The Effect of Monochromatic Light on α-Linolenic and Trans-3-Hexadecenoic Acids Biosynthesis, and Its Correlation to the Development of the Plastid Lamellar System

Seven day old etiolated Zea mays L. (cv. Wisconsin 355) seedlings were illuminated for 20 h under monochromatic radiations (100 Á pass band) produced by a spectral illuminator of high energy. Four regions of the visible spectrum were observed to stimulate chlorophyll synthesis. With poorly developed leaves (grown for 7 days at 22°C: experiment A). the most efficient wavelengths were found to be in the blue and green (between 445 and 505 nm). yellow (between 580 and 605 nm) and red (maximum 650 nm) parts of the spectrum. With well developed leaves (grown for 7 clays al 27°C: experiment B), a slight displacement of the maxima towards shorter wavelengths was observed. ¹⁴C-acetate was furnished to illuminated maize seedlings to follow lipid synthesis during greening. In the leaves of experiment A, the biosynthesis of α-linolenic acid and monogalactosyldiacylglycerol followed chlorophyll accumulation. In the more developed leaves of experiment B. containing higher amounts of galactolipids, the biosynthesis of α-linolenic acid and monogalactosyldiacylglycerol followed chlorophyll accumulation only in blue and yellow light. The biosynthesis of trans-3-hexadecenoic acid was strictly dependent on the wavelength of the irradiating light in the leaves of experiment A; it was optimal under blue (420 nm) and still very high under yellow (580 nm) and red (650 nm). In the more developed leaves of experiment B, it was optima in blue (445 nm) and in yellow (580 nm), and the red maximum was shifted to 630 nm. All C-trans-3-hexadecenoic acid was incorporated into phosphatidylglycerol. A marked relationship was observed between the intensity of galactolipid synthesis and the development of the lamellar system of maize plastids during greening. A positive correlation could be established between the biosynthesis of trans-3-hcxadeccnoie acid and the development of well constituted grana stacks in the plastids.     

Far‐red dependent changes in the chemical composition of Spirulina platensis

The influence of far‐red light (FRL) was studied on the chemical composition of Spirulina platensis biomass. The following light compositions were used during the culture white light, blue‐red LED light (BRL) and BRL supplemented with FRL (BRFRL). Chlorophyll and phenol contents were measured by spectrophotometric methods, whereas presence of carotenoids, lipids, and phycobiliproteins were estimated by Fourier‐transform Raman spectrometry. Additionally, phenol content was investigated by fluorescence intensity of algae culture in the range of 430–650 nm. The content of chlorophyll and phenols in algae cells depended on the spectral composition of light and was the highest under BRL (16.7 ± 0.5 and 9.1 ± 0.6, respectively). It was shown that there is a positive linear correlation (R = 0.902 at p < 0.0000001) between the ratio of relative fluorescence intensity of S. platensis suspensions at 450 nm to the suspensions at 540 nm (F450/F540) and the content of phenolic compounds in the biomass. Changes in the F450/F540 ratio can explain approximately 80% changes of phenol contents in algae cells. Spirulina platensis Raman spectra demonstrated that the biomass of algae growing under white light and BRL had a significantly higher intensity of phycobiliprotein bands than the algae growing under BRFRL.     

Microalga <Emphasis Type="Italic">Scenedesmus obliquus</Emphasis> as a potential source for biodiesel production

Biodiesel from microalgae seems to be the only renewable biofuel that has the potential to completely replace the petroleum-derived transport fuels. Therefore, improving lipid content of microalgal strains could be a cost-effective second generation feedstock for biodiesel production. Lipid accumulation in Scenedesmus obliquus was studied under various culture conditions. The most significant increase in lipid reached 43% of dry cell weight (dcw), which was recorded under N-deficiency (against 12.7% under control condition). Under P-deficiency and thiosulphate supplementation the lipid content also increased up to 30% (dcw). Application of response surface methodology in combination with central composite rotary design (CCRD) resulted in a lipid yield of 61.3% (against 58.3% obtained experimentally) at 0.04, 0.03, and 1.0 g l⁻¹ of nitrate, phosphate, and sodium thiosulphate, respectively for time culture of 8 days. Scenedesmus cells pre-grown in glucose (1.5%)-supplemented N 11 medium when subjected to the above optimized condition, the lipid accumulation was boosted up to 2.16 g l⁻¹, the value ~40-fold higher with respect to the control condition. The presence of palmitate and oleate as the major constituents makes S. obliquus biomass a suitable feedstock for biodiesel production.     

