Estimations of Bacterial Growth Rates in Natural Waters

Specific growth rates as low as 0.005 hr⁻¹ (generation times of 20 to 200 hr) of aquatic bacteria in natural waters have been calculated from significant differences between dilution rates and washout rates in a chemostat. The measured growth rates were affected by the treatment of the water samples (type of sterilization) and by competition with the natural microflora for the unknown growth-limiting substrate.     

Growth Rates of Sulfolobus acidocaldarius in Nature

Turnover times for water passing through several Sulfolobus acidocaldarius-containing springs were determined by measuring the dilution rates of small amounts of sodium chloride that were added to the springs. Chloride was diluted out exponentially, while concentrations of the bacteria remained constant. Additionally, temperature, pH, and chemical composition of the springs also remained constant during the time that the chloride was being diluted. The springs are thus steady-state systems, and since the rates of bacterial growth must be at least equal to the chloride dilution rates, minimal doubling times for the bacterial populations can be calculated. Half-times for chloride dilution, equivalent to bacterial doubling times, were on the order of 10 to 20 h for springs ranging in volume from about 20 to 2,000 liters, but approximately 30 days for two larger springs of about 1 million liters. Formaldehyde-fixed cells of a serologically distinguishable strain of S. acidocaldarius were also added as markers to four of the smaller springs, and the dilution rates of these bacteria were compared with the chloride dilution rates. The rates agreed reasonably well, thus verifying the growth rates obtained from the chloride dilution rates. In three springs, exponential growth was studied by draining the springs and allowing them to refill with bacteria-free water. Exponential doubling times were on the order of a few hours, much more rapid than steady-state doubling times. The methods used in this work may have wider utility in aquatic environments.     

Rates of accumulation of glycosidase activities during growth and differentiation of Dictyostelium discoideum.

1. The rates of accumulation (enzyme units/h per 10(8) cells) of a number of glycosidase activities were studied in Dictyostelium discoideum cells during the growth and differentiation phases of this organism's life cycle. 2. The rates of accumulation of the enzymes beta-N-acetylglucosaminidase, alpha-glucosidase and beta-galactosidase remain unchanged during the growth and early differentiation phases. 3. The considerable changes in specific activity of the enzymes which occur in the early differentiation phase are due to the massive loss of total cellular protein which occurs at this time. 4. Significant alterations can occur in the rates of accumulation of alpha-mannosidase during both the growth and differentiation phases, and since, on the onset of differentiation, beta-glucosidase activity is excreted and degraded, the rate of accumulation of this enzyme differs in the growth and differentiation phases. 5. The characteristic rates of accumulation of all these glycosidases change markedly with changes in the growth conditions of the myxamoebae, and thus these rates of synthesis must be regulated independently; however, addition of cyclic AMP to the growth medium has no effect on them.     

Growth Analysis of Contrasting Cultivars of Zea mays L. at Different Rates of Nitrogen Supply

The effects of nitrogen supply on the growth and nitrogen contentsof four cultivars of Zea mays L. of different origins were examinedunder water-culture conditions at the seedling stage. Seedlingsof cultivars CNIA12, LG11, Tusa Finn, and UNPHU XC301 were grownunder three different relative addition rates of nitrogen. Growthparameters were determined by means of functional growth analysisconducted on 10 to 19 d-old seedlings. No differences in relativegrowth rates were found among cultivars when nitrogen supplywas high. However, at the lowest rate of nitrogen supply, TusaFina and LG11 showed lower relative growth rates than CNIA12and UNPHU XC301, where relative growth rates were sustainedeven at the lowest rate of nitrogen supply, due to a higherunit leaf rate. The higher unit leaf rate of these two cultivarscorresponds directly to higher leaf and plant nitrogen contents.High positive correlations were found between plant nitrogencontents and both relative growth rate and unit leaf rate. Theresults suggest a potential for selection of genotypes withimproved performance under conditions where high rates of nitrogen-fertilizerapplication are too costly or not desirable.Copyright 1994,1999 Academic Press Maize, Zea mays, growth analysis, maize, nitrogen nutrition, nitrogen content, relative addition rates, relative growth rates, unit leaf rate     

Estimating Cytomegalovirus Growth Rates by Using Only a Single Point

Calculation of pathogen growth rates is important in understanding the natural history of infection and effects of therapy. However, it is often difficult to estimate pathogen growth because patients are treated immediately upon the detection of infection, leaving only one nonzero untreated reading. Previous approaches have relied on the flawed assumption that pathogen loads just prior to detection are at the assay detection threshold. We have developed a novel method for estimating the pathogen growth rate from a single reading and investigated the initial growth of cytomegalovirus (CMV) in allogeneic hematopoietic stem cell transