Colonization and degradation of rubber pieces by Nocardia sp.

The growth of a Nocardia sp. occurs essentially on the insoluble rubber substrate and the cells are tightly bound to the rubber in the initial stage of the growth in spite of vigorous stirring of the cultures. The colonization of rubber pieces was followed by staining with Schiff reagent, and it was revealed that not only the thickness of rubber pieces, but also their length and width greatly influenced microbial colonization and degradation of natural rubber products. Among rubber pieces of various shapes, long strips were most rapidly covered by many microbial colonies and experienced the highest rate of rubber degradation. The rate of degradation (expressed by % weight loss) of the long strips of rubber was a linear function of surface area per unit weight of rubber. Thin and wide films of rubber were also rapidly colonized and degraded, while the colonization and degradation of short and narrow pieces were substantially slower and less extensive.     

Inhibition of microbial growth and metabolism by excess turbulence

Excess turbulence caused by high-intensity stirring inhibited microbial growth and metabolism. In stirred tank bioreactors, the growth rate and lysine biosynthesis decreased in Brevibacterium flavum beyond 900 rpm, the growth rate of Trichoderma reesei on wheat straw beyond 150 rpm, and the growth rate of Saccharomyces cerevisae beyond 800 rpm. The term turbohypobiosis was introduced to describe this inhibition. Turbohypobiosis was characterized by a stress factor F(str) expressing the interaction of medium flow with microbial cells in local turbulent zones, dependent on the energy distribution of the stirring regime. Lysine synthesis was inhibited at significantly lower F(str) values than the growth of B. flavum. The main reason for the inhibition was shear effects causing decreased adenosine triphosphate (ATP) generation, lower O(2) uptake, and lower specific growth rate of bacteria.     

Effects of mechanical stress on Anammox granules in a sequencing batch reactor (SBR)

The effect of shear stress on Anammox process was studied in a sequencing batch reactor (SBR). The reactor was operated during 218 days under different stirring speeds (60-250 rpm) in order to expose the system to different shear conditions and to study the stability of the Anammox granules referred to their biological activity and size. The nitrogen loading rate (NLR) fed to the SBR was kept around 0.3g N(L day)(-1). The nitrite (limiting substrate) removal percentage was 98% during most of the operational period. The specific Anammox activity of the biomass was practically constant and around 0.4 g N(g VSSday)(-1) and the average feret diameter of the formed granules was 0.64 mm. Obtained results indicated that stirring speeds up to 180 rpm have no negative effect on the performance of the Anammox process, whereas Anammox activity decreased to 40% when a rotating speed of 250 rpm was tested and the average diameter decreased in 45%, the concentration of solids in the effluent increased to 0.2g TSSL(-1) and nitrite was accumulated in the reactor up to 60 mg NL(-1).     

Influence of dissolved oxygen tension and agitation speed on alginate production and its molecular weight in cultures of Azotobacter vinelandii*

The alginate production by Azotobacter vinelandii, as well as the molecular weight of the polymer, are strongly influenced by the dissolved oxygen tension (DOT) and stirring speed of the culture. Under high DOT (5% of air saturation), the bacteria produced more alginate (4.5 g/l) than that obtained at low (0.5%) oxygen tension (1.0 g/l) in cultures conducted at 300 rpm. On the other hand, under constant DOT (3%), the higher the stirring speed (from 300 to 700 rev./min), the higher the specific growth rate and the alginate production rate. However, low agitation speed (300 rev./min) lead the culture to produce a polymer of high molecular weight (680 000 g/g mol) whereas a low molecular weight (352 000 g/g mol) alginate was isolated from cultures conducted at high (700 rev./min) stirring speed. At 700 rev./min, the MMW increased to a plateau between 1 and 3% DOT and then decreased to a minimum of 0.11 x 10(6) g/g mol at 7%. Microscopic observations revealed the presence of cell aggregates (one order of magnitude larger than individual cells) when the culture was conducted at 300 rev./min. Oxygen gradients occurring within the aggregates could be responsible of this phenomenon. At high agitation rate, the MMW of the alginate dropped towards the end of the culture in all conditions evaluated. Alginase activity was detected, which would be responsible for this phenomenon.     

