An efficient biosurfactant-producing bacterium Selenomonas ruminantium CT2, isolated from mangrove sediment in south of Thailand

Biosurfactant-producing bacteria, isolate CT2, was isolated from mangrove sediment in the south of Thailand. The sequence of the 16S rRNA gene from isolate CT2 showed 100?% similarity with Selenomonas ruminantium. The highest biosurfactant production (5.02?g/l) was obtained when the cells were grown on minimal salt medium containing 15?g/l molasses and 1?g/l commercial monosodium glutamate supplemented with 1?g/l NaCl, 0.1?g/l leucine, 5?% (v/v) inoculum size at 30?°C and 150?rpm after 54?h of cultivation. The biosurfactant obtained by extraction with ethyl acetate showed high surface tension reduction (25.5?mN/m), a small CMC value (8?mg/l), thermal and pH stability with respect to surface tension reduction and emulsification activity and a high level of salt tolerance. The biosurfactant obtained was confirmed as a lipopeptide by using a biochemical test, FT-IR, MNR and mass spectrometry. The crude biosurfactant showed a broad spectrum of antimicrobial activity and also had the ability to emulsify oil and enhance PAHs solubility.     

Hydrocarbon Degradation and Biosurfactant Production by an Acenaphthene-degrading Pseudomonas Species

An acenaphthene-degrading bacterium putatively identified as Pseudomonas sp. strain KR3 and isolated from diesel-contaminated soil in Lagos, Nigeria was investigated for its degradative and biosurfactant production potentials on crude oil. Physicochemical analysis of the sampling site indicates gross pollution of the soil with high hydrocarbon content (2100 mg/kg) and detection of various heavy metals. The isolate grew luxuriantly on crude oil, engine oil and acenaphthene. It was resistant to septrin, amoxicillin and augmentin but was susceptible to pefloxacin, streptomycin and gentamycin. It was also resistant to elevated concentration of heavy metals such as 1–15 mM lead, nickel and molybdenum. On acenaphthene, the isolate exhibited specific growth rate and doubling time of 0.098 day^?1 and 3.06 days, respectively. It degraded 62.44% (31.2 mg/l) and 91.78% (45.89 mg/l) of 50 mg/l acenaphthene within 12 and 21 days. On crude oil, the specific growth rate and doubling time were 0.375 day^?1 and 1.85 days with corresponding percentage degradation of 33.01% (903.99 mg/l) and 87.79% (2403.71 mg/l) of crude oil (2738.16 mg/l) within 9 and 18 days. Gas chromatographic analysis of residual crude oil at the end of 18 days incubation showed significant reductions in the aliphatic, alicyclic and aromatic fractions with complete disappearance of benzene, propylbenzene, pristane, phytane, and nC₁₈-octadecane fractions of the crude oil. The isolate produced growth-associated biosurfactant on crude oil with the highest emulsification index (E₂₄) value of 72% ± 0.23 on Day 10 of incubation. The partially purified biosurfactant showed zero tolerance for salinity and had its optimal activity at 27°C and pH 2.0.     

Production of erythritol and mannitol by Yarrowia lipolytica yeast in media containing glycerol

Glycerol is a by-product generated in large amounts during the production of biofuels. This study presents an alternative means of crude glycerol valorization through the production of erythritol and mannitol. In a shake-flasks experiment in a buffered medium, nine Yarrowia lipolytica strains were examined for polyols production. Three strains (A UV'1, A-15 and Wratislavia K1) were selected as promising producers of erythritol or/and mannitol and used in bioreactor batch cultures and fed-batch mode. Pure and biodiesel-derived crude glycerol media both supplemented (to 2.5 and 3.25?%) and not-supplemented with NaCl were applied. The best results for erythritol biosynthesis were achieved in medium with crude glycerol supplemented with 2.5?% NaCl. Wratislavia K1 strain produced up to 80.0?g?l(-1) erythritol with 0.49?g?g(-1) yield and productivity of 1.0?g?l(-1)?h(-1). Erythritol biosynthesis by A UV'1 and A-15 strains was accompanied by the simultaneous production of mannitol (up to 27.6?g?l(-1)). Extracellular as well as intracellular erythritol and mannitol ratios depended on the glycerol used and the presence of NaCl in the medium. The results from this study indicate that NaCl addition to the medium improves erythritol biosynthesis, and simultaneously inhibits mannitol formation.     

