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Chlorellacean members are common in aquatic or subaerial habitats, and many of them have significant economic value. Taxonomic reports and organelle genome data for the Nannochloris clade, an important subgroup within this family, are limited, hindering the understanding and exploitation of this clade. In this study, a fusiform-celled strain, FACHB-3607, was isolated from a pond in China. Through examination of morphological characteristics and phylogenetic analyses of rbcL, 18S rDNA, and ITS, it was identified as a new species within the Nannochloris clade, named Koliella bifissiva sp. nov. In addition, this study provided a first insight into the organellar genomes of the genus Koliella. The K. bifissiva chloroplast had a 99.8 kb genome, and the mitochondrion had a 40.8 kb genome, which are moderate sizes within the Nannochloris clade. Phylogenomic analysis showed that K. bifissiva is most closely related to Nannochloris sp. "desiccata", followed by Marvania. In contrast, Picochlorum was the most distantly related species. The organelle genomes of the Nannochloris clade display dynamic evolution, reflected in variations in genome size, gene content and order, and selection pressure. This research enhances our knowledge of species diversity and evolutionary history in the Nannochloris clade. [ABSTRACT FROM AUTHOR]

Chlorellacean members are common in aquatic or subaerial habitats, and many of them have significant economic value. Taxonomic reports and organelle genome data for the Nannochloris clade, an important subgroup within this family, are limited, hindering the understanding and exploitation of this clade. In this study, a fusiform-celled strain, FACHB-3607, was isolated from a pond in China. Through examination of morphological characteristics and phylogenetic analyses of rbcL, 18S rDNA, and ITS, it was identified as a new species within the Nannochloris clade, named Koliella bifissiva sp. nov. In addition, this study provided a first insight into the organellar genomes of the genus Koliella. The K. bifissiva chloroplast had a 99.8 kb genome, and the mitochondrion had a 40.8 kb genome, which are moderate sizes within the Nannochloris clade. Phylogenomic analysis showed that K. bifissiva is most closely related to Nannochloris sp. “desiccata”, followed by Marvania. In contrast, Picochlorum was the most distantly related species. The organelle genomes of the Nannochloris clade display dynamic evolution, reflected in variations in genome size, gene content and order, and selection pressure. This research enhances our knowledge of species diversity and evolutionary history in the Nannochloris clade.

The atmosphere contains diverse living microbes, of which the heterotrophic community has been the best studied. Microbes with other trophic modes, such as photoautotrophy, have received much less attention. In this study, cultureindependent and dependent methods were used to examine the presence and diversity of oxygenic photoautotrophic microbes in clouds and rain collected at or around puy de Dôme Mountain, central France. Cloud water was collected from the summit of puy de Dôme (1,465 m above sea level [a.s.l.]) for cultivation and metagenomic analysis. Cyanobacteria, diatoms, green algae, and other oxygenic photoautotrophs were found to be recurrent members of clouds, while green algae affiliated with the Chlorellaceae were successfully cultured from three different clouds. Additionally, rain samples were collected below the mountain from Opme meteorological station (680 m a.s.l.). The abundance of chlorophyll a-containing cells and the diversity of cyanobacteria and green algae in rain were assessed by flow cytometry and amplicon sequencing. The corresponding downward flux of chlorophyll a-containing organisms to the ground, entering surface ecosystems with rain, varied with time and was estimated to be between ~1 and >300 cells cm-2 day-1 during the sampling period. Besides abundant pollen from Pinales and Rosales, cyanobacteria of the Chroococcidiopsidales and green algae of the Trebouxiales were dominant in rain samples. Certain members of these taxa are known to be ubiquitous and stress tolerant and could use the atmosphere for dispersal. Overall, our results indicate that the atmosphere carries diverse, viable oxygenic photoautotrophic microbes and acts as a dispersal vector for this microbial guild. [ABSTRACT FROM AUTHOR]

Microalgae have been reported in many studies with high biomass, high carbohydrate content, fast growth rate and multiple bio-activities, while Dictyosphaerium sp. was rarely studied. Polysaccharide prove to be remarkable in many biological activities. To optimize the effects of the ultrasonic-assisted extraction parameters on the yield of polysaccharide from Dictyosphaerium sp., a single-factor experiment and response surface methodology (RSM) with a central composite rotatable design were employed. Four independent variables were investigated: X1 (ratio of raw microalgal powder to water), X2 (extraction temperature), X3 (extraction time), X4 (extraction power). The optimal conditions obtained via single-factor experiment were: X1 (1:25), X2 (50 °C), X3 (50 min), X4 (500 W), while according to the analysis of RSM, the optimum conditions were: X1 (1:26), X2 (58 °C), X3 (55 min), X4 (525 W). The refined polysaccharide were further prepared and characterized using SEM, FT-IR, XRD and TGA/DSC. Five kinds of antioxidant assays were carried out and the results indicated that the refined polysaccharide had strong scavenging ability to DPPH· and OH·. This study provides theoretical and experimental basis for the development and utilization of microalgal resources. [ABSTRACT FROM AUTHOR]

We report the first mitochondrial genome of the Antarctic microalga Micractinium simplicissimum KSF0127. The circular mitochondrial genome was 67,923 bp in length and contained 45 protein-coding genes, one ribosomal RNA gene, and 60 transfer RNA genes. The phylogenetic tree was constructed with eight previously reported mitogenome sequences and showed the phylogenetic position of M. simplicissimum KSF0127 within the Chlorellaceae family.