Fluid mixing and oxygen transfer in cell suspensions ofTaxus chinensis in a novel stirred bioreactor

In high-density plant cell cultures, mixing and mass transfer are two key issues, which should be emphasized for process optimization. In this work, both mixing and oxygen transfer characteristics of cell suspensions ofTaxus chinensis were studied in a new centrifugal impeller bioreactor with a working volume of 1.2 L. The mixing time (t _M) and the volumetric oxygen transfer coefficient (K _L a) under different operational conditions were determined in both tap water and cell suspensions of 100–400 g fresh weight/L (i.e., 5.65–23.1 g DW/L). At an aeration rate of 0.1 L/min,t _M decreased from 10.6s at 30 rpm to 2.89 s at 200 rpm under 100 g FW/L, and from 9.63 s (120 rpm) to 4.05 s (300 rpm) under 400 g FW/L. Compared with the effect of agitation, aeration was less significant to the suspension mixing. At a relatively high agitation speed (e.g., 200 rpm),t _M remained almost the same even though aeration rate was changed from 0.1 to 0.4 L/min. Thet _M value increased slowly from 3.98 to 5.26 s at 120 rpm when the cell density was raised from 100 to 250 g FW/L. A rapid increase of botht _M and the suspension viscosity was observed at a cell density above 300 g FW/L. As expected, theK _L a value increased with an increase of aeration rate and agitation speed, but decreased with an increase of cell density. The quantitative data obtained here are useful to investigate the effect of mixing stress on the cell physiology and metabolism ofTaxus chinensis in the bioreactor. This paper is dedicated by JJZ to his colleague Prof. Jun-Tang Yu on the occasion of his 70 birthday.     

A new fluid distribution system for scale-flexible expanded bed adsorption

A new fluid distribution system designed for expanded bed adsorption was introduced and studied in a 150-cm diameter column. Based on fluid application through a rotating distributor, it eradicates the need for perforated plates, meshes, or local mixers. The effect of rotation rate on column performance was examined by fluidizing a 30-cm high bed of supports with tap water and introducing pulses of dye or acetone tracer. Linear bed expansion was seen as the superficial fluid velocity was raised from 170 x h(-1) to 450 cm x h(-1) (3000 L x h(-1) to 8000 L x h(-1)), and there was little change in expansion characteristics as distributor rotation rate was increased from 2.5 to 10 rpm. The distributor was observed to generate a flow pattern suitable for expanded bed adsorption when the supports were fluidized at a superficial fluid velocity of 283 cm center dot h(-1) and dye pulses introduced. At a rotation rate of 2.5 rpm, no significant dead zones were observed, and a discrete band was formed that moved up through the bed. Furthermore, the pattern of dye movement could be used to calculate interstitial linear fluid velocities of 460 cm x h(-1) and 572 cm x h(-1) at the column wall and center, respectively, indicating a parabolic flow profile. The distributor rotation rate giving the best operating conditions was found to be 2.5 rpm when the bed was fluidized at a flow velocity of 283 cm x h(-1) and the residence time distribution of acetone tracer examined. Under these conditions, the coefficient of axial dispersion was 6.1 x 10(-6) m(2) x s(-1) and 29 theoretical plates were measured. When the rotation rate was raised to 10 rpm, the coefficient of axial dispersion increased to 8.08 x 10(-6) m(2) x s(-1) and the number of theoretical plates decreased to 22.     

Evaluation of ultrafiltration membranes with biological macromolecules

Eighteen ultrafiltration membranes ranging in molecular weight cutoff ratings from 500 to 300,000 were tested with water, 0.5M NaCl solution, and, in some cases, with macromolecules and urea in a 3-in. stirred filter cell. Approximately half of the membranes showed a significant decrease in filtration rate during the first 24-hr period. The steady-state rates were less than the manufacturers' rating for about two thirds of the membranes, the discrepancy being greater for the membranes with high molecular weight cutoffs. The filtration rates were linearly dependent on applied pressure over the range at least as great as 15 to 55 psig. The rate decreased as the concentration of macromolecules such as transfer ribonucleic acid (tRNA) increased; the rate for a concentration of 3 mg tRNA/per ml was one-fourth of that observed when no tRNA was present. Some increase in rate (～33 to 50%) was obtained by increasing the stirring speed from 100 rpm to 1000 rpm. The membranes were effective for desalting and concentration of macromolecules but not for separation of large molecules from each other, such as tRNA from bovine serum albumin. Easily denatured molecules such as catalase were not deactivated by filtration at 4°C.     