Isolation and characterization of biosurfactant/bioemulsifier-producing bacteria from petroleum contaminated sites

Biosurfactant-producing bacteria were isolated from terrestrial and marine samples collected in areas contaminated with crude oil or its byproducts. Isolates were screened for biosurfactant/bioemulsifier production in different carbon sources (glucose, fructose, sucrose and kerosene) using the qualitative drop-collapse test. Glucose produced the highest number of positive results (17 of 185 isolates). All 17 isolates produced emulsions with kerosene and 12 exhibited high emulsion-stabilizing capacity, maintaining 50% of the original emulsion volume for 48 h. Eight of the 17 isolates reduced the growth medium surface tension below 40 mN m(-1) with 5 exhibiting this capacity in cell-free filtrates. Onset of biosurfactant production differed among the isolates, with some initiating synthesis during the exponential growth phase and others after the stationary phase was reached. Increasing temperature from 25 to 35 degrees C accelerated onset of biosurfactant production in only two isolates while pH (6.5-7.6) had no effect in any isolate tested. Isolation from petroleum contaminated sites using the screening protocol presented proved to be a rapid and effective manner to identify bacterial isolates with potential industrial applications.     

Enhanced degradation of α-chitin materials prepared from shrimp processing byproduct and production of N-acetyl-D-glucosamine by thermoactive chitinases from soil mesophilic fungi

Soil isolates of mesophilic Penicillium monoverticillium CFR 2, Aspergillus flavus CFR 10 and Fusarium oxysporum CFR 8 were cultivated in solid state fermentation (SSF) using wheat bran solid medium supplemented with α-chitin in order to produce chitinolytic enzyme. Under SSF cultivation, maximum enzymes (U/g IDS) production was 41.0 (endo-chitinase) and 195.4 (β-N-acetylhexosaminidase) by P. monoverticillium, 26.8 (endo-chitinase) and 222.1 (β-N-acetylhexosaminidase) by A. flavus and 13.3 (endo-chitinase) and 168.3 (β-N-acetylhexosaminidase) by F. oxysporum after 166?h of incubation. The crude endo-chitinase and β-N-acetylhexosaminidase derived from A. flavus and F. oxysporum revealed optimum temperature at 62?±?1°C, but the enzymes from P. monoverticillium showed optimum temperature at 52?±?1°C for maximum activity. Several fold increase in endo-chitinase and β-N-acetylhexosaminidase activities in the crude enzymes preparation was achieved after concentrating with polyethylene glycol. The concentrated crude chitinases from P. monoverticillium, A. flavus and F. oxysporum, respectively yielded 95.6, 96.6 and 96.1?mmol/l of N-acetyl-D: -glucosamine (GlcNAc) in 48?h of reaction from colloidal chitin. While, the crude enzyme preparations of P. monoverticillium, A. flavus and F. oxysporum produced 10.11, 6.85 and 10.7?mmol/l of GlcNAc respectively, in 48?h of reaction from crystalline α-chitin. HPLC analysis of colloidal chitin hydrolysates prepared with crude chitinases derived from P. monoverticillium, A. flavus and F. oxysporum revealed that the major reaction product was monomeric GlcNAc (~80%) and a small amount of (GlcNAc)(4) (~20%), indicating the potential of these enzymes for efficient production of GlcNAc from α-chitin.     

