An image analysis technique to estimate the cell density and biomass concentration of Trichoderma reesei

Aim:  The objective is to develop an automated image analysis protocol to quantify the cell volume fraction of filamentous fungi ( Trichoderma reesei ) and estimate the biomass concentration.
Methods and Results:  Both dry weight and image analyses were performed on samples collected periodically from 7-l stirred tank fermentations. Using the projected area of lactophenol blue-stained hyphae, the fraction occupied by the cells in a given volume was estimated. Combined with the biomass dry weight obtained by filtration, the method was used to estimate the density of filamentous fungi. Knowing the density of fungi, the algorithm was employed to quantitatively assess the biomass evolution during the course of fermentation even in the presence of solid particles.
Conclusions:  A density of 0.334 g dry weight cm⁻³ was found for T. reesei RUT C-30. The image analysis protocol allowed successful estimation of biomass concentration in the presence or absence of solid particles.
Significance and Impact of the Study:  Methods to quantify biomass during the industrial production of cellulase with T. reesei are often limited due to the presence of solid substrates. The image analysis protocol presented here offers a quick and easy way to estimate biomass concentration of filamentous micro-organisms in insoluble medium.     

搅拌式光生物反应器培养海带配子体细胞：不同脉冲补料方式的研究

本文以批次培养为对照,研究了七种脉冲补料方式对搅拌式光生物反应器中培养大型褐藻海带配子体细胞生长和培养液内氮磷营养盐消耗的影响,并首次探讨了脉冲补料方式下不同补料时间点和补料量的影响作用。培养条件设定为50 mg DCW (细胞干重) L-1接种密度、培养液为改良的APSW人工海水、光强60 µE m-2 s-1、光周期16/8 h L/D、通气速率和搅拌速率分别为50 mL min-1和100 rpm。结果表明少量补料利于细胞对氮磷的协同吸收,进而利于生物量扩增。当培养液内氮磷富足或耗尽时补料对于生物量大量生产效果甚微,可能由于氮磷吸收变缓、其储存现象显著,或是其吸收协同性降低。文中当细胞生长至对数中期开始频繁补加少量氮磷营养盐,即维持培养液内氮磷浓度在各自起始浓度的1/3至1/2之间,对生物量生产最有效,生物量增长倍数高达12.270倍。     

Improved algal oil production from Botryococcus braunii by feeding nitrate and phosphate in an airlift bioreactor

To improve biomass and microalgal oil production of Botryococcus braunii, fed‐batch culture was investigated in an airlift photobioreactor. The optimal feeding time of the fed‐batch culture was after 15 days of cultivation, where 1.82 g/L of the microalgal biomass was obtained in the batch culture. Nitrate nutrient was the restrictive factor for the fed‐batch cultivation while phosphate nutrient with high concentration did not affect the microalgal growth. The optimal mole ratio of nitrate to phosphate was 34.7:1, where nitrate concentration reached the initial level and phosphate concentration was one quarter of its initial level. With one feeding, the biomass of B. braunii reached 2.56 g/L after 18 days. Two feedings in 2‐day interval enhanced the biomass production up to 2.87 g/L after 19 days of cultivation. The hydrocarbon content in dry biomass of B. braunii kept at high level of 64.3% w/w. Compared with the batch culture, biomass production and hydrocarbon productivity of B. braunii were greatly improved by the strategic fed‐batch cultivation.     

Factors enhancing lycopene production by a new Mycobacterium aurum mutant

A mutant strain of Mycobacterium aurum was isolated that produced mainly lycopene (>80%) with a total carotenoid content of 1.2 mg g(-1) dry biomass when grown on yeast extract and glucose. Lycopene content of the cells could be significantly increased, up to 7.4 mg g(-1) biomass, by growing the cells at suboptimal initial culture pH (pH 6-6.4) or by using high salt concentration (85 mM NaCl) in the culture medium, although a 25-40% decrease in biomass production occurred in both cases. Highestproductivity (4 mg lycopene l(-1) d(-1)) was obtained by cultivating the cells at pH 6.     