Brood-cell size does not influence the susceptibility of honey bees (Apis mellifera) to infestation by tracheal mites (Acarapis woodi)

Tracheal mites have been associated with the condition in honey bees that devastated colonies in Britain and Ireland in the early 1900s. The first outbreak of this condition, that became known as the ‘Isle of Wight’ disease, coincided with the period when brood-cell size was increased from about 5.0 mm to about 5.5 mm in width. We undertook an inoculation experiment over a 7-day period to establish if the act of increasing the brood-cell size could have triggered the onset of tracheal mites in honey bees. The standard-sized cells used had a cell width of 5.44 mm and the small-sized cells a width of 5.07 mm. Using callow (newly emerged) bees, from three colonies that had mixed cell sizes, we compared the susceptibility of bees reared in standard-sized cells with that of those raised in small-sized cells. The results indicated similar levels of female mite abundance (0.49 vs. 0.52 mites per bee) and mean fecundity (4.33 vs. 4.22 offspring per female mite), and produced no evidence of any difference in the overall susceptibility between the bees raised in the standard-sized cells versus small-sized brood cells.     

Mass cultivation of the nitrogen-fixing cyanobacteriumGloeotrichia natans,indigenous to rice-fields

Gloeotrichia natans, a nitrogen fixing cyanobacterium common in rice fields in the Philippines, was used for studies to establish key features of its physiology and potential production in outdoor cultures. Under optimal growth conditions (38 °C, pH 8.0, no carbon enrichment) the specific growth rate of rice-field isolate was 0.076 h^–1. The pH of the medium (between 6.5 and 9.0) did not influence the growth rate, but it did affect phycobiliprotein content, as reflected by a change in colour. At pH 7.0 the culture was green-brown, with phycobiliproteins constituting up to 10% of the total protein, while at pH 9.0 the culture was brownish-black and the pigment content was as high as 28% of the total protein. In outdoor cultures the specific growth rate was related directly to cell density in the range of 0.7–1.5 g dry weight 1^–1 at a rate of stirring of 30 rpm, and inversely related to cell density at half this rate. At a stirring of 30 rpm, daily production of outdoor cultures harvested to maintain cell densities of 0.7, 1.15 andw 1.5 g 1^–1 were 14.7, 17.1 and 18.1 g m^–2 d^t, respectively. This rate of production was maintained for more than 45 days. Phycobiliprotein content in the culture kept at a density of 1.5 g 1^–1 reached 14% of the total biomass.     

Linoleic acid improves the robustness of cells in agitated cultures

The murine hybridoma (CC9C10) was subjected to high shear rates in a spinner flask to determine the effect of various culture additives on cell survival. At 500 rpm, the half-life of the viable cell concentration in a low protein serum-free medium was 50 min. Both bovine serum albumin and Pluronic F-68 had a significant effect in protecting cells under these conditions. The effects of the two supplements were additive, so that in the presence of both supplements there was minimal cell damage at 500 rpm. The survival rate of cells grown in media supplemented with linoleic acid improved significantly under high stirring rates. Cells grown for one passage in 50 μM linoleic acid and stirred at 500 rpm had a significantly higher survival rate than control cells. For cells grown over 5 passages in 25 μM linoleic acid, the survival rate at 470 rpm was ×3 greater than that determined for control cells. This difference gradually decreased at higher stirring rates up to 610 rpm when the half-life of the viable cell population was reduced to ∼10 min. Supplementation of cultures with linoleic acid has previously been shown to result in incorporation into all three cellular lipid fractions - polar, non-polar and free fatty acid (Butler et al., 1997). Our explanation for the increased survivability of the cells at high agitation rates in the presence of linoleic acid is that the structural lipid components of the cell including the outer membrane attained a higher unsaturated/saturated ratio which was more robust than that of control cells. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of mixing rate on beta-carotene production and extraction by dunaliella salina in two-phase bioreactors

