Biomass yields of Chlorella from iron (Y x/Fe) in iron-limited batch cultures

The maximum biomass in iron-limited photosynthetic batch cultures of chlorella increased as the logarithm of the iron concentration. The growth yield from iron (Y _x/Fe) showed a marked inverse relation to the specific growth rate. The maximum biomass yield, g dry biomass/g iron consumed, was 7.5x10³ with specific growth rate 0.108 h^-1; the minimum was 0.79×10³ with specific growth rate 0.145 h^-1. The maximum specific growth rate in the exponential phase of Fe limited cultures varied as the initial Fe concentration. Fe-limited growth made the cells adhere to a glass surface.Abbreviation O.D. optical density     

Thermodynamic aspects of plant cell adhesion to polymer surfaces

Summary A thermodynamic model of particle adhesion from a suspension onto a solid surface is used to predict the extent of adhesion of suspension-cultured Catharanthus roseus cells to the following polymer substrates: fluorinated ethylene-propylene (FEP), polystyrene (PS), polyethylene terephthalate (PET), sulphonated polystyrene (SPS), and glass. According to this model, the extent of adhesion is determined by the surface tensions of the plant cells, the polymer substrates, and the suspending liquid medium. Experimentally, adhesion of the washed plant cells was found to decrease with increasing substrate surface tension, following the sequence FEP>PS>PET>SPS>glass, when the surface tension of the liquid was greater than that of the plant cells, in agreement with the model. However, adhesion increased with increasing substrate surface tension when the liquid surface tension was lower than the cellular surface tension, also in agreement with the model. When the liquid and cellular tensions were equal the extent of adhesion was independent of the substrate surface tension. This also agrees with model predictions and leads to a value for the surface tension of C. roseus cells of approximately 54 ergs/cm² which is in agreement with a value obtained from contact angle measurements on layers of cells and sedimentation volume analysis. The cellular surface tension determined by the sedimentation volume method showed a biphasic alteration during growth cycles of C. roseus cell cultures. These variations (between 55 and 58 ergs/cm²) agree with the pattern of adhesion previously described.     

The effect of nutrients and environmental conditions on biomass and oil production in Botryococcus braunii Race B strains

The green alga Botryococcus braunii is widely recognized as a source of non-fossil oil. However, limitations in Botryococcus biomass production hamper its commercial exploitation. This study examines the effects of nutrients (nitrogen and iron) and environmental conditions (temperature, light intensity and photoperiod) on biomass and oil production in two B. braunii Race B strains, Kossou-4 and Overjuyo-3. The highest biomass and oil production were obtained at a nitrogen concentration of 750 mg l^?1, iron concentration of 6 mg l^?1, at 25°C and at 135 µmol photons m^?2 s^?1 with a photoperiod of 16 h light:8 h darkness. Culturing the strains in Blue-green (BG11) medium containing optimized nutrients under optimal conditions resulted in an up to ~10.6-fold increase in biomass. In Kossou-4 and Overjuyo-3 strains, biomass increased from 1.647 g 10 l^?1 and 3.137 g 10 l^?1 respectively in normal BG11 medium to 17.390 g 10 l^?1 and 21.721 g 10 l^?1 in optimized BG11 media and growth conditions. This was accompanied by ~8–10.5-fold increase in oil production compared with that in normal BG11 medium. Oil (0.324 g 10 l^?1 and 0.211 g 10 l^?1) was produced in normal BG11 medium in Kossou-4 and Overjuyo-3 strains respectively, compared with 2.642 g 10 l^?1 (Kossou-4) and 2.206 g 10 l^?1 (Overjuyo-3) in modified BG11 media under optimized conditions. Therefore, optimization of nutrients and environmental conditions can increase biomass and oil production in the two strains of B. braunii.     