Spore Yield and Microcycle Conidiation of Colletotrichum gloeosporioides in Liquid Culture

The effect of V8 juice concentration (5 to 40%, vol/vol), spore inoculum density (10⁵ and 10⁷ spores per ml), and liquid batch or fed-batch culture condition on mycelium and spore production by Colletotrichum gloeosporioides was evaluated. The amount of mycelium produced, the time required for initiation of sporulation following attainment of maximum mycelium, and the time for attainment of maximum spore concentration increased with increasing V8 juice concentration in batch culture. Cultures containing V8 juice at >10% achieved a similar spore density (apparent spore-carrying capacity) of about 0.8 mg of spores per ml (1 × 10⁷ to 2 × 10⁷ spores per ml) independent of inoculum density and V8 juice concentration. The relative spore yield decreased from a high of 64% of the total biomass for the low-inoculum 5% V8 culture, through 13% for the analogous 40% V8 culture, to a low of 2% for the high-inoculum 27% V8 culture. Fed-batch cultures were used to establish conditions of high spore density and low substrate availability but high substrate flux. The rate of addition of V8 juice was adjusted to approximate the rate of substrate utilization by the (increasing) biomass. The final spore concentration was about four times higher (3.0 mg of spores per ml) than the apparent spore-carrying capacity in batch culture. This high spore yield was obtained at the expense of greatly reduced mycelium, resulting in a high relative spore yield (62% of the total biomass). Microcycle conidiation occurred in the fed-batch but not batch systems. These data indicate that substrate-limited, fed-batch culture can be used to increase the amount and efficiency of spore production by C. gloeosporioides by maintaining microcycle conidiation conditions favoring allocation of nutrients to spore rather than mycelium production.     

补料方式对酵母菌生产谷胱甘肽的影响

比较了酵母菌发酵生产谷胱甘肽（GSH）的几种补料分批培养方式。实验发现补料可以明显地促进酵母菌的生长和谷胱甘肽的合成,同时还发现不同的补料方式对发酵液中的菌体浓度和GSH浓度有不同的影响。采用指数流加方式可获得极高的菌体浓度,但菌体中的GSH浓度较低;而采用恒－pH补料分批培养既可以达到较高菌体浓度,菌体中又含有较高的GSH含量,因此,其总的GSH产量最高,可达到977.8mg/L。     

Histochemical changes in the rabbit cornea and plasmin activity in the tear fluid during contact lens wear. Favourable influence of protease inhibitors (aprotinin, PC5, elastatinal).

Plasmin activity in the tear fluid of the rabbit eye was examined during the wearing of soft contact lenses (SCL) and compared with the occurrence of corneal disturbances assessed in cryostat sections. Plasmin activity was determined with a semiquantitative method using dry punches of filter paper previously soaked in 0.1 M Tris-HCl buffer solution containing mmol/l D-Val-Leu-Lys-FCA (trifluoromethylaminocoumarine), pH 7.2. Punches were applied to the corneal surface for 5 s (tear collection) and incubated in wet chamber. The time of appearance of the bright yellow fluorescence in UV light was recorded and taken as a measure of plasmin activity. For calibration punches soaked in solutions containing plasmin in various concentrations, and processed in the same manner were used. Changes in the cornea were examined histochemically using methods of choice for acid glycosidases, proteases, dehydrogenases, and Na(+)-K(+)-ATPase. SCL with high and low water content were worn in rabbits in 1, 2, 4, 7, 14, 21 and 28 days. Decreased activity of Na(+)-K(+)-ATPase, GGT, and SDH in the corneal endothelium and epithelium were not accompanied by detectable plasmin activity in the tear fluid. Pronounced damage of the corneal epithelium (increased activities of acid glycosidases, acid proteases, LDH, markedly decreased activity of SDH) was accompanied by low concentration of plasmin (0.4-1.0 micrograms/ml) in the tear fluid. Middle activity of plasmin (1.0-2.0 micrograms/ml) was detectable when PMNs were present in the corneal stroma. High plasmin activity (2.0-3.0 micrograms/ml) correlated with corneal ulceration and vascularization.(ABSTRACT TRUNCATED AT 250 WORDS)     

