The effect of high pH on structural lipids in diatoms

We tested the hypothesis that increased pH reduces the amount of structural lipids. To do this, we used three different diatoms (Phaeodactylum tricornutum CCAP strain, P. tricornutum TV strain and Amphiprora sp). We tested the effect of rapid increase from pH?7.5 to 10 by adding NaOH. The total lipid content was reduced by 13, 36 and 47 % in the P. tricornutum CCAP strain, TV strain and Amphiprora sp., respectively, 1 h after increasing the pH. The P. tricornutum CCAP strain was used for further testing the effect of pH on the lipid content during active growth. This strain was cultivated at pH?7.5 and 10, and the pH was regulated by the CO₂ inflow. The growth rate was similar (0.3 day^?1) in both pH treatments, but the lipid content in the pH?10 treatment was on average 28 % lower than in the pH?7.5 treatment. Our data support the hypothesis that structural lipids are reduced when pH increases to high levels. The results suggest that regulating the pH during algae cultivation could be used to refine the lipid composition in the harvested algal biomass.     

Isolation and characterization of Pseudomonas sp. strain capable of degrading diethylstilbestrol

Since diethylstilbestrol (DES) interrupts endocrine systems and generates reproductive abnormalities in both wildlife and human beings, methods to remove DES from the environments are urgently recommended. In this study, bacterial strain J51 was isolated and tested to effectively degrade DES. J51 was identified as Pseudomonas sp. based on its nucleotide sequence of 16S rRNA. The quinoprotein alcohol dehydrogenase and isocitrate lyase were identified to be involved in DES degradation by MALDI–TOF–TOF MS/MS analysis. In the presence of 40 mg/l DES, increase of the genes encoding quinoprotein alcohol dehydrogenase and isocitrate lyase in both RNA and protein levels was determined. The HPLC/MS analysis showed that DES was hydrolyzed to a major degrading metabolite DES-4-semiquinone. It was the first time to demonstrate the characteristics of DES degradation by specific bacterial strain and the higher degradation efficiency indicated the potential application of Pseudomonas sp. strain J51 in the treatment of DES-contaminated freshwater and seawater environments.     

Nocardia casuarinae sp. nov., an actinobacterial endophyte isolated from root nodules of Casuarina glauca

An actinobacterium strain BMG51109a was isolated from surface sterilized root nodules of Casuarina glauca collected in Tunisia. The 16S rRNA gene sequence of strain BMG51109a showed most similarity (96.53–96.55 %) to the type strains of Nocardia transvalensis, N. aobensis and N. elegans. Chemotaxonomic analysis supported the assignment of the strain to Nocardia genus. The major menaquinone was MK-8(H₄c) while the polar lipid profile contained diphosphatidylglycerol, phosphatidylmonomethylethanolamine, glycophospholipid, phosphatidylinositol, one uncharacterized phospholipid and three glycolipids. Whole-cell sugar analysis revealed the presence of meso-diaminopimelic acid, arabinose and galactose as diagnostic sugars, complemented by glucose, mannose and ribose. The major cellular fatty acids were tuberculostearic, oleic, palmitoleic and stearic acids. Physiological and biochemical tests showed that strain BMG51109a could be clearly distinguished from its closest phylogenetic neighbours. On the basis of these results, strain BMG51109a^T (= DSM 45978^T = CECT 8469^T) is proposed as the type strain of the novel species Nocardia casuarinae sp. nov.     

Physiological characterization of lipid accumulation and in vivo ester formation in Gordonia sp. KTR9

Previous work has demonstrated the feasibility of in vivo biodiesel synthesis in Escherichia coli, however, ethyl ester formation was dependent on an external fatty acid feedstock. In contrast to E. coli, actinomycetes may be ideal organisms for direct biodiesel synthesis because of their capacity to synthesize high levels of triacylglcerides (TAGs). In this study, we investigated the physiology and associated TAG accumulation along with the in vivo ability to catalyze ester formation from exogenous short chain alcohol sources in Gordonia sp. KTR9, a strain that possesses a large number of genes dedicated to fatty acid and lipid biosynthesis. Total lipid fatty acids content increased by 75 % and TAG content increased by 50 % under nitrogen starvation conditions in strain KTR9. Strain KTR9 tolerated the exogenous addition of up to 4 % methanol, 4 % ethanol and 2 % propanol in the media. Increasing alcohol concentrations resulted in a decrease in the degree of saturation of recovered fatty acid alcohol esters and a slight increase in the fatty acid chain length. A linear dose dependency in fatty alcohol ester synthesis was observed in the presence of 0.5–2 % methanol and ethanol compared to control KTR9 strains grown in the absence of alcohols. An inspection of the KTR9 genome revealed the presence of several putative wax ester synthase/acyl-coenzyme A?:?diacylglycerol acyltransferase (WS/DGAT) enzymes, encoded by atf gene homologs, that may catalyze the in vivo synthesis of fatty acid esters from short chain alcohols. Collectively, these results indicate that Gordonia sp. KTR9 may be a suitable actinomycete host strain for in vivo biodiesel synthesis.     

The effect of toxic malachite green on the bacterial community in Antarctic soil and the physiology of malachite green-degrading Pseudomonas sp. MGO

The effects of malachite green (MG) on the bacterial community in Antarctic soil were assessed. Culture-independent community analysis using 16S rRNA gene pyrosequencing showed that, in the presence of MG, the relative abundance of Pseudomonas dramatically increased from 2.2 % to 36.6 % (16.6-fold), and Pseudomonas became the predominant genus. The reduction in bacterial biodiversity was demonstrated by diversity indices and rarefaction curves. MG-degrading Pseudomonas sp. MGO was isolated from Antarctic soil. MG tolerance and decolorization activity were confirmed by growth, spectrophotometric, high-performance liquid chromatography, and thin-layer chromatography analyses in high MG concentrations. Our data showed that the decolorization process occurred via biodegradation, while biosorption also occurred after some time during the fed-batch decolorization process. Significant inductions in laccase, nicotinamide adenine dinucleotide–2,6 dichlorophenol indophenol reductase, and MG reductase activities suggested their involvement in the decolorization process. We also showed that the high tolerance of strain MGO to toxic MG might be mediated by upregulation of oxidative stress defense systems such as superoxide dismutase and protease. Collectively, these results demonstrated the response of the Antarctic soil bacterial community to MG and provided insight into the molecular mechanism of MG-tolerant Pseudomonas strains isolated from Antarctic soil.     

Microbial Community Structure at Different Fermentation Stages of Kutajarista, a Herbal Formulation

Kutajarista is an Ayurvedic fermented herbal formulation prescribed for gastrointestinal disorders. This herbal formulation undergoes a gradual fermentative process and takes around 2 months for production. In this study, microbial composition at initial stages of fermentation of Kutajarista was assessed by culture independent 16S rRNA gene clone library approach. Physicochemical changes were also compared at these stages of fermentation. High performance liquid chromatography–mass spectrometry analysis showed that Gallic acid, Ellagic acid, and its derivatives were the major chemical constituents recovered in this process. At 0 day of fermentation, Lactobacillus sp., Acinetobacter sp., Alcaligenes sp., and Methylobacterium sp. were recovered, but were not detected at 8 day of fermentation. Initially, microbial diversity increased after 8 days of fermentation with 11 operational taxonomic units (OTUs), which further decreased to 3 OTUs at 30 day of fermentation. Aeromonas sp., Pseudomonas sp., and Klebsiella sp. dominated till 30 day of fermentation. Predominance of γ- Proteobacteria and presence of gallolyl derivatives at the saturation stage of fermentation implies tannin degrading potential of these microbes. This is the first study to highlight the microbial role in an Ayurvedic herbal product fermentation.     

Pseudomonas hunanensis sp. nov., Isolated from Soil Subjected to Long-Term Manganese Pollution

A Gram-negative, polar flagella, rod-shaped bacterium LV ^T was isolated from a soil sample subjected to long-term manganese pollution in Hunan Province, China. Cells grow optimally on Luria–Bertani agar medium at 30 °C in the presence of 0–5.0 % (w/v) NaCl and pH 7–8. 16S rRNA gene sequence analysis revealed that strain LV ^T belonged to the genus Pseudomonas, with sequence similarity values of 98.6, 98.2, 98.7, and 97.3 % to Pseudomonas monteilii BCRC 17520 ^T , Pseudomonas putida BCRC 10459 ^T , Pseudomonas plecoglossicida BCRC 17517 ^T , and Pseudomonas asplenii BCRC 17131 ^T , respectively. The level of DNA–DNA relatedness between the five strains was <30 %. The DNA G+C content of strain LV ^T is 68.8 mol%. Chemotaxonomic data revealed that the strain LV^T possesses ubiquinone Q-9. The polar lipid profile of strain LV ^T contained diphosphatidylglycerol, phosphatidylglycerol, phosphatidylcholine, and phosphatidylethanolamine. The major cellular fatty acids present are C_10:03-OH (12.33 %), C_16:0 (23.99 %), summed feature 3(C_16:1ω7c and/or C_16:1ω6c), and summed feature 8(C_{18:1 ω7c} and C_{18:1 ω6c}). Based on the genotypic, chemotaxonomic and phenotypic data, strain LV ^T is distinguishable from related members of the genus Pseudomonas. Thus, strain LV ^T represents a novel species of the genus Pseudomonas, for which the name Pseudomonas hunanensis sp. nov. is proposed. The type strain is LV ^T (=CICC 10558^T = NCCB 100446^T).     

Assessment of atrazine decontamination by epiphytic root bacteria isolated from emergent hydrophytes

Aim of the study was to identify atrazine remediating bacteria that can potentially succeed in situ where they encounter varied environmental conditions. Three epiphytic root bacteria, genus Pseudomonas and Arthrobacter, were isolated from rhizoplanes of hydrophytes Acorus calamus, Typha latifolia, and Phragmites karka. Potential of these strains to decontaminate environmentally relevant concentrations of atrazine was determined in liquid atrazine medium (LAM) and Luria-Bertani (LB) medium at varying pH and temperature. There was an increase in decontamination by the strains with time upon exposure to 2.5 to 10 mg l^?1 atrazine over a period of 15 days, notably, in both minimal and nutrient-rich media. Growth in terms of O.D.₆₀₀ and biomass determined during the same period also showed a corresponding surge. Pseudomonas sp. strain AACB mitigated atrazine in a wide range of pH (5 to 8). Pseudomonas sp. strains AACB and TTLB decontaminated >?62% atrazine at 10 °C. All the strains exhibited plant growth–promoting traits in vitro, reported for the first time in the presence of atrazine. Strain AACB exhibits the novel trait of atrazine decontamination under harsh environmental conditions mimicked in lab. Strains isolated in the present study promise success in in situ remediation. Bioreactors and water treatment plants can be designed comprising the hydrophytes and the strains inoculated into their rhizospheres to improve efficacy of the treatment. They can be used to study plant-bacterium mutualistic symbiosis or other interactions occurring during atrazine mitigation.     

Adhesive properties of predominant bacteria in raw cow’s milk to bovine mammary gland epithelial cells

Various bacteria have been found in raw cow’s milk, and identifying milk microflora and its functions is critical for maintaining cow health and farm hygiene. Although studies on pathogens and spoilage bacteria in milk have been widely reported, the relationship between milk bacteria, including nonpathogenic bacteria, and the bovine udder is poorly understood. We investigated milk microflora over 1 year using a culture-dependent method and culture-independent analysis by denaturing gradient gel electrophoresis. Among 240 isolates, Lactococcus lactis (81/240) was predominant. The predominant genera were Lactococcus, Stenotrophomonas, Microbacterium, Chryseobacterium, Serratia and Pseudomonas. Among seven strains belonging to these predominant genera, two strains of L. lactis (ssp. lactis and ssp. cremoris) exhibited the highest adherence to bovine mammary gland epithelial cells (BMECs) derived from the bovine udder; 3.4 % of the inoculated bacteria adhered to BMECs. This was followed by Serratia sp. (1.6 %), Microbacterium sp. (0.8 %), Stenotrophomonas maltophilia (0.5 %), Pseudomonas sp. (0.3 %) and Chryseobacterium sp. (0.1 %). The two L. lactis isolates exhibited higher adherence to BMECs than type strains and isolates of various origins.     

Kinetics of growth and caffeine demethylase production of Pseudomonas sp. in bioreactor

The effect of various initial caffeine concentrations on growth and caffeine demethylase production by Pseudomonas sp. was studied in bioreactor. At initial concentration of 6.5 g l^?1 caffeine, Pseudomonas sp. showed a maximum specific growth rate of 0.2 h^?1, maximum degradation rate of 1.1 g h^?1, and caffeine demethylase activity of 18,762 U g CDW^?1 (CDW: cell dry weight). Caffeine degradation rate was 25 times higher in bioreactor than in shake flask. For the first time, we show highest degradation of 75 g caffeine (initial concentration 20 g l^?1) in 120 h, suggesting that the tested strain has potential for successful bioprocess for caffeine degradation. Growth kinetics showed substrate inhibition phenomenon. Various substrate inhibition models were fitted to the kinetic data, amongst which the double-exponential (R ² = 0.94), Luong (R ² = 0.92), and Yano and Koga 2 (R ² = 0.94) models were found to be the best. The Luedeking–Piret model showed that caffeine demethylase production kinetics was growth related. This is the first report on production of high levels of caffeine demethylase in batch bioreactor with faster degradation rate and high tolerance to caffeine, hence clearly suggesting that Pseudomonas sp. used in this study is a potential biocatalyst for industrial decaffeination.     

Pseudomonas silesiensis sp. nov. strain A3T isolated from a biological pesticide sewage treatment plant and analysis of the complete genome sequence

Microorganisms classified in to the Pseudomonas genus are a ubiquitous bacteria inhabiting variety of environmental niches and have been isolated from soil, sediment, water and different parts of higher organisms (plants and animals). Members of this genus are known for their metabolic versatility and are able to utilize different chemical compounds as a source of carbon, nitrogen or phosphorus, which makes them an interesting microorganism for bioremediation or bio-transformation. Moreover, Pseudomonas sp. has been described as a microorganism that can easily adapt to new environmental conditions due to its resistance to the presence of high concentrations of heavy metals or chemical pollution. Here we present the isolation and analysis of Pseudomonas silesiensis sp. nov. strain A3^T isolated from peaty soil used in a biological wastewater treatment plant exploited by a pesticide packaging company. Phylogenetic MLSA analysis of 4 housekeeping genes (16S rRNA, gyrB, rpoD and rpoB), complete genome sequence comparison (ANIb, Tetranucleotide identity, digital DDH), FAME analysis, and other biochemical tests indicate the A3^T strain (type strain PCM 2856^T = DSM 103370^T) differs significantly from the closest relative species and therefore represents a new species within the Pseudomonas genus. Moreover, bioinformatic analysis of the complete sequenced genome showed that it consists of 6,823,539 bp with a 59.58 mol% G + C content and does not contain any additional plasmids. Genome annotation predicted the presence of 6066 genes, of which 5875 are coding proteins and 96 are RNA genes.     

Biomass and oil content of Chlorella sp., Haematococcus sp., Nannochloris sp. and Scenedesmus sp. under mixotrophic growth conditions in the presence of technical glycerol

The growth of algae strains Chlorella sp., Haematococcus sp., Nannochloris sp. and Scenedesmus sp. under mixotrophic conditions in the presence of different concentrations of technical glycerol was investigated with the aim of increasing biomass growth and algae oil content. The highest concentration of lipid obtained in media with 5 g L^?1 glycerol for Chlorella sp., Scenedesmus sp., Nannochloris sp. and Haematococcus sp. was 17.77, 22.34, 27.55 and 34.22 % larger than during the autotrophic growth of these species. Increases in triacylglycerols of up to ten times was observed for Scenedesmus sp. under mixotrophic conditions (using 10 g L^?1 glycerol), whereas an increase of 2.28 times was found for Haematococcus sp. The content of saturated fatty acids of Scenedesmus, Chlorella, Haematococcus and Nannochloris was 67.11, 34.63, 23.39 and 24.23 %, and the amount of unsaturated fatty acids was 32.9, 65.06, 79.61 and 75.78 % of total fatty acids, respectively. Growth on technical glycerol of these strains with light produced higher biomass concentrations and lipid content compared with autotrophic growth. The fatty acid content of oils from these species suggests their potential use as biodiesel feedstock.     

Nocardioides rubroscoriae sp. nov., isolated from volcanic ash

A rod-shaped actinobacterium, designated Sco-A25^T, was isolated from a red-coloured layer of scoria (volcanic ash) in the Republic of Korea and subjected to a polyphasic taxonomic characterization. Phylogenetic analysis based on the 16S rRNA gene sequence showed that strain Sco-A25^T is a member of the genus Nocardioides and formed a tight monophyletic unit with the type strain of Nocardioides plantarum (98.7 % gene similarity). LL-Diaminopimelic acid was detected in the cell wall. The predominant menaquinone is MK-8(H₄). The polar lipids found were phosphatidylinositol, diphosphatidylglycerol, phosphatidylglycerol, and an unknown phospholipid. The fatty acid profile was represented by large amounts of saturated, unsaturated and iso-branched fatty acids. The DNA G+C content was 71.6 mol %. Genomic DNA similarity between strain Sco-A25^T and N. plantarum KCTC 9577^T was 47.8 %. On the basis of the results of phenotypic, genetic and phylogenetic analyses presented here, strain Sco-A25^T is considered to represent a novel species of the genus Nocardioides, for which the name Nocardioides rubroscoriae sp. nov. is proposed. The type strain is Sco-A25^T (=KCTC 19805^T = DSM 23986^T = NBRC 107916^T).     

Beneficial native bacteria improve survival and mycorrhization of desert truffle mycorrhizal plants in nursery conditions

Sixty-four native bacterial colonies were isolated from mycorrhizal roots of Helianthemum almeriense colonized by Terfezia claveryi, mycorrhizosphere soil, and peridium of T. claveryi to evaluate their effect on mycorrhizal plant production. Based on the phylogenetic analysis of the 16S rDNA partial sequence, 45 different strains from 17 genera were gathered. The largest genera were Pseudomonas (40.8 % of the isolated strains), Bacillus (12.2 % of isolated strains), and Varivorax (8.2 % of isolated strains). All the bacteria were characterized phenotypically and by their plant growth-promoting rhizobacteria (PGPR) traits (auxin and siderophore production, phosphate solubilization, and ACC deaminase activity). Only bacterial combinations with several PGPR traits or Pseudomonas sp. strain 5, which presents three different PGPR traits, had a positive effect on plant survival and growth. Particularly relevant were the bacterial treatments involving auxin release, which significantly increased the root-shoot ratio and mycorrhizal colonization. Moreover, Pseudomonas mandelii strain 29 was able to considerably increase mycorrhizal colonization but not plant growth, and could be considered as mycorrhiza-helper bacteria. Therefore, the mycorrhizal roots, mycorrhizosphere soil, and peridium of desert truffles are environments enriched in bacteria which may be used to increase the survival and mycorrhization in the desert truffle plant production system at a semi-industrial scale.     

Characterization of a novel antarctic plant growth-promoting bacterial strain and its interaction with antarctic hair grass (Deschampsia antarctica Desv)

Deschampsia antarctica is the only hair grass that has been able to successfully colonize the Antarctic continent. However, there is little research on the role of microorganisms associated with the rhizosphere that may participate in its growth and development. The objective of this research was to characterize a psychrotolerant bacterial strain isolated from the rhizosphere of D. antarctica. Biochemical and molecular studies were performed to characterize this bacterium. It was determined that this strain secretes a neutral polysaccharide that presents different compositions at different temperatures (4 and 20 °C). Based on biochemical and phylogenetic analyses, the Antarctic rhizobacterium could be a new species of Pseudomonas. To determine their ability to solubilize different sources of inorganic phosphate, qualitative and quantitative analyses were conducted to determine P released at 4 °C. The Antarctic strain of Pseudomonas sp. was able to solubilize all sources of phosphates, and 34.2 mg P/L was released from rock phosphate. Growth physiological parameters were evaluated for seedlings of D. antarctica inoculated with the rhizobacteria. It was found that the bacterial inoculation promoted plant root development. SEM analysis of the roots showed that the bacterium is mainly located in the root hairs of D. antarctica.     

Cold-Adapted RTX Lipase from Antarctic Pseudomonas sp. Strain AMS8: Isolation, Molecular Modeling and Heterologous Expression

A new strain of psychrophilic bacteria (designated strain AMS8) from Antarctic soil was screened for extracellular lipolytic activity and further analyzed using molecular approach. Analysis of 16S rDNA showed that strain AMS8 was similar to Pseudomonas sp. A lipase gene named lipAMS8 was successfully isolated from strain AMS8, cloned, sequenced and overexpressed in Escherichia coli. Sequence analysis revealed that lipAMS8 consist of 1,431 bp nucleotides that encoded a polypeptide consisting of 476 amino acids. It lacked an N-terminal signal peptide and contained a glycine- and aspartate-rich nonapeptide sequence at the C-terminus, which are known to be the characteristics of repeats-in-toxin bacterial lipases. Furthermore, the substrate binding site of lipAMS8 was identified as S²⁰⁷, D²⁵⁵ and H³¹³, based on homology modeling and multiple sequence alignment. Crude lipase exhibited maximum activity at 20 °C and retained almost 50 % of its activity at 10 °C. The molecular weight of lipAMS8 was estimated to be 50 kDa via sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The optimal expression level was attained using the recombinant plasmid pET32b/BL21(DE3) expressed at 15 °C for 8 h, induced by 0.1 mM isopropyl β-D thiogalactoside (IPTG) at E. coli growth optimal density of 0.5.     

Pseudomonas sihuiensis sp. nov., isolated from a forest soil in South China

A Gram-stain negative, motile, rod-shaped bacterium, designated strain WM-2^T, was isolated from a forest soil in Sihui City, South China, and characterized by means of a polyphasic approach. Growth occurred with 0–5 % (w/v) NaCl (optimum 0–1 %) and at pH 5.0–10.5 (optimum pH 8.5) and 4–40 °C (optimum 30 °C) in Luria–Bertani medium. Comparative 16S rRNA gene sequence analyses showed that strain WM-2^T is a member of the genus Pseudomonas and most closely related to P. guguanensis, P. oleovorans subsp. lubricantis, P. toyotomiensis, P. alcaliphila and P. mendocina with 97.1–96.6 % sequence similarities. In terms of gyrB and rpoB gene sequences, strain WM-2^T showed the highest similarity with the type strains of the species P. toyotomiensis and P. alcaliphila. The DNA–DNA relatedness values of strain WM-2^T with P. guguanensis and P. oleovorans subsp. lubricantis was 48.7 and 37.2 %, respectively. Chemotaxonomic characteristics (the main ubiquinone Q-9, major fatty acids C_18:1 ω7c/C_18:1 ω6c, C_16:0 and C_16:1 ω7c/C_16:1 ω6c and DNA G+C content 65.2 ± 0.7 mol%) were similar to those of members of the genus Pseudomonas. Polar lipids consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, an unknown aminophospholipid, an unknown phospholipid and five unknown lipids. According to the results of polyphasic analyses, strain WM-2^T represents a novel species in the genus Pseudomonas, for which the name Pseudomonas sihuiensis sp. nov. is proposed. The type strain is WM-2^T (=KCTC 32246^T=CGMCC 1.12407^T).     

Coralslurrinella hongkonensis gen. nov., sp. nov., a novel bacterium in the family Psychromonadaceae, isolated from the coral Platygyra carnosus

A novel bacterial strain, JLT2006^T, was isolated from the scleractinian coral Platygyra carnosus, located in Hong Kong, China. Cells of this strain were Gram-negative, rod-shaped or oval-shaped and motile by the means of polar flagella. They formed faint-yellow, round colonies on marine agar medium. Phylogenetic analyses based on the 16S rRNA gene sequence indicated that the strain JLT2006^T belonged to the class Gammaproteobacteria and was most closely related to Alteromonas-like bacteria of the genera Psychromonas, Pseudoalteromonas, Moritella, Shewanella and Ferrimonas, with less than 93 % sequence similarity. The predominant fatty acids were identified as C18:1ω7c/C18:1ω6c (23.0 %), C16:1ω7c/C16:1ω6c (18.2 %) and C16:0 (16.4 %). The quinone was menaquinone-7 (100 %). The polar lipids were determined to be phosphatidylglycerol, phosphatidylethanolamine, phospholipid, glycolipid and lipid. The genomic DNA G+C content was 40.3 mol%. Based on the 16S rRNA gene sequence as well as the physiological and biochemical features that separate the strain JLT2006^T from other recognized bacteria, a novel species of a new genus with the name Coralslurrinella hongkonensis gen. nov., sp. nov. is proposed. The type strain is JLT2006^T (=JCM 18796^T = CGMCC 1.10992^T).     

Effects of initial population density (IPD) on growth and lipid composition of Nannochloropsis sp.

The microalga Nannochloropsis sp. was cultured under different initial population densities (IPDs) ranging from 0.11 to 9.09 g L^?1. The IPD affected the biomass and lipid accumulation significantly. The algal cultured with higher IPD resulted higher biomass concentration (up to 13.07 g L^?1) in 10 days growth. The biomass productivity with 0.98 g L^?1 IPD was 0.75 g L^?1 d^?1 which was higher than that of other IPDs. For IPDs ranging from 0.11 to 0.98 g L^?1, with the increase of IPD, the biomass productivity increased, while for IPD over 0.98 g L^?1, the biomass productivity decreased. Lipid content of the algal culture started with 0.11 g L^?1 IPD reached to 42 % of dry weight. But with the increase of IPD, the lipid content decreased. Lipid composition was analyzed using thin layer chromatography coupled with flame ionization detection (TLC/FID). Seven lipid classes were identified and quantified. The main reserve lipid, triacylglyceride (TAG), accumulated under all different IPD conditions. However, with the increasing IPD values, TAG content decreased from 59.1 to 23.5 % of the total lipids. Based on these results, to obtain the maximal biomass productivity and lipid productivity of Nannochloropsis sp. in mass cultivation systems, it is necessary to select an appropriate IPD.