In situ autofluorescence detection of a fouling marine diatom on different surfaces

A new technique for quantifying fouling diatoms adhering to different surfaces was developed and tested. The method is based on recording the in vivo chlorophyll autofluorescence of diatom cells in situ. The enhanced signal obtained after addition of DCMU was used as a biomass estimate, and the enhancement itself as an indicator of the photosynthetic capacity. A fluorescence spectrometer equipped with a “well plate reader”; accessory was programmed to scan predetermined positions on the microscope slide based test surfaces. In standard tests, a matrix of 7 × 25 equidistant locations was applied to record the central 17 × 67 mm² area of the test surface. Thus, both spatial distributions and the mean value of chlorophyll associated with the specified area could be obtained directly. Microscopical counting was performed for calibration on transparent glass surfaces as well as PVA‐SbQ based hydrogels. There was a good correlation between counting and fluorescence recordings, with a linear range up to 1100 cells mm^?2. Due to the inherent inaccuracies of background estimates, the detection limit on glass and gel was approximately 200 cells mm^?2. The method was also applied successfully to test non‐transparent surfaces. In addition to standard mass screening of different test surfaces, the method may be found useful in studies of algal physiology related to cell adhesion, photosynthesis, growth, detachment and spatial migration.     

The development of the photosynthetic apparatus and energy transduction in malate-limited phototrophic cultures of Rhodobacter capsulatus

The question was studied whether limited availability of the carbon source controls the development of the photosynthetic apparatus in Rhodobacter capsulatus. The organisms were grown phototrophically in a chemostat limited by malate as the sole source of reducing equivalents and carbon. The incident light-energy flux, representing the only energy source, was kept constant. Steady state levels of protein and dry weight of cells as well as molar growth yield coefficients (Y) decreased with increasing dilution rate (D, representing the growth rate, ) up to about D=0.14 h^-1. At higher D-values biomass levels as well as Y stayed largely constant. The specific rate of malate consumption leading to biomass production increased linearly while the rate representative of processes other than conversion of carbon into biomass increased almost exponentially with . Specific bacteriochlorophyll (Bchl) contents of cells as well as the specific rate of Bchl synthesis were rather low at low D-values. They increased as D was increased. Light energy fluxes required to half-maximally saturate proton extrusion by whole cells decreased when D was increased up to 0.1 h^-1; at higher D-values, however, they reached constancy. Maximal rates of proton extrusion as well as of photophosphorylation calculated on a Bchl basis decreased when D was increased up to 0.14 h^-1 and reached constancy at higher D-values. The results suggest that the availability of the growth limiting substrate controls the formation of the photosynthetic apparatus and, consequently, its functional properties including the efficiency of light-energy transduction. A relationship is assumed between malate conversion into biomass, i.e. Y-values, and the efficiency of light-energy transduction.Abbreviations ALA 5-aminoleyulinic acid - Bchl bacteriochlorophyll - D dilution rate [h^-1] - R Rhodobacter - Y molar growth yield coefficient - growth rate [h^-1]     

Lantana camara L. invasions in dry rainforest - open forest ecotones: The role of disturbances associated with fire and cattle grazing

Abstract A field experiment was used to evaluate the effects of fire and cattle grazing on the initiation of Lantana camara invasions in dry rainforest-open forest ecotones in the gorges of the Macleay River, NSW. A factorial combination of four factors (burning, biomass removal, soil scarification, and fertilization) at two levels (presence and absence) was established to assess the suitability of disturbed patches for germination, survival, and growth in association with changes in microclimate and resource availability. Burning, biomass removal and soil scarification, either singularly or in any combination, significantly increased germination, on average, by 19%, from 50.2% to 59.7%. Survival increased on average 26% across all treatments while mortality decreased by 26% when compared with the control. The differences between treatment combinations were not significant. Seedling growth was significantly enhanced by all disturbances, except by soil scarification alone. Treatment combinations that reduced vegetation cover (burning and/or biomass removal) and, therefore reduced shading, significantly increased L. camara biomass production by an average of 140% for all treatments. The control yielded 14.0 g m^?2, while fertilizer alone and biomass removal alone yielded 27.6 g m^?2 and 40.5 g m^?2, respectively. Other treatment combinations averaged 35.2 g m^?2 and were not significantly different from each other. Consequently, successful invasions are likely to occur whenever canopy disturbances create patches of greatly decreased competition and/or increased resource availability. Shading plays a greater role as a limiting factor than any other, while surface soil macronutrient levels are also important, particularly when combined with canopy disturbances that increase light availability. The effects of biomass reduction and soil disturbance associated with fire and cattle grazing are significant in the successful invasion of L. camara. Management strategies to reduce weed encroachment and community degradation must identify and maintain ecological barriers to L. camara invasion in order to promote rainforest conservation and biodiversity.     

