Möglichkeiten zur Steigerung der Schwermetallsorptionsleistung von Mikroorganismen

The sorption capacity of silver on different biological materials has been investigated depending on physico-chemical pretreatments. The maximum silver loading values measured were compared with the values obtained with nontreated biomasses. The results show an increase of the loading capacity up to a factor of 10 in case of the alkalitreated biomasses. When the biomasses are extracted before being used as adsorbent with a solvent mixture of chloroform/methanol in a ratio of 2:1 the efficiency of the silver adsorbing power can be increased. Beyond that, the ability to adsorb silver can also be influenced when microorganisms are used as biocatalysts in a product synthesis before they are used as adsorbents. A strain of Acetobacter methanolicus possesses 1.8 times higher affinity to silver when it is employed in a process of gluconic acid production before adsorption. Physico-chemical pretreatments influence not only the loading capacity of the biological material, but also the contacting time required for the establishment of the adsorption equilibrium can be considerable reduced.     

Evaluation of a combined activated carbon prefilter and biotrickling filter system treating variable ethanol and ethyl acetate gaseous emissions

The removal of a 1:1 by weight mixture of ethanol and ethyl acetate was studied in a gas phase biotrickling filter running under conditions that simulated industrial emissions from the flexographic sector, i.e. discontinuous loading (twelve hours per day and five days per week) and oscillating concentration of the inlet stream. Three sets of experimental conditions were tested in which empty‐bed residence time varied from 60 to 25 s (inlet loads from 50 to 90 g C m^?3 h^?1). The biotrickling filter reached a maximum elimination capacity of 48.5 g C m^?3 h^?1 (removal efficiency=68.9%) for an empty‐bed residence time of 40 s. A decrease in the residence time from 40 to 25 s adversely affected the elimination capacity (40.3 g C m^?3 h^?1, removal efficiency=46.6%). For the three tested residence times, outlet concentrations during pollutant feeding were above 100 mg C m^?3 (EU legal limit for flexographic facilities). Then an activated carbon prefilter was installed to buffer the fluctuating concentration, enabling a more stable operation. The desorbed pollutant from the activated carbon during non‐feeding hours also served as an extra source of substrate, avoiding severe starvation. The use of the activated carbon prefilter with a volume 25 times lower than that of the bioreactor was shown to reach an average outlet emission concentration lower than 50 mg C m^?3 operating the biotrickling filter at an empty‐bed residence time of 40 s, with a maximum elimination capacity of 59.6 g C m^?3 h^?1 (removal efficiency=92.0%).     

Biotrickling air filtration of 2-chlorophenol at high loading rates

The degradation of 2-chlorophenol vapours in air was performed in a trickling biofilter packed with ceramic material seeded with the bacterium Pseudomonas pickettii, strain LD1. The system performance was evaluated under varying operating conditions (inlet 2-chlorophenol air concentrations from 0.10 to 3.50 g m^?3, and superficial air velocities of 30.0, 60.0, and 120.0 m h^?1). For all air velocity the maximum degradation rate was obtained for loading rates of 40 g m^?2 h^?1. Higher loading conditions resulted in strong inhibition of microbial activity, particularly severe at high air velocity. Process analysis, performed using data on pollutant concentration profiles along the filter packing obtained under different conditions of inlet concentration and air velocity, proves that best performance (i.e. maximum degradation efficiency and capacity) can be obtained for a narrow range of operating conditions, which can be ensured by proper design of biofilter size (i.e. diameter and height). Kinetic analysis of experimental data confirms that 2-CP inhibits microbial activity in the biofilter bed. Experimental data are satisfactorily fitted by the Haldane kinetic equation up to a critical value of loading rate, beyond which the experimental degradation rate is overestimated by the kinetic model. The inhibition appears to be affected by the loading rate, and the estimated inhibition constant linearly increases with increasing empty bed residence time.     

