Oil-accumulating microalgae have the potential to enable large-scale biodiesel production without competing for arable land or biodiverse natural landscapes. High lipid productivity of dominant, fast-growing algae is a major prerequisite for commercial production of microalgal oil-derived biodiesel. However, under optimal growth conditions, large amounts of algal biomass are produced, but with relatively low lipid contents, while species with high lipid contents are typically slow growing. Major advances in this area can be made through the induction of lipid biosynthesis, e.g., by environmental stresses. Lipids, in the form of triacylglycerides typically provide a storage function in the cell that enables microalgae to endure adverse environmental conditions. Essentially algal biomass and triacylglycerides compete for photosynthetic assimilate and a reprogramming of physiological pathways is required to stimulate lipid biosynthesis. There has been a wide range of studies carried out to identify and develop efficient lipid induction techniques in microalgae such as nutrients stress (e.g., nitrogen and/or phosphorus starvation), osmotic stress, radiation, pH, temperature, heavy metals and other chemicals. In addition, several genetic strategies for increased triacylglycerides production and inducibility are currently being developed. In this review, we discuss the potential of lipid induction techniques in microalgae and also their application at commercial scale for the production of biodiesel.

Microalgae have been widely reported as a promising source of biofuels, mainly based on their high areal productivity of biomass and lipids as triacylglycerides and the possibility for cultivation on non-arable land. The isolation and selection of suitable strains that are robust and display high growth and lipid accumulation rates is an important prerequisite for their successful cultivation as a bioenergy source, a process that can be compared to the initial selection and domestication of agricultural crops. We developed standard protocols for the isolation and cultivation for a range of marine and brackish microalgae. By comparing growth rates and lipid productivity, we assessed the potential of subtropical coastal and brackish microalgae for the production of biodiesel and other oil-based bioproducts. This study identified Nannochloropsis sp., Dunaniella salina and new isolates of Chlorella sp. and Tetraselmis sp. as suitable candidates for a multiple-product algae crop. We conclude that subtropical coastal microalgae display a variety of fatty acid profiles that offer a wide scope for several oil-based bioproducts, including biodiesel and omega-3 fatty acids. A biorefinery approach for microalgae would make economical production more feasible but challenges remain for efficient harvesting and extraction processes for some species.

Linear gramicidin is a membrane channel forming pentadecapeptide that is produced via the nonribosomal pathway. It consists of 15 hydrophobic amino acids with alternating L-and D-configuration forming a ␤-helix-like structure. It has an N-formylated valine and a C-terminal ethanolamine. Here we report cloning and sequencing of the entire biosynthetic gene cluster as well as initial biochemical analysis of a new reductase domain. The biosynthetic gene cluster was identified on two nonoverlapping fosmids and a 13-kilobase pair (kbp) interbridge fragment covering a region of 74 kbp.Four very large open reading frames, lgrA, lgrB, lgrC, and lgrD with 6.8, 15.5, 23.3, and 15.3 kbp, were identified and shown to encode nonribosomal peptide synthetases with two, four, six, and four modules, respectively. Within the 16 modules identified, seven epimerization domains in alternating positions were detected as well as a putative formylation domain fused to the first module LgrA and a putative reductase domain attached to the C-terminal module of LgrD. Analysis of the substrate specificity by phylogenetic studies using the residues of the substrate-binding pockets of all 16 adenylation domains revealed a good agreement of the substrate amino acids predicted with the sequence of linear gramicidin. Additional biochemical analysis of the three adenylation domains of modules 1, 2, and 3 confirmed the colinearity of this nonribosomal peptide synthetase assembly line. Module 16 was predicted to activate glycine, which would then, being the C-terminal residue of the peptide chain, be reduced by the adjacent reductase domain to give ethanolamine, thereby releasing the final product N-formyl-pentadecapeptideethanolamine. However, initial biochemical analysis of this reductase showed only a one-step reduction yielding the corresponding aldehyde in vitro.Gramicidin is a pentadecapeptide antibiotic produced by Bacillus brevis ATCC 8185 during its sporulation phase (1). The primary structure of gramicidin A was determined as formyl-