Interactions Between Escherchia coli and the Colloids of Three Variable Charge Soils and Their Effects on Soil Surface Charge Properties

The adhesion of Escherchia coli (E. coli) to the colloids of three variable charge soils and its effect on surface charge properties and potassium adsorption of these soil colloids were investigated. The adhesion isotherms of E. coli by soil colloids can be described using the Langmuir equation. The amount of E. coli adhered by the soil colloids varied with soil type and followed the order: Ultisol from Guangxi > Oxisol from Yunnan > Ultisol from Jiangxi. The iron and aluminum oxide contents and CECs of the soils are the important factors affecting the adhesion of E. coli to soil colloids. The relatively lower iron and aluminum oxide contents and higher CEC of the Ultisol from Jiangxi led to the lower adhesion of E. coli to the soil colloids compared to the Ultisol from Guangxi and the Oxisol from Yunnan. The amount of E. coli adhered to the soil colloids decreased with increasing pH, which was consistent with the results predicted from the DLVO theory. E. coli adhesion made the zeta potential of the soil colloids more negative and reduced the isoelectric point of the soil colloids, suggesting that E. coli decreased the surface positive charge and increased negative charge of the soil colloids. In addition, E. coli adhesion increased K⁺ adsorption by the soil colloids. Therefore, bacterial adhesion improves the fertility of variable charge soils by increasing soil CEC because the CECs of variable charge soils are usually low.     

Influence of physico-chemical properties of porous microcarriers on the adhesion of an anaerobic consortium

The ability for biomass colonization of four porous mineral microcarriers (sepiolite, clay, pozzolana and foam glass-Poraver), was studied and related to their surface properties. The surface hydrophobicity of the mineral carriers was a more important factor influencing colonization by the anaerobic consortium than was surface charge. It was possible to correlate linearly the degree of hydrophobicity with the biomass retention capacity. Although the thermodynamic theory did not explain adhesion, an increase in cell attachment was directly related to the decrease of the positive values of the free energy of adhesion. Surface roughness, porosity and the amount of surface Mg²⁺, were also determinant factors in bacterial immobilization. However a great biomass accumulation can originate a decrease in biological activity due to mass transfer limitations. Journal of Industrial Microbiology & Biotechnology (2000) 24, 181–186. Received 09 August 1999/ Accepted in revised form 01 December 1999     

Immobilization of cultured Catharanthus roseus cells using a fibreglass substratum

Summary Cultured Catharanthus roseus cells were immobilized using geometrically identical needled fibreglass mats prepared with a range of surface coatings. The phenyl (PS), polyglycol (PG), aldehyde (CHO), alkyl (CTMS), and silanol (AW) coatings, along with the untreated glass (HC) surface, produced surfaces with a range of surface tensions. The immobilization efficiency of the substratum, measured as the percentage of cells immobilized, increased with increasing substratum surface tension in the order PS < PG < CHO < CTMS < AW < HC. The dependence of immobilization efficiency on substratum surface tension can be described using a thermodynamic model of adhesion that considers the extent of plant cell adhesion to be a function of the surface tensions of the substratum, the suspending liquid, and the plant cells. In addition, this dependence also demonstrates the fundamental role of adhesion in the immobilization process involving a glass fibre matrix. However, cell entrapment processes are also implicated. The untreated glass fibre substratum (HC), which demonstrated the greatest immobilization efficiency, was used for further characterization of the immobilization strategy. Maximum inoculum biomass was determined to be approximately 1.9 g cells (fresh weight)/g substratum (dry weight) to achieve greater than 90% immobilization efficiency. The growth rate of immobilized cultures was slower than suspension cultures, probably due to mass transfer limitations. Production of the indole alkaloids, tryptamine, catharanthine, and ajmalicine, was also suppressed relative to suspension-cultured cells. These results are considered in relation to other immobilization strategies and their apparent effects on cellular processes. Offprint requests to: F. Dicosmo     

