Buoyant Densities and Dry-Matter Contents of Microorganisms: Conversion of a Measured Biovolume into Biomass

Several isolates of bacteria and fungi from soil, together with cells released directly from soil, were studied with respect to buoyant density and dry weight. The specific volume (cubic centimeters per gram) of wet cells as measured in density gradients of colloidal silica was correlated with the percent dry weight of the cells and found to be in general agreement with calculations based on the partial specific volume of major cell components. The buoyant density of pure bacterial cultures ranged from 1.035 to 1.093 g/cm³, and their dry-matter content ranged from 12 to 33% (wt/wt). Average values proposed for the conversion of bacterial biovolume into biomass dry weight are 1.09 g/cm³ and 30% dry matter. Fungal hyphae had buoyant densities ranging from 1.08 to 1.11 g/cm³, and their dry-matter content ranged from 18 to 25% (wt/wt). Average values proposed for the conversion of hyphal biovolume into biomass dry weight are 1.09 g/cm³ and 21% dry matter. Three of the bacterial isolates were found to have cell capsules. The calculated buoyant density and percent dry weight of these capsules varied from 1.029 g/cm³ and 7% dry weight to 1.084 g/cm³ and 44% dry weight. The majority of the fungi were found to produce large amounts of extracellular material when grown in liquid cultures. This material was not produced when the fungi were grown on either sterile spruce needles or membrane filters on an agar surface. Fungal hyphae in litter were shown to be free from extracellular materials.     

不同海拔地区种植的水稻地上部干物质的生产和分配

根据1983—1985年“高原水稻高产栽培的生理生态规律研究”中低热的元江(海拔400米左右)、温凉的昆明(约1900米)和冷凉的丽江(约2400米)的资料,以六个处理、十八个小区、三年总平均值,比较了不同海拔地区种植的水稻中地上部干物质生产和分配的总趋势。主要结果如下: 1.全生育期总的干物质生产量以温凉地区最高,低热地区居中,冷凉地区最低。 2.抽穗前干物质生产速率和齐穗期干物重占黄熟期干物重的比例随海拔降低而增加;抽穗期至黄熟期干物质生产速率,以温凉地区最高,低热地区居中,冷凉地区最低,但低热地区低于前期,高海拔地区高于前期,不过冷凉的丽江增加的更多。 3.抽穗前(旗叶完全展开后)叶干重占当时植株总干重的比例,随海拔升高而降低。 4.抽穗期至黄熟期的次库(茎 叶鞘)干重的改变,不同海拔地区种植的水稻表现不同:低热地区减重,温凉地区稍增,冷凉地区明显增加。 5.与高海拔地区种植的水稻相比,在黄熟期低海拔地区的有较高的穗重/总重和穗增重/总增重的比例。另外低海拔地区的穗增重超过总增重。结实率和谷/草比例均随海拔增高而减低。     

Physiological and Ecological Studies in the Analysis of Plant Environment: XII. The Role of the Light Factor in Limiting Growth

Previous investigations in southern England on twenty-two herbaceousspecies have demonstrated that for widely spaced plants thediurnal solar radiation limits the net assimilation rate ofall species and restricts the relative growth rate of many.In examining how far these limitations apply to other environmentsit is now shown that in the subtropics and tropics the levelsof net assimilation rate and relative growth rate can greatlyexceed those so far recorded for cool temperate regions, andthese differences are attributed to the higher insolation andtemperatures. From a variety of evidence it is concluded that as the distancebetween plants is reduced 8O the net assimilation rate is progressivelydiminished even in regions of high insolation through the enhancedmutual shading. In consequence levels of light which may besupra-optimal for relatively isolated individuals may yet limitthe dry-matter production of a dense population. There is anoptimal ratio of leaf area to ground surface (leaf-area index)for the maximal exploitation of the incoming radiation in carbonfixation by the population and this optimum will vary with thespecies and the light intensity. Where other environmental factorsare favourable, light may limit dry-matter production everywhere. On an annual basis dry-matter production will be dependent ontwo components—the length of the ‘growing season’and the period over which the leaf-area index remains optimal.In the tropics the highest annual rate of production so farrecorded is 7⁸ tonnes/hect. produced by Saccharum officinarumandin north-east Europe 23.5 tonnes by Fagus sylvatica. Over shortperiods the rate of dry-matter production can attain 3⁸g./m.²/dayand the utilization of solar energy can be as high as 4.2 percent., or 9.5 per cent, for the range 4, 000–7, 000 A. Although information on the productivity of natural communitiesis still ex-ceedingly scanty, an attempt has been made to interpretthe general pattern in terms of the length of the growing season,the level of solar radiation, the magni-tude of the leaf-areaindex of the whole community, and the period over which theleaf canopy remains green. It is postulated that in any regionthe vegetation reaches a dynamic equilibrium when there is themaximum exploitation of the incoming radiation to produce thegreatest production of dry matter.     

Influence of potassium concentration on growth and potassium uptake by rice plants

Summary Rice plants (Oryza sativa L.) were grown for 125 days in nutrient solutions maintained at constant potassium concentrations over the rate 51 to 1534 M. Data are recorded at different growth stages for relative growth rate, potassium content, absorption rate of this element per gram dry weight of roots per day and its utilization in dry-matter production. Optimum concentration for maximum growth was found to be about 256 M or 10 ppm potassium. Growth was more or less constant beyond this concentration. The maximum growth was characterized by a certain relative absorption rate (I_M) for maximum growth ranging from 106 to 757 g-atom of potassium per g dry weight of roots per day, during the period of cultivation. In general the content of this element in tops as a percentage of the total content does not change appreciably either under different concentrations or at different ages. When the concentration of the solution increased, the utilization of potassium (dry-matter production per unit element content) decreased. The ratio between the relative growth rate (RGR) and relative absorption rate (I_M) for maximum growth of rice ranged 1.4 during the first phase of growth to 1.3 at maturity of the crop. Higher ratios indicate an insufficient nutrient supply, lower ratios, however, either an abundant supply or a depressing effect of the solution on growth.     

The effects of topping and plant population on dry matter synthesis and distribution in Brussels sprouts

The effects of topping at different dates, and of different plant populations on dry-matter production and distribution in Brussels sprouts were studied. Total dry-matter production per unit area was unaffected by either topping or density. Leaf area was decreased by topping, resulting in a temporary increase in net assimilation rate. Topping resulted in a redistribution of dry matter; that which would have formed new stem and leaf tissue was directed into sprout production. Increasing plant density did not affect the distribution of dry matter but increased the number of smaller sprouts. The apparent optimum plant spacing in this series was 21×21 in (53×53 cm). At maturity assimilation approximately balances respiration.     

Changes in respiration,dry-matter production and its partition in rice (Oryza sativa L.) in response to water deficits during the grain-filling period

A simple, physiologically based model was devised and used for estimating the respiration rate and the overall conversion efficiency of photosynthate into the grain dry-matter in dehydrated plants relative to well watered controls. The model described mathematically the partitioning of assimilate produced by current photosynthesis and of assimilate stored previously between the grain and those plants parts other than grain (the “straw”). Using data obtained from the dry-matter analysis and CO₂ gas exchange measurements, the model gave us two independent estimates of the respiration rate and the overall conversion efficiency; one for the plants given a prolonged dark period and the other for those grown in a normal light and dark cycle. The rate of dark respiration increased with mild water stress: 4.3 mg g⁻¹ day⁻¹ in control plants with leaf water potential of around −0.4 MPa and 11.3 mg g⁻¹ day⁻¹ in dehydrated plants with leaf water potential of around −1 MPa, when both the control and dehydrated plants were left in the dark for ten days. Similar values were obtained for plants in a normal light and dark cycle: 5.6 in well watered and 8.1 mg g⁻¹ day⁻¹ in the stressed plants. Accordingly, the overall conversion efficiency (the ratio of grain dry-matter against the gross carbohydrate input to the construction and maintenance processes) was 0.7 to 0.8 for the well hydrated control and 0.4 to 0.5 for moderately dehydrated plants. With increasing water deficits, however, the respiration rate decreased: 4.8 mg g⁻¹ day⁻¹ when plants were severely stressed (below −3 MPa in midday leaf water potential). The decrease in straw dry weight alone overestimates dry-matter partition of the stored assimilate in the straw into grain by 20 to 30% in well watered plants and the error increases to 50 to 60% in more dehydrated plants.     

Aboveground dry-matter allocation in ungrazed and grazed stands of Indigofera spinosa in the arid zone of Turkana, Kenya

The dwarf shrub Indigofera spinosa , indigenous to arid and semi-arid rangelands of northeastern Africa, is an important food source for livestock. Proper management of the shrub requires improved understanding of the effects of grazing and climatic variability on aboveground dry-matter allocation. Between 1986 and 1990, we compared the temporal variability of aboveground dry-matter allocation to different plant biomass compartments. We also compared dry-matter transfers between components; total live biomass to litter, standing dead to litter and live biomass to standing dead between continuously grazed and an ungrazed treatments. Partitioning of combined total dry-matter production among different structural organs (called allocation ratio) is influenced by phenological changes, episodic rainfall and her-bivory. Dry-matter production in the grazed treatment responded more markedly to episodic rainfall events more than in the ungrazed treatment. Exclusion of grazers failed to improve the relative growth rate (RGR) of shrub biomass, while grazing improved it. RGR declined in the ungrazed treatment following the accumulation of standing dead dry-matter, while m the grazed treatment it declined following the shedding of leaves. The shrub allocated more to total live biomass than to standing dead. Greater reduction of total live allocation ratio in the grazed than in the ungrazed treatment occurred during a dry year. The ungrazed treatment had higher standing dead allocation ratio than did the grazed treatment. Plants transferred more dry-matter from total live biomass compartment to litter, than from standing dead to or from total live biomass to standing dead independent of treatment. The rates of transfer were higher in the ungrazed than in the grazed treatment. The results suggest that I spinosa has evolved to respond to climatic variability and grazmgbyallocating dry allocating dry-matter differently between various compartments.     

Light intensity, gibberellin content and the resolution of shoot growth in Brassica

The role of gibberellins (GAs) in the regulation of shoot elongation is well established but the phytohormonal control of dry-matter production is poorly understood. In the present study, shoot elongation and dry-matter production were resolved by growing Brassica napus L. seedlings under five light intensities (photon flux densities) ranging from 25 to 500 μmol m⁻² s⁻¹. Under low light, plants were tall but produced little dry weight; as light intensity was increased, plants were progressively shorter but had increasing dry weights. Endogenous GAs in stems of 16- and 17-d-old plants were analyzed by gas chromatography-selected ion monitoring with [²H₂] internal standards. The contents of GAs increased dramatically with decreasing light intensity: GA₁, GA₃, GA₈ and GA₂₀ were 62, 15, 16 and 32 times higher, respectively, under the lowest versus highest light intensities. Gibberellin A₁₉ was not measured at 25 μmol m⁻² s⁻¹ but was 9␣times greater in the 75 compared to 500 μmol m⁻² s⁻¹ treatment. Shoot and hypocotyl lengths were closely positively correlated with (log) GA concentration (for example: r ² = 0.93 for GA₁ and hypocotyl length) but shoot dry matter was negatively correlated with GA concentration. The application of gibberellic acid (GA₃) produced elongation of plants grown under high light, indication that their low level of endogenous GA was limiting shoot elongation. Although endogenous GA₂₀ showed the greatest influence of light treatment, metabolism of [³H]GA₂₀ and of [³H]GA₁ was only slightly influenced by light intensity, suggesting that neither 2β- nor 3β-hydroxylation were points of metabolic regulation. The results of this study indicate that GAs control shoot elongation but are not directly involved in the regulation of shoot dry weight in Brassica. The study also suggests a role of GAs in photomorphogenesis, serving as an intermediate between light condition and shoot elongation response. Received: 18 June 1998 / Accepted: 29 July 1998     

红光与远红光比值对温室切花菊形态指标、叶面积及干物质分配的影响

以切花菊品种‘神马’(Chrysanthemum morifolium Ramat ‘Jinba’)为试材,于2010-2011年设计不同红光(R: (660 ±10) nm)与远红光(FR: (730±10)nm)比值(R/FR分别为0.5、2.5、4.5、6.5)的LED灯照射处理,研究不同R/FR值对温室切花菊形态指标、叶面积形成及干物质分配的影响。结果显示R/FR=2.5处理的植株叶片数、株高、茎粗、花径、叶面积及总干重均为各个处理中最高,R/FR=0.5处理的节间最长。所有R/FR处理的单株地上干物质重量与光质处理天数呈指数-线性模型。随处理天数的增加不同R/FR值处理菊花植株地上部分及地下部分干物质分配指数差异均不显著,叶片和花的干物质分配指数随处理天数的增加分别呈降低和升高的趋势,茎干物质分配指数则呈现先升高后降低的趋势,R/FR=2.5处理下,菊花叶片干物质分配指数和花干物质分配指数最高,而茎干物质分配指数却为最低;R/FR=6.5处理茎干物质分配指数最高,叶片干物质分配指数最低;0.5处理花朵干物质分配指数最低,说明远红光比例增加能够促进干物质向茎中分配,R/FR=2.5处理利于干物质向花朵中分配。     

Peculiarities of sexual reproduction inFagus crenata forests in relation to annual production of reproductive organs

Annual production rates of reproductive organs inFagus crenata forests in the lower area of the species' range were studied using 10 litter traps in 1980–1986. The production rates of dispersed pollen were estimated by multiplying the number of fallen male inflorescences per ha per year by the mean amount of pollen per inflorescence before anthesis. Large annual fluctuations in the production rates of male and female inflorescences were recognized, whereas their annual trends were synchronized with each other. Pollen production rates were within the range 1.0–6900 (mean: 1630)×10⁹ha⁻¹ yr⁻¹, the maximum/minimum ratio attaining 7000.F. crenata was the lowest producer of pollen among seven tree species studied: the number of pollen grains equivalent to a single ovule was in the range 6.0–14×10⁴. Furthermore, the mean dry weight of a single pollen grain (3.77×10⁻⁵mg) was higher than for wind-pollinated species. Three factors seemed to cause the low seed fertility ofF. crenata. The dry-matter production rate in the best seed year reached 3252 kg ha⁻¹ yr⁻¹, of which pollen accounted for 259 kg ha⁻¹ yr⁻¹. Unproductive years with less than 10% of the maximum production occurred four times in a 7-yr period. In such years there were fewer male and female inflorescences, and more fruit dropped as a result of insect damage. Lower nut dissemination would play an important role in suppressing any increase in nut predators, and fewer flowers would be produced to avoid wastage of photosynthates in a cool-temperate climate.     

Population dynamics and production of Daphnia hyalina in a eutrophic reservoir

The population dynamics and production of Daphnia hyaiina^ the dominant cladoceran i n Eglwys Nynydd, a shallow eutrophic reservoir in South Wales, were studied for 2 years against a background of limnological measurements. The appearance and development of successive generations from egg to adult could be followed from changing numbers in arbitrarily defined size classes. Seasonal variations in mean length, mean brood-size and proportion of gravid adults were recorded and mean brood-size was related to changing food and temperature conditions. Egg-development times for D. hyaiina were determined in culture and the population parameters finite birth (S), instantaneous birth (b′), instantaneous population change (r′), instantaneous death (d′) and finite death rates (D) were estimated from field data. Turnover and production estimates were calculated from finite death rates and biomass. The calculated potential rate of increase (b′) was nearly always greater than the observed rate of increase (r′): seasonal changes in death rate (d′) generally parallel changes in birth rate (b′) but remain somewhat out of phase. Population oscillations are probably due t o a delay in the expression of the effects of population density upon birth and death rates. The mean biomass of Daphnia in 1970 was 0-57 mg dry wt/l (0-88 g C/m²) and in 1971 0-32 mg dry wt/l (0.49 g C/m²). Annual production for Daphnia was 11-8 mg dry wt/l (18-2 g C/m²) in 1970 and 8-30 mg dry wt/l (12 8 g C/m²) in 1971. Information available on primary production in the reservoir suggests that the production of Daphnia accounts for less than 2% of gross primary production. However, the pattern of population growth of Daphnia in Eglwys Nynydd almost certainly reflects a food limited system. In summer, blue-green algae may be abundant but serve as a poor food source: throughout the blue-green bloom egg production remains low, at times remaining below 0-5 eggs/adult.     

Wet- vs. Dry-Season Transpiration in an Amazonian Rain Forest Palm Iriartea deltoidea

The wet and dry seasons in tropical rain forests can differ in precipitation, soil moisture and irradiance more significantly than often assumed. This could potentially affect the water relations of many tree species that may exhibit either increased transpiration in the dry season as a response to the increased irradiance or decreased transpiration as a result of decreases in soil moisture and increases in atmospheric vapor pressure deficit (VPD). Atmospheric data, soil moisture data and sap fluxes in Iriartea deltoidea palms were measured in eastern Ecuador during the wet and dry seasons. There were no differences between total daily sap fluxes in I. deltoidea palms during the wet and dry seasons; however, evaporative demand was significantly higher in the dry season and therefore, transpiration was more restricted by stomatal closure during the dry season than the wet season. This is likely the result of larger atmospheric VPD during the dry season compared with the wet season and possibly the result of reduced soil moisture availability. Additionally, based on published tree abundances in this area, measured sap fluxes in I. deltoidea were scaled up to the hectare level. Transpiration from I. deltoidea palms was estimated to be around 0.03 mm/d, which could represent about 1 percent of total transpiration in this area of the Amazon rain forest. If climate change predictions for more lengthy tropical dry periods are realized, greater stomatal control of dry-season sap flux has the potential to become even more prevalent in tropical species.     

Nutrient Supply, Dry-matter Production and Nutrient Uptake of Forest Tree Seedlings

The dry-matter production and nutrient uptake of forest-treeseedlings grown under controlled levels of nutrition in sub-irrigatedsand culture were investigated. Hardwood seedlings attainedgreater dry weight than conifer seedlings, and Pinus radiataa greater dry weight than P. contorta and P. nigra, but thesegreater dry weights were not related to greater leaf/weightratios, although seed size may have been an important influenceon final seedling dry weight. P. radiata was found to have alower requirement for P than P. contorta and P. nigra in oneexperiment. The demand (total nutrient uptake per unit of time) made bythree species for nutrients upon a site was shown to dependmore upon growth-rate per annum than on efficiency (quantityof nutrients required to produce a unit of dry matter). It isconcluded that the ability of tree species to grow satisfactorilyon soils of low nutrient status depends largely on their abilityfor relatively slow growth. On the other hand, species showinggood response to favourable sites may also make satisfactorygrowth on poor sites.     

Life history and production of the predatory caddisfly Rhyacophila vao Milne in a spring-fed stream

