Dissolved air flotation and centrifugation as methods for oil recovery from ruptured microalgal cells

Solvent-free microalgal lipid recovery is highly desirable for safer, more sustainable and more economical microalgal oil production. Dispersed air flotation and centrifugation were evaluated for the ability to separate oil and debris from a slurry mixture of osmotically fractured Chaetoceros muelleri cells with and without utilizing collectors. Microalgal oil partially phase-separated as a top layer and partially formed an oil-in-water emulsion. Although collectors, such as sodium dodecyl sulphate enhanced selective flotation, by just adjusting the pH and cell concentration of the mixture, up to 78% of the lipids were recovered in the froth. Using centrifugation of fractured microalgal slurry resulted in removal of 60% cell debris and up to 68.5% of microalgal oil was present in the supernatant. Both methods, centrifugation and flotation provided options for separation of microalgal oil from C. muelleri slurry with similar fatty acid recoveries of 57% and 60%, respectively

Development of an environmental functional gene microarray for soil microbial communities

Functional attributes of microbial communities are difficult to study, and most current techniques rely on DNA- and rRNA-based profiling of taxa and genes, including microarrays containing sequences of known microorganisms. To quantify gene expression in environmental samples in a culture-independent manner, we constructed an environmental functional gene microarray (E-FGA) consisting of 13,056 mRNA-enriched anonymous microbial clones from diverse microbial communities to profile microbial gene transcripts. A new normalization method using internal spot standards was devised to overcome spotting and hybridization bias, enabling direct comparisons of microarrays. To evaluate potential applications of this metatranscriptomic approach for studying microbes in environmental samples, we tested the E-FGA by profiling the microbial activity of agricultural soils with a low or high flux of N2O. A total of 109 genes displayed expression that differed significantly between soils with low and high N2O emissions. We conclude that mRNA-based approaches such as the one presented here may complement existing techniques for assessing functional attributes of microbial communities. Copyright © 2010, American Society for Microbiology

Phylogenetic and molecular analysis of the ribulose-1,5-bisphosphate carboxylase small subunit gene family in banana

Despite being the number one fruit crop in the world, very little is known about the phylogeny and molecular biology of banana (Musa spp.). Six banana rbcS gene families encoding the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase from six different Musa spp. are presented. For a comprehensive phylogenetic study using Musa rbcS genes, a total of 57 distinct rbcS sequences was isolated from six accessions that contained different combinations of the A and B ancestral/parental genomes. As a result, five of the six members of the rbcS gene family could be affiliated with the A and/or B Musa genomes and at least three of the six gene families most likely existed before Musa A and B genomes separated. By combining sequence data with quantitative real-time PCR it was determined that the different Musa rbcS gene family members are also often multiply represented in each genome, with the highest copy numbers in the B genome. Expression of some of the rbcS genes varied in intensity and in different tissues indicating differences in regulation. To analyse and compare regulatory sequences of Musa rbcS genes, promoter and terminator regions were cloned for three Musa rbcS genes. Transient transformation assays using promoter–reporter–terminator constructs in maize, wheat, and sugarcane demonstrated that the rbcS-Ma1, rbcS-Ma3, and rbcS-Ma5 promoters could be useful for transgene expression in heterologous expression systems. Furthermore, the rbcS-Ma1 terminator resulted in a 2-fold increase of transgene expression when directly compared with the widely used Nos terminator

Nitrogen affects cluster root formation and expression of putative peptide transporters

Non-mycorrhizal Hakea actites (Proteaceae) grows in heathland where organic nitrogen (ON) dominates the soil nitrogen (N) pool. Hakea actites uses ON for growth, but the role of cluster roots in ON acquisition is unknown. The aim of the present study was to ascertain how N form and concentration affect cluster root formation and expression of peptide transporters. Hydroponically grown plants produced most biomass with low molecular weight ON>inorganic N>high molecular weight ON, while cluster roots were formed in the order no-N>ON>inorganic N. Intact dipeptide was transported into roots and metabolized, suggesting a role for the peptide transporter (PTR) for uptake and transport of peptides. HaPTR4, a member of subgroup II of the NRT1/PTR transporter family, which contains most characterized di- and tripeptide transporters in plants, facilitated transport of di- and tripeptides when expressed in yeast. No transport activity was demonstrated for HaPTR5 and HaPTR12, most similar to less well characterized transporters in subgroup III. The results provide further evidence that subgroup II of the NRT1/PTR family contains functional di- and tripeptide transporters. Green fluorescent protein fusion proteins of HaPTR4 and HaPTR12 localized to tonoplast, and plasma- and endomembranes, respectively, while HaPTR5 localized to vesicles of unknown identity. Grown in heathland or hydroponic culture with limiting N supply or starved of nutrients, HaPTR genes had the highest expression in cluster roots and non-cluster roots, and leaf expression increased upon re-supply of ON. It is concluded that formation of cluster roots and expression of PTR are regulated in response to N suppl