Inhibitory effect of a lipopeptide biosurfactant produced by Bacillus subtilis on planktonic and sessile cells of Trichosporon spp.

The present study aimed to investigate the inhibitory effect of a bacterial biosurfactant (TIM96) on clinical strains of Trichosporon. Additionally, the effect of TIM96 on the ergosterol content, cell membrane integrity, and the hydrophobicity of planktonic cells was assessed. The inhibitory activity of TIM96 against Trichosporon biofilms was evaluated by analyzing metabolic activity, biomass and morphology. MIC values ranged from 78.125 to 312.5 μg ml^?1 for TIM96; time-kill curves revealed that the decline in the number of fungal cells started after incubation for 6 h with TIM96 at both MIC and 2×MIC. The biosurfactant reduced the cellular ergosterol content and altered the membrane permeability and the surface hydrophobicity of planktonic cells. Incubation at 10×MIC TIM96 reduced cell adhesion by up to 96.89%, thus interfering with biofilm formation. This concentration also caused up to a 99.2% reduction in the metabolic activity of mature biofilms. The results indicate potential perspectives for the development of new antifungal strategies.     

Iron binding to Azotobacter salinestris melanin,iron mobilization and uptake mediated by siderophores

Iron-sufficient Azotobacter salinestris cells bound large amounts of ⁵⁵Fe to cell-associated catechol melanin in an energy-independent manner. Iron was mobilized from the cell surface by citric acid and transported into the cell in a process that was inhibited by azide, carbonyl cyanide m-chlorophenyl-hydrazone (CCCP), KCl or RbCl, the latter two known to inhibit Na⁺-dependent activities in A. salinestris. Iron-limited cells produced a hydroxamate compound (HDX) which promoted ⁵⁵Fe-uptake into iron-limited cells in a two step process. Initial uptake was inhibited by azide or CCCP, but not by KCl, while subsequent uptake was blocked by all inhibitors. Citric acid also mediated energy-dependent ⁵⁵Fe-uptake in iron-limited cells, but initial iron-uptake was less sensitive to CCCP than HDX-mediated iron-uptake. The results show that melanin serves as an iron trap, probably to protect the cells from oxidative damage mediated by H₂O₂ and the Fenton reaction. A model for HDX siderophore-mediated iron-uptake is proposed which requires energy to concentrate iron in the periplasm and H⁺/Na⁺-dependent events to bring iron into the cell.     

Evaluation of soil bacterial biomass using environmental DNA extracted by slow-stirring method

A simple and rapid method (slow-stirring method) for extracting environmental DNA (eDNA) from soils was constructed by physical mild stirring with chemical treatment. eDNA was extracted efficiently with minimal damage from various kinds of soil. The amount of eDNA and soil bacterial biomass showed a linear proportional relation [Y=(1.70×10⁸)X, r ²=0.96], indicating that bacterial biomass could be evaluated by quantifying levels of eDNA. Consequently, the average bacterial biomass in an agricultural field was calculated as 5.95×10⁹ cells/g sample, approximately 10–100 times higher than that in non- and oil-polluted fields.     

