Ingredient selection for plastic composite supports for L-(+)-lactic acid biofilm fermentation by Lactobacillus casei subsp. rhamnosus.

Plastic composite supports containing 50% agricultural products (oat hulls, soybean hulls, yeast extract, soybean flour, dried bovine erythrocytes, bovine albumin, and/or mineral salts) and 50% (wt/wt) polypropylene were produced by high-temperature twin-screw extrusion. The research employed two half sets of a five-factorial fractional design (2(5 - 1)) to evaluate the effects of different agricultural components on the properties of the plastic composite supports and to select the best plastic composite support formulation for lactic acid fermentation. The biofilm population was affected by the contact angle and relative hydrophobicity of the supports (r = 0.79 to 0.82). Lactic acid was produced by the suspended cells (r = 0.96) and the biofilm on the plastic composite support discs (r = 0.85). Incorporation of yeast extract into plastic composite supports enhanced growth of free and attached cells in minimal medium (P < 0.0001). The presence of soybean hulls, yeast extract, or mineral salts in plastic composite supports produced less hydrophobic supports (P < 0.0001) and enhanced cell attachment (P < 0.03). Under all conditions, suspended-cell and polypropylene disc controls gave negligible lactic acid production and cell density. Plastic composite supports containing soybean hulls, yeast extract, soybean flour, bovine albumin, and mineral salts gave the highest biofilm population (2.3 x 10(9) CFU/g of support), cell density (absorbance of 1.8 at 620 nm), and lactic acid concentration (7.6 g/liter) in minimal medium.     

Optimization of L-(+)-lactic acid production by ring and disc plastic composite supports through repeated-batch biofilm fermentation.

Four customized bioreactors, three with plastic composite supports (PCS) and one with suspended cells (control), were operated as repeated-batch fermentors for 66 days at pH 5 and 37 degrees C. The working volume of each customized reactor was 600 ml, and each reactor's medium was changed every 2 to 5 days for 17 batches. The performance of PCS bioreactors in long-term biofilm repeated-batch fermentation was compared with that of suspended-cell bioreactors in this research. PCS could stimulate biofilm formation, supply nutrients to attached and free suspended cells, and reduce medium channelling for lactic acid production. Compared with conventional repeated-batch fermentation, PCS bioreactors shortened the lag time by threefold (control, 11 h; PCS, 3.5 h) and sixfold (control, 9 h; PCS, 1.5 h) at yeast extract concentrations of 0.4 and 0.8% (wt/vol), respectively. They also increased the lactic acid productivity of Lactobacillus casei subsp. rhamnosus (ATCC 11443) by 40 to 70% and shortened the total fermentation time by 28 to 61% at all yeast extract concentrations. The fastest productivity of the PCS bioreactors (4.26 g/liter/h) was at a starting glucose concentration of 10% (wt/vol), whereas that of the control (2.78 g/liter/h) was at 8% (wt/vol). PCS biofilm lactic acid fermentation can drastically improve the fermentation rate with reduced complex-nutrient addition.     

Evaluation of biofilm reactor solid support for mixed-culture lactic acid production

A combination of lactobacilli and biofilm-forming bacteria were evaluated in continuous fermentations for lactic acid production using various supports. Twelve different bacteria, including species of Bacillus, Pseudomonas, Streptomyces, Thermoactinomyces, and Thermomonospora were tested for biofilm-forming capabilities. Solid supports that were evaluated in either batch or continuous fermentations were pea gravels, 3M-macrolite ceramic spheres, and polypropylene mixed with 25% of various agricultural materials (e.g. corn starch, oat hulls) and extruded to form chips (pp-composite). Biofilm formation was evaluated by the extent of clumping of solid supports, weight gain and (in some instances) Gram stains of the supports after drying overnight at 70° C. The supports consistently producing the best biofilm were pp-composite chips followed by 3M-Macrolite spheres then by pea gravels. The best biofilm formation was observed with P. fragi (ATCC 4973), S. viridosporus T7A (ATCC 39115), and Thermoactinomyces vulgaris (NRRL B-5790), grown optimally at 25, 37, and 45° C, respectively, on various pp-composite chips. Lactic acid bacteria used in the fermentations were Lactobacillus amylophilus (NRRL B-4437), L. casei (ATCC 11443), and L. delbrueckii mutant DP3; these grow optimally at 25, 37 and 45° C, respectively. Lactic acid and biofilm bacteria with compatible temperature optima were inoculated into 50-ml reactors (void volume 25 ml) containing sterile pp-composite supports. Lactic acid production and glucose consumption were determined by HPLC at various flow rates from 0.06 to 1.92 ml/min. Generally, mixed-culture biofilm reactors produced higher levels of lactic acid than lactic acid bacteria alone. S. viridosporus T7A and L. casei on pp-composite chips were the best combination of those tested, and produced 13.0 g/l lactic acid in the reactors without pH control. L. casei produced 10.3 g/l lactic acid under similar conditions.Journal paper no. J-14840 of the Iowa Agriculture and Home Economics Experiment Station, Ames Iowa. Project nos. 2889 and 0178 Correspondence to: A. L. Pometto     