Mixotrophic cultivation of Scenedesmus dimorphus in sugarcane bagasse hydrolysate

Overuse of the fossil fuels to fulfill existing energy requirements has generated various environmental problems like global warming. Emergence of environmental issues due to burning of the fossil fuel resources has provoked researchers to explore alternative sources of fuel. In this scenario, microalgal biofuels could present a promising alternative fuel if produced cost-effectively without competing for freshwater resources and arable land. Aim of the present study was to grow microalgae by employing lignocellulosic waste for production of lipids. Scenedesmus dimorphus NT8c was chosen based on its ability to tolerate heat, rapid growth, and ease of harvesting by overnight settling. Biochemical composition and growth parameters of microalgae were analyzed when cultivated mixotrophically on sugarcane bagasse hydrolysate, a low-value agricultural by-product, that is, currently underutilized. Despite a slight increase in turbidity in the medium, S. dimorphus NT8c cultures raised mixotrophically in 5 g/L sugarcane bagasse hydrolysate displayed significantly higher growth rates compared to photoautotrophic cultivation with an overall biomass productivity of 119.5 mg L d, protein contents of 34.82% and fatty acid contents of 15.41%. Thus, microalgae cultivated mixotrophically are capable of photosynthesizing while metabolizing and assimilating organic carbon, significant increases of biomass and lipid productivity can be achieved. However, high supplementation with organic carbon can result in unfavorable levels of turbidity and bacterial growth, reducing microalgal biomass productivity

Activation of the salicylic acid signalling pathway in wheat had no significant short-term impact on the diversity of root-associated microbiomes

Salicylic acid (SA) plays an important role in plant defence against biotrophic pathogens. Recent work with Arabidopsis thaliana mutants indicates an association between SA signalling and the diversity of root-associated microbial communities. This has led to the idea that activation of the SA pathway may help plants to rapidly recruit microbes that enhance stress tolerance and could be exploited as an approach to engineer beneficial plant microbiomes in agriculture. Nonetheless, unlike plants in natural environments, mutants with altered SA signalling constitutively express their phenotype. For this reason, we investigated whether transient activation of the SA pathway in wheat (Triticum aestivum) leads to rapid changes in the composition of root microbiomes. High throughput phylogenetic marker gene sequencing demonstrated that, 72 h post-treatment, SA had no significant effects on the richness, evenness and composition of bulk soil and root-associated microbiomes in two soil types. These findings indicate that the structure of wheat root-associated microbiomes did not undergo significant rapid changes in response to activation of the SA signalling pathway

Effect of drying, storage temperature and air exposure on astaxanthin stability from Haematococcus pluvialis

Astaxanthin is a powerful antioxidant with various health benefits such as prevention of age-related macular degeneration and improvement of the immune system, liver and heart function. To improve the post-harvesting stability of astaxanthin used in food, feed and nutraceutical industries, the biomass of the high astaxanthin producing alga Haematococcus pluvialis was dried by spray- or freeze-drying and under vacuum or air at -20 degrees C to 37 degrees C for 20 weeks. Freeze-drying led to 41% higher astaxanthin recovery compared to commonly-used spray-drying. Low storage temperature (-20 degrees C, 4 degrees C) and vacuum-packing also showed higher astaxanthin stability with as little as 123 +/- 3.1% degradation during 20 weeks of storage. Cost-benefit analysis showed that freeze-drying followed by vacuum-packed storage at -20 degrees C can generate AUD$600 higher profit compared to spray-drying from 100 kg H. pluvialis powder. Therefore, freeze-drying can be suggested as a mild and more profitable method for ensuring longer shelf life of astaxanthin from H. pluvialis. (C) 2015 Elsevier Ltd. All rights reserved

Selection and adaptation of microalgae to growth in 100% unfiltered coal-fired flue gas

Microalgae have been considered for biological carbon capture and sequestration to offset carbon emissions from fossil fuel combustion. This study shows that mixed biodiverse microalgal communities can be selected for and adapted to tolerate growth in 100% flue gas from an unfiltered coal-fired power plant that contained 11% CO. The high SOx and NOx emissions required slow adaptation of microalgae over many months, with step-wise increases from 10% to 100% flue gas supplementation and phosphate buffering at higher concentrations. After a rapid decline in biodiversity over the first few months, community profiling revealed Desmodesmus spp. as the dominant microalgae. To the authors’ knowledge this work is the first to demonstrate that up 100% unfiltered flue gas from coal-fired power generation can be used for algae cultivation. Implementation of serial passages over a range of photobioreactors may contribute towards the development of microalgal-mediated carbon capture and sequestration processes