Enhanced cellulase production in fed-batch culture of Trichoderma reesei C30

The use of a fed-batch cultivation of the fungus Trichoderma reesei (C30) allows cellulase [see 1,4-(1,3;1,4)-β-d-glucan 4-glucanohydrolase, EC 3.2.1.4] production to occur under optimum conditions, and results in extremely high enzyme titres and productivities. Enzyme levels of 26 U ml^?1 at productivities >130 U l^?1 h^?1 have been achieved. These results are compared with the values obtained in two-stage continuous cultivation of the organism at optimum pH and temperature.     

Evaluation of different bio-kinetic parameters of Curvularia lunata at different environmental conditions

Growth kinetic parameters for Curvularia lunata were determined in yeast extract, peptone and dextrose medium under different environmental conditions. The values of specific growth rate () were found to be different at different cultivation (pH and temperature) conditions. At the optimum growth conditions (pH 7.0 and temperature 28 °C) the values of specific growth rate and maintenance coefficient for C. lunata were maximum (0.19 h^-1) and minimum (0.04 h^-1) respectively, whereas the growth yield coefficient (Y_EG) decreased with the increase of cultivation temperature. The values of saturation constant (K_S) did not change appreciably with the change of cultivation conditions.     

Oxidative capacity determines the growth rate with Acetobacter methanolicus

The cultivation of Acetobacter methanolicus on various substrates revealed that the respective maximum growth rates are obtained at an almost identical oxidative capacity of about 16 mmoles of oxygen g (biomass)^?1·h^?1 under conditions of energy generations by complete substrate oxidation. This is considered to be an indication that the energy production rate determined by the capacity of the respiratory chain limits the growth rate in this strain. However, with glucose and glycerol, for example, a further increase in the growth rate is observed accompanied by the generation of products (gluconic acid or dihydroxyacetone, respectively). The incomplete oxidation should play the role of an additional energy generation. The potential for this rate increase is looked for in a higher energy gain derived from reduction equivalents (PQQH₂) in this periplasmic oxidation step in relation to the cytoplasmic reduction equivalents.     

Oxygen requirements for d-xylose fermentation to ethanol and polyols by Pachysolen tannophilus

The oxygen requirements for ethanol production from d-xylose (10 or 20 g l^?1) by Pachysolen tannophilus have been determined by controlling the availability of oxygen to shake flasks. Under anaerobic conditions no ethanol was produced whereas under aerobic conditions mainly biomass was formed. Semi-anaerobic conditions resulted in maximum ethanol production. By varying the stirring speed of a fermenter and supplying air to the liquid surface at various rates, the oxygen transfer rate (OTR) was controlled under semi-anaerobic conditions. By increasing the OTR from 0.05 to 16.04 mmol l^?1 h^?1, the ethanol yield coefficient decreased from 0.28 to 0.18 while the cell yield coefficient increased from 0.14 to 0.22. The accumulation of polyols decreased from 0.88 to 0.56 g l^?1 with increasing OTR. At OTRs between 0.09 and 1.18 mmol l^?1 h^?1, specific ethanol productivity attained a maximum value of 0.07 h^?1 and decreased with either increasing or decreasing OTR. The results indicate that the OTR must be carefully controlled for efficient ethanol production from d-xylose by P. tannophilus.     

Successful operation of continuous reactors at short retention times results in high-density,fast-rate Dehalococcoides dechlorinating cultures

The discovery of Dehalococcoides mccartyi reducing perchloroethene and trichloroethene (TCE) to ethene was a key landmark for bioremediation applications at contaminated sites. D. mccartyi-containing cultures are typically grown in batch-fed reactors. On the other hand, continuous cultivation of these microorganisms has been described only at long hydraulic retention times (HRTs). We report the cultivation of a representative D. mccartyi-containing culture in continuous stirred-tank reactors (CSTRs) at a short, 3-d HRT, using TCE as the electron acceptor. We successfully operated 3-d HRT CSTRs for up to 120 days and observed sustained dechlorination of TCE at influent concentrations of 1 and 2 mM TCE to ≥97 % ethene, coupled to the production of 10¹² D. mccartyi cells L_culture ^?1. These outcomes were possible in part by using a medium with low bicarbonate concentrations (5 mM) to minimize the excessive proliferation of microorganisms that use bicarbonate as an electron acceptor and compete with D. mccartyi for H₂. The maximum conversion rates for the CSTR-produced culture were 0.13?±?0.016, 0.06?±?0.018, and 0.02?±?0.007 mmol Cl^? L_culture ^?1 h^?1, respectively, for TCE, cis-dichloroethene, and vinyl chloride. The CSTR operation described here provides the fastest laboratory cultivation rate of high-cell density Dehalococcoides cultures reported in the literature to date. This cultivation method provides a fundamental scientific platform for potential future operations of such a system at larger scales.     