Enhancement of total lipid yield by nitrogen,carbon, and iron supplementation in isolated microalgae

The biochemical contents and biodiesel production ability of three microalgal strains grown under different sodium nitrate, sodium carbonate, and ferric ammonium citrate (iron) levels were investigated. The highest biomass and lipid contents were found in Scenedesmus sp., Chlorella sp., and Chlamydomonas sp. when grown in normal BG‐11 containing sodium carbonate concentration at 0.03 g · L^?1, and in normal BG‐11 containing iron concentration (IC) at 0.009 or 0.012 g · L^?1. Increasing the sodium nitrate level increased the biomass content, but decreased the lipid content in all three microalgae. Among the three microalgae, Scenedesmus sp. showed the highest total lipid yield of 0.69 g · L^?1 under the IC of 0.012 g · L^?1. Palmitic and oleic acids were the major fatty acids of Scenedesmus sp. and Chlamydomonas sp. lipids. On the other hand, Chlorella sp. lipids were rich in palmitic, oleic, and linolenic acids, and henceforth contributing to poor biodiesel properties below the standard limits. The three isolated strains had a potential for biodiesel production. Nevertheless, Scenedesmus sp. from stone quarry pond water was the most suitable source for biodiesel production with tolerance toward the high concentration of sodium carbonate without the loss of its biodiesel properties.     

Culture of microalgae Chlorella minutissima for biodiesel feedstock production

Microalgae are among the most promising of non‐food based biomass fuel feedstock alternatives. Algal biofuels production is challenged by limited oil content, growth rate, and economical cultivation. To develop the optimum cultivation conditions for increasing biofuels feedstock production, the effect of light source, light intensity, photoperiod, and nitrogen starvation on the growth rate, cell density, and lipid content of Chlorella minutissima were studied. The fatty acid content and composition of Chlorella minutissima were also investigated under the above conditions. Fluorescent lights were more effective than red or white light‐emitting diodes for algal growth. Increasing light intensity resulted in more rapid algal growth, while increasing the period of light also significantly increased biomass productivity. Our results showed that the lipid and triacylglycerol content were increased under N starvation conditions. Thus, a two‐phase strategy with an initial nutrient‐sufficient reactor followed by a nutrient deprivation strategy could likely balance the desire for rapid and high biomass generation (124 mg/L) with a high oil content (50%) of Chlorella minutissima to maximize the total amount of oil produced for biodiesel production. Moreover, methyl palmitate (C16:0), methyl oleate (C18:1), methyl linoleate (C18:2), and methyl linolenate (C18:3) are the major components of Chlorella minutissima derived FAME, and choice of light source, intensity, and N starvation impacted the FAME composition of Chlorella minutissima. The optimized cultivation conditions resulted in higher growth rate, cell density, and oil content, making Chlorella minutissima a potentially suitable organism for biodiesel feedstock production. Biotechnol. Bioeng. 2011;108: 2280–2287. © 2011 Wiley Periodicals, Inc.     

Scenedesmus sp. NJ-1 isolated from Antarctica: a suitable renewable lipid source for biodiesel production

Microalgal lipids are promising alternative feedstocks for biodiesel production. Scenedesmus sp. NJ-1, an oil-rich freshwater microalga isolated from Antarctica, was identified to be a suitable candidate to produce biodiesel in this study. This strain could grow at temperatures ranging from 4 to 35?°C. With regular decrease in nitrate concentration in the medium, large quantities of triacylglycerols accumulated under batch culture conditions detected by thin layer chromatography and BODIPY 505/515 fluorescent staining. Scenedesmus sp. NJ-1 achieved the average biomass productivity of 0.105?g?l^?1?d^?1 (dry weight) and nearly the highest lipid content (35?% of dry cell weight) was reached at day 28 in the batch culture. Neutral lipids accounted for 78?% of total lipids, and C18:1 (n-9), C16:0 were the major fatty acids in total lipids, composing 37 and 20?% of total fatty acids of Scenedesmus sp. NJ-1 grown for 36?days, respectively. These results suggested that Scenedesmus sp. NJ-1 was a good source of microalgal oils for biodiesel production.     