beta-Carotene has many applications in the food, cosmetic, and pharmaceutical industries; Dunaliella salina is currently the main source for natural beta-carotene. We have investigated the effect of mixing rate and whether it leads to the facilitated release of beta-carotene from the cells of Dunaliella salina in two-phase bioreactors. Three pairs of bioreactors were inoculated at the same time, operated at 100, 150, and 170 rounds per minute, respectively, and illuminated with a light intensity of 700 micromol m(-2) s(-1). Each pair consisted of one bioreactor containing only aqueous phase for the blank and one containing the water phase together with dodecane, which is biocompatible with the cells. Comparison of the viability and growth of the cells grown under different agitation rates shows that 170 rpm and 150 rpm are just as good as 100 rpm. The presence and absence of the organic phase also has no influence on the viability and growth of the cells. In contrast to the growth rate, the extraction rate of beta-carotene is influenced by the stirrer speed. The extraction rate increases at a higher stirring rate. The effectiveness of extraction with respect to power input is comparable for all the applied mixing rates, even though it is slightly lower for 100 rpm than the others. The chlorophyll concentration in the organic phase remained very low during the experiment, although at higher mixing rates, chlorophyll impurity increased up to 3% (w/w) of the total extracted pigments. At 170 rpm carotenoid and chlorophyll undergo the highest extraction rate for both pigments-0.5% of the chlorophyll and 6% of the carotenoid is extracted.     

The effects of cations on the structure and photochemistry of the photosystem II core complex

We have studied the effects of cations and detergents on the structure (molecular weight) and photochemistry of Triton X-100 Photosystem II subchloroplast particles (TSF-IIa). The effect of Mg²⁺ ions on activity depended on the Triton X-100 content of the preparation. If the residual Triton X-100 was not removed prior to assay, MgCl₂ increased the rate of electron transport, acting at a site on the reducing side of Photosystem II. Lowering the pH also increased the rate of electron transport. If the Triton X-100 was removed from the particles, both MgCl₂ and NaCl caused a decrease in the rate of electron transport. Addition of Triton X-100 caused a reversible decrease in the number of active Photosystem II reaction centers. Both cations and Triton X-100 had a profound effect on the molecular weight of the Photosystem II particles as determined by gel filtration. At 20 °C, addition of 0.05% Triton X-100 decreased the molecular weight from a high value (≥800,000) to 250,000. At 4 °C, addition of 1 mm MgCl₂ or 100 mm NaCl increased the molecular weight of the complex. In the absence of these salts 67% of the protein eluted with a molecular weight of 460,000 (the rest was >800,000-in the void volume). In the presence of these salts all of the material had a molecular weight of ≥800,000. A similar effect was observed when the pH was lowered from 8 to 6. Further work is needed to determine whether there is a correlation between the changes in molecular weight and activity.     

Growth characteristics of Pleurotus ostreatus in bioreactors

Pleurotus ostreatus was cultured in a bioreactor equipped with different impeller geometries under non-limiting nutrient conditions. With a Rushton turbine impeller the specific growth rate decreased 30% and pellet diameter was reduced 15% when the aeration rate was increased from 1 to 1.5 vvm. Agitation rate reduced the pellet diameter from 5.1 mm to 2.8 mm using 200 rpm and 400 rpm of agitation, respectively. Specific growth rates of 0.036, 0.020 and 0.041 h–1 were obtained with Roshton (disc turbine), Helical Ribbon and InterMIG impellers, respectively. Impeller geometry is important to control the pellet size and consequently growth rate of P. ostreatus.     