Isolation and Characterization of Biosurfactant-and Bioemulsifier-Producing Bacteria from Petroleum Contaminated Sites in Western Canada

Biosurfactant-producing bacteria were isolated from two petroleum contaminated sites in western Canada. Seven potential biosurfactant/bioemulsifier-producing isolates were screened and characterized. All of the seven isolates were able to form emulsions. Emulsion-stabilizing capacity was also measured up to 48 hrs. Strain C-111-2 and C-203-2 would lead to highly reduced surface tension. For strain C-203-2, the optimum conditions that supported bacteria growth and production were investigated. The influences of carbon sources, medium pH values, and temperature were taken into account. The experimental results indicated that the crude oil and glucose were promising carbon sources for biosurfactants production; the isolated strains produced a maximum concentration of biosurfactant in a neutral pH environment and showed a higher surface activity under the temperature level of 35°C than that under 10°C. To further optimize the carbon and nitrogen source for biosurfactant production, response surface methodology (RSM) was applied to explore the favorable concentration of two carbon sources: glucose, crude oil, and one nitrogen source, NaNO₃. The optimal concentration of 8.1g/L, 4% and 3.9 g/L for glucose, crude oil, and NaNO₃, respectively, which can be obtained through RSM analysis.     

Valorisation of chicken feathers for xanthan gum production using Xanthomonas campestris MO-03

Xanthan gum is an important commercial polysaccharide produced by Xanthomonas species. In this study, xanthan production was investigated using a local isolate of Xanthomonas campestris MO-03 in medium containing various concentrations of chicken feather peptone (CFP) as an enhancer substrate. CFP was produced with a chemical process and its chemical composition was determined. The addition of CFP (1–8?g/l) increased the conversion of sugar to xanthan gum in comparison with the control medium, which did not contain additional supplements. The highest xanthan production (24.45?g/l) was found at the 6?g/l CFP containing control medium in 54?h. This value was 1.73 fold higher than that of control medium (14.12?g/l). Moreover, addition of CFP improved the composition of xanthan gum; the pyruvate content of xanthan was 3.86% (w/w), higher than that of the control (2.2%, w/w). The xanthan gum yield was also influenced by the type of organic nitrogen sources. As a conclusion, CFP was found to be a suitable substrate for xanthan gum production.     

Influence of carbon source on growth and mycotoxin production by isolates of Pyrenophora tritici-repentis from wheat

The fungus Pyrenophora tritici-repentis can infect wheat kernels, causing red smudge, and has been shown to produce the anthraquinone mycotoxins emodin, catenarin, and islandicin. The growth of 8 fungal isolates from diverse regions was evaluated on various culture media and was found to be generally slowest on the semisynthetic Fries medium. The choice of carbon source had a significant effect on mycotoxin production, as assessed by high-performance liquid chromatography. The highest emodin concentration (194.18 ± 16.26 μg/g medium) was observed for isolate Alg 3-24 on Fries medium supplemented with fructose, while the highest catenarin concentration (302.54 ±13.92 μg/g medium) was observed for TS93-71B on Fries medium supplemented with starch. Islandicin was not produced by any isolate under the conditions tested. Evaluation of the dynamics of mycotoxin production by isolate 331-2 on V8-potato dextrose agar medium revealed a rapid accumulation of emodin and catenarin during the first week of incubation, followed by a large decline by 14 days. Differences in the growth of and mycotoxin production by isolates of P. tritici-repentis likely resulted from the differential composition of the media and (or) intraspecies variability. Accordingly, the optimization of growth medium should be considered when evaluating the potential of specific isolates for mycotoxin production.     

Production of Extracellular Biopolymers and Identification of Intracellular Proteins and Rhizobium tropici

