https://www.cti2000.it/Bionett/BioD-1999-101%20Biodiesel%20production%20review.pdf

Biodiesel production : a review

Microalgae represent an exceptionally diverse but highly specialized group of micro-organisms adapted to various ecological habitats. Many microalgae have the ability to produce substantial amounts (e.g. 20-50% dry cell weight) of triacylglycerols (TAG) as a storage lipid under photo-oxidative stress or other adverse environmental conditions. Fatty acids, the building blocks for TAGs and all other cellular lipids, are synthesized in the chloroplast using a single set of enzymes, of which acetyl CoA carboxylase (ACCase) is key in regulating fatty acid synthesis rates. However, the expression of genes involved in fatty acid synthesis is poorly understood in microalgae. Synthesis and sequestration of TAG into cytosolic lipid bodies appear to be a protective mechanism by which algal cells cope with stress conditions, but little is known about regulation of TAG formation at the molecular and cellular level. While the concept of using microalgae as an alternative and renewable source of lipid-rich biomass feedstock for biofuels has been explored over the past few decades, a scalable, commercially viable system has yet to emerge. Today, the production of algal oil is primarily confined to high-value specialty oils with nutritional value, rather than commodity oils for biofuel. This review provides a brief summary of the current knowledge on oleaginous algae and their fatty acid and TAG biosynthesis, algal model systems and genomic approaches to a better understanding of TAG production, and a historical perspective and path forward for microalgae-based biofuel research and commercialization.

https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1365-313X.2008.03492.x

Microalgal triacylglycerols as feedstocks for biofuel production: perspectives and advances

This review discusses the analysis of whole-community phospholipid fatty acid (PLFA) profiles and the composition of lipopolysaccharides in order to assess the microbial biomass and the community structure in soils. For the determination of soil microbial biomass a good correlation was obtained between the total amount of PLFAs and the microbial biomass measured with methods commonly used for determinations such as total adenylate content and substrate-induced respiration. Generally, after the application of multivariate statistical analyses, whole-community fatty acid profiles indicate which communities are similar or different. However, in most cases, the organisms accounting for similarity or difference cannot be determined, and therefore artefacts could not be excluded. The fatty acids used to determine the biomass vary from those which determine the community structure. Specific attention has to be paid when choosing extraction methods in order to avoid the liberation of fatty acids from non-living organic material and deposits, and to exclude the non-target selection of lipids from living organisms, as well. By excluding the fatty acids which were presumed to be common and widespread prior to multivariate statistical analysis, estimates were improved considerably. Results from principal component analysis showed that determining the levels of fatty acids present in both low and high concentrations is essential in order to correctly identify microorganisms and accurately classify them into taxonomically defined groups. The PLFA technique has been used to elucidate different strategies employed by microorganisms to adapt to changed environmental conditions under wide ranges of soil types, management practices, climatic origins and different perturbations. It has been proposed that the classification of PLFAs into a number of chemically different subgroups should simplify the evaluating procedure and improve the assessment of soil microbial communities, since then only the subgroups assumed to be involved in key processes would be investigated.

http://www.evisdom.com/pdf/1150507076.pdf

Fatty acid patterns of phospholipids and lipopolysaccharides in the characterisation of microbial communities in soil: a review

The Aquatic Species Program was a relatively small research effort intended to look at the use of aquatic plants as sources of energy. Its history dates back to 1978, but much of the research from 1978 to 1982 focused on using algae to produce hydrogen. The program switched emphasis to other transportation fuels, particularly biodiesel, beginning in the early 1980's. This report summarizes the research activities carried out from 1980 to 1996, with an emphasis on algae for biodiesel production.

/pdf/look-back-at-the-u-s-department-of-energy-s-aquatic-species-3j2xsi0wk0.pdf

Look Back at the U.S. Department of Energy's Aquatic Species Program: Biodiesel from Algae; Close-Out Report

Soil microorganisms as controllers of atmospheric trace gases (H2, CO, CH4, OCS, N2O, and NO).