Effect of trace elements and optimization of their composition for the nitrification of a heterotrophic nitrifying bacterium, <Emphasis Type="Italic">Acinetobacter harbinensis</Emphasis> HITLi7<Superscript>T</Superscript>, at low temperature

The effects of trace elements on ammonium degradation performance and extracellular polymeric substances (EPS) secretion of Acinetobacter harbinensis HITLi7^T at low temperature were investigated. Response surface methodology (RSM) was applied to obtain the optimal composition of trace elements and analyze their correlation. In this study, the results indicated that the ammonium removal performance could be enhanced by the presence of 0.1 mg L^?1 Fe, Mn, or B in pure cultivation. When the concentrations of Fe and Mn were 0.2 mg L^?1, the ammonium removal rates of the novel strain HITLi7^T were 0.49 ± 0.01 mg L^?1·h^?1 and 0.58 ± 0.01 mg L^?1·h^?1, respectively, while it was the low concentration of 0.05 mg L^?1 B that showed the maximum ammonium removal rate (0.56 ± 0.02 mg L^?1·h^?1) of strain HITLi7^T. The regression model was obtained and the optimal formulation of trace elements was: B 0.064 mg L^?1, Fe 0.12 mg L^?1, and Mn 0.1 mg L^?1. Based on these values, the experimental ammonium removal rate could reach 0.59 mg L^?1·h^?1, which matched well with the predicted response. The study also found that the addition of trace elements, causing high ammonium removal rates, resulted in a high polysaccharide (PS) ratio in the EPS secreted by Acinetobacter harbinensis HITLi7^T. Especially under the optimal conditions, the PS ratio reached the highest value of 49.9%.     

Process optimization of the integrated synthesis and secretion of ectoine and hydroxyectoine under hyper/hypo‐osmotic stress

The synthesis and secretion of the industrial relevant compatible solutes ectoine and hydroxyectoine using the halophile bacterium Chromohalobacter salexigens were studied and optimized. For this purpose, a cascade of two continuously operated bioreactors was used. In the first bioreactor, cells were grown under constant hyperosmotic conditions and thermal stress driving the cells to accumulate large amounts of ectoines. To enhance the overall productivity, high cell densities up to 61 g L^?1 were achieved using a cross‐flow ultrafiltration connected to the first bioreactor. In the coupled second bioreactor the concentrated cell broth was subjected to an osmotic and thermal down‐shock by addition of fresh distilled water. Under these conditions, the cells are forced to secrete the accumulated intracellular ectoines into the medium to avoid bursting. The cultivation conditions in the first bioreactor were optimized with respect to growth temperature and medium salinity to reach the highest synthesis (productivity); the second bioreactor was optimized using a multi‐objective approach to attain maximal ectoine secretion with simultaneous minimization of cell death and product dilution caused by the osmotic and thermal down‐shock. Depending on the cultivation conditions, intracellular ectoine and hydroxyectoine contents up to 540 and 400 mg per g cell dry weight, respectively, were attained. With a maximum specific growth rate of 0.3 h^?1 in defined medium, productivities of approximately 2.1 g L^?1 h^?1 secreted ectoines in continuous operation were reached. Biotechnol. Bioeng. 2010;107: 124–133. © 2010 Wiley Periodicals, Inc.     

Synthesis of bacteriochlorophyll <Emphasis Type="Italic">a</Emphasis> by the purple nonsulfur bacterium <Emphasis Type="Italic">Rhodobacter capsulatus</Emphasis>

The ability of purple nonsulfur bacteria Rhodobacter capsulatus B10 to synthesize bacteriochlorophyll under phototrophic and dark conditions was studied. The modes for cultivation in the dark with oxygen limitation in a continuous culture at D = 0.1 h^?1 were selected. The yield of biomass reached 20 g/l; the bacteriochlorophyll a output of the process amounted to 16.6 mg/l h^?1.     

