Modification of xylan in secondary walls alters cell wall biosynthesis and wood formation programs and improves saccharification.

Wood of broad-leaf tree species is a valued source of renewable biomass for biorefinery and a target for genetic improvement efforts to reduce its recalcitrance. Glucuronoxylan (GX) plays a key role in recalcitrance through its interactions with cellulose and lignin. To reduce recalcitrance, we modified wood GX by expressing GH10 and GH11 endoxylanases from Aspergillus nidulans in hybrid aspen (Populus tremula L. × tremuloides Michx.) and targeting the enzymes to cell wall. The xylanases reduced tree height, modified cambial activity by increasing phloem and reducing xylem production, and reduced secondary wall deposition. Xylan molecular weight was decreased, and the spacing between acetyl and MeGlcA side chains was reduced in transgenic lines. The transgenic trees produced hypolignified xylem having thin secondary walls and deformed vessels. Glucose yields of enzymatic saccharification without pretreatment almost doubled indicating decreased recalcitrance. The transcriptomics, hormonomics and metabolomics data provided evidence for activation of cytokinin and ethylene signalling pathways, decrease in ABA levels, transcriptional suppression of lignification and a subset of secondary wall biosynthetic program, including xylan glucuronidation and acetylation machinery. Several candidate genes for perception of impairment in xylan integrity were detected. These candidates could provide a new target for uncoupling negative growth effects from reduced recalcitrance. In conclusion, our study supports the hypothesis that xylan modification generates intrinsic signals and evokes novel pathways regulating tree growth and secondary wall biosynthesis.

Xylan glucuronic acid side chains fix suberin-like aliphatic compounds to wood cell walls.

Wood is the most important repository of assimilated carbon in the biosphere, in the form of large polymers (cellulose, hemicelluloses including glucuronoxylan, and lignin) that interactively form a composite, together with soluble extractives including phenolic and aliphatic compounds. Molecular interactions among these compounds are not fully understood. We have targeted the expression of a fungal α-glucuronidase to the wood cell wall of aspen (Populus tremula L. × tremuloides Michx.) and Arabidopsis (Arabidopsis thaliana (L.) Heynh), to decrease contents of the 4-O-methyl glucuronopyranose acid (mGlcA) substituent of xylan, to elucidate mGlcA's functions. The enzyme affected the content of aliphatic insoluble cell wall components having composition similar to suberin, which required mGlcA for binding to cell walls. Such suberin-like compounds have been previously identified in decayed wood, but here, we show their presence in healthy wood of both hardwood and softwood species. By contrast, γ-ester bonds between mGlcA and lignin were insensitive to cell wall-localized α-glucuronidase, supporting the intracellular formation of these bonds. These findings challenge the current view of the wood cell wall composition and reveal a novel function of mGlcA substituent of xylan in fastening of suberin-like compounds to cell wall. They also suggest an intracellular initiation of lignin-carbohydrate complex assembly.

Performance analysis of Pseudomonas sp. strain SA3 in naphthalene degradation using phytotoxicity and microcosm studies.

The present study is aimed to develop a microbial system for efficient naphthalene bioremediation. A phytotoxicity study was carried out to check the naphthalene detoxification efficiency of Pseudomonas sp. strain SA3 in mung bean (Vigna radiata). For this, administration of the degraded product (supernatant) of 500 mg L-1 naphthalene by Pseudomonas sp. strain SA3 was studied on V. radiata till 168 h. The growth parameters of mung bean seedlings exposed to treated naphthalene solution were statistically similar to distilled water but a twofold decrease when exposed to untreated naphthalene solution. Further, through the soil microcosm study, the naphthalene degradation by pure colonies of Pseudomonas sp. strain SA3 was 6.8% higher as compared to when the natural microflora was mixed with Pseudomonas sp. strain SA3. Further naphthalene degradation by a microcosm model revealed that with an increased concentration of glucose, the carbon dioxide trap rate decreases.

Fluorescence Quenching Property of C-Phycocyanin from Spirulina platensis and its Binding Efficacy with Viable Cell Components.

Phycocyanin is a natural brilliant blue colored, fluorescent protein, which is commonly present in cyanobacteria. In this study, C-phycocyanin was extracted and purified from Spirulina platensis, which are multicellular and filamentous cyanobacteria of greater importance because of its various biological and pharmacological potential. It was analyzed for its binding affinity towards blood cells, algal cells, genomic DNA of microalgae, and bacteria at different temperature and incubation time. It showed good binding affinity with these components even at low concentration of 2.5 µM. The purpose of this study was to evaluate the applicability of C-phycocyanin as a green fluorescent dye substituting carcinogenic chemical dyes.

Multiproduct biorefinery from Arthrospira spp. towards zero waste: Current status and future trends.

Considering the high- and low-value product perspectives, Arthrospira spp. are one of the most industrially exploited microalgae. However, currently, the biomass is being utilized for one specific product resulting in a steep upsurge in the overall production cost. Hence, to boost the economic viability of Arthrospira biorefinery process, every high- and low-value products from it ought to be valorized. Envisioning how costlier can be the multiproduct biorefinery concept owing to the downstream processing at an industrial scale, it is quite essential to look for new trends and encouraging solutions. This article intended to propose a sustainable biorefinery in the wake of the current understanding of the present constraints and challenges associated with Arthrospira biorefinery. The current review aimed at defining the future aspects of this biorefinery including integration and optimization of the culture strategy, and, implementation of new ingenious techniques to improve downstream processing (harvesting, extraction, fractionation, and purification).