Altered lipid composition and enhanced lipid production in green microalga by introduction of brassica diacylglycerol acyltransferase 2

Higher lipid biosynthesis and accumulation are important to achieve economic viability of biofuel production via microalgae. To enhance lipid content, Chlamydomonas reinhardtii was genetically engineered with a key enzyme diacylglycerol acyltransferase (BnDGAT2) from Brassica napus, responsible for neutral lipid biosynthesis. The transformed colonies harbouring aph7 gene, screened on hygromycin‐supplemented medium, achieved transformation frequency of ~120 ± 10 colonies/1 × 10⁶ cells. Transgene integration and expression were confirmed by PCR, Southern blots, staining lipid droplets, proteins and spectro‐fluorometric analysis of Nile red‐stained cells. The neutral lipid is a major class (over 80% of total lipids) and most significant requirement for biodiesel production; this was remarkably higher in the transformed alga than the untransformed control. The levels of saturated fatty acids in the transformed alga decreased to about 7% while unsaturated fatty acids increased proportionately when compared to wild type cells. Polyunsaturated fatty acids, especially α‐linolenic acid, an essential omega‐3 fatty acid, were enhanced up to 12% in the transformed line. Nile red staining confirmed formation of a large number of lipid globules in the transformed alga. Evaluation of long‐term stability and vitality of the transgenic alga revealed that cryopreservation produced significantly higher quantity of lipid than those maintained continuously over 128 generations on solid medium. The overexpression of BnDGAT2 significantly altered the fatty acids profile in the transformed alga. Results of this study offer a valuable strategy of genetic manipulation for enhancing polyunsaturated fatty acids and neutral lipids for biofuel production in algae.     

Metabolic activity,the chemical composition of biomass and photosynthetic activity of Chlorella vulgaris under different light spectra in photobioreactors

Omitting the far‐red in LED lighting for bioreactors is inexplicable because it affects photosynthetic efficiency and photomorphogenetic activity. Therefore, this work compares three light sources (fluorescent—white light (WL), and LED: blue + red—BRL and blue + red + far‐red—BRFRL) for cultures of Chlorella vulgaris. Metabolic activity was determined by isothermal calorimetry. Changes in the chemical composition of biomass were examined by spectrofluorimetry and Raman spectroscopy. Maximum quantum yield of photosystem II was determined on the basis of chlorophyll a fluorescence parameters. The algae grown under BRL produced significantly more thermal energy than those cultured under BRFRL and WL. The Raman spectra of cultures showed characteristic bands for carotenoids, chlorophyll, phenolics, lipids, aliphatic carbohydrates, pectins, and disaccharides. According to the cluster analysis, the chemical composition of cultures grown under BRL and BRFRL was very similar, whereas the WL represented a distinct group. BRL and BRFRL stimulated the biosynthesis of an unidentified compound(s) with fluorescence maximum at 614 nm. At the beginning of the cultivation, photosystem II had very weak photochemical activity. Under BRFRL, ratios of Fv/Fm reached the maximum after 4 days, whereas under BRL and WL, after 6 days of cultivation. The results point to the favorable influence of the far‐red on the metabolism of microalgae.     

Lipid analysis of Neochloris oleoabundans by liquid state NMR

This study is an evaluation of liquid state NMR as a tool for analyzing the lipid composition of algal cultures used for biodiesel production. To demonstrate the viability of this approach, ¹³C NMR was used to analyze the lipid composition of intact cells of the algal species, Neochloris oleoabundans (UTEX #1185). Two cultures were used in this study. One culture was “healthy” and grown in conventional media, whereas the other culture was “nitrogen‐starved” and grown in media that lacked nitrate. Triglyceride was determined to be present in both cultures by comparing the algal NMR spectra with published chemical shifts for a wide range of lipids and with a spectrum obtained from a triglyceride standard (glyceryl trioleate). In addition, it is shown that (1) the signal‐to‐noise ratio of the ～29.5 ppm methylene peak is indicative of the lipid content and (2) the nitrogen‐starved culture contained a greater lipid content than the healthy culture, as expected. Furthermore, the nitrogen‐starved culture produced spectra that primarily contained the characteristic peaks of triglyceride (at ～61.8 and ～68.9 ppm), whereas the healthy culture produced spectra that contained several additional peaks in the glycerol region, likely resulting from the presence of monoglyceride and diglyceride. Finally, potential interferences are evaluated (including the analysis of phospholipids via ³¹P NMR) to assess the specificity of the acquired spectra to triglyceride. These results indicate that NMR is a useful diagnostic tool for selectively identifying lipids in algae, with particular relevance to biodiesel production. Biotechnol. Bioeng. 2010;106: 573–583. © 2010 Wiley Periodicals, Inc.     

The microalga Parachlorella kessleri––A novel highly efficient lipid producer

The alga Parachlorella kessleri, strain CCALA 255, grown under optimal conditions, is characterized by storage of energy in the form of starch rather than lipids. If grown in the complete medium, the cultures grew rapidly, producing large amounts of biomass in a relatively short time. The cells, however, contained negligible lipid reserves (1–10% of DW). Treatments inducing hyperproduction of storage lipids in P. kessleri biomass were described. The cultures were grown in the absence or fivefold decreased concentration of either nitrogen or phosphorus or sulfur. Limitation by all elements using fivefold or 10‐fold diluted mineral medium was also tested. Limitation with any macroelement (nitrogen, sulfur, or phosphorus) led to an increase in the amount of lipids; nitrogen limitation was the most effective. Diluted nutrient media (5‐ or 10‐fold) were identified as the best method to stimulate lipid overproduction (60% of DW). The strategy for lipid overproduction consists of the fast growth of P. kessleri culture grown in the complete medium to produce sufficient biomass (DW more than 10 g/L) followed by the dilution of nutrient medium to stop growth and cell division by limitation of all elements, leading to induction of lipid production and accumulation up to 60% DW. Cultivation conditions necessary for maximizing lipid content in P. kessleri biomass generated in a scale‐up solar open thin‐layer photobioreactor were described. Biotechnol. Bioeng. 2013; 110: 97–107. © 2012 Wiley Periodicals, Inc.     

Temporal and metabolic overlap between lipid accumulation and programmed cell death due to nitrogen starvation in the unicellular chlorophyte Chlamydomonas reinhardtii

Lipid accumulation due to nitrogen depletion has been studied extensively in Chlamydomonas reinhardtii and the metabolic changes that lead to triacylglycerol biosynthesis have been of particular interest to researchers in the biodiesel industry. The induction of programmed cell death (PCD) in response to nitrogen starvation has also been documented in related chlorophytes. Here, we examined the temporal and metabolic overlap of lipid accumulation and PCD in response to nitrogen starvation in the important model organism C. reinhardtii. Nitrogen starvation induced physiological stress, measured by the progressive decline in chlorophyll a fluorescence, reduced photosynthetic efficiency and decreased growth. In keeping with previous reports, cells accumulated lipids reaching a peak after 2–3 days. At the same time, DNA nicking and caspase‐like protease activity was observed in a proportion of cells, and ultrastructural observations confirmed that death was via PCD. Our results demonstrate that DNA nicking and caspase‐like activity are observed during PCD in C. reinhardtii in response to nitrogen starvation, and that death occurs at the same time as lipid biosynthesis. Microalgal lipid production due to nitrogen depletion in C. reinhardtii is limited by the decrease in culture growth and knowing that the loss of culture density is, at least in part, due to PCD is important for the biotechnology industry.     

Photophosphorylation and Ultrastructural Development in Pinus nigra Chloroplasts, Grown under Different Spectral Composition of Light

Developed pine seedlings synthesize chlorophyll in darkness. Their photosystem II reducing capacity is very low. The development of chloroplast structure and of photophosphorylation ability has been studied in plastids isolated from Pinus nigra (var. austriaca) developed for 14 days under different spectral compositions of light as compared with chloroplasts isolated from seedlings grown under white light or in darkness. Chloroplast structure was studied by electron microscopy. Cyclic and non-cyclic photophosphorylation were studied under white light. The spectral bands which are efficient for the development of granal structures are different from those needed to make photosystem II functional: red light makes photosystem II functional but does not permit the formation of granal structure, and under yellow light the granal structure develops but photosystem II is not fully functional. Orange light alone fulfils both these purposes. The spectral band around 650 nm seems effective in making the photosystem II functional.     

Effect of light emitting diodes on the cultivation of Spirulina platensis using NPK‐10:26:26 complex fertilizer

NPK‐10:26:26 complex fertilizer based culture medium was studied for the mass production of Spirulina platensis using different light emitting diodes (LEDs). First, cultivation was carried out under white LED to formulate the optimum fertilizer loading for which Spirulina growth was maximized. Optimum composition for newly formulated fertilizer medium was NPK fertilizer ?0.76 g L^?1 and sodium bicarbonate ?10.0 g L^?1 and corresponding biomass productivity was found to be 76.67 mg L^?1 day^?1. The effect of different LEDs (for example, blue, white, red, green and yellow) on Spirulina growth kinetics and the accumulation of chlorophyll, protein and lipid content was determined using the optimum NPK fertilizer medium. Kinetic parameters (i.e., biomass productivity, maximum specific growth rate, maximum biomass concentration, nitrogen‐to‐biomass conversion factor and phosphorus‐to‐biomass conversion factor) and chlorophyll accumulation were affected by the use of different LEDs and follow the following trend: blue > white > red > green > yellow, whereas protein and lipid accumulation was almost independent of LEDs used. Elemental C, N, P and K concentrations were measured to find the effects of nutrients for the growth of Spirulina platensis. Physicochemical parameters (pH and conductivity) were also monitored during biomass growth under different LEDs. Finally, biomass growth using NPK‐10:26:26 fertilizer under different LEDs was compared with standard Zarrouk medium and better growth results were obtained using optimally formulated NPK‐10:26:26 fertilizer medium.     

Red light and carbon dioxide differentially affect growth,lipid production,and quality in the microalga, <Emphasis Type="Italic">Ettlia oleoabundans</Emphasis>

Ettlia oleoabundans, a freshwater unicellular green microalga, was grown under different light qualities ± carbon dioxide-enriched air to determine the combined effects on growth and lipid production of this oleaginous species. Keeping total light intensity constant, when a portion of the cool white was replaced by red, volumetric lipid yield increased 2.8-fold mainly due to the greater yield of oleic acid, a desirable biodiesel precursor. Only 30 min of red light treatment was sufficient to increase lipid yield and quality to the same level as cultures provided red light for >14 days, indicating the potential role of red light in stimulating lipid production of this species. Carbon dioxide enrichment via air sparging enhanced exponential growth, carbon conversion efficiency, and nutrient consumption. Together, these results showed that light quality plays an important role in microalgal lipid production. Adjustment in light quality and gas delivery efficiency with carbon dioxide enrichment improved lipid yield and quality in this and possibly other oleaginous algal species.     

Organic nitrogen of tomato waste hydrolysate enhances glucose uptake and lipid accumulation in Cunninghamella echinulata

Aims: To investigate the effect of organic nitrogen on lipogenesis during growth of Cunninghamella echinulata on tomato waste hydrolysate (TWH) media. Methods and Results: Cunninghamella echinulata grown on a TWH medium rapidly took up glucose and produced large amounts of lipids. However, when some quantities of the organic nitrogen were removed from TWH (by acid followed by alkaline precipitation of proteins) the uptake of glucose was dramatically reduced and large quantities of fungal biomass having low lipid content were produced. Nevertheless, when glycerol was used as carbon source instead of glucose, the uptake rate as well as the biomass production and the lipid accumulation processes were unaffected by the TWH organic nitrogen removal. Finally, when the fungus was grown on a glucose supplemented TWH medium that contained no assimilable organic nitrogen (after further precipitation of proteins with methanol), the produced biomass contained non-negligible quantities of lipids, although glucose uptake remained low. Lipid analysis showed that the produced lipids comprised mainly of neutral lipids, which were preferentially consumed during lipid turnover. Lipid production on the original TWH medium having glucose as carbon source was 0·48 g of lipid per gram of dry biomass, corresponding to 8·7 g of lipid per litre of growth medium. The produced lipids contained 11·7%γ-linolenic acid (GLA), hence the GLA yield was more than 1 g l⁻¹. Conclusions: Organic nitrogen compounds found in TWH favour glucose (but not glycerol) uptake and lipid accumulation in C. echinulata. Significance and Impact of the Study: Agro-industrial wastes containing organic nitrogen, such as tomato waste, are produced in vast amounts causing severe environmental problems. These wastes could be used as fermentation feedstock to produce microbial lipids.     

Direct bioconversion of rice residue from canteen waste into lipids by new amylolytic oleaginous yeast Sporidiobolus pararoseus KX709872

The new amylolytic oleaginous red yeast, Sporidiobolus pararoseus KX709872, produced both α-amylase (540?±?0.09?mU/mL) and amyloglucosidase (23?±?0.00?mU/mL) and showed good ability to directly convert rice residue from canteen waste to biomass and lipids. Effects of medium composition and cultivation conditions on growth and lipid accumulation for strain KX709872 were investigated under shaking flask and upscaling levels. At C?:?N ratio of 25?:?1, pH 5.45, 22.36°C, and 199.40?rpm for 7 days, volumetric production of biomass and lipids, lipid content, and lipid productivity reached 17.69?±?0.44, 8.35?±?0.19?g/L, 49.48?±?0.41% (w/w), and 1.67?±?0.11?g/L/day, respectively. Production of lipids was also implemented in 5.0-L stirred tank bioreactor with 2.5?L of optimized medium at 300?rpm and 3.0 vvm for 5 days. Volumetric production of biomass and lipids, lipid content, and lipid productivity were 16.33?±?0.49, 8.75?±?0.13?g/L, 56.61?±?0.04% (w/w), and 2.19?±?0.03?g/L/day, respectively. Meanwhile, the fatty acids of lipids from strain KX709872 had high oleic acid content (60?62%) which was similar to those of vegetable oils, indicating that these lipids are promising as an alternative biodiesel feedstock. Moreover, the biodiesel derived from lipids of strain KX709872 had properties satisfying the criteria of ASTM D6751 and EN 14214 standards.     

A new combined approach to improved lipid production using a strictly aerobic and oleaginous yeast

Microbial lipids have potential applications in energy, and food industry, because most of those lipids are triacylglycerol with long‐chain fatty‐acids that are comparable to conventional vegetable oils and can be obtained without arable land requirement. Rhodosporidium toruloides is a strictly aerobic strain, where oxygen plays a crucial role in growth, maintenance, and metabolite production, such as lipids and carotenoids. Dissolved oxygen concentration is one of the major factors affecting yeast physiological and biochemical characteristics. In this context, different approaches have been developed to increase available oxygen by the increasing the aeration and the addition of an oxygen‐vector. The growth of R. toruloides in 2‐L mechanical stirred tank reactor equipped with 1 or 2 porous spargers and a 70 C/N ratio, revealed a lipid content of 0.47 and 0.52 g/g and a lipidic productivity of 0.16 and 0.17 g/L day, respectively. The oxygen‐vector addition, increased the lipidic productivity for 0.20 g/L day and a lipid contend of 0.51 g of lipids/g of biomass. The combined approach, combining high aeration (AA), and 1% of n‐dodecane addition (DA), produced a significant improvement in the lipid accumulation (62%, w/w), when compared with the DA (51%, w/w) and the AA (52%, w/w) approaches. The increasing of lipids accumulation and smaller culture time are key factors for the success of scale‐up and profitability of a bioprocess.     

Profiles of photosynthetic pigment accumulation and expression of photosynthesis-related genes in the marine cyanobacteria Synechococcus sp.: Effects of LED wavelengths

Light quality is a significant environmental factor that influences photosynthetic pigments in cyanobacteria. In the present study, we illuminated the marine cyanobacteria Synechococcus sp. with white (350 ～ 700 nm), red (630 nm), green (530 nm), and blue (450 nm) light emitting diodes (LEDs) and measured pigment levels (chlorophyll, carotenoid, and phycobiliprotein) and expression of photosynthesis-related genes (pebA, psbB, and psaE). The amount of photosynthetic pigments (total pigments, chlorophyll, and phycobiliproteins) was higher in the green and blue LED groups than in the white and red LED groups after 8 days of culture. The cells were prepared in a 1.5 mL solution for the analysis of the total pigments, chlorophyll, and carotenoid, and in a 2 mL for analysis of phycobiliproteins. The mRNA expression levels of pebA and psbB significantly increased after 8 days of cultivation under green and blue light, while the mRNA expression levels of psaE decreased. These results indicate that green and blue light increase the accumulation of photosynthetic pigments. In contrast red light induced mRNA expression of psaE and stimulated cell growth in Synechococcus sp.     

Ultrastructural studies of neutral lipid localisation inStreptomyces

Triacylglycerol is accumulated by Streptomyces spp. when grown in submerged culture. Ultrastructural studies using transmission electron microscopy (TEM), staining and freeze-fracture/freeze-etch procedures, and light microscopy confirmed the accumulation of neutral lipid by S. lividans and S. coelicolor during the stationary phase and its storage within membrane-bound globular structures within the cytoplasm. These structures were of various sizes and occupied up to approximately 80% of the total cell volume at that time. There was no evidence of such material within cells examined during the early exponential phase of growth. The globules visualised by TEM were electron-transparent since they comprised lipids containing saturated fatty acids that did not react with osmium tetroxide. The globules appeared to be bounded by a single membrane. Received: 6 June 1995 / Accepted: 4 September 1995