The mitochondrial genome of Micractinium singularis MM0003 was completely sequenced. This mitogenome has 75,931 bp in length and consists of 62 genes including 32 protein-coding, 3 rRNA, and 27 tRNA genes. The overall GC content of the genome is 27.5%.

The chloroplast genome of Micractinium singularis MM0003 was completely sequenced. This plastome has 139,597 bp in length and consists of 106 genes including 77 protein-coding, 3 rRNA, and 26 tRNA genes. The overall GC content of the genome is 34.0%.

The chloroplast genome of Micractinium pusillum CCAP 231/1 was completely sequenced. This chloroplast genome has 115,638 bp in length and consists of 111 genes including 81 protein-coding, 4 rRNA, and 26 tRNA genes. The overall GC content of the genome is 35.3%.

The mitochondrial genome of Micractinium pusillum CCAP 231/1 was completely sequenced. This mitogenome has 70,061 bp in length and consists of 62 genes including 32 protein-coding, 3 rRNA, and 27 tRNA genes. The overall GC content of the genome is 31.3%.

Microalgae are gaining interest as food ingredient. Assessments of functional and nutritional properties are necessary to forward their implementation. In this study, protein content and composition of eight commercially available microalgae biomasses were determined and compared to conventional food proteins. A novel procedure for the determination of the true protein content was proposed: Multiplication of proteinic nitrogen with a sample-specific nitrogen-to-protein conversion factor k A . The proteinic nitrogen was derived from the difference of total nitrogen minus non-protein nitrogen. The average k A for microalgae was 5.3 and considerable variation between different microalgae biomasses were detected. In addition, the content of non-protein nitrogen varied between 3.4% and 15.4%. The amino acid profiles of Chlorella samples were nutritionally superior to the tested plant proteins but indicated lower protein interaction tendency, potentially limiting their structuring functionality. In contrast, Auxenochlorella contained lower amounts of indispensable amino acids while showing comparable interaction potential to plant proteins., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Abstract Calcium oxide (CaO) catalyst was prepared using chicken egg shell waste and tested as a catalyst for the production of biodiesel from Chlorella vulgaris biomass. The calcination method was adopted for the synthesis of CaO catalyst. Transmission electron microscope (TEM) image showed that the catalyst had a spherical structure with average particle size of 46.1 ± 2.1 nm, further analysis was carried out using Brunauer-Emmett-Teller (BET) adsorption, scanning electron microscopy, elemental analysis, X-ray diffraction and Fourier-transform infrared spectroscopy. Transesterification process was conducted by using response surface methodology (RSM) based on central composite design (CCD). The optimum reaction conditions were observed at 70 °C, 10:1 methanol: dry biomass ratio, 1.39% catalyst loading, 3 h reaction time, and 140 rpm stirring rate resulted 92.03% biodiesel yield. The key fuel properties includes; iodine value (88.5 g I 2 100/g), cetane number (50.0), cloud point (9.2 °C), pour point (3.1 °C), oxidation stability (7.4 h), higher heating value (44.7), kinematic viscosity (4.5 mm2/s) and density (0.9 g/cm3) resulted good quality of microalgae biodiesel. Our research finding shows that the CaO catalyst derived from egg shell waste is an economically potential and eco-friendly catalyst for biodiesel production. Graphical abstract Image 1 Highlights • CaO catalyst was synthesized using egg shell waste as natural raw material. • A response surface methodology (RSM) was used to optimise transesterfication reaction parameters. • Biodiesel conversation was analysed by nuclear magnetic resonance (NMR). • The catalyst was stable upto six reusable cycle. [ABSTRACT FROM AUTHOR]

Some green extraction methods were selected and tested for the extraction of volatile compounds from different samples of the microalga Chlorella vulgaris: ultrasound‐assisted liquid–liquid extraction using environment‐friendly solvents (LLE) and solid‐phase microextraction (SPME). The obtained profiles of volatile chemical compounds were different. Only one molecule was found in common to both extractions. Using the SPME method, the main chemical classes of identified volatile compounds were sulfuric compounds, aldehydes, and alcohols. Using the LLE method, the volatile profile was more balanced with alkanes, fatty acids, terpenes, alcohols, and aldehydes. Multivariate data analyses permitted discrimination among samples. Additionally, the relationship between the physicochemical properties of identified volatile compounds and the methods of extraction was studied. The results showed that the LLE extraction allowed the extraction of volatile compounds having a high boiling point (>160°C) and a high log P (>3). The SPME method was more effective to extract volatile compounds with a low boiling point (<160°C) and a low log P (<3). It is thus necessary to combine several extraction methods to obtain a complete view of the volatile profile for microalgae samples. Green extraction methods were selected for the extraction of volatile compounds from different samples of the microalga Chlorella vulgaris: ultrasound‐assisted liquid–liquid extraction using environment‐friendly solvents (LLE) and solid‐phase microextraction (SPME). LLE extraction allowed the extraction of volatile compounds having a high boiling point (>160°C) and a high log P (>3). The SPME method was more effective to extract volatile compounds with a low boiling point (<160°C) and a low log P (<3). [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Variability in Chlorella and Spirulina products demands process optimization. • A high protein or lipid content does not necessarily imply a high nutritional value. • Safe consumption doses indicate capacity as protein source rather than as supplement. • Potential PAH contamination requires systematic control to guarantee product safety. • Based on price and nutritional quality, Spirulina was preferred above Chlorella. Abstract Microalgal biomass production is a resource-efficient answer to the exponentially increasing demand for protein, yet variability in biomass quality is largely unexplored. Nutritional value and safety were determined for Chlorella and Spirulina biomass from different producers, production batches and the same production batch. Chlorella presented a similar protein content (47 ± 8%) compared to Spirulina (48 ± 4%). However, protein quality, expressed as essential amino acid index, and digestibility were lower for Chlorella (1.1 ± 0.1 and 51 ± 9%, respectively) compared to Spirulina (1.3 ± 0.1 and 61 ± 4%, respectively). Generally, variability was lower between batches and within a batch. Heavy metals, pesticides, mycotoxins, antibiotics and nitrate did not violate regulatory limits, while polycyclic aromatic hydrocarbon levels exceeded the norm for some samples, indicating the need for continuous monitoring. This first systematic screening of commercial microalgal biomass revealed a high nutritional variability, necessitating further optimization of cultivation and post-processing conditions. Based on price and quality, Spirulina was preferred above Chlorella. [ABSTRACT FROM AUTHOR]

Abstract Microalgae require a large amount of carbon (C) fertilizer for efficient biomass production. We explored the feasibility of using bicarbonate-rich wastewater as a carbon fertilizer for algal cultures and characterized the morphological and physiological features of C-deficient Dictyosphaerium sp. algae. Addition of bicarbonate-rich wastewater to media increased peak algal biomass by more than four-fold, and removal of the bicarbonate from the wastewater decreased the peak algal biomass by more than 3 times, and both the algal biomass productivity and the bicarbonate depletion rate were positively and significantly (P < 0.01) related to the bicarbonate level. We observed a giant pyrenoid in Dictyosphaerium cells. Consistently, this species exhibited an exceptionally high CO 2 enrichment and the expression level of limiting CO 2 inducible protein gene was extremely high. The disruption in structural integrity was evident in the algae cultured under 0.4 g/L of bicarbonate. Transcript profiling accurately revealed the C and N status in the algae. Our results indicate that the bicarbonate-rich and Na-low wastewater could provide adequate and excellent C source for algal growth. Highlights • The bicarbonate-rich and Na-low wastewater could be used as an excellent C fertilizer in algal production. • Dictyosphaerium sp. of a giant pyrenoid exhibited an exceptionally high CO 2 enrichment. • Transcript profiling could accurately reveal the C and N status in the algae. [ABSTRACT FROM AUTHOR]

The current study aimed to evaluate if the addition of pentoses along with variations in light intensity and photoperiod can stimulate the production of polyhydroxybutyrate (PHB) and other biomolecules by Chlorella fusca LEB 111. The variables evaluated were the addition of xylose and arabinose as sources of organic carbon, different photoperiods (18 h, 12 h and 6 h light) and variations in light intensities (58, 28 and 9 μmol photons  m −2  s −1 ). The highest PHB accumulation (17.4% w w −1 ) and protein production (53.2% ww −1 ) were observed in assays with xylose addition and a photoperiod of 6 h of light provided at 28 and 58 μmol photons  m −2  s −1 , respectively. The highest lipid content (24.7% w w −1 ) was obtained with 18 h of light. The current study contributes to the development of sustainable alternatives for the use of wastes and the production of biomolecules from algae. [ABSTRACT FROM AUTHOR]

The Chlorellaceae is a family in the order Chlorellales that includes mostly coccoid algae of minute sizes, and a portion of this family was separated into two sister groups (the Chlorella clade and the Parachlorella clade) according to molecular phylogenetic analyses. To date, the Parachlorella clade comprises 11 genera that exhibit a range of morphological variation. In this study, we discovered from China a strain marked as FACHB-2137; we use a polyphasic approach, including phylogenetic analyses of SSU+ITS rDNA, an ITS2/CBC (compensatory base changes) approach, light microscopy and transmission electron microscopy, to characterise the strain. Molecular analyses revealed that the strain was nested within the Parachlorella clade (Chlorellaceae, Trebouxiophyceae), forming an independent lineage separated from other genera. The new strain's morphology has the characteristic autospores that release by rupturing or splitting of the cell wall into several (two to four) portions; this strain differs from other members of the Parachlorella clade in that the mother cell wall remains rather distinct, and the daughter cells remain as cup-shaped in the colonial mucilage for an extended period. Morphologically, this new strain closely resembles members of the Radiococcaceae. This indicates that inferring family-level relationships based exclusively on morphology can be problematic. We describe this alga as a new genus and species, Coronacoccus hengyangensis gen. et sp. nov. This morphotype is described for the first time in the Parachlorella clade. [ABSTRACT FROM AUTHOR]

A potential novel genus of microalgae was isolated from swine wastewater. According to a phylogenetic analysis of 18S rRNA and internal transcribed spacer (ITS) sequences, as well as the ITS2 secondary structure, this strain was designated as Chlorellaceae sp. P5. Acclimatization to various temperatures, pH conditions, and salinities demonstrated that this strain can grow at temperatures of 20 °C–40 °C, in an acidity range of pH 4–7, and with salinity as high as 3% NaCl. To optimize biomass production, response surface methodology was used which included variables associated with carbon and nitrogen sources. In this study, flask cultivation yielded 1.66 g l−1 d−1 of biomass under 15.19 g l−1 glucose and 8.26 mM ammonium bicarbonate. The fatty acid composition suggested that the lipid from Chlorellaceae sp. P5 can be typically used for biodiesel production, with a low degree of unsaturated fatty acids. Moreover, a high content of the first-limiting amino acid (lysine) and 9,12-Octadecadienoic acid (linoleic acid, C18:2) for nutritional supplements was also observed. With respect to swine wastewater treatment, the isolated strain showed an excellent removal rate of ammonia and phosphate over 97.3 mg l−1 of NH3-N and 20.3 mg of l−1 PO43− in the sterilized and none-sterilized wastewater. The biomass and lipid derived from Chlorellaceae sp. P5 can be attained at 0.49 g l−1 d−1 and 0.13 g l−1 d−1 by swine wastewater cultivation with 5% CO2 supply, respectively. According to the various characteristic analyses, Chlorellaceae sp. P5 has great potential for different industrial developments such as biodiesel and wastewater treatment. [ABSTRACT FROM AUTHOR]

Abstract: The biomass obtained from microalgae, such as Chlorella, is used to make dietary products, supplements and pharmaceuticals. However, microalgae are produced very far from consumption places. One of the most usual distribution forms is as a dry product, a process that entails high production costs and leads to the loss of certain nutritional properties. Therefore, the aim of this study was to evaluate alternative preservation strategies for microalgae Chlorella other than dehydration and freezing. To that end, sterilization, acidification, and packaging material were analyzed during 2 months of storage under different temperature and light exposure conditions. The results showed that color was modified considerably by sterilization, regardless of light exposure and type of package, whereas citric acid preserved color, especially at low storage temperatures. Furthermore, the study shows that acidification with 3.5% of citric acid and vacuum packaging are the recommended treatment for microalgae, without the need for cold storage. Practical applications: Stabilization of microalgae Chlorella from production to consumption places could increase the possibilities of commercialization of this product, recently labeled “superfood” by the UN Food and Agriculture Organization. In order to preserve all their nutritional properties for at least 2 months, acidification with 3.5% of citric acid and vacuum packaging are the recommended treatments, without the need for cold storage. [ABSTRACT FROM AUTHOR]

SUMMARY: Many freshwater protists harbor unicellular green algae within their cells and these host‐symbiont relationships slowly are becoming better understood. Recently, we reported that several ciliate species shared a single species of symbiotic algae. Nonetheless, the algae from different host ciliates were each distinguishable by their different genotypes, and these host‐algal genotype combinations remained unchanged throughout a 15‐month period of sampling from natural populations. The same algal species had been reported as the shared symbiont of several ciliates from a remote lake. Consequently, this alga appears to play a key role in ciliate‐algae symbioses. In the present study, we successfully isolated the algae from ciliate cells and established unialgal cultures. This species is herein named Brandtia ciliaticola gen. et sp. nov. and has typical ‘Chlorella‐like’ morphology, being a spherical autosporic coccoid with a single chloroplast containing a pyrenoid. The alga belongs to the Chlorella‐clade in Chlorellaceae (Trebouxiophyceae), but it is not strongly connected to any of the other genera in this group. In addition to this phylogenetic distinctiveness, a unique compensatory base change in the SSU rRNA gene is decisive in distinguishing this genus. Sequences of SSU‐ITS (internal transcribed spacer) rDNA for each isolate were compared to those obtained previously from the same host ciliate. Consistent algal genotypes were recovered from each host, which strongly suggests that B. ciliaticola has established a persistent symbiosis in each ciliate species. [ABSTRACT FROM AUTHOR]

Mucidosphaerium sphagnale, a new record for New Zealand, is reported from Awarua Wetland. The genusMucidosphaeriumhas recently been separated from the well-knownDictyosphaerium, a colonial green alga with cells connected by thin, branching stalks, to encompass those forms with near-spherical adult cells. The previous name for this taxon,Dictyosphaerium sphagnale, is not recorded from New Zealand; however,Mucidosphaerium pulchellum(syn.Dictyosphaerium pulchellum), which has been reported here many times and is very difficult to distinguish without DNA sequences, may represent previously misidentified instances ofM. sphagnale. TheM. sphagnaleis reported here from aSphagnumbog, as is typical of its European range, whereasM. pulchellumin New Zealand appears to have been reported exclusively from lakes and rivers. The organism reported here is therefore quite likely a genuine new occurrence. Co-introduction to New Zealand with foreignSphagnumis a possibility. [ABSTRACT FROM PUBLISHER]