Resistance of Lactobacillus casei in plastic-composite-support biofilm reactors during liquid membrane extraction and optimization of the lactic acid extraction system

Lactic acid fermentations were performed with plastic-composite-support (PCS) disks in solvent-saturated media with Lactobacillus casei subsp. rhamnosus (ATCC 11443). The PCS disks contained 50% (w/w) polypropylene, 35% (w/w) ground soybean hulls, 5% (w/w) yeast extract, 5% (w/w) soybean flour, and 5% (w/w) bovine albumin. Bioassays were performed by growing L. casei in solvent-saturated media after soaking the PCS disks. Eighteen different solvent and carrier combinations were evaluated. Overall, L. casei biofilm fermentation demonstrated the same lactic acid production in solvent-saturated medium as suspended cells in medium without solvents (control). To evaluate PCS solvent-detoxifying properties, two bioassays were developed. When solvent-saturated medium in consecutive equal volumes (10 mL then 10 mL) was exposed to PCS, both media demonstrated lactic acid fermentation equal to the control. However, when solvent-saturated medium with two consecutive unequal volumes (10 mL then 90 mL) was exposed to PCS, some degree of toxicity was observed. Furthermore, iso-octane, tributylphosphate (TBP), and Span 80 were optimized for recovery as 91%, 5%, and 4% (v/v), respectively, with a 1:1 ratio of 1.2 M Na(2)CO(3) stripping solution. Also, recovery by emulsion liquid extraction in the hollow-fiber contactor was minimal due to low recovery at pH 5.0 and incompatibility of the solvent and hollow-fiber material. These results suggest that PCS biofilm reactors can benefit lactic acid fermentation by eliminating the toxic effect from solvent leakage into the fermentation medium from liquid-liquid extractive integrated fermentations.     

Use of the diaminobenzoic acid fluorescence assay in conjunction with uv absorbance as a means of quantifying and ascertaining the purity of a DNA preparation

In the course of a study conducted to determine the correlation between covalently bound DNA-ethyl adducts and specific locus mutation induction in maize (W. E. Schy and M. J. Plewa Mutat. Res., 211, 231-241), it was necessary to accurately quantify and ascertain the purity of small amounts of DNA isolated from germinating maize kernels. DNA was purified from leaf primordial tissue that was dissected from germinating maize kernels and quantified by measuring its absorbance at 260 nm. Its absorbance at 260 nm relative to its absorbance at 280 nm (A260/A280 ratio) fell within the range of values that indicated a pure preparation. An attempt to verify the quantity of DNA using a second independent method specific for DNA, the diaminobenzoic acid dihydrochloride fluorescence assay, revealed a significant discrepancy between the two methods. The difference appeared to result from impurities present within the DNA preparation, despite a A260/A280 ratio that indicated otherwise. We found the A260/A280 ratio to be a poor indicator of the purity of DNA preparations, and determined that significant error may result from quantifying DNA using spectrophotometric methods alone. We propose as an alternative, quantifying DNA using the diaminobenzoic acid dihydrochloride assay in conjunction with uv absorbance at 260 nm and using a FLUOR/A260 ratio as an indicator of DNA purity.     

Continuous lactic acid fermentation using a plastic composite support biofilm reactor

An immobilized-cell biofilm reactor was used for the continuous production of lactic acid by Lactobacillus casei subsp. rhamnosus (ATCC 11443). At Iowa State University, a unique plastic composite support (PCS) that stimulates biofilm formation has been developed. The optimized PCS blend for Lactobacillus contains 50% (wt/wt) agricultural products [35% (wt/wt) ground soy hulls, 5% (wt/wt) soy flour, 5% (wt/wt) yeast extract, 5% (wt/wt) dried bovine albumin, and mineral salts] and 50% (wt/wt) polypropylene (PP) produced by high-temperature extrusion. The PCS tubes have a wall thickness of 3.5 mm, outer diameter of 10.5 mm, and were cut into 10-cm lengths. Six PCS tubes, three rows of two parallel tubes, were bound in a grid fashion to the agitator shaft of a 1.2-1 vessel for a New Brunswick Bioflo 3000 fermentor. PCS stimulates biofilm formation, supplies nutrients to attached and suspended cells, and increases lactic acid production. Biofilm thickness on the PCS tubes was controlled by the agitation speed. The PCS biofilm reactor and PP control reactor achieved optimal average production rates of 9.0 and 5.8 g l(-1) h(-1), respectively, at 0.4 h(-1) dilution rate and 125-rpm agitation with yields of approximately 70%.     

酸雨对缙云山林地黄壤汞溶出的影响

Forest yellow soil and arable yellow soil in Jinyun Mountain were collected to study the effect of simulated acid rain(adjusted to pH 2.0, 3.0, 4.0 and 5.0) on the Hg leaching from soils by the methods of static extraction and dynamic leaching. The results showed that in forest yellow soils, surface accumulation of Hg occurred, and the accumulated Hg was easier to be leached out than that in arable yellow soil by acid rain. The amount of leached Hg was the largest at pH 4.0. To abate the risk of Hg pollution in water bodies by the Hg leaching from this forest soil, the Mountain should be closed, and timber-felling should be forbidden.     

Effect of temperature on the microbiological leaching of sulfide ore material in percolators containing chalcopyrite,pentlandite, sphalerite and pyrrhotite as main minerals

Summary Microbiological leaching of complex sulfide ore material was evaluated in percolators at 4, 10, and 20°C. The onset of leaching was associated with an increase in redox potential and a decrease in pH. Copper from chalcopyrite was leached at a slow rate at each test temperature compared with the leaching of zinc from sphalerite and nickel from pentlandite.     

Mobilization of DOC from sandy loamy soils under different land use (Lower Saxony,Germany)

The conversion of natural forests into cultivated lands causes changes of the carbon cycle, which are of particular importance for fragile landscapes. We examined the mobilization of organic carbon in undisturbed soil monoliths of a deciduous forest, a pine plantation, and a pasture under constant temperature (20°C) and moisture via a leaching experiment. Soil percolation was performed with synthetic rainfall solution (pH 5) for a period of 20 weeks. The leachates of the first 12 weeks were analyzed for the pH, DOC content, light absorbance at 260 and 330 nm. At the end of the experiment soil pH, total carbon, C:N ratio, content of fractions of humic substances were examined. After 20 weeks of the leaching experiment the decrease of soil total C_org reached 29, 23, and 50% in soil monoliths of deciduous forest, pasture, and coniferous forest, respectively. The amounts of DOC removed constituted 6.4, 3.8, and 6.2% of initial soil C_org, respectively. Cumulative values of DOC production decreased in the sequence coniferous forest > deciduous forest > pasture. UV-Vis absorptivities of DOC were similar in both forests and differed from those in pasture. UV-Vis characteristics showed that DOC composition changed during the experiment. The intensive soil percolation caused alterations of the properties of soil organic matter, in particular a change of fraction composition of humic substances occurred.     

Abscisic acid relationships in the chill-related dormancy mechanism in apple seeds

Abscisic acid (ABA) levels in seeds from three cultivars of apple (Malus domestica Borkh.) which have substantially different chilling requirements were investigated by gas chromatography mass-spectrometry selected ion monitoring (GCMS-SIM) during stratification. The ABA content of dormant unchilled seeds was similar in the three cultivars, suggesting no relationship between the chilling requirement of those seeds and their ABA status. That chilling is not related to ABA changes during stratification was confirmed by warm (20°C) and cold (5°C) stratification experiments. ABA content dropped rapidly and nearly identically under both temperature regimes, but only cold stratification promoted germination. The decline in ABA during stratification was due in large part to leaching from the seed coat and nucellar membrane; the ABA content of the embryo remained nearly constant. The radicle in intact seeds stratified at 5°C began growing 20–30 days after the ABA in the seed coat and nucellar membrane had nearly disappeared. Radicle growth did not occur in unchilled seeds, even though ABA had leached from them as well. It is possible that the leaching of ABA from the seed allows certain promotive forces to develop, but if so, these can develop only at chilling temperatures. Studies were also conducted on 2-trans ABA relationships to apple seed dormancy, but no association was evident.Report No. 12, Department of Fruit and Vegetable Science, Cornell University.     