Patterns of growth and β-galactosidase production by Bifidobacteria

We investigated the patterns of growth and β-galactosidase production in the strains Bifidobacterium adolescentis GO-13, MS-42, 91-BIM, and 94-BIM and b. bifidum No.1, LVA-3, 791 on media with various carbon sources. The synthesis of β-galactosidase was shown to be associated with exponential growth of the cultures involved. The maximum specific rate of β-galactosidase synthesis of 0.20 U mg^?1 h^?1 was observed in B. bifidum LVA-3 after 3–6 h of cultivation. This value for B. adolescentis 91-BIM and 94-BIM was lower and amounted to 0.03–0.08 U mg^?1h^?1. On the medium with lactose, the highest specific growth rates for B. bifidum LVA-3 and B. bifidum No.1 were 0.38 and 0.60 h^?1, respectively, after 3–6 h of cultivation. For B. adolescentis 91-BIM and 94-BIM, this parameter peaked at 12–15 h of cultivation at 0.13 and 0.22 h^?1, respectively. The hydrolytic activity of β-galactosidase in the growth medium decreased during the stationary growth phase of the tested cultures.     

Effects of salinity,light intensity and sediment on growth,pigments, agar production and reproduction in Gracilaria tenuistipitata from Songkhla Lagoon in Thailand

The effects of salinity, light intensity and sediment on Gracilaria tenuistipitata C.F. Chang & B.M. Xia on growth, pigments, agar production, and net photosynthesis rate were examined in the laboratory under varying conditions of salinity (0, 25 and 33 psu), light intensity (150, 400, 700 and 1000 µmol photons m^?2 s^?1) and sediment (0, 0.67 and 2.28 mg L^?1). These conditions simulated field conditions, to gain some understanding of the best conditions for cultivation of G. tenuistipitata. The highest growth rate was at 25 psu, 700 µmol photons m^?2 s^?1 with no sediments, that provided a 6.7% increase in weight gain. The highest agar production (24.8 ± 3.0 %DW) was at 25 psu, 150–400 µmol photons m^?2 s^?1 and no sediment. The highest pigment contents were phycoerythrin (0.8 ± 0.5 mg g^?1FW) and phycocyanin (0.34 ± 0.05 mg g^?1 FW) produced in low light conditions, at 150 µmol photons m^?2 s^?1. The highest photosynthesis rate was 161.3 ± 32.7 mg O₂ g^?1 DW h^?1 in 25 psu, 400 µmol photons m^?2 s^?1 without sediment in the short period of cultivation, (3 days) and 60.3 ± 6.7 mg O₂ g^?1 DW h^?1 in 25 psu, 700 µmol photons m^?2 s^?1 without sediment in the long period of cultivation (20 days). The results indicated that salinity was the most crucial factor affecting G. tenuistipitata growth and production. This would help to promote the cultivation of Gracilaria cultivation back into the lagoon using these now determined baseline conditions. Extrapolation of the results from the laboratory study to field conditions indicated that it was possible to obtain two crops of Gracilaria a year in the lagoon, with good yields of agar, from mid‐January to the end of April (dry season), and from mid‐July to the end of September (first rainy season) when provided sediment was restricted.     

Development of a simultaneous bioreactor system for characterization of gas production kinetics of methanogenic archaea at high pressure

Cultivation of methanogens under high pressure offers a great opportunity in biotechnological processes, one of which is the improvement of the gas‐liquid transfer of substrate gases into the medium broth. This article describes a newly developed simultaneous bioreactor system consisting of four identical cultivation vessels suitable for investigation of microbial activity at pressures up to 50 bar and temperatures up to 145°C. Initial pressure studies at 10 and 50 bar of the autotrophic and hydrogenotrophic methanogens Methanothermobacter marburgensis, Methanobacterium palustre, and Methanobacterium thermaggregans were performed to evaluate the reproducibility of the system as well as to test the productivity of these strains. The strains were compared with respect to gas conversion (%), methane evolution rate (MER) (mmol L^‐1 h^?1), turnover rate (h^?1), and maximum conversion rate (k_min) (bar h^?1). A pressure drop that can be explained by the reaction stoichiometry showed that all tested strains were active under pressurized conditions. Our study sheds light on the production kinetics of methanogenic strains under high‐pressure conditions. In addition, the simultaneous bioreactor system is a suitable first step screening system for analyzing the substrate uptake and/or production kinetics of gas conversion and/or gas production processes for barophilic or barotolerant microbes.     