The objective of this study was to identify species of rhizobia (from the IPA 403 and IPA 49 isolates), to assess the physico-chemical characteristics of the biopolymers produced by these rhizobia and to determine the soluble intracellular proteins that are present in these rhizobia. The polysaccharides containing acetyl and pyruvic acid groups that were produced by different strains that had been cultivated in yeast extract mannitol (YEM) medium for 132, 144, and 168?h were evaluated for yield, viscosity, and concentration. Based on the analysis of their partial 16S rDNA sequences, both isolates were identified as Rhizobium tropici. The polymers produced in liquid YEM medium were recovered, dried and weighed to determine culture yield. Soluble intracellular proteins were identified through the techniques of 2D-PAGE and mass spectrometry for cultures that were cultivated for 168?h. The largest biopolymer yield and the highest viscosity and concentration of acetyl and pyruvic acids were obtained from the IPA 403 isolate after 168?h of culture. The proteins that were identified for the CIAT 899 isolate included elongation factor TU, a chaperone; GroE/GroEs and a putative glycosyltransferase, all of which catalyze the production of polysaccharides. For the IPA 403 strain, dinitrogenase and nitrogenase iron proteins were found. In the IPA 49 strain, glyceraldehyde-3-phosphate dehydrogenase was found along with two other proteins, the beta subunit of an electron-transferring flavoprotein and a dehydrogenase.     

Plant growth promoting activity of an auxin and siderophore producing isolate of <Emphasis Type="Italic">Streptomyces</Emphasis> under saline soil conditions

A biocontrol Streptomyces isolate (C) was tested for its plant growth promoting qualities under saline conditions. Exposure to elevated osmotic strengths up to 300 mM NaCl increased dry weight and cfu/ml significantly. The isolate C produced indolyl-3-acetic acid (IAA) into the medium in the amount of 2.4 μg/ml. The amount of auxin increased after adding salt and reached to 4.7 μg/ml in 300 mM NaCl. Biosynthesis of siderophore was detectable and increased in presence of NaCl. Streptomyces isolate C showed good solubilization of tricalcium phosphate in culture medium with 92 mg/l. Solubilization decreased in presence of NaCl. Soil treatment with isolate C increased the growth and development of wheat plant in normal and saline conditions. In this treatment there were significant increases in germination rate, percentage and uniformity, shoot length and dry weight compared to the control. Applying the bacterial inocula increased the concentration of N, P, Fe and Mn in wheat shoots grown in normal and saline soil, but had non-significant effect on other micro and macronutrients concentrations. Results of this study show that Streptomyces isolate C has potential to be utilized as biofertilizer in saline soils.     

Utilization of palm oil decanter cake as a novel substrate for biosurfactant production from a new and promising strain of Ochrobactrum anthropi 2/3

A biosurfactant-producing bacterium, isolate 2/3, was isolated from mangrove sediment in the south of Thailand. It was evaluated as a potential biosurfactant producer. The highest biosurfactant production (4.52 g/l) was obtained when the cells were grown on a minimal salt medium containing 25 % (v/v) palm oil decanter cake and 1 % (w/v) commercial monosodium glutamate as carbon and nitrogen sources, respectively. After microbial cultivation at 30 °C in an optimized medium for 96 h, the biosurfactant produced was found to reduce the surface tension of pure water to 25.0 mN/m with critical micelle concentrations of 8.0 mg/l. The stability of the biosurfactant at different salinities, pH and temperature and also its emulsifying activity was investigated. It is an effective surfactant at very low concentrations over a wide range of temperatures, pH and salt concentrations. The biosurfactant obtained was confirmed as a glycolipid type biosurfactant by using a biochemical test, fourier-transform infrared spectroscopy, MNR and mass spectrometry. The crude biosurfactant showed a broad spectrum of antimicrobial activity and also had the ability to emulsify oil and enhance polyaromatic hydrocarbons solubility.     

Effect of salinity on vanadate biosorption by Halomonas sp. GT-83: Preliminary investigation on biosorption by micro-PIXE technique