Oil production from five marine microalgae for the production of biodiesel

Marine microalgae were studied as potential resources for the production of biodiesel. Five marine microalgae, Tetraselmis suecica, Phaeodactylum tricornutum, Chaetoceros calcitrans, Isochrysis galbana, and Nannochloropsis oculata were cultured in f/2 media, 12:12 L:D cycle at 20 ± 1°C with a light intensity of 36.3 μmol/m²/sec using a 15-L circular cylindrical photobioreactor. The dry cell weight, specific growth rate, biomass productivity, oil content and fatty acid composition of palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid of microalgae were determined. T. suecica, I. galbana, and N. oculata showed high dry cell weights of 0.58, 0.57, and 0.57 g/L, respectively. The culture period of T. suecica to reach the stationary phase was 9 days. On the other hand, N. oculata showed the longest culture period of 28 days to reach the stationary phase. T. suecica absorbed nitrate at the initial stages of cell growth, decreasing the nitrate concentration to 0.5 mg/L on day-7 of the culture. The highest oil contents were observed in P. tricornutum with a 25.31% dry cell weight and I. galbana with a 23.15% dry cell weight on day-9 after the stationary phase. I. galbana showed 417.33 mg of palmitic acid per g oil and T. suecica showed 235.61 mg of oleic acid per g oil. Stearic acid, linoleic acid, and linolenic acid did not exceed 30.02 mg/g oil in any of the microalgae. T. suecica showed the shortest culture period of 9 days to reach the stationary phase. Therefore, the highest biomass production of 0.58 g/L was obtained and I. galbana showed high biomass production of 0.57 g/ L and oil content of 23.15% of dry cell weight. Therefore, T. suecica and I. galbana can be selected as a potential candidate for the production of biodiesel.     

法夫酵母高密度培养及虾青素的高产研究*

本文对法夫酵母Phaffia rhodozyma的不同流加培养模式进行了研究。实验结果表明,采用指数流加,虾青素产率和细胞干重具有较大值,分别达到14.52mg/l和32.56g/l;其次是恒pO2流加和恒速流加培养,虾青素产率分别达到8.89mg/l和6.70mg/l; 恒pH流加方式更有利于法夫酵母细胞的生长(14.62g/l DCW)。但是,不同流加培养模式所得的μmax和qasta具有较大的差距。恒pH、恒pO2流加培养及间歇培养有较大值,分别为0.0613 h-1、0.056 h-1、0.053 h-1;指数流加的μmax较小。间歇培养中虾青素生成比率最大,qasta=0.048×10-3h-1。     

Accumulation of conjugated linoleic acid in <Emphasis Type="Italic">Lactobacillus plantarum</Emphasis> WU-P19 is enhanced by induction with linoleic acid and chitosan treatment

Production of conjugated linoleic acid (CLA) by the potential probiotic bacterium Lactobacillus plantarum WU-P19 was investigated with the aim of enhancing production. CLA produced using this bacterium may be used to supplement dietary intake. Cultures were fed linoleic acid for conversion to CLA and the CLA produced was measured. In some cases, chitosan was added to cultures to improve cellular uptake of linoleic acid. Under static conditions at 37 °C, the bacterium grew and produced CLA in the pH range of 5.5–6.5. At pH 6.0, a 36-h incubation period maximized the concentration of the dry biomass (0.82 g/L), the CLA content in the biomass (4.1 mg/g), and linoleic acid in the biomass (1.2 mg/g). In comparison with cultures grown without linoleic acid in the medium, supplementing the medium with linoleic acid at 600 μg/mL slowed the production of CLA, but the CLA content in the dry biomass increased to 12–14 mg/g and the linoleic acid content increased to 8–11 mg/g. Supplementing the culture medium with chitosan and linoleic acid enhanced production of CLA in the dry biomass to 21 mg/g within 36 h. Nearly 50% of the CLA was cis-9, trans-11-CLA, and the remainder was trans-10, cis-12-CLA. Linoleic acid content of the dry biomass was increased to 37 mg/g. Accumulation of CLA in the cells was enhanced by feeding linoleic acid. Supplementing the culture with linoleic acid and chitosan further increased accumulation of CLA.     

Evaluation of an electrochemical bioreactor system in the biotransformation of 6-bromo-2-tetralone to 6-bromo-2-tetralol

