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The economic challenges of microalgae biodiesel production, including the energy burden and water shortage, can be addressed simultaneously by using wastewater as a nitrogen source. However, as a major form of nitrogen, ammonium is toxic to most microalgae strains, which limits the use of ammonium-containing wastewater. High-ammonium-tolerant algal strains remain to be explored. In this study, a microalgal strain named HDMA-01, which was isolated from Lake Dongfeng in China, was selected using a high ammonium medium. Phylogenetic analysis suggested that HDMA-01 belongs to the genus Monoraphidium (Selenastraceae, Sphaeropleales), and both 18S ribosomal DNA and ITS sequences of HDMA-01 appeared to be new molecular records of the Monoraphidium species. HDMA-01 can multiply vigorously using acetic acid and ammonium in TAP medium, reaching a density of 2 ×107 mL−1 within 7 days. HDMA-01 showed strong tolerance for ammonium. At a high ammonium concentration of 14 mM, HDMA-01 achieved maximum biomass and lipid productivity of 78.9 mg L−1 day−1 and 13.8 mg L−1 day−1, which is the highest among other Monoraphidium strains under similar cultivation conditions. Together with its ideal fatty acid profile, HDMA-01 has great potential for development as a promising strain used in biodiesel feedstock and high-ammonium tolerance biotechnology.

In 2013, UNESCO classified the ‘University of Coimbra – Alta and Sofia’ (Portugal) as World Heritage site. Some of the limestone monuments that compose the site, such as the Old Cathedral of Coimbra, show clear visual effects of biological colonization by cyanobacteria and microalgae. The aim of this study was to thoroughly characterize the structural diversity of the photoautotrophic community at this site, combining isolation and molecular identification with next-generation sequencing techniques. Culture-dependent approaches resulted on the identification of green microalgae belonging to Prasiolales, Chlorellales, Watanabea, Chlamydomonadales and Sphaeropleales clades, and cyanobacteria belonging to Nostocales and Synechococcales clades. Culture-independent methods using Illumina Platform resulted in the identification of 610 Operational Taxonomic Units (OTUs), revealing the presence of populations within phyla Chlorophyta, Cyanobacteria, Rhodophyta and Stramenopiles/Bacillariophyta. In addition, principal component analysis (PCA) and a network analysis were generated and successfully related the different populations to specific biodeterioration scenarios observed at this monument. The use of culture-dependent and -independent techniques together with PCA and network analysis allowed us to understand the distribution patterns of the photoautotrophic community among the different biofilms observed at this monument, as well as their ecological specifications. This study highlights that both cultivation and metagenomics methodologies should be employed synergistically in similar biodeterioration studies.

α-Linolenic acid (ALA) is an essential fatty acid which cannot be synthesized de novo in mammals and must be ingested regularly in the diet. In this study, a microalgal strain named HDMA-11 was isolated from Lake Ming, China, and was found to accumulate a high ALA content (39.2% of total lipids). Phylogenetic neighbor-joining analysis indicated that HDMA-11 belongs to the genus Monoraphidium (Selenastraceae, Sphaeropleales) and its 18S ribosomal DNA sequence seemed to be a new molecular record of a Monoraphidium species. The fatty acid profiles, biomass productivity and lipid content of HDMA-11 were also investigated in autotrophic conditions. The high levels of polyunsaturated fatty acids in HDMA-11, especially ALA, make it suitable as a source of nutritional supplementation for human health. Furthermore, HDMA-11 exhibited good properties for biodiesel production, characterized by high lipid content (28.5% of dry weight), moderate biomass productivity (31.5 mg L−1 day−1) and a promising lipid profile.

Chloroplast sequence data are widely used to infer phylogenies of plants and algae. With the increasing availability of complete chloroplast genome sequences, the opportunity arises to resolve ancient divergences that were heretofore problematic. On the flip side, properly analyzing large multi-gene data sets can be a major challenge, as these data may be riddled with systematic biases and conflicting signals. Our study contributes new data from nine complete and four fragmentary chloroplast genome sequences across the green algal order Sphaeropleales. Our phylogenetic analyses of a 56-gene data set show that analyzing these data on a nucleotide level yields a well-supported phylogeny - yet one that is quite different from a corresponding amino acid analysis. We offer some possible explanations for this conflict through a range of analyses of modified data sets. In addition, we characterize the newly sequenced genomes in terms of their structure and content, thereby further contributing to the knowledge of chloroplast genome evolution.

Asterarcys is a resilient microalgal species which can sustain high light intensities and have high biomass and lipid productivity under mixotrophy. These attributes make it a potential candidate to produce biodiesel and biofuels. However, no genetic information is currently available for this species. Here, we report the chloroplast genome sequence of Asterarcys sp. and compare it with the chloroplast genome of closely related chlorophyceaen microalgae. The chloroplast genome of Asterarcys sp. is present as a ~111 kb circular molecule with 88 genes and a coding density of 50.28%. The 111,776 bp genome shows a quadripartite structure with two 6297 bp long inverted repeats separating single copy regions (SSC) of almost equal sizes. The small and compact genome of Asterarcys shows similarity in gene structure and organization with that of its closest relative Scenedesmus obliquus. It reinforces the compact nature of chloroplast genomes of Sphaeropleales as compared to that of inflated genomes in Chlamydomonadales. The genome shows a biased distribution of genes with 50 of the protein-coding genes encoded from one strand and 15 from the opposite strand. This biased distribution of genes is likewise to that of Scenedesmus obliquus. The phylogenetic tree based on protein-coding genes from chlorophycean species places Asterarcys close to Scenedesmus. The chloroplast genome information of Asterarcys will help understand the phylogeny of Sphaeropleales and Chlorophyceae. In the present study, we also report a simple and effective method for isolation of Asterarcys sp. chloroplast DNA of high quality and purity which is an essential prerequisite for efficient genome sequencing.

The development of efficient algae cryopreservation methods is pivotal to the establishment of long-term culture collections as well as algae breeding and genetic modification programs. However, the unpredictable responses of distinct algal species to cryopreservation agents and protocols have hampered the standardization of universal methods so far. The results presented in this study indicate that intrinsic biological factors (i.e.: cell morphology and phylogenetic origin) play a role in the definition of which culture age and cryoprotectant agent type and concentration should be used to achieve successful cryopreservation. Through the use of Central Composite Rotatable Design (CCRD) it was possible to define optimized protocols for cryopreserving three major morphotypic groups found among chlorophytes (i.e.: coenobium, coccoid or palmella forming strains). These optimized protocols were then validated upon fifteen strains from Sphaeropleales, Chlamydomonadales and Chlorelalles clades. Analysis reveals that the use of DMSO as the sole cryoprotectant provided the highest post-freezing cell viability recovery rates for 80% of the coccoid strains tested, while the combination of glycerol and PEG400 allowed efficient cryopreservation of 100% of the coenobium and palmella forming strains evaluated. In addition, results suggest that coenobium-forming strains have higher resistance to freeze/thawing when frozen at mid-log phase of growth, while coccoid and plamelloid strains present higher survival rates when cryopreserved at late-log phase. Such information is of valuable practical use since a simple visual inspection of algae strain's predominant morphotype can guide the choice of the most suitable cryopreservation protocol.