Fluorometric determination of the neutral lipid content of microalgal cells using Nile Red

Alkaline pH stress resulted in triglyceride (TG) accumulation in Chlorella CHLOR1 and was independent of medium nitrogen or carbon levels Based on morphological observations, alkaline pH inhibited autospore release, thus increasing the time for cell cycle completion Autospore release has been postulated to coincide with TG utilization within the microalgal cell division cycle The alkaline pH stress affected lipid accumulation by inhibiting the cell division cycle prior to autospore release and, therefore, prior to TG utilization Cells inhibited in this manner showed an increase in TG accumulation but a decrease in both membrane lipid classes (glycolipid and polar lipid) Unlike TG fatty acid profiles, membrane lipid fatty acid profiles were not stable during TG accumulation The membrane profiles became similar to the TG, ie less unsaturated than in the membrane lipids of unstressed control cells

TRIGLYCERIDE ACCUMULATION AND FATTY ACID PROFILE CHANGES IN CHLORELLA (CHLOROPHYTA) DURING HIGH pH‐INDUCED CELL CYCLE INHIBITION1

Summary: A polyphasic approach to bacterial taxonomy attempts to integrate phylogenetic relationships with phenotypic marker analysis. This study describes the application of membrane fatty acids as a phenotypic marker for methylotrophs. Detailed phospholipid, ester-linked fatty acid (PLFA) profiles are reported for 17 methylotrophic eubacterial strains. These profiles included verification of double bond positions and geometries, both critical features for this analysis. Multivariate cluster analysis was used to indicate groupings of these strains along with literature values of both methylotrophs and non-methylotrophs based on the PLFA phenotype. Like many phenotypic characteristics, PLFA profiles were influenced by environmental conditions. The instabilities displayed, however, were predictable from physiological studies including increased trans/cis and cyclopropyl/cis ratios. Cluster analysis of PLFA profiles generated by separate investigators with different culture conditions indicated reproducibility by strain and species. The PLFA phenotype relationships compare favourably with phylogenetic associations based on 16S rRNA data for methylotrophs and will continue to be a valuable phenotypic marker for Proteobacteria taxonomy.

Membrane fatty acids as phenotypic markers in the polyphasic taxonomy of methylotrophs within the Proteobacteria.

Biochemical and traditional methods were used to determine the influence of Caflianassa trilobata on microbiological and meiofaunal communities within its large, hghly consolidated burrow. Sediment was collected from the lining of the shrimp's burrow, the burrow matrix, and ambient, subsurface sediment. The lining and matrix were composed of poorly sorted, fine-grained material compared to sandy ambient sediment. Meiofauna, predominantly nematodes, were most abundant in ambient sediment, not in the burrow as has been found for other species of macrofauna. Concentrations of chlorophyll a were very high in the lining, consistent with the suggestion that C. trilobata lines its burrow walls with seagrass. Analyses of lipids indicated that relative to the matrix and ambient sediment, the lining abounds with proand eukaryotic biomass. Thirty-four phospholipid, ester-linked fatty acids (PLFA) were identified and quantified. Fatty acids were assigned to functional groups of microorganisms to assess spatial variations in the absolute abundance and relative proportions of microbial populations. Dominance of prokaryotes was pronounced in all 3 areas, especially the matrix. The lining was the most aerobic location, but anaerobic microhabitats simultaneously allowed proliferation of sulfate-reducing bacteria, e. g. Desulfobacter. A radial trend was detected in the ratio of bacteria with terminally branched PLFA, typical of Gram-positive organisms, to those with unsaturated PLFA common to Gram-negative bacteria. The ratio increased from lining to matrix to ambient sediment. The ratios of tram to cls isomers of 16:lw7 indicated that prokaryotes in the matrix were starved. Through construction and maintenance of its burrow, C. trilobata determines not only the absolute and relative abundances of microbes in its sedimentary environment, but their physiologic state as well.

/pdf/callianassa-trilobata-crustacea-thalassinidea-influences-3362b2ycb4.pdf

Callianassa trilobata (Crustacea: Thalassinidea) influences abundance of meiofauna and biomass, composition, and physiologic state of microbial communities within its burrow

James B. Guckert

Papers

Fluorometric determination of the neutral lipid content of microalgal cells using Nile Red

TRIGLYCERIDE ACCUMULATION AND FATTY ACID PROFILE CHANGES IN CHLORELLA (CHLOROPHYTA) DURING HIGH pH‐INDUCED CELL CYCLE INHIBITION1

Membrane fatty acids as phenotypic markers in the polyphasic taxonomy of methylotrophs within the Proteobacteria.

Callianassa trilobata (Crustacea: Thalassinidea) influences abundance of meiofauna and biomass, composition, and physiologic state of microbial communities within its burrow

Lipid sovent systems are not equivalent for analysis of lipid classes in the microeukaryotic green alga, Chlorella