growth and product formation of Porphyridium purpureum

In this contribution experimental data and simulations of growth and product formation of the unicellular microalgae Porphyridium purpureum are presented. A mathematical model has been developed for a better understanding of growth and product formation in production plants. The model has been refined with the results of several cultivations in a new photobioreactor designed especially for the study of microalgal kinetics under highly defined illumination conditions. In this photobioreactor light is generated by an external light source and then distributed by means of optical fibres into an internal draft tube which also serves as irradiation element. All cultivations were performed in turbidostate mode. The influence of different light intensity changes, including stepwise change and light-dark cycles in the range from millisecond to second, has been investigated and the results were integrated into the mathematical model. The structured mathematical model consists of three levels: metabolic flux, control of macromolecules and the reactor level. A new linear optimization approach has been realized, enabling the model to describe even very different cultivation conditions. Output variables are among others the commercially interesting macromolecules of the microalgae, e.g. polysaccharides, pigments and polyunsaturated fatty acids. Thus, reliable predictions of the specific production rates of these products are possible for the production in a larger scale.

A flow-lane incubator for studying freshwater and marine phototrophic biofilms

Phototrophic biofilms are defined as interfacial microbial communities mainly driven by light as energy source and are studied for both ecological and technological reasons. Field investigations of biofilms usually do not offer the opportunity to study the effects of a large number of external parameters. In order to investigate the temporal development of phototrophic communities a laboratory flow-lane incubator for cultivation of freshwater and marine biofilms was developed. The incubator has four lanes which accommodate microscope slides used as substratum and for sampling. The slides can be of different material and may be employed for characterisation of phototrophic biofilms by means of gravimetry, microscopy, taxonomy, molecular biology and chemical analysis. The design allows control of irradiance, temperature and flow velocity. Furthermore, on-line control of biomass accumulation via specially adapted light sensors was proved to be a suitable indicator of temporal developmental stages (initial adhesion, active growth and mature stage). Spatial heterogeneity of the cultivated phototrophic biofilms along the flow direction within each flow-lane was low. Biofilm growth characteristics (e. g. lag time, net accrual rate, peak biomass) recorded in dependency from external conditions may be used as input data for training of artificial neural networks (ANN) and mechanistic modelling. The material and devices used in combination with low maintenance costs and ease of handling suggests the flow-lane incubator as a useful tool for studying the influence of abiotic and biotic factors on the development of freshwater and marine phototrophic biofilms.

Recovery of microalgal biomass and metabolites: process options and economics

Commercial production of intracellular microalgal metabolites requires the following: (1) large-scale monoseptic production of the appropriate microalgal biomass; (2) recovery of the biomass from a relatively dilute broth; (3) extraction of the metabolite from the biomass; and (4) purification of the crude extract. This review examines the options available for recovery of the biomass and the intracellular metabolites from the biomass. Economics of monoseptic production of microalgae in photobioreactors and the downstream recovery of metabolites are discussed using eicosapentaenoic acid (EPA) recovery as a representative case study.