The chloroplast genome contains information that is applicable in many scientific fields, such as plant systematics, phylogenetic reconstruction and biotechnology, because its features are highly conserved among species. To date, several complete green algal chloroplast genomes have been sequenced and assembled. In this study, the nucleotide sequence of the chloroplast genome (cpDNA) ofChlorella sorokinianaSAG 211-8k is reported and compared for the first time to the chloroplast genomes of 10 Chlorellaceae. The recently updatedChlorella sorokinianacpDNA sequence, assembled as a circular map of 109 811 bp, encodes 113 genes. Similar to otherChlorellastrains, this chloroplast genome does not show a quadripartite structure and lacks the large rRNA operon-encoding Inverted Repeat (IR). TheChlorella sorokinianaplastid encodes the tRNA(Ile)-lysidine synthetase (tilS), which is responsible for modifying the CAU anticodon of a unique tRNA. Gene ordering and clustering highlight the close relationships amongChlorellaclade members and the preservation of crucial gene clusters in photosynthetic strains. The features ofChlorella sorokinianapresented here reinforce the monophyletic character of Chlorellaceae and provide important information that sheds light on chloroplast genome evolution among species ofChlorella. [ABSTRACT FROM AUTHOR]

To investigate the effects of bacteria contaminated in microalgal cultivation, several bacteria were isolated from four photobioreactors for Chlorella sp. KR-1 culture. A total of twenty-one bacterial strains isolated from the reactors and identified by 16S rRNA gene sequencing. Six bacteria, which were found from more than two reactors of the four photobioreactors, were introduced into co-culturing experiments with Chlorella sp. KR-1. Then, the bacterial influences on the productivity of microalgal biomass and lipids were assessed in the photoautotrophic- and mixotrophic microalgal cultivation by comparing them with axenic culture of Chlorella sp. KR-1. The results showed that both biomass and lipid production were significantly enhanced under mixotrophic conditions compared to photoautotropic conditions. However, an excess ratio (more than 10%) of bacterial cells to microalgal cells at the initial stage of mixotrophic cultivation has limited the growth of Chlorella sp. KR-1 because of the relatively fast growth of bacteria, especially under mixotrophic conditions. Moreover, it was proven that the strong biofilm formability of Sphingomonas sp. MB6 is the responsible strain to cause the biomass aggregation observed during the early stage of co-culture. The high abundance of Sphingomonas sp. MB6 during early cultivation period shown by qPCR results was also well corresponded with the period shown a strong biofilm formation, which suggested the applicability of qPCR to monitor a specific bacterial group in a microalgal culture. [ABSTRACT FROM AUTHOR]

The cultivation of microalgae is of great interest due to the high yields and rapid growth rates that can be produced. The fatty acids from microalgal biomass may have therapeutic effects for humans and can be used for biodiesel production. The aim of this study was to evaluate the fatty acid profile of microalgae grown in a heterotrophic mode. Cultures that were carried out with BG11 medium supplemented with 10 g.L-1 of glucose produced the highest cellular concentrations (1.62; 1.53; 1.14 g.L-1) for Chlorella sp., C. homosphaera and C. minutissima, respectively, while the assays without glucose remained at a cellular concentration equal to that at the beginning of the experiments (0.15 g.L-1). The microalga C. homosphaera grown in BG11 supplemented with 10 g.L-1 of glucose had the highest concentration of lipids in dry biomass (22.4% w/w). The maximum concentration of total PUFA (35.25% w/w) and essential fatty acids (35.05% w/w) was found in C. homosphaera in Basal medium without glucose, which is the most suitable method for producing PUFAs and essential fatty acids. [ABSTRACT FROM AUTHOR]

Chlorella vulgaris was cultivated in a hybrid (two-stage) system. The effect of the transferring time from nutrient-replete phase with a low light intensity (photobioreactor) to the nutrient deprivation phase (open pond) with a higher light intensity, as well as the effect of initial cell concentration in the deprivation phase, on the growth rate and lipid content of the microalgae was investigated. The microalgae were transferred to the nutrient deprived medium at different intervals with various initial cell concentrations. Transferring the cultivated medium of the 4th day with the initial cell concentration of 66 mg L-1 into the deprivation phase resulted in a highest lipid productivity of 9.21 ± 0.64 mg L-1 d-1 and lipid content of 53.97 ± 4.30%. In a single-stage cultivation where a medium with nitrogen deficiency was used, despite a low lipid content (maximum 30%), a lipid productivity of 9.95 ± 0.46 mg L-1 d-1 was observed that was slightly higher than that for the hybrid system. [ABSTRACT FROM AUTHOR]

Two algal cultures,TvBandSH, were isolated from extreme habitats along the Syrian-African rift Valley (Israel). These cultures were initially identified asChlorellaspp. according to their morphology and lack of bristles, but following molecular phylogenetic analyses, re-identified asMicractiniumspp. closely related toChlorella. The strains were subjected to a bi-factorial study in the search for algae that grow well at elevated temperatures and salinities for future biotechnological uses. Cell density (CD) and optical density (OD) were measured for each strain at three temperatures: 35, 40 and 45ºC, and five salinities of seawater (SW): 34.8 ppt (100% SW), 26.5 ppt (75% SW), 18.3 ppt (50% SW) 10 ppt (25% SW) and 1.8 ppt (0% SW). Both strains grew best at 35–40ºC and at 0–50% SW. Increased salinity enhanced temperature tolerance to 45ºC, particularly for strainTvB. At 45ºC, following a short initial growth spurt, cultures underwent a lag period ofc. 7 days, followed by a significant growth phase. During the lag period, algae underwent a substantial increase in average cell diameter (ACD). These enlarged or gigantic cells with diameters of up to ~20 μm, produced and eventually released multiple autospores. By day 13, original size distribution was almost restored. The observed morphological alterations appear to enable these strains to survive and grow autotrophically at supra-optimal temperatures (SOT). These natural adjustments may be exploited for reducing costs associated with both cooling and desalination in future cultivation. [ABSTRACT FROM AUTHOR]