Utilisation of soil organic P by agroforestry and crop species in the field,western Kenya

A field experiment in western Kenya assessed whether the agroforestry species Tithonia diversifolia (Hemsley) A. Gray, Tephrosia vogelii Hook f., Crotalaria grahamiana Wight & Arn. and Sesbania sesban (L) Merill. had access to forms of soil P unavailable to maize, and the consequences of this for sustainable management of biomass transfer. The species were grown in rows at high planting density to ensure the soil under rows was thoroughly permeated by roots. Soil samples taken from beneath rows were compared to controls, which included a bulk soil monolith enclosed by iron sheets within the tithonia plot, continuous maize, and bare fallow plots. Three separate plant biomass samples and soil samples were taken at 6-month intervals, over a period of 18 months. The agroforestry species produced mainly leaf biomass in the first 6 months but stem growth dominated thereafter. Consequently, litterfall was greatest early in the experiment (0–6 months) and declined with continued growth. Soil pH increased by up to 1 unit (from pH 4.85) and available P increased by up to 38% (1 g P g^–1) in agroforestry plots where biomass was conserved on the field. In contrast, in plots where biomass was removed, P availability decreased by up to 15%. Coincident with the declines in litterfall, pH decreased by up to 0.26 pH units, plant available P decreased by between 0.27 and 0.72 g g^–1 and P_o concentration decreased by between 8 and 35 g g^–1 in the agroforestry plots. Declines in P_o were related to phosphatase activity (R²=0.65, P<0.05), which was greater under agroforestry species (0.40–0.50 nmol MUB s^–1 g^–1) than maize (0.28 nmol MUB s^–1 g^–1) or the bare fallow (0.25 nmol MUB s^–1 g^–1). Management of tithonia for biomass transfer, decreased available soil P by 0.70 g g^–1 and P_o by 22.82 g g^–1. In this study, tithonia acquired P_o that was unavailable to maize. However, it is apparent that continuous cutting and removal of biomass would lead to rapid depletion of P stored in organic forms.     

Growth inhibition by ammonia and use of a pH-controlled feeding strategy for the effective cultivation of Mycobacterium chlorophenolicum

The inhibitory effect of ammonia on the growth of the polychlorinated xenobiotic-degrading bacterium Mycobacterium chlorophenolicum was examined. The strain is inhibited by both the ionized and nonionized forms of ammonia. At pH 6.9 50% reduction of the growth rate was observed at 6.8 g l^–1 total ammonium. For 23 experiments performed in shake-flask culture at different pH values and ammonium concentrations a growth model based on the extended Monod kinetic fits the data with a deviation of 5.3%. To overcome growth inhibition in bioreactors a pH-controlled feeding strategy was developed for effective cultivation of M. chlorophenolicum at an ammonium level below 0.3 g l^–1. The ammonium addition was controlled on-line by the stoichiometric interdependence of ammonium consumption and pH decline. With this on-line control strategy a biomass concentration as high as 26.2 g l^–1 can be achieved within less than 1 week of cultivation, compared to a biomass concentration of 15.5 g l^–1 in normal batch culture after 2 weeks of cultivation. The yield is also increased from 0.32 g to 0.43 g biomass (g glucose)^–1. The strategy developed provides an effective method for the production of biomass of M. chlorophenolicum serving as the inoculum in remediation technologies.     

Determination of bacterial cell surface hydrophobicity of single cells in cultures and in wastewater in situ

Bacterial cell surface hydrophobicity is one of the most important factors that influence bacterial adhesion. A new method, microsphere adhesion to cells, for measuring bacterial cell surface hydrophobicity was developed. Microsphere adhesion to cells is based on microscopic enumeration of hydrophobic, fluorescent microspheres attaching to the bacterial surface. Cell surface hydrophobicity estimated by microsphere adhesion to cells correlates well with adhesion of bacteria to hydrocarbons or hydrophobic interaction chromatography for a set of hydrophilic and hydrophobic bacteria (linear correlation coefficients, R², were 0.845 and 0.981 respectively). We also used microsphere adhesion to cells to investigate the in situ properties of individual free-living bacteria directly in activated sludge. Results showed that the majority of the bacteria were hydrophilic, indicating the importance of cell surface hydrophobicity for bacterial adhesion in sludge, and for the overall success of the wastewater treatment process.     

Distribution and Composition of Microbial Populations in a Landfill Leachate Contaminated Aquifer (Grindsted, Denmark)

Abstract To investigate whether landfill leachates affected the microbial biomass and/or community composition of the extant microbiota, 37 samples were collected along a 305-m transect of a shallow landfill-leachate polluted aquifer. The samples were analyzed for total numbers of bacteria by use of the acridine orange direct count method (AODC). Numbers of dominant, specific groups of bacteria and total numbers of protozoa were measured by use of the most probable number method (MPN). Viable biomass estimates were obtained from measures of ATP and ester-linked phospholipid fatty acid (PLFA) concentrations. The estimated numbers of total bacteria by direct counts were relatively constant throughout the aquifer, ranging from a low of 4.8 × 10⁶ cells/g dry weight (dw) to a high of 5.3 × 10⁷ cells/g dw. Viable biomass estimates based on PLFA concentrations were one to three orders of magnitude lower with the greatest concentrations (up to 4 × 10⁵ cells/g dw) occurring at the border of the landfill and in samples collected from thin lenses of clay and silt with sand streaks. Cell number estimates based on ATP concentrations were also found to be lower than the direct count measurements (<2.2 × 10⁶ cells/g dw), and with the greatest concentrations close to the landfill. Methanogens (Archaea) and reducers of sulfate, iron, manganese, and nitrate were all observed in the aquifer. Methanogens were found to be restricted to the most polluted and reduced part of the aquifer at a maximum cell number of 5.4 × 10⁴ cells/g dw. Populations of sulfate reducers decreased with an increase in horizontal distance from the landfill ranging from a high of 9.0 × 10³ cells/g dw to a low of 6 cells/g dw. Iron, manganese, and nitrate reducers were detected throughout the leachate plume all at maximum cell numbers of 10⁶ cells/g dw. Changes in PLFA profiles indicated that a shift in microbial community composition occurred with increasing horizontal distance from the landfill. The types and patterns of lipid biomarkers suggested that increased proportions of sulfate- and iron-reducing bacteria as well as certain microeukaryotes existed at the border of the landfill. The presence of these lipid biomarkers correlated with the MPN results. There was, however, no significant correlation between the abundances of the specific PLFA biomarkers and quantitative measurements of redox processes. The application of AODC, MPN, PLFA, and ATP analyses in the characterization of the extant microbiota within the Grindsted aquifer revealed that as distance increased from the leachate source, viable biomass decreased and community composition shifted. These results led to the conclusion that the landfill leachate induced an increase in microbial cell numbers by altering the subsurface aquifer so that it was conducive to the growth of methanogens and of iron-and sulfate-reducing bacteria and fungi. Received: 11 June 1998; Accepted: 10 December 1998     

A Possible Role for Ligatin and the Phosphoglycoproteins It Binds in Calcium-Dependent Retinal Cell Adhesion

Ligatin is a filamentous plasma membrane protein that serves as a baseplate for the attachment of peripheral glycoproteins to the external cell surface. Ligatin can be released from intact, embryonic chick neural retinal cells by treatment with 20 mM Ca⁺⁺ without adversely affecting their viability. α-Glucose-1-phos phate is also effective in removing ligatin-associated glycoproteins from intact cells. After either of these treatments, the retinal cells seem not to exhibit Ca⁺⁺ -dependent adhesion for one another. It is thus suggested that ligatin in neural retina may serve as a baseplate for the attachment to the cell surface of glycoproteins active in Ca⁺⁺-dependent adhesion. The finding that Ca⁺⁺ serves to protect Ca⁺⁺-dependent adhesion molecules from digestion by trypsin is discussed in relation to steric constraints on trypsin's accessibility to these adhesion molecules because of their possible binding to arrayed ligatin filaments.     