Thirty-eight soil samples were collected from crude oil contaminated land in south of Iran. Initial screening of a total of 100 bacterial isolates, resulted in the selection of one isolate with maximum adsorption capacity of 52.7 mg vanadate/g dry weight. It was tentatively identified as Halomonas sp. according to morphological and biochemical properties and named strain GT-83. Removal of vanadate by biosorption with Halomonas sp. GT-83 was very sensitive to solution pH. Vanadate adsorption decreased with increasing pH, with maximum adsorption capacities achieved in at pH 3.0 in the absence and in the presence of increasing concentrations of salt. Vanadate-salt biosorption studies were also performed at this pH value. Equilibrium uptakes of vanadate increased with increasing vanadate concentration up to 600 mg/l. Maximum metal removal (91.8%) took place at pH 3.0 with initial vanadate concentration of 100 mg/l, which got reduced (84.8%) in the presence of 50 g/l salt. The equilibrium sorption data were analyzed by using Freundlich isotherm. The specific uptake of vanadate increased at low cell concentration and decreased when cell concentration exceeded 0.75 g/l. The paper also demonstrates the potential value of micro-PIXE in biosorption studies.     

Genetic diversity and differential in vitro responses to Ni in <Emphasis Type="Italic">Cenococcum geophilum</Emphasis> isolates from serpentine soils in Portugal

Amplified fragment length polymorphism (AFLP) analysis was used to investigate the genetic diversity in isolates of the ectomycorrhizal fungus Cenococcum geophilum from serpentine and non-serpentine soils in Portugal. A high degree of genetic diversity was found among C. geophilum isolates; AFLP fingerprints showed that all the isolates were genetically distinct. We also assessed the in vitro Ni sensitivity in three serpentine isolates and one non-serpentine isolate. Only the non-serpentine isolate was significantly affected by the addition of Ni to the growth medium. At 30 microg g(-1) Ni, radial growth rate and biomass accumulation decreased to 73.3 and 71.6% of control, respectively, a highly significant inhibitory effect. Nickel at this concentration had no significant inhibitory effect on serpentine isolates, and so the fitness of serpentine isolates, as evaluated by radial growth rate and biomass yield, is likely unaffected by Ni in the field. In all isolates, the Ni concentration in the mycelia increased with increasing Ni concentration in the growth medium, but two profiles of Ni accumulation were identified. One serpentine isolate showed a linear trend of Ni accumulation. At the highest Ni exposure, the concentration of Ni in the mycelium of this isolate was in the hyperaccumulation range for Ni as defined for higher plants. In the remaining isolates, Ni accumulation was less pronounced and seems to approach a plateau at 30 microg g(-1) Ni. Because two profiles of Ni accumulation emerged among our Ni-insensitive serpentine isolates, this result suggests that different Ni detoxification pathways may be operating. The non-serpentine isolate whose growth was significantly affected by Ni was separated from the other isolates in the genetic analysis, suggesting a genetic basis for the Ni-sensitivity trait. This hypothesis is further supported by the fact that all isolates were maintained on medium without added Ni to avoid carry-over effects. However, because AFLP analysis failed to distinguish between serpentine and non-serpentine isolates, we cannot conclude that Ni insensitivity among our serpentine isolates is due to evolutionary adaptation. Screening a larger number of isolates, from different geographical origins and environments, should clarify the relationships between genetic diversity, morphology, and physiology in this important species.     

Distillery and curd whey wastes as viable alternative sources for biosurfactant production

Biosurfactant production from synthetic medium and industrial waste, viz. distillery and whey wastes was investigated by using an oily sludge isolate Pseudomonas aeruginosa strain BS2. In synthetic medium separately supplemented with glucose and hexadecane as water-soluble and -insoluble carbon sources, respectively, strain BS2 reduced the surface tension of the fermentation broth from 57 to 27 mN/m. The culture produced biosurfactant during the stationary growth phase and its yield was 0.97 g/l. The culture utilized distillery and whey wastes for its growth, as maximum cell counts reached to 54 × 10⁸ and 64 × 10⁹ c.f.u./ml from an initial inoculum size of 1 × 0⁵ c.f.u./ml, respectively, within 48 h of incubation and in these wastes the yields of biosurfactant obtained were 0.91 and 0.92 g/l, respectively. In synthetic medium, distillery and whey wastes, strain BS2 produced a crystalline biosurfactant which belonged to the category of secondary metabolites and its maximum production occurred after the onset of nitrogen-limiting conditions. After recovering biosurfactant from the fermented waste, the chemical oxygen demand (COD) of distillery and whey wastes was significantly reduced by 81 and 87%, respectively. Total acids, nitrogen and phosphate levels in distillery waste were reduced by 90, 92 and 92%, respectively, while in case of whey waste the concentration of these nutrients was reduced by 88, 95 and 93%, respectively. The isolated biosurfactant possessed potent surface active properties, as it effectively reduced the surface tension of water from 72 to 27 mN/m and formed 100% stable emulsions of a variety of water-insoluble compounds such as hydrocarbons, viz. hexadecane, crude oil, kerosene and oily sludge and pesticides, viz. dichlorodiphenyltrichloroethane (DDT) and benzene hexachloride (BHC). The effectiveness of biosurfactant was also evident from its low critical micellar concentration (CMC) which was 0.028 mg/ml.     