Biodesulphurization of mengen lignite by Rhodoccocus rhodochrous in a batch stirred and aerated tank fermenter

The biodesulphurization of Mengen lignite by a mesophilic bacterium, Rhodococcus rhodochrus ATCC 53968, was investigated in a batch stirred and aerated reactor. The experiments were carried out at 28°C with an inoculum percentage, initial pH, initial sodium acetate and lignite concentration of the biodesulphurization medium of 8% [v/v], 6.5 mM, 20 mM and 20 g/l, respectively. Variations in the sulphur contents of the lignite relative to the biodesulphurization period were monitored. The effects of the stirring and aeration rates on the removal of different sulphur forms from coal were investigated in the ranges 450–1,200 rpm and 0.1–0.53 vvm and the optimum values were found to be 500 rpm and 0.18 vvm, respectively. An increase in the total sulphur reduction with increasing biodesulphurization time was observed. The maximum total sulphur removal percentage was found to be 15.2% at 1,200 rpm after four days of incubation. The highest total sulphur removal rate was calculated on the second day of microbial desulphurization for each run. The total and organic sulphur contents of the coal after biodesulphurization were correlated with the stirring and aeration rates by using the non-linear least squares regression method. In the experimental runs lasting 8 days, the highest organic sulphur reducing percentage of 10.1% was obtained at a stirring rate of 500 rpm and an aeration rate of 0.40 vvm.     

Effect of the dissolved oxygen on the bioproduction of glycerol and ethanol by Hansenula anomala growing under salt stress conditions

The effect of the dissolved oxygen on glycerol and ethanol productions by an osmotolerant yeast Hansenula anomala was examined during growth in media at low water activity resulting from the addition of 2M NaCl in the culture medium. High stirring rate, high culture medium aeration, as well as high mass transfer surface inhibited both glycerol and ethanol biosynthesis. In absence of oxygen, yeast used acetaldehyde as a hydrogen acceptor, leading to the stimulation of ethanol biosynthesis and accounting for the low biomass and glycerol production; the experimental ratio ethanol on glycerol produced was 5.1 when the available oxygen was lowered (low stirring rate, 500rpm) and increased to 10.2 in absence of aeration. Extracellular glycerol production was therefore optimal for a moderate stirring (1000rpm) and aeration (1.4vvm) rates. These optimal conditions resulted in an experimental ratio ethanol on glycerol produced of 4.1, namely close to the theoretical value of 4, illustrating the osmodependent channelling of carbon towards polyols production.     

EFFECT OF INITIAL SIZE ON GROWTH OF PLANT TISSUE CULTURES

Caplin , Samuel M. (LOS Angeles State Coll., Los Angeles, Calif.) Effect of initial size on growth of plant tissue cultures . Amer. Jour. Bot. 50(1): 91–94. Illus. 1963.—Using different slice thicknesses and cannula diameters, cylindrical expiants of different size were obtained from tubers of Jerusalem artichoke. Slice thickness ranged from 0.5 to 2.5 mm and expiant diameter from 1.30 to 3.22 mm. Initial fresh weights ranged from 2.3 to 29.8 mg, a 13-fold range. After 17 days growth at 26 C in 10 ml basal medium containing 15% coconut milk, relative increase was inversely related to initial weight and ranged from 36-fold for 2.3-mg expiants to 8-fold for 29.8-mg expiants, a range of 4.5 × in relative increase between the largest and smallest cultures. Secondary phloem expiants of the same diameter from carrot root slices of different thickness, all removed at 1 mm from the cambium, also showed decreased relative growth with increasing size of explant; this was true for each of the different diameters used. Further investigation showed clearly that the growth of the large inocula was not limited by the amount of culture medium used during the period of culture. Initial weight has, therefore, a decided effect on the rate of relative growth.     

Enzyme formation during solid-substrate fermentation in rotating vessels

Aspergillus awamori NRRL 4869 was cultured on the solid substrate, wheat bran, in a modified Rollacell apparatus to produce alpha-galactosidase and invertase. The swivel cap on the elongated bottle permits the introduction of air while the bottle rotates. Parameters of air flow rate (0.05-0.2 liter/kg/min), rpm (0.15-15 rpm), and weight of solids (150 and 300 g) were varied. At low air flow rates (0.05 liter/kg solids/min), alpha-galactosidase production was minimal independent of the rotation rate. At 0.15 rpm and 0.2 liter/kg solids/min air flow rate, invertase production ceased after five days; whereas alpha-galactosidase production continued. The modified Rollacell can be a useful apparatus for studying solid-substrate cultures.     