Dilute alkaline pretreatment of two different types of microalgal biomass ( Tetraselmis suecica and Chlorella sp.) was investigated and the pretreated biomass was subjected for enzymatic saccharification. The effect of pretreatment parameters such as alkaline concentration, temperature and reaction time on reducing sugar production from both microalgal biomass has been investigated. The maximum reducing sugar concentration from T. suecica (81 mg/g driedbiomass ) was obtained when the biomass was pre-treated with 2% (w/v) of potassium hydroxide (KOH) at 120 °C for 120 min. While, maximum reducing sugar concentration from Chlorella sp. biomass (88 mg/g driedbiomass ) was obtained when the pretreatment was carried out using 2% (w/v) sodium hydroxide (NaOH) at 120 °C for 30 min. Solid residue post pretreatment was analyzed using Fourier transform infrared spectroscopy and scanning electron microscopy. These analyses revealed that the functional group such as acetyl and hydroxyl groups, structure and surface of both biomass were changed through pretreatment, which is favorable for enzymatic saccharification. Enzymatic saccharification of both pretreated microalgal biomass showed 2–2.5 times higher reducing sugar concentration compared to untreated biomass. Overall, this study concluded that dilute alkaline pretreatment could be a promising alternative method replacing acid pretreatment to enhance the reducing sugar production through enzymatic saccharification of microalgal biomass. [ABSTRACT FROM AUTHOR]

This study evaluates the effect of different concentrations of glucose supplementation on growth, lipid accumulation, and the fatty acid profile in the Auxenochlorella protothecoides . Addition of glucose promoted the growth rate and decreased the chlorophyll content. Compared with photoautotrophic cells, an increase in the lipid content was observed in mixotrophic cells. The glucose addition induced changes in the fatty acid profile. Higher content of saturated fatty acids was found in the case of cells growing in the glucose-free medium. Oleic acid was the predominant component in mixotrophic cells supplemented with 5 g L −1 glucose, while linoleic acids dominated in cultures supplemented with both 1 and 3 g L −1 glucose. The use of glucose was associated with decreased levels of linolenic acid and PUFA. The changes in the fatty acid profile in mixotrophic cells are favourable for biodiesel production. [ABSTRACT FROM AUTHOR]

Extraction of lipids from Chlorella algae with supercritical hexane resulted in the high lipids yield of approximately 10% obtained at optimum conditions in terms of extraction time and agitation compared to the total content of lipids being 12%. Furthermore, an easiness of hexane recovery may be considered as economically and ecologically attractive. For the first time, in the current work catalytic hydrodeoxygenation (HDO) of Chlorella algal lipids was studied over 5 wt % Ni/SiO2 at 300 °C and under 30 bar total pressure in H2. The conversion of lipids was about 15% as the catalyst was totally deactivated after 60 min. The transformation of lipids proceeded mostly via hydrogenation and hydrogenolysis with formation of free fatty acid (FFA). Lower activity might be attributed to deactivation of catalysts caused by chlorophylls and carotenoids. Even though the conversion is low, future studies in HDO of lipids extracted from other algae species having higher lipid content could be proposed. A coke resistant catalyst might be considered to improve catalytic activity. [ABSTRACT FROM AUTHOR]

This study evaluated the effectiveness of pressure-assisted ozonation (PAO) in Chlorella vulgaris (C. vulgaris) cell disruption, and compared the disruption result with that of the ultrasonication (US) by using four quantification indicators: cell counting, ultra violet (UV) absorbance, turbidity and visible light absorbance. It was found that under the condition of 0.8 MPa and 80 cycles, PAO treatment achieved cell rupture of 80.3%, with the power of 1080 W and treatment time of 60 min, US achieved cell rupture of 83.8%. Cell counting was a reliable indicator and applicable to both PAO and US treatments. Turbidity and visible light absorbance gave similar results and featured as the simplest operation. UV absorbance reflected the metabolite release due to cell breakage; however, it was less reproducible when it was applied to quantify the cell rupture by PAO. Its trend indicated that during cell disruption metabolite degradation occurred, especially after significant rupture in the case of excessive PAO treatment. The cellular morphology of C. vulgaris cells during PAO and US treatments was investigated by scanning electron microscope (SEM) which certified that the cells damage was caused by both physical and chemical attack. [ABSTRACT FROM AUTHOR]