Biotransformation of 6-bromo-2-tetralone (Br-beta-tetralone) to 6-bromo-2-tetralol (Br-beta-tetralol) by yeast cells of Trichosporon capitatum (ATCC 74312) and its partially purified Br-beta-tetralone reductase was evaluated in an electrochemical bioreactor. The biotransformation rates and final product formation were significantly affected by substrate concentration, biomass and electric potential. At 2 g/l of substrate, the initial reaction rate and final product were increased by 35% and 15%, respectively, with -1.5 V of electric potential compared to without electric potential. Additional substrate (2 g/l) provided by pulse feeding to the reaction mixture at different intervals resulted in 2.1 g/l Br-beta-tetralol compared to a total of 1.2 g/l without feeding. However, the increased production was not proportionate to the amount of additionally fed substrate. Increased substrate availability by the addition of 5% (v/v) ethanol resulted in the highest reaction rate and product formation, but addition of ethanol at a concentration higher than 5% decreased the reaction rate. At low biomass, the initial reaction rates were enhanced significantly when electric potential was high, but a higher biomass was necessary to obtain a similar reaction rate when electric potential was reduced. The highest initial reaction rate (59.2 mg/l per min) was achieved with a two-fold biomass concentration of 15.6 g of dry cell weight/l, substrate at 4 g/l and electric potential at -6 V. The conversion of Br-beta-tetralone to Br-beta-tetralol with partially purified Br-beta-tetralone reductase was slow in the presence of electric potential.     

Fixed-bed biosorption of Cu2+ by polyacrylonitrile-immobilized dead cells of Saccharomyces cerevisiae

Dead cells of Saccharomyces cerevisiae 54 were immobilized by entrappment in polyacrylonitrile. The beads obtained were used to adsorb copper in an up-flow fixed-bed column. The effect of polymer content and cell loading were studied to optimize the porosity and the efficiency in copper removal of the biosorbent beads in a batch system. The optimal concentration of the polyacrylonitrile was assumed to be 12%(w/v) and a concentration of 0.5 g cell dry weight in 1 g polymer was most effective in adsorption of Cu²⁺. The adsorption capacity of this biosorbent was 27 mg Cu²⁺/g dry biomass at 200 mg/l initial concentration of copper ions. Adsorption of Cu²⁺ in a batch system was studied using different initial concentrations of the solute. The optimal conditions in the up-flow column of the following parameters were determined: flow rate, bed height, and initial concentration of Cu²⁺ of the solutions. Results of fixed-bed biosorption showed that breakthrough and saturation time appeared to increase with the bed height, but decrease with the flow rate and the initial concentration. The linearized form of the Thomas equation was used to describe dynamic adsorption of metal ions. As a result, the adsorption capacity of the batch system and the column system was compared. Desorption of copper ions was achieved by washing the column biomass with 0.1 M HCl at an eluent flow rate of 1 ml/min. The reusability of the immobilized biomass was tested in five consecutive adsorption-desorption cycles. The regenerated beads retained over 45% of their original adsorption capacity after five A/D cycles. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of amino acid supplement on cell yield and gene product in Escherichia coli harboring plasmid

Escherichia coli harboring a recombinant plasmid was cultivated in fed-batch culture to enhance production of a gene product. Expression of the leucine gene from Thermus thermophilus in the recombinant plasmid was examined by the assay of beta-isopropylmalate dehydrogenase activity at 75 degrees C. When E. coli was cultivated in medium without leucine, biomass concentration reached 15 g/L and the specific activity became 0.082 U/mg protein. When leucine was fed in the medium throughout cultivation, although biomass concentration reached 63 g/L, the specific activity decreased to 0.016 U/mg protein. When E. coli was cultivated in medium containing 1 g leucine/L, the specific activity remained virtually constant (about 0.13 U/mg protein) and biomass concentration reached 32 g dry cells/L. In these cultivations, growth yields of several amino acids and glucose were examined. When leucine was not added to the medium, growth yields except for histidine were lowest. When leucine was fed throughout the cultivation, growth yields of glucose and tryptophan were highest. The pH-stat was useful for feeding amino acids.     

Effective production of Pseudomonas fluorescens lipase by semi-batch culture with turbidity-dependent automatic feeding of both olive oil and iron ion

Summary An automatic feeding system to supply olive oil in semi-batch culture was established by monitoring cell concentration with a laser turbidimeter combined with a microcomputer and a pulse motor. In this automatic feeding system, specific olive oil supply rate (g olive oil) · (g dry cell)^-1 · h^-1, q ₀, was changed in an appropriate range. Attempts were made to produce lipase by a turbidity-dependent automatic fed-batch culture of Pseudomonas fluorescens. It was found from the semi-batch cultures with turbidity-dependent feeding of olive oil and with varied initial Fe ion concentrations that excess Fe ion was inhibitory to formation of the lipase. Turbidity-dependent automatic simultaneous feeding of olive oil and Fe ion was performed to obtain semi-deficiencies of both the oily substrate in the culture liquid and Fe content of the cells. Using this semi-batch culture, high lipase activity, 5600 units/ml, was attained at an optimal value of q ₀.     