Effect of oxygen transfer rate on the composition of the pectolytic enzyme complex of Aspergillus niger

Optimal agitation and aeration conditions [assuring O₂ transfer rates (OTR) from 12 to 179 mmol L^?1 h^?1] were determined for pectin lyase (PL) synthesis of an Aspergillus niger strain. Components of the pectolytic enzyme complex were also investigated in order to determine whether their O₂ demand is identical with or different from that of pectin lyase. Should the latter be the case, a possibility would be given to produce enzyme complexes of different agitation and aeration conditions. According to our results, mycelium yield of Aspergillus niger attained a maximum at an OTR of 100 mmol L^?1 h^?1. The yields of the various pectolytic enzymes reached maxima at different OTRs. Pectin lyase production was the highest (0.555 µmol min^?1 mL^?1) at an OTR of 60 mmol L^?1 h^?1. Endopolygalacturonase (PG) production showed a maximum at the OTR of 49 mmol L^?1 h^?1 with a second peak at 100?135 mmol O₂ L^?1 h^?1. Pectin esterase (PE) synthesis showed a maximum at on OTR of 12?14 mmol L^?1 h^?1, while both apple juice clarifying and macerating activities gave two maxima at 14 and 60 mmol L^?1 h^?1 due to the optima of PE and endo-PG. Macerating activity showed a high value at OTR optimal for PL production as well.     

Rapid assessment of oxygen transfer impact for Corynebacterium glutamicum

Oxygen supply is crucial in industrial application of microbial systems, such as Corynebacterium glutamicum, but oxygen transfer is often neglected in early strain characterizations, typically done under aerobic conditions. In this work, a new procedure for oxygen transfer screening is presented, assessing the impact of maximum oxygen transfer conditions (OTR_max) within microtiter plate-based cultivation for enhanced throughput. Oxygen-dependent growth and productivity were characterized for C. glutamicum ATCC13032 and C. glutamicum DM1933 (lysine producer). Biomass and lysine product yield are affected at OTR_max below 14 mmol L^?1 h^?1 in a standardized batch process, but not by further increase of OTR_max above this threshold value indicating a reasonable tradeoff between power input and oxygen transfer capacity OTR_max. The described oxygen transfer screening allows comparative determination of metabolic robustness against oxygen transfer limitation and serves identification of potential problems or opportunities later created during scale-up.     

Quantitative physiology of Lactococcus lactis at extreme low‐growth rates

This paper describes the metabolic adaptation of Lactococcus lactis during the transition from a growing to a non‐growing state using retentostat cultivation. Under retentostat cultivation, the specific growth rate decreased from 0.025 h^?1 to 0.0001 h^?1 in 42 days, while doubling time increased to more than 260 days. Viability of the overall culture was maintained above 90% but included approximately 20% damaged cells, which had lost their colony forming capacity on solid media. Although culture biomass and viability had reached a steady‐state after 14 days of retentostat cultivation, the morphology of the cells changed from coccus‐to‐rod shape at later stages of retentostat cultivation, by which the cell's surface to volume ratio was estimated to increase 2.4‐fold. Furthermore, the metabolic patterns switched between homolactic and mixed‐acid fermentation during the retentostat cultivation. Retentostat cultivation enabled the calculation of accurate substrate‐ and energy‐related maintenance coefficients and biomass yields under non‐growing conditions, which were in good agreement with those calculated by extrapolation from chemostat cultivations at high dilution rates. In this study, we illustrate how retentostat cultivation allows decoupling of growth and non‐growth associated processes in L. lactis, enabling the analysis of quantitative physiological responses of this bacterium to near zero‐specific growth rates.     

Removal of chromium (VI) using poly(methylacrylate) functionalized guar gum

Using persulfate/ascorbic acid redox pair, poly(methylacrylate) was grafted on to guar gum and the conditions for the grafting were optimized. The copolymer sample having maximum %G was evaluated for the removal of Cr(VI) and the sorption conditions were optimized. The sorption was found pH dependent, pH 1.0 being the optimum value. Sorption data at pH 1.0 were modeled using both the Langmuir and Freundlich isotherms where the data fitted better to Freundlich isotherm. The equilibrium sorption capacity of 29.67 mg/g was determined from the Langmuir isotherm. The sorption followed a pseudo-second-order kinetics with a rate constant 2.5 × 10^?4 g mg^?1 min^?1. The grafted product was also evaluated for Cr(VI) removal from local electroplating industrial waste water. The regeneration experiments revealed that the guar-graft-poly(methylacrylate) could be successfully reused for five cycles. In the present study conductivity measurements were used instead of conventional photometric method for determining Cr(VI) concentration in the equilibrium solutions and the results obtained have been compared with photometric method. Optimum Cr(VI) binding under highly acidic conditions indicated significant contribution of non electrostatic forces in the adsorption process.     

Assessing the antifouling properties of cold-spray metal embedment using loading density gradients of metal particles

Particles of copper, bronze and zinc were embedded into a polymer using cold-spray technology to produce loading density gradients of metal particles. The gradients were used to identify the species with the highest tolerance to the release of copper and zinc ions. The gradients also established the minimum effective release rates (MERRs) of copper and zinc ions needed to prevent the recruitment of fouling under field conditions. Watersipora sp. and Simplaria pseudomilitaris had the highest tolerances to the release of metal ions. Copper and bronze gradient tubes were similar in their MERRs of copper ions against Watersipora sp. (0.058?g?m^?2?h^?1 and 0.054?g?m^?2?h^?1, respectively) and against S. pseudomilitaris (0.030?g?m^?2?h^?1 and 0.025?g?m^?2?h^?1, respectively). Zinc was not an effective antifoulant, with failure within two weeks. In conclusion, cold-spray gradients were effective in determining MERRs and these outcomes provide the basis for the development of cold-spray surfaces with pre-determined life-spans using controlled MERRs.     

Seasonal Growth and Photosynthetic Performance of the Antarctic Macroalga Desmarestia menziesii (Phaeophyceae) Cultivated under Fluctuating Antarctic Daylengths

Growth, photosynthesis, dark respiration and pigment contents were monitored in adult sporophytes of the Antarctic brown alga Desmarestia menziesii J. Agardh grown under fluctuating Antarctic daylength conditions. Growth rates were closely coupled to daylength variations with values varying from 0.05% d^?1 in winter condition (July-August) to 0.5% d^?1 in early summer (December). Photosynthetic pigments had maximum values of 1.8 mg g^?1 FW (chlorophyll a), 0.4 mg g^?1 FW (chlorophyll c) and 0.9 mg g^?1 FW (fucoxanthin) in summer. These changes were also closely related to individual size and biomass of the plants. Net photosynthesis (P_max), on a fresh weight basis, showed a clear seasonal pattern with highest rates of 25μmol O₂ g^?1 FW h^?1 in October and minima close to 9μmol O₂ g^?1 FW h^?1 in April. Dark respiration was high in spring (13μmol O₂ g^?1 FW h^?1) approximately coinciding with growth peaks. Likewise, photosynthetic efficiency (α) and the initial saturating light point of photosynthesis (l_k) increased significantly in spring [1.3 μimol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 and 26μmol photons m^?2 s^?1, respectively]. In the case of α, no significant differences between fresh weight and Chl a based rates were found. The results of the present study are the first that demonstrate seasonality of physiological parameters in D. menziesii sporophytes and confirm also that phenology and physiology of macroalgae can be simulated in the laboratory. On the other hand this study adds new elements to the explanation of the life strategy of D. menziesii, in particular that algal growth and photosynthesis occur under a programmed seasonal pattern.