Role of antibiosis in the biological control of spot blotch (Cochliobolus sativus) of wheat by Chaetomium globosum

Chaetomium globosum Kunze, has been identified as a potential antagonist of Cochliobolus sativus (S. Ito & Kurib.) Deschler ex Dastur. (Syn = Drechslera sorokiniana). Production of antifungal compounds by Chaetomium globosum (Cg) and their role in suppression of spot blotch of wheat caused by this fungus under in vitro and in vivo has been evaluated. Interaction between Chaetomium globosum isolates and C. sativus showed mycoparasitism by isolates Cg 1 and Cg 6 whereas isolates Cg 2, Cg 3, Cg 4 and Cg 5 showed antibiosis. Syringe filtered culture extracts of Cg 2 completely inhibited mycelial growth of C. sativus in liquid broth. In vitro bioassays were undertaken by amending the medium with crude extracts and agar diffusion method in order to assess the fungistatic activity of crude extracts from culture filtrates of different isolates of Chaetomium globosum. Significant differences in antagonism between isolates were observed. Antifungal metabolite profiling, on TLC (Thin Layer Chromatography) plates identified 13 compounds in isolate Cg 2, 11 compounds in Cg 3 and 7 compounds in Cg 6. Isolate Cg 1 produced only two faint bands and Cg 5 produced two bands of the same Rf value but of higher intensity. The production of antifungal compounds by isolates was positively correlated with antagonism to C. sativus on seedlings in glasshouse studies. The results showed high antifungal metabolite production by isolate Cg 2, which also gave maximum bioefficacy under laboratory and glasshouse conditions.     

Biodegradation of petroleum hydrocarbons by filamentous fungi (Aspergillus ustus and Purpureocillium lilacinum) isolated from used engine oil contaminated soil

The use of microorganisms for remediation and restoration of hydrocarbons contaminated soils is an effective and economic solution. The current study aims to find out efficient telluric filamentous fungi to degrade petroleum hydrocarbons pollutants. Six fungal strains were isolated from used engine (UE) oil contaminated soil. Fungi were screened for their ability to degrade crude oil, diesel and UE oil using 2.6-dichlorophenol indophenol (DCPIP). Two isolates were selected, identified and registered at NCBI as Aspergillus ustus HM3.aaa and Purpureocillium lilacinum HM4.aaa. Fungi were tested for their tolerance to different concentration of petroleum oils using radial growth diameter assay. Hydrocarbons removal percentage was evaluated gravimetrically. The degradation kinetic of crude oil was studied at a time interval of 10 days. A.ustus was the most tolerant fungi to high concentration of petroleum oils in solid medium. Quantitative analysis showed that crude oil was the most degraded oil by both isolate; P. lilacinium and A. ustus removed 44.55% and 30.43% of crude oil, respectively. The two fungi were able to degrade, respectively, 27.66 and 21.27% of diesel and 14.39 and 16.00% of UE oil. As compared to the controls, these fungi accumulated high biomass in liquid medium with all petroleum oils. Likewise, crude oil removal rate constant (K) and half-lives (t_1/2) were 0.02 day⁻¹, 34.66 day and 0.015 day⁻¹, 46.21 day for P. lilacinium and A. ustus, respectively. The selected fungi appear interesting for petroleum oils biodegradation and their application for soil bioremediation require scale-up studies.     