Purification and Characterization of Banana Bunchy Top Virus

Abstract Banana bunchy top virus (BBTV) was successfully purified by a procedure which included pulverizing diseased tissues frozen in liquid nitrogen, clarification of the extract with chloroformbutanol, concentration of the virus by cycles of differential centrifugation, stirring and incubating at 4°C followed by a second cycle of differential centrifugation and sucrose density gradient centrifugation. The concentrations of BBTV obtained from leaf blades and midribs plus petioles were up to 0.34 and 0.56mg/kg tissue, respectively. The virus concentration was highest in diseased leaves collected from October to December, and lowest in those collected from June to September. BBTV is a luteovirus (particles 20– 22 nm in diameter), preparations of which have maximum absorbance at 257 nm, minimum absorbance at 240 nm and a A260/280 ratio of 1.46. The relative molecular mass (M_r) of BBTV coat protein subunit is 21,000, and that of its ssRNA is 2.0 × 10⁶.     

A simple method for the quantitative determination of muramic acid

A simple method for microdetermination of muramic acid is elaborated. The method is based on the degradation of muramic acid to lactic acid, followed by degradation of the latter to acetaldehyde which can be determined colorimetrically with p-hydroxydiphenyl (PHD). A linear relationship exists between the concentration of muramic acid (up to 20 μg), and absorbance at 560 nm. Substances usually present in the hydrolysates of bacterial cell wall peptidoglycan do not interfere in the determination.     

落叶松林土壤可溶性碳、氮和官能团特征的时空变化及与土壤理化性质的关系

土壤可溶性有机碳(DOC)、可溶性有机氮(DON)及其官能团特征在土壤碳、氮循环中作用非常重要。对25个不同年龄落叶松林样地、4个深度(0-20、20-40、40-60和60-80 cm)土壤DOC、DON、有机物官能团(芳香性、分子量和疏水性)特征指标(254、260、272 nm和280 nm的单位吸光度值SUVA:吸光度值/DOC含量)和土壤理化指标(土壤全碳SOC、全氮SON、pH值、电导率、容重)进行测定,旨在探究它们的时、空变化特征及与土壤理化指标相关关系。在空间尺度上,与SOC、SON一致,表层土壤DOC、DON多显著高于深层(P<0.05),但是4个单位吸光度值SUVA₂₅₄、SUVA₂₆₀、SUVA₂₇₂和 SUVA₂₈₀均不存在差异(P>0.05);在时间尺度上,仅表层土壤DOC、SOC 和SON随落叶松年龄显著线性增长(P<0.05),而深层DOC、SOC、SON、不同层土壤DON及各官能团指标均没有显著变化(P>0.05)。可见,土壤可溶性有机物内碳的累积(7 mg kg^-1 a^-1)是SOC累积的一部分(762 mg kg^-1 a^-1),但其DON及可溶性有机物芳香性比例、分子量大小及疏水性容量等官能团特征并未受落叶松生长时间以及土壤深度的显著影响。进一步回归分析表明这些官能团指标随土壤DOC含量增加而指数下降,深层土壤同时受DON显著影响。表层土壤DOC、DON与土壤SOC、SON、土壤电导率显著正相关(P<0.05),深层相关不显著(P>0.05),而官能团指标与土壤理化性质的相关性在各个土层均不显著,显示出表层土壤可溶性有机物的量,而不是官能团组成对土壤理化性质影响显著,而深层土壤可溶性有机物量对土壤理化性质不构成显著影响。对于从可溶性组分、官能团角度,分析落叶松人工林成长过程中土壤碳、氮时空变化具有科学意义。     

Leaching of plasticizers from and surface characterization of PVC blood platelet bags.