Optimal conditions for bioconversion of ferulic acid into vanillic acid by Pseudomonas fluorescens BF13 cells

Pseudomonas fluorescens BF13 is especially capable of promoting the formation of vanillic acid during ferulic acid degradation. We studied the possibility of enhancing the formation of this intermediary metabolite by using suspensions of cells at high density. The bioconversion of ferulic into vanillic acid was affected by several parameters, such as the concentration of the biomass, the amount of ferulic acid that was treated, the carbon source on which the biomass was grown. The optimal yield of vanillic acid was obtained with 6 mg/ml cells pre-grown on p-coumaric acid and 2 mg/ml ferulic acid. Under these conditions the bioconversion rate was 95% in 5 h. Therefore BF13 strain represents a valid biocatalyst for the preparative synthesis of vanillic acid. Received: 1 July 1997 / Received revision: 28 October 1997 / Accepted: 16 November 1997     

Heterotrophic production of lutein by selected Chlorella strains

Seven Chlorella strains representing three species obtained from culture collections and research laboratories were screened for their potential of heterotrophic production of lutein on two different media (Basal and Kuhl) containing glucose. While both media supported good growth and lutein formation of the seven strains in darkness, higher biomass concentrations and lutein content were achieved on Basal medium. Chlorella protothecoides CS-41 was chosen from the seven strains for further investigation due to its higher productivities of both biomass and lutein. The maximal biomass concentration and lutein content of C. protothecoides cultivated heterotrophically with 9 g L^-1 glucose in a 3.7-L fermentor were respectively 4.6 g dry cells L^-1 and 4.60 mg lutein g^-1 dry cells on Basal medium, and 4.0 g dry cells L^-1 and 4.36 mg lutein g^-1 dry cells on Kuhl medium. The heterotrophic cultivation process was scaled up successfully to 30 L using a fermentor, in which the Basal medium containing 36 g L^-1 glucose was used; the maximal biomass concentration of 16.4 g dry cells L^-1, specific growth rate of 0.92 d^-1,lutein content of 4.85 mg lutein g^-1 dry cells,growth yield of 0.47 g dry cells g^-1 glucose and lutein yield of 1.93 mg lutein g^-1 glucose were respectively achieved. This revised version was published online in August 2006 with corrections to the Cover Date.     

Lead removal by Spirulina platensis biomass

In this investigation, we report on the biosorption of Pb (II) from aqueous solutions by the nonliving biomass of the micro-alga (cyanobacterium) Spirulina platensis. Propagation of the micro-alga was carried out in outside oblong raceway ponds. The biomass was cleaned, dried and used for the investigation. The effects of pH, adsorbent dose, temperature, initial concentration of Pb (II), and contact time on the adsorption of lead by the dry biomass were studied. The experiments were carried out in 250 ml conical flasks containing 100 ml of test solutions using an orbital incubator at 150 rpm. Concentrations of the metal before and after the experiments were measured using Atomic Absorption Spectrophotometer. Very high levels of Pb (II) removal (>91%) were obtained. The optimum conditions for maximal adsorption by S. platensis were found to be pH 3; 2 g of adsorbent dose; incubation at 26°C; 100 mg/l of lead initial concentration and 60 minutes of contact time. The experimental data fitted well with Freundlich isotherm equation with R² values greater than 0.97. Based on our results, we recommend the utilization of S. platensis biomass for heavy metal removal from aqueous solutions.     

Distribution and effects of 2,4,5-trichlorophenoxyacetic acid in cells of Bacillus megaterium.

Cell death in a resting population of an asporogenous Bacillus megaterium was accelerated by ambient concentrations of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) equal to or greater than 10 mug/ml or 5 mug/mg of cells (dry weight), but only after prolonged exposure. Conversely, populations of growing cells were not markedly influenced even at 100 mug/ml. Effects on cell respiration were not manifest until the ambient concentration reached 1,000 mug of 2,4,5-T/ml, or 500 mug/mg. Cells of B. megaterium did, however, accumulate 2,4,5-T passively to a level approximately twofold above the ambient concentration. Most of the accumulated compound was easily washed from the cells, but, of the firmly bound herbicide, about 0.5 mug/mg of cells (dry weight), nearly 60% by weight, was localized in the protoplast membrane. The foregoing results, obtained with a purified preparation of 2,4,5-T were also elicited by 2,4,5-T analytical standards. The extracted contaminants did not produce the results alone nor did they influence the results when present in combination with 2,4,5-T.     