Optimal conditions for hepatitis B core antigen production in shaked flask fermentation

The effects of various environmental factors such as pH (5, 6, 7, 8 and 9), temperature (30, 37 and 40°C) and rotational speed (150, 200 and 250 rpm) on the growth and the hepatitis B core antigen (HBcAg) production ofEscherichia coli W3110IQ were examined in the present study. The highest growth rate is achieved at PH 7, 37°C and at a rotational speed of 250 rpm which is 0.927 h⁻¹. The effect of pH on cell growth is more substantial compared to other parameters; it recorded a 123% different between the highest growth rate (0.927 h⁻¹) at pH 7 and lowest growth at pH 5. The highest protein yield is achieved at pH 9, rotational speed of 250 rpm and 40°C. The yield of protein at pH 7 is 154% higher compared to the lowest yield achieved at pH 5. There is about 28% different of the protein yield for theE. coli cultivated at 250 rpm compared to that at 150 rpm which has the lowest HBcAg yield. The yield of protein at 40°C is 38% higher compared to the lowest yield achieved, at 30°C.     

耕层调控与有机肥处理下麦田土壤和小麦冠层结构特性及其相互关系

本研究基于5年的耕作定位试验,设置深耕(DT)、深耕有机肥(DTF)、浅耕(ST)、浅耕有机肥(STF)、免耕(NT)和免耕有机肥(NTF)处理,以期通过改良耕层土壤结构,优化小麦冠层结构特性.结果表明: 同一耕作处理下,增施有机肥可降低土壤容重、提高土壤孔隙度,提高20～40 cm土层2～5和0.25～2 mm粒级土壤团聚体含量,降低>5 mm粒级团聚体含量、>0.25 mm粒级团聚体的平均质量直径(MWD)和几何平均直径(GMD).与其他处理相比,NTF处理改善了0～20 cm土层土壤容重、增加土壤孔隙度;DTF处理降低了40～60 cm土壤容重和>0.25 mm粒级机械团聚体的稳定性,增加了土壤透气性.花后各时期,有机肥处理的叶片角度指数降低,叶面积指数(LAI)和旗叶净光合速率(P_n)提高.STF处理的角度指数最低,DTF处理的P_n最高,显著大于其他处理.通径分析表明,自变量容重、孔隙度、>0.25 mm粒级团聚体的数量(R_0.25)和MWD对因变量角度指数、LAI和P_n的直接通径系数均达到极显著水平.0～20 cm土层,MWD值增大有利于P_n和LAI的提高;20～40 cm土层,土壤容重在一定范围内的增加可优化叶夹角,提高冠层透光率;40～60 cm土层,高的土壤容重和低的孔隙度限制了LAI和P_n的增加.综上,豫中补灌区增施有机肥下的深耕或浅耕处理有利于改良土壤结构、增加土壤通透性,优化冠层结构,提高冠层受光率、叶面积指数和光合速率.     

Biomass and porosity profiles in microbial granules used for aerobic wastewater treatment

AIMS: To obtain biomass and porosity profiles for aerobically grown granules of different diameters and to determine a suitable range of granule diameters for application in wastewater treatment. METHODS AND RESULTS: Microbial granules were cultivated in an aerobic granulated sludge reactor with model wastewaters containing acetate, or ethanol plus acetate, or glucose as the main carbon source. Granules were formed by retaining microbial aggregates using a settling time of 2 min. Sampled granules had diameters ranging from 0.45 to 3 mm. Microbial biomass in the granules was detected with the nucleic acid stain SYTO 9 and confocal laser scanning microscopy. The thickness of the microbial biomass layer was proportional to the granule diameter, and had a maximum value of 0.8 mm. The thickness of the microbial biomass layer correlated with the penetration depth of 0.1 microm fluorescent beads into the granule. CONCLUSIONS: The microbial biomass and porosity studies suggest that aerobically grown microbial granules should have diameters less than a critical diameter of 0.5 mm, if deployed for wastewater treatment applications. This critical diameter is based on the assumption that whole granules should have a porous biomass-filled matrix. SIGNIFICANCE AND IMPACT OF THE STUDY: This work could contribute to the development of aerobic granulation technology for effective biological wastewater treatment.