1. The predatory caddisfly Rhyacophila vao Milne (Rhyacophilidae) displayed a 2-year, semivoltine life cycle in a small, spring-fed stream in southern Alberta, Canada. Three overlapping cohorts were identified throughout the 2-year sampling program, with five larval instars recognized. Larvae overwintered in instars I —ELI, developed to instar IV by summer and instar V by autumn. The second winter was spent in instar V, Pupation occurred from late May to August and did not commence until stream temperature exceeded 3°C. Adults were collected from mid-June to early September. 2. Larvae displayed a diphasic growth pattern: Phase I, a positive, non-linear growth rate for instars I-IV; Phase II, a constant growth rate during instar V. Phase I coincided with increasing stream temperatures in late winter and spring, where mean instantaneous growth rates (maximum of 2.78% dry wt day^?1) were significantly correlated with stream temperatures. Although the duration of Phase II spanned a temperature range similar to that in Phase I, the instantaneous growth rate remained temperature-independent at 0.87% dry wt day^?1. 3. Larvae exhibited a type III survivorship curve (i.e. an exponential decrease on an arithmetic scale), with the finite rate of mortality averaging 0.80% larvae day^?1. 4. Cohort 1 (later part of 1983 year class) displayed lower total production compared with the equivalent growth phase in the 1984 year class (Cohort 2). In contrast, production of the non-linear and linear growth phases of Cohort 2 was similar. Periods of similar growth characteristics for Cohorts 1 and 2 had comparable P/B ratios for both the unadjusted and time-adjusted annual estimates, although higher ratios were observed for the non-linear growth phase of Cohort 2. Total cohort production (linear + non-linear growth phases) could only be calculated for Cohort 2, and was 870.2 ± 1011.4 mg dry wt m^?2. The corresponding cohort P/B ratio was 5.01 and the adjusted annual P/B, 3.01. 5. Annual larval production (±SE) for the first and second years of the study was similar (Year 1, 480.0 ± 387.5mg dry wt m^?2; Year 2, 526.9 ± 967.5mg dry wt m^?2) as were unadjusted and annual P/B ratios.     

The Effects of Soil Water and Atmospheric Vapour Pressure Deficit on Stomatal Behaviour and Photosynthesis in the Oil Palm

The oil palm (Elaeis guineensis Jacq.) maintains a large leafarea throughout the year, but its productivity is limited bya low rate of dry matter production per unit leaf area. Stomatalclosure, at times of low soil water availability and high atmosphericvapour pressure deficit, is an important factor limiting photosynthesisand hence dry matter production. In this paper, laboratory andfield data are used to prepare a model of the relationshipsbetween net photosynthetic rate and stomatal conductance, andbetween stomatal conductance and environmental variables. Resultsshow that high atmospheric vapour pressure deficits may limitproduction even in parts of the world where oil palms are notnormally considered to suffer from water stress. The model canbe used to design and evaluate irrigation systems, and to helpquantify the potential value of oil palm genotypes with lowstomatal sensitivity to either VPD or available soil water foruse where irrigation is impractical. Key words: Elaeis guineensis Jacq., drought, irrigation, plant breeding     

Continuous fermentation to produce fungal protein. Effect of growth rate on the biomass yield and chemical composition of Fusarium moniliforme

Fusarium moniliforme was grown on a carob aqueous extract in a chemostat for fungal protein production. The substrate was adjusted to provide 0.5% carob sugars supplemented with inorganic salts. The dilution rate varied from 0.086 to 0.227 hr^?1 under constant conditions of temperature (30°C), pH (4.5), and oxygen saturation (60–80%). A yield of 0.709 g dry mycelium/g consumed carob sugar and a productivity value of 0.687 g dry mycelium/liter hr^?1 were obtained at μ = 0.205 hr^?1. The maintenance coefficient was 0.077 g carob sugar/g dry mycelium hr^?1. While the carbohydrate and purine content of dry mycelium increased at μ values from 0.114 to 0.205 hr^?1 both true (Lowry) and crude (N × 6.25) protein contents decreased at the same μ range. Maximum values of 36.3% true and 47.9% crude protein of dry mycelium were obtained at μ = 0.114 hr^?1, whereas a minimum purine content of 99.8 μmol/g corresponding to 6.42% nucleic acids was recorded at μ = 0.086 hr^?1. It was concluded that a continuous fermentation of carob aqueous extract using F. moniliforme should be operated at growth rates of approximately 0.205 hr^?1 in order to maximize protein production.     