Abiotic stresses as tools for metabolites in microalgae.

Microalgae, due to various environmental stresses, constantly tune their cellular mechanisms to cope with them. The accumulation of the stress metabolites is closely related to the changes occurring in their metabolic pathways. The biosynthesis of metabolites can be triggered by a number of abiotic stresses like temperature, salinity, UV- radiation and nutrient deprivation. Although, microalgae have been considered as an alternative sustainable source for nutraceutical products like pigments and omega-3 polyunsaturated fatty acids (PUFAs) to cater the requirement of emerging human population but inadequate biomass generation makes the process economically impractical. The stress metabolism for carotenoid regulation in green algae is a 2-step metabolism. There are a few major stresses which can influence the formation of phycobiliprotein in cyanobacteria. This review would primarily focus on the cellular level changes under stress conditions and their corresponding effects on lipids (including omega-3 PUFAs), pigments and polymers.

Cultivation of Nannochloropsis oceanica biomass rich in eicosapentaenoic acid utilizing wastewater as nutrient resource.

The eicosapentaenoic acid rich marine eustigmatophyte Nannochloropsis oceanica was grown in wastewaters sampled from four different industries (i.e. pesticides industry, pharmaceutical industry, activated sludge treatment plant of municipality sewage and petroleum (oil) industry). Under the wastewater based growth conditions used in this study, the biomass productivity ranged from 21.78±0.87 to 27.78±0.22mgL(-1)d(-1) in relation to freeze dried biomass, while the lipid productivity varied between 5.59±0.02 and 6.81±0.04mgL(-1)d(-1). Although comparatively higher biomass, lipid and EPA productivity was observed in Conway medium, the %EPA content was similarly observed in pesticides industry and municipal effluents. The results highlight the possibility of selectively using wastewater as a growth medium, demonstrating the elevated eicosapentaenoic acid content and biodiesel properties, that complies with the European standards for biodiesel.

Applications of de-oiled microalgal biomass towards development of sustainable biorefinery.

In view of commercialization of microalgal biofuel, the de-oiled microalgal biomass (DMB) is a surplus by-product in the biorefinery process that needs to be exploited to make the process economically attractive and feasible. This DMB, rich in carbohydrates, proteins, and minerals, can be used as feed, fertilizer, and substrate for the production of bioethanol/bio-methane. Further, thermo-chemical conversion of DMB results into fuels and industrially important chemicals. Future prospects of DMB also lie with its conversion into novel biomaterials like nanoparticles and carbon-dot which have biomedical importance. The lowest valued application of DMB is to use it for adsorption of dyes and heavy metals from industrial effluents. This study reviews how DMB can be utilized for different applications and in the generation of valuable co-products. The value addition of DMB would thereby improve the overall cost economics of the microalgal bio-refinery.

Integrated process of two stage cultivation of Nannochloropsis sp. for nutraceutically valuable eicosapentaenoic acid along with biodiesel.

The marine eustigmatophyte Nannochloropsis is one of the potential producers of eicosapentaenoic acid (EPA), a valued nutraceutical. Nannochloropsis sp. was cultivated under photoautotrophic condition utilizing CO2 in a two phase cultivation process in order to enhance the eicosapentaenoic acid (EPA) productivity. It was cultivated in a photobioreactor up to late log phase for cell growth (phase I). Then, the culture was harvested and confronted to relatively low temperature (10 °C) and low light (30 µmol photons m(-2) s(-1)) in both photobioreactor and Erlenmeyer flask (phase II), thus augmenting EPA% by 3.4 fold. Lower temperature with low light favored the synthesis of EPA although, biomass productivity, lipid content and lipid productivity were slightly decreased relative to phase I. The total lipids extracted from Nannochloropsis sp. fractionated into neutral lipids (NLs), glycolipids (GLs) and phospholipids (PLs) and a major proportion of EPA was found in phospholipids. Results suggested that low temperature and low light may ameliorate partitioning towards EPA in phospholipids.

Potential of Monoraphidium minutum for carbon sequestration and lipid production in response to varying growth mode.

Mixotrophic growth at flask level and, autotrophic-mixotrophic and autotrophic growth in photobioreactor by utilizing CO2/air/flue gas were checked for the isolated strain of Monoraphidium minutum from polluted habitat. Our study confirmed that it is a saturated fatty acid rich (30.92-68.94%) microalga with lower degree of unsaturation oil quality (42.06-103.99) making it potential biodiesel producing candidate. It showed encouraging biomass productivity (80.3-303.8mgl(-1)day(-1)) with higher total lipid (22.80-46.54%) under optimum glucose, fructose, microalgal biodiesel waste residue and sodium acetate fed mixotrophic conditions. The pH control by intermittent CO2, continuous illumination with 30% flue gas, and utilization of biodiesel glycerin were effective schemes to ameliorate either biomass productivity or % lipids or both of these parameters at photobioreactor scale (7.5L working volume). The modulation of environmental variables (pH control, CO2 and organic substrates concentration) could augment % saturated fatty acids, such as C16:0.