Marine microalgae are used in aquaculture as a suspension to feed young fishes and shrimps. Marine Chlorella sp. is one of the most attractive marine microalgae because in addition to pigments it can accumulate lipids at a high content (>30 %) and release exopolymeric substances (EPSs) into the culture medium. This study aimed to evaluate the optimal cultivation of marine Chlorella sp. as potential sources of lipids, EPSs and pigments. Among the culturing regimes tested, mixotrophic cultivation mode produced the highest yields of biomass, lipids and EPSs. Several factors affecting mixotrophic cultivation were optimized. An increase in light intensity up to 65 μmol m s and carbon dioxide up to 10 % v/v in air enhanced both biomass and product formation. An increase in glucose concentration up to 1 % w/v enhanced biomass and EPS yields but decreased lipid and chlorophyll contents. A semi-continuous cultivation under optimal conditions produced microalgal biomass of 2.76 g L with a high lipid content of 44.9 % and EPS of 1.46 g L. This study has also shown that the microalgal lipid and EPS have potential to be used as biodiesel feedstocks and bioflocculants, respectively. The concomitant production of these valuable products together with the microalgal biomass would be a potential way to offset the production cost and contribute greatly to developing industrialized microalgae cultivation. [ABSTRACT FROM AUTHOR]

Key message: Photorespiration in Chlorella protothecoides plays an important role in photoprotection of photosystem (PS) II in the late phase of H photoproduction, allowing PSII to supply more electrons to hydrogenase. [ABSTRACT FROM AUTHOR]

This study investigated the effects of eighteen l -amino acids on the growth and biochemical composition of Chlorella pyrenoidosa . Under the nitrate deficiency condition, ten l -amino acids were found to exert stronger stimulative effects on the algal growth than the other amino acids. After 10-day culture, addition of 0.5 g L −1 the above mentioned ten amino acids significantly increased the cellular protein contents by 441.3–110.8%, respectively, and significantly decreased the carbohydrate contents by 60.7–16.2%, respectively. Under the normal nitrate condition, the cellular biochemical composition was not significantly affected by addition of serine, leucine, proline, aspartic acid, asparagine, and glycine, whereas addition of aspartic acid and arginine increased the algal biomass by 110.2% and 62.8% compared with the control. Finally, the significance of this work in the biotechnological application of culturing C. pyrenoidosa in organic wastewater rich in amino acids was further discussed. [ABSTRACT FROM AUTHOR]

Glutamine is a metabolite of central importance in nitrogen metabolism of microorganisms and plants. The Chlorella PII signaling protein controls, in a glutamine-dependent manner, the key enzyme of the ornithine/arginine biosynthesis pathway, N-acetyl-L-glutamate kinase (NAGK) that leads to arginine formation. We provide evidence that glutamine promotes effective growth of C. variabilis strain NC64A. The present study shows that externally supplied glutamine directly influences the internal pool of arginine in NC64A. Glutamine synthetase (GS) catalyzes the ATP-dependent conversion of glutamate and ammonium to glutamine. The results of this study demonstrate that glutamine acts as a negative effector of GS activity. These data emphasize the importance of glutamine-dependent coupling of metabolism and signaling as components of an efficient pathway allowing the maintenance of metabolic homeostasis and sustaining growth of Chlorella. [ABSTRACT FROM AUTHOR]

Increasing concerns about limited fossil fuel and elevated level of atmospheric carbon dioxide are driving force to develop renewable biofuels, and microalgae are considered a particularly promising feedstock for industrialized biofuel due to their inherent advantages. It is imperative to further optimize the growth conditions in order to achieve maximal algal biomass productivity and low down the cost of microalgal biomass production. The research in this project aimed to enhance lipid production of Chlorella vulgaris by optimizing the nutrient supply and growth conditions. The effects of temperature, nitrogen concentration and initial cell density on neutral lipid productivity were evaluated and optimized by response surface method with a 17-run Box-Behnken design (BBD). With the increase of temperature from 20 to 30°C, the neutral lipid productivity increased up to its peak value at 27°C. However, the 2D contour lines showed the temperature has a significant effect on neutral lipid productivity compared with those of cell density and/or nitrogen concentration. The optimal conditions for the algal growth are 1.5 g L−1 of nitrogen concentration and 50% of cell density at 27.4°C. The optimal lipid productivity obtained from the experiment was in agreement with the model prediction, confirming the validity of the model. © 2015 American Institute of Chemical Engineers Environ Prog, 34: 1801-1807, 2015 [ABSTRACT FROM AUTHOR]

Chlorella vulgaris , a marine microalgae strain adaptable to 0–50 g L −1 of salinity, was selected for studying the coupling system of saline wastewater treatment and lipid accumulation. The effect of total nitrogen (TN) concentration was investigated on algal growth, nutrients removal as well as lipid accumulation. The removal efficiencies of TN and total phosphorus (TP) were found to be 92.2–96.6% and over 99%, respectively, after a batch cultivation of 20 days. To illustrate the response of lipid accumulation to nutrients removal, C. vulgaris was further cultivated in the recycling experiment of tidal saline water within the photobioreactor. The lipid accumulation was triggered upon the almost depletion of nitrate (<5 mg L −1 ), till the final highest lipid content of 40%. The nitrogen conversion in the sequence of nitrate, nitrite, and then to ammonium in the effluents was finally integrated with previous discussions on metabolic pathways of algal cell under nitrogen deficiency. [ABSTRACT FROM AUTHOR]