A quantitative analysis of varietal and moisture status effects on the growth of Vicia faba in relation to radiation absorption

Growth of two cultivars of Vicia faba, under various conditions of moisture status, was analysed in terms of solar radiation absorbed by their foliage. The relationship between dry-matter production and absorbed photosynthetically active radiation was linear throughout the growing season for both cultivars (Minica and Alfred) and for all levels of soil moisture status. A straight line was used, the slope of which represented a constant mean seasonal ‘efficiency’ of conversion of radiation into biomass. Moisture stress reduced both the amount of radiation intercepted, by limiting the size of the canopy, and the efficiency of its conversion into dry matter. Efficiency of both cultivars grown under optimal water regimes was similar, however, drought had a more drastic effect on conversion efficiency of Minica. Mean crop growth rates were highly dependent upon both absorption and efficiency, as were maximum crop growth rates during the linear portion of growth. Reductions in seed yield were similar to trends in total biomass production. Harvest index was reduced by moisture stress in Minica, and increased to compensate for dry-matter loss in Alfred.     

The Apical Organization and Phyllotaxis of the Oil Palm

The oil palm apex is described, together with investigationsof its phyllotaxis as revealed by apical dissection and measurementson mature stems and axillary structures. The rate of growthof the apex is remarkably low, being correlated with both plastochroneand phyllotaxis height. This is discussed in relation to therates of dry-matter production determined for adult palms. Thephyllotaxis as determined in the apex is remarkably constant,irrespective of extremes of age and habitat, and the same patternis found almost unchanged in the leaf bases on mature stemsgrowing under plantation conditions. Modification of the characteristicphyllotaxis height occurs due to internal factors resultingin the basal swelling of the palm stem and the different phyllotaxisof branching systems, both vegetative and reproductive, andalso due to external factors which cause constrictions in thestem. These modifications result from different rates of longitudinaland radial growth during development, and cause considerablechange in phyllotaxis.     

Influence of exponentially decreasing feeding rates on fed-batch ethanol fermentation of sugar cane blackstrap molasses

Summary The ethanol yield was not affected and the ethanol productivity was increased when exponentially decreasing feeding rates were used instead of constant feeding rates in fed batch ethanol fermentations. The influences of the initial sugar feeding rate on the ethanol productivity, on the constant ethanol production rate during the feeding phase and on the initial ethanol production specific rate are represented by Monod-like equations.Nomenclature F reactor feeding rate (L.h^–1) - F_o initial reactor feeding rate (L.h^–1) - K time constant; see equation (l) (h^–1) - M_E mass of ethanol in the fermentor (g) - M_s mass of TRS in the fermentor (g) - M_x mass of yeast cells (dry matter) in the fermentor (g) - P ethanol productivity (g.L^–1.h^–1) - R ethanol constant production rate during the feeding phase (g.h^–1) - s standard deviation - S_o TRS concentration in the feeding mash (g.L^–1) - t time (h) - T fermentor filling-up-time (h) - T time necessary to complete the fermentation (h) - TRS total reducing sugars calculated as glucose (g.L^–1) - V_o volume of the inoculum (L) - V_f final volume of medium in the fermentor (L) - X_o yeast concentration of the inoculum (dry matter) (g.L^–1) - ethanol yield (% of the theoretical value) - initial specific rate of ethanol production (h^–1)     

High yeast concentration in continuous fermentation with cell recycle obtained by tangential microfiltration

Summary Continuous fermentation fed by 150 kg/m³ of glucose with total cell recycling by tangential microfiltration enabled yeasts concentration of 300 kg/m³ (dry weight) to be reached with a dilution rate of 0,5h^–1 and a cell viability greater than 75%. The stability of this system was tested for 50 residence times of the permeate. The method can be used both for the production of cell concentrates and for high rates of metabolite production.Nomenclature D. W. dry weight - X_T (kg/m³) total cell concentration D.W. - X_V (kg/m³) viable cell concentration D.W. - V viability of cell culture in per cent of total cell concentration - S (kg/m³) glucose concentration - P (kg/m³) ethanol concentration - D (h) dilution rate - R (kg/kg) fermentation yield - (h) specific growth rate - vp(kg/kg/h) specific alcohol production rate - (m) yeast size - (kg/kg) kg of intracellular water per kg of dry cells