Microbial community structure and biomass estimates of a methanogenic Antarctic Lake ecosystem as determined by phospholipid analyses

Phospholipid analyses were performed on water column particulate and sediment samples from Ace Lake, a meromictic lake in the Vestfold Hills, Antarctica, to estimate the viable microbial biomass and community structure in the lake. In the water column, methanogenic bacterial phospholipids were present below 17 m in depth at concentrations which converted to a biomass of between 1 and 7×10⁸ cells/liter. Methanogenic biomass in the sediment ranged from 17.7×10⁹ cells/g dry weight of sediment at the surface to 0.1×10⁹ cells/g dry weight at 2 m in depth. This relatively high methanogenic biomass implies that current microbial degradation of organic carbon in Ace Lake sediments may occur at extremely slow rates. Total microbial biomass increased from 4.4×10⁸ cells/ liter at 2 m in depth to 19.4×10⁸ cells/liter at 23 m, near the bottom of the water column. Total nonarchaebacterial biomass decreased from 4.2 ×10⁹ cells/g dry weight in the surface sediment (1/4 the biomass of methanogens) to 0.06×10⁸ cells/g dry weight at 2 m in depth in the sediment. Phospholipid fatty acid profiles showed that microeukaryotes were the major microbial group present in the oxylimnion of the lake, while bacteria dominated the lower, anoxic zone. Sulfate-reducing bacteria (SRB) comprised 25% of the microbial population at 23 m in depth in the water column particulates and were present in the surface sediment but to a lesser extent. Biomass estimates and community structure of the Ace Lake eco-system are discussed in relation to previously measured metabolic rates for this and other antarctic and temperate ecosystems. This is the first instance, to our knowledge, in which the viable biomass of methanogenic and SRB have been estimated for an antarctic microbial community.     

Growth of microalgae Botryococcus sp. in domestic wastewater and application of statistical analysis for the optimization of flocculation using alum and chitosan

Microalga biomass has been recognized as a sustainable bio-product to replace terrestrial biomass in biofuel production. The microalga industry has high operating costs, specifically on harvesting and biomass recovery. Therefore, the development of an efficient harvesting method is crucial to the minimization of production cost. A statistical analysis through response surface methodology was used to investigate the optimization of harvesting efficiency using alum and chitosan as a coagulant. Growth rate and biomass productivity were also determined. This research revealed that the harvesting efficiency using alum was 99.3%, with optimum dosage and pH of 177.74 mg L^?1 and 8.24, respectively. Chitosan achieved 94.2% biomass recovery at an optimal dosage of 169.95 mg L^?1 at pH of 12. Moreover, Botryococcus sp. achieved the maximum growth of 0.7551 µ_max d^?1, with an average total biomass productivity of 9.81 mg L^?1?d^?1 in domestic wastewater. Overall, this study shows that both alum and chitosan coagulants have great potential for efficient microalgal biomass recovery. It suggests that domestic wastewater as a potential growth medium for the large-scale production of microalga biomass.     

Liming and nitrogen fertilization affects phosphatase activities, microbial biomass and mycorrhizal colonisation in upland grassland

We have studied the effects of factorial combinations of lime and N additions on soil microbial biomass, respiration rates and phosphatase activity of an upland grassland. We also used an Agrostis capillaris seedling bioassay to assess the effect of the treatments on the activity of arbuscular-mycorrhizal (AM) fungi and root surface phosphatase enzymes and the concentrations of N and P in the bioassay plant shoots. In the F and H horizons, soil microbial biomass carbon (C^mic) decreased in response to the liming, while addition of lime and N together reduced basal respiration rates. In the Ah horizon, C^mic was unaffected by the treatments but basal respiration rates decreased in the plots receiving nitrogen. Soil phosphatase activity decreased only in the Ah horizon in plots receiving lime, either in combination with N or alone. The mass of root fwt. colonized by AM fungi increased in response to the treatments in the order nitrogenR²=28.7%, P=0.004). The results demonstrate the sensitivity of both free-living heterotrophic microorganisms and symbiotic mycorrhizal fungi to short-term (2 years) applications of lime and N to long-term upland grassland, particularly in relation to the key P cycling activities undertaken by these organisms.