Simultaneous use of sodium nitrate and urea as nitrogen sources improves biomass composition of Arthrospira platensis cultivated in a tubular photobioreactor

Arthrospira platensis is widely cultivated in open ponds for industrial purposes. However, high‐protein A. platensis biomass produced in photobioreactors (PBRs) is recommended for pharmaceutical and cosmetic formulations. A. platensis was cultivated in a 3.5 L tubular airlift PBR using both sodium nitrate and urea as nitrogen sources. Sodium nitrate was added from the start of the cultivation using a batch process. Urea was supplied daily at exponentially increasing feeding rate using a fed‐batch process. The simultaneous optimization of the independent variables, namely, total quantity of sodium nitrate (m_T1) and total quantity of urea (m_T2), led to an optimal condition of m_T1 = 15.0 mmol/L and m_T2 = 7.5 mmol/L. Maximum biomass concentration (5183 ± 94 mg/L) corresponding to the highest biomass productivity (683 ± 13 mg/L/day) was obtained under such condition. The addition protocol of both nitrogen sources resulted in high productivities of protein (6.2 ± 0.4 mg/L/day) as well as chlorophyll‐a (372.2 ± 7.7 mg/L/day). Such innovative process could be applied in the large‐scale production of A. platensis using tubular PBR for novel applications.     

Biosorption and desorption studies of chromium (III) by free and immobilized Rhizobium (BJVr 12) cell biomass

Experiments with free cell biomass (cells + exopolysaccharides) ofRhizobium BJVr 12 (mungbean isolate) showed that amount ofCr³⁺ ion sorbed is influenced by the amount of biomass toCr³⁺ concentration ratio and time of contact. A ratio of 0.5 gfresh biomass to 10.0 ml 5.03 ppm Cr³⁺ sorbed 0.0275 mg Crequivalent to an uptake of 2.86 mg Cr g-¹ dry biomass and 1.0g: 10.0 ml sorbed 0.0366 mg Cr equivalent to an uptake of 1.9 mg Crg-¹ biomass. Immobilized cell biomass in ceramic beads and inaquacel (a porous cellulose carrier with a charged surface) were moreefficient than free cell biomass in adsorbing Cr(III). A reduction of49.7percnt; of Cr(III) for free cells, 95.6% for cells immobilized inceramic beads and 94.6% for cells in aquacel was achieved after 48hours under shaken conditions. Sorption capacities of immobilized cellbiomass in ceramic beads and aquacel ranged from 5.01 to 5.06 mg Crg^-1 dry cell biomass. The biosorption of Cr³⁺follows generally the Langmuir and Freundlich models of adsorption at lowCr³⁺ concentrations. The Langmuir constant for immobilizedcells in ceramic beads are: Q₀, 0.065 mmol Crg^-1 biomass; b (affinity constant), - 694 lmmol^-1 Cr and for cells in aquacel Q, 0.07 mmol Crg^-1 biomass; b, - 694 l mmol Cr g^-1 Cr. TheFreundlich constants are: K, 0.071 mmol Cr g^-1 biomass; n,0.13 g^-1 biomass l^-1 and for aquacel: K, 0.074mmol g^-1 biomass; n, 0.13 g^-1 biomass. Biotrapsmade up of immobilized cells in ceramic beads and aquacel were tested foradsorbing Cr(III) using two different flow rates: 0.5 ml/min and 1.5 ml/min.A significantly higher amount of Cr(III) was adsorbed at the lower flow rateof 0.5 ml/min. Biosorption of Cr³⁺ is competitive. Thetreatment of a waste water sample containing 6.03 ppm Cr³⁺ andother cations with the biomass reduced the Cr³⁺ concentrationto that much lower than for the test solution containing only Cr. Recoveryof biosorbed Cr(III) was by treatment at a different pH using dilute HClsolution. Recovery was higher for cells imbibed in ceramic beads thanaquacel. Percentage recoveries for cells in aquacel are 46.4% at pH1.0, 33.0% at pH 3.0 and 6.6% at pH 6.0–7.0. For cellsin ceramic beads, percentage recoveries are: 93.1% at pH 1.0,75.6% at pH 3.0 and 16.4% at pH 6.0–7.0. Biosorption ofCr³⁺ by cells immobilized in ceramic beads is reversible butonly partially for cells in aquacel.