The leaching of phthalate plasticizers from four types of blood platelet bags was investigated. The anticoagulant solutions used in the blood collection bags had pH values of 5.64 +/- .04 and contained no detectable amounts of phthalates. Platelet bag materials from each bag were soaked in normal salines for up to 5 days. The salines were tested for the leached phthalates from the bags but none could be found. However, di-(2-ethylhexyl) phthalate (DEHP) leached out of the PL-146 and Terumo bags into bovine calf serum used for soaking the bag materials. There was an increase in the amount of DEHP leached from about 1.1 mg at the end of one day to about 3.3 mg per gm of bag material at the end of a five day extraction with the serum. In PL-732 sets, a platelet bag made of a specialty polyolefin, the amount of DEHP leached out was less than 0.02 mg per g of bag material. CLX bags, which contained tri-(2-ethylhexyl) trimelliate (TETM) as a plasticizer, showed a negligible amount of it leaching into the calf serum. Infra-red spectra showed that PL-146 bags had been coated with a layer of a fatty acid amide while the Terumo bags contained a layer of a silicone fluid on their inner surfaces. CLX bags showed a coating of stearates, which were probably soaps of calcium or zinc. Scanning electron microscopy (SEM) showed that the inner surfaces of each brand of the bag were distinctly different morphologically. The two PVC bags were very similar whereas the surfaces morphology of PL-732 was rougher. Terumo bag had a different surface morphology than those of the other bags whereas the CLX bags had a very regular surface pattern. The exact significance of the surface morphology is not certain but excessively rough surfaces may not be desirable for the bags.     

水氮配合对绿洲沙地农田玉米产量、土壤硝态氮和氮平衡的影响

在黑河中游边缘绿洲沙地农田研究了不同的水氮配合对玉米产量、土壤硝态氮在剖面中的累积和氮平衡的影响.结果表明,施氮处理较不施氮处理产量增加48.22%～108.6%,施氮量超过225 kg hm-2,玉米产量不再显著增加.受土壤结构影响土壤硝态氮在土壤中呈"W"型分布,即土壤硝态氮含量在0～20 cm、140～160 cm和260～300 cm土层均出现峰值,并随施氮量增加,峰值增高.在常规高灌溉量处理硝态氮含量峰值最高值出现在260～300 cm土层,节水25%灌溉处理硝态氮含量峰值最高值出现在土壤表层0～20 cm土层.在常规高灌溉量处理0～300 cm土层中200～300土层硝态氮累积量所占比例最高,介于27.56%～51.86%之间;节水25%灌溉处理在0～300 cm土层中100～200土层硝态氮累积量所占比例最高,介于32.94%～38.07%之间;表明低灌溉处理下土壤硝态氮在土壤浅层累积较多,而高灌溉处理使更多的硝态氮淋溶至土壤深层.与2006年相比,2007年不施氮处理0～200 cm土层土壤硝态氮含量和积累量均明显减少;而施氮处理变化很小,在低灌溉处理甚至表现出硝态氮含量和积累量增加,表明施氮是土壤硝态氮累积的主要来源,而灌溉则使硝态氮向土壤深层淋溶.0～200 cm 土层土壤硝态氮累积量平均介于27.66～116.68 kg hm-2、氮素表观损失量平均介于77.35～260.96 kg hm-2,和施氮量均呈线性相关,即随施氮量增加,土壤硝态氮累积量和氮素表观损失量均增加,相关系数R2介于0.79～0.99之间,相关均显著.随施氮量增加,玉米总吸氮量和氮收获指数增加,氮的农学利用率降低,而灌溉的影响较小.施氮量超过225 kg hm-2时,地上部植株氮肥吸收利用率和籽粒氮肥吸收利用率开始有降低趋势.所以,在沙地农田,节水10%～25%的灌溉水平和225 kg hm-2的施氮水平可以在避免水肥过量投入的基础上减少土壤有机氮淋溶对地下水造成的污染威胁.     

Treatment of dialysis membranes for simultaneous dialysis and concentration

Dialysis membranes used for simultaneous dialysis-concentration required pretreatment to remove uv-absorbing compounds leached from the membranes and to reduce the absorption of protein to the membranes. This was accomplished with sodium carbonate and ethanol or with "sulfur-removal solutions." Protein determinations were made with a micro-Bradford protein reaction and with uv absorbance at 280 nm. Soluble membrane components contributed to aberrant uv spectra and altered the ratio of 280/260-nm absorbance. Simultaneous dialysis and concentration in the micro protein dialyzer-concentrator apparatus, combining aspects of thin-layer dialysis and ultrafiltration, resulted in rapid removal of salts from the protein solutions. Prior treatment of membranes reduced uncertainties in retentate recoveries, eliminated uv-absorbing components of membranes, and improved recoveries of protein.     