Cell surface properties of Pseudomonas stutzeri in the process of diesel oil biodegradation

Pseudomonas stutzeri, isolated from crude oil-contaminated soil, was used to degrade diesel oil. Of three surfactants, 120?mg rhamnolipids 1(-1) significantly increased degradation of diesel oil giving 88% loss after 14?days compared to 54% loss without the surfactant. The system with rhamnolipids was characterised by relatively high particle homogeneity. However, the addition of saponins to diesel oil caused the cells to aggregate (the polydispersity index: 0.542) and the biodegradation of diesel oil was only 46%. The cell yield was 0.22?g?l(-1).     

Single cell oil (SCO) production by Mortierella isabellina grown on high-sugar content media

Mortierella isabellina cultivated in nitrogen-limited media presented remarkable cell growth (up to 35.9 g/l) and high glucose uptake even with high initial sugar concentrations (e.g. 100 g/l) in media. After nitrogen depletion, significant fat quantities were accumulated inside the fungal mycelia (50-55%, wt/wt oil in dry biomass), resulting in a notable single cell oil production of 18.1 g/l of culture medium. Total dry biomass and lipid yields presented greatly increased values (0.34 and 0.17 g respectively per gram of glucose consumed). The microbial lipid produced contained gamma-linolenic acid (GLA) at a concentration of 3.5+/-1.0%, wt/wt, which corresponded to 16-19 mg GLA per gram of dry microbial mass and a maximum concentration of 0.801 g GLA per liter of culture medium.     

Long-chain n−3 polyunsaturated fatty acid production by members of the marine protistan group the thraustochytrids: screening of isolates and optimisation of docosahexaenoic acid production

Following an isolation programme for thraustochytrids (marine fungoid protists) from three different locations, 57 isolates were screened for biomass, oil and docosahexaenoic acid production (DHA). Although a common fatty acid profile for the thraustochytrid isolates emerged, there was considerable variation in the DHA content of the oil. In some isolates from a cold temperate environment, DHA represented almost 50% of the total fatty acids present. Although isolates from a sub-tropical environment produced higher levels of biomass, with up to 37% (w/w) oil, the DHA fraction of the fatty acids was low. Cool temperate isolates gave intermediate values. Studies to optimise biomass and DHA production by manipulation of growth medium composition were carried out on a tropical strain. Results indicated that medium with a high C:N ratio stimulated DHA production. The use of such media in bioreactor cultivations gave maximum biomass, lipid and DHA content of 14 g l⁻¹, 78 and 25% (w/w), respectively. Optimum DHA production was 2.17 g l⁻¹ after 107 h cultivation.     

Effects of Rapeseed Oil on Activity of Methylmalonyl-CoA Carboxyltransferase in Culture of Streptomyces fradiae

To investigate why more tylosin was produced when Streptomyces fradiae T1558 was cultured in a rapeseed oil medium than in a glucose or starch medium, we measured the activity of methylmalonyl-CoA carboxyltransferase (EC 2.1.3.1) and intracellular propionic acid. The activity of the enzyme, which catalyzes the formation of the precursor of tylosin, protylonolide, was 0.19 U/mg protein in 5 days of culture in rapeseed oil medium, which was 2.5- and 1.3-fold that with the glucose or starch medium, respectively. The intracellular propionic acid concentration was 1.2 g/g of dry weight, which was 4.3- and 2.1-fold that with the glucose or starch medium, respectively. The addition of propionic acid increased tylosin production in batch culture: when 0.2 g/l (final concentration) propionic acid was added to the glucose medium, 3.8 g/l tylosin was produced in 10 days of culture, 4.7-fold the amount without propionic acid. These findings suggest that in glucose medium, intracellular propionic acid is a limiting factor because of the low activity of methylmalonyl-CoA carboxyltransferase of the tylosin biosynthesis pathway.