A model for the autotrophic growth of Chlorella vulgaris ( C. vulgaris ) under photolimitation and photoinhibition in cylindrical photobioreactor was developed by taking into account the interactions between the biomass concentration and light intensity. The growth kinetic model for a batch system was developed by coupling the light distribution under photolimitation and photoinhibition effects with the biomass growth with respect to incident light intensity on the surface of the reactor. The developed model could successfully simulate the specific growth rates, light intensity distribution in the reactor, average light intensities, and biomass concentrations at a given incident light intensity with good accuracy. The prediction of the cell density primarily depended on the determination of the parameters included in the specific growth rate expression, which is a function of the light intensity distribution. Despite the limitation of the semi-empirical specific growth rate expression, the coupled model could predict the biomass growth in different reactor sizes. [ABSTRACT FROM AUTHOR]

In the present study, process engineering strategy was applied to achieve lipid-rich biomass with high density of Chlorella sp. FC2 IITG under photoautotrophic condition. The strategy involved medium optimization, intermittent feeding of limiting nutrients, dynamic change in light intensity, and decoupling growth and lipid induction phases. Medium optimization was performed using combinations of artificial neural network or response surface methodology with genetic algorithm (ANN-GA and RSM-GA). Further, a fed-batch operation was employed to achieve high cell density with intermittent feeding of nitrate and phosphate along with stepwise increase in light intensity. Finally, mutually exclusive biomass and lipid production phases were decoupled into two-stage cultivation process: biomass generation in first stage under nutrient sufficient condition followed by lipid enrichment through nitrogen starvation. The key findings were as follows: (i) ANN-GA resulted in an increase in biomass titer of 157 % (0.95 g L) in shake flask and 42.8 % (1.0 g L) in bioreactor against unoptimized medium at light intensity of 20 μE m s; (ii) further optimization of light intensity in bioreactor gave significantly improved biomass titer of 5.6 g L at light intensity of 250 μE m s; (iii) high cell density of 13.5 g L with biomass productivity of 675 mg L day was achieved with dynamic increase in light intensity and intermittent feeding of limiting nutrients; (iv) finally, two-phase cultivation resulted in biomass titer of 17.7 g L and total lipid productivity of 313 mg L day which was highest among Chlorella sp. under photoautotrophic condition. [ABSTRACT FROM AUTHOR]

Biological fixation of CO 2 using microalgae is an environmentally sustainable option for CO 2 capture. In this study, response surface methodology (RSM) was used to model the CO 2 uptake rate and specific growth rate of Chlorella kessleri , which had been identified previously as a promising strain for CO 2 fixation, cultivated in oil sands process water (OSPW). The quadratic models developed were used to determine the optimal sets of CO 2 concentration, phosphate concentration and light intensity for CO 2 uptake rate and specific growth rate in batch operation. The optimal CO 2 concentration, phosphate concentration and light intensity of 35%, 29 mM and 70 μmol photons m −2 s −1 , respectively, were estimated to maximize the CO 2 uptake rate to 65.03 mg/L/day. Also, the maximum specific growth rate of 0.310 per day was obtained at 22% CO 2 concentration, 29 mM phosphate concentration and 70 μmol photons m −2 s −1 . Finally, a multi-objective optimization technique was used to maximize the CO 2 uptake rate and specific growth rate simultaneously. The optimal Pareto set was found to occur at CO 2 uptake rate of 62.98 mg/L/day and specific growth rate of 0.309 per day at 28% CO 2 , 29 mM phosphate concentration and 70 μmol photons m −2 s −1 light intensity. Thus, each of the optimal conditions correspond to high phosphate concentration and high light intensity in the ranges investigated, while the CO 2 concentration varied between high and intermediate levels in the range investigated. [ABSTRACT FROM AUTHOR]

This study evaluated methane production and nutrient recovery from industrially produced, lipid extracted algal biomass (LEA) of Auxenochlorella protothecoides using semi-continuous anaerobic digestion (AD) at different organic loading rates (OLRs) and hydraulic retention times (HRTs). It was shown, that AD can improve biofuel production efficiency and sustainability, especially for scaled processes, through up to 30% increase in energy generation (up to 0.25 L of methane per g of LEA volatile solids) and partial nutrient recovery and recycling. The nutrient recycling with the AD effluent may reduce the cost of the supplied fertilizers by up to 45%. However, methane production was limited to nearly 50% of theoretical maxima potentially due to biomass recalcitrance and inhibition effects from the residual solvent in the LEA. Therefore, further AD optimization is required to maximize methane yield and nutrient recovery as well as investigation and elimination of inhibition from solvent residues. [ABSTRACT FROM AUTHOR]

Biological methods for wastewater treatment are becoming more accepted over the world. This study it was focused on the benzene, toluene, ethylbenzene and xylenes (BTEX) biodegradation under model conditions by Parachlorella kessleri. BTEX-mixture was added to the cultures as the sole carbon source, at concentration of 100 µg L-1. It was observed loss of BTEX after 24, 48 and 72 h, respect-tively. Benzene and xylenes of 40% was degraded within 48 h. The highest toluene degradation of 63% was achieved. Only 30% of ethylbenzene was degraded after 72 h. On the other hand the elementary analysis of algal biomass was assayed before and after the biodegradation process. After biodegradation the ratio C/N was increased 2.7 times from the value of 14.69 to 39.68. These results favor the biomass after biodegradation process and make it attractive for further use as a suitable substrate for subsequent processing into biofuels of third generation. [ABSTRACT FROM AUTHOR]