Assay of penicillin acylase in organic media

Summary The synthetic substrate 6-nitro-3-(phenylacetamido) benzoic acid (NIPAB) is an appropriate substrate for assaying penicillin acylase activity in reversed micellar systems of Aerosol - OT in isooctane. Accumulation of 6-nitro-3-aminobenzoic acid (NABA) produced by the enzymatic hydrolysis of NIPAB, followed by the increase in absorbance at 405 nm, was linear at 4 to 20 mM for up to 30 minutes and 15 °C to 40 °C.Abbreviations PA penicillin acylase (penicillin amidohydrolase EC 3.5.1.11) - AOT Aerosol OT (sodium bis- (2-ethylhexyl) sulfosuccinate) - NIPAB 6-nitro-3-(phenylacetamido)-benzoic acid - NABA 6-nitro-3-aminobenzoic acid - BSA bovine serum albumin     

Optimization of tannase production by Aureobasidium pullulans DBS66

Tannase production by Aureobasidium pullulans DBS66 was optimized. The organism produced maximum tannase in the presence of 1% tannic acid after 36 h. Maximum gallic acid accumulation was observed within 36 h and tannic acid in the fermented broth was completely degraded after 42 h of growth. Glucose had a stimulatory effect on tannase synthesis at 0.1% (w/v) concentration. The organism showed maximum tannase production with (NH4)2HPO4 as nitrogen source. Shaking speed of 120 rpm and 50-ml broth volume have been found to be suitable for maximum tannase production.     

Mineralization of the carbon and nitrogen of plant material added to soil and of the soil humus during incubation following periodic drying and rewetting of the soil

Summary The production of mineralized carbon and nitrogen by a slightly acid sandy loam soil, in the presence and absence of finely chopped fresh plant material or powdered dry plant material, was followed by determination of the amounts of carbon and nitrogen mineralized at intervals during continuous incubation over a period of twelve weeks. Mineralization of carbon and nitrogen was also followed in parallel soil samples and soil plant material mixtures which were dried at 35°C or 105°C and then rewetted every two weeks during the incubation period.The amounts of carbon and nitrogen mineralized were determined at intervals during the incubation period.Mineralization of the carbon and nitrogen of the humus of the soil was stimulated by periodic drying of the soil and particularly when the soil was dried at 105°C.It was found that more mineral nitrogen was produced from fresh plant material than from dried plant material in all the treatments. Periodic drying of the soil-plant material mixtures did not stimulate the production of mineral nitrogen from the added plant material and reduced it considerably when the drying was carried out at 105°C.Periodic drying at 35°C did not stimulate the mineralization of the carbon of fresh or dried plant material. It is clear therefore that, at temperatures occurring in nature, it is unlikely that the decomposition of plant material added to the soil will be stimulated as a consequence of drying of the soil. Periodic drying of the soil-plant material mixture at 105°C increased the mineralization of the carbon of the dried plant material. The amounts of carbon mineralized in 12 weeks from the dried plant material did not, however, exceed the amounts from fresh plant material incubated continuously in fresh soil or in soil periodically dried at 35°C.     

Excitonic interactions in wild-type and mutant PSI reaction centers

Femtosecond excitation of the red edge of the chlorophyll a Q(Y) transition band in photosystem I (PSI), with light of wavelength > or = 700 nm, leads to wide transient (subpicosecond) absorbance changes: positive DeltaA between 635 and 665 nm, and four negative DeltaA bands at 667, 675, 683, and 695 nm. Here we compare the transient absorbance changes after excitation at 700, 705, and 710 nm at 20 K in several PSI preparations of Chlamydomonas reinhardtii where amino acid ligands of the primary donor, primary acceptor, or connecting chlorophylls have been mutated. Most of these mutations influence the spectrum of the absorbance changes. This supports the view that the chlorophylls of the electron transfer chain as well as the connecting chlorophylls are engaged in the observed absorbance changes. The wide absorption spectrum of the electron transfer chain revealed by the transient measurements may contribute to the high efficiency of energy trapping in photosystem 1. Exciton calculations, based on the recent PSI structure, allow an assignment of the DeltaA bands to particular chlorophylls: the bands at 675 and 695 nm to the dimers of primary acceptor and accessory chlorophyll and the band at 683 nm to the connecting chlorophylls. The subpicosecond transient absorption bands decay may reflect rapid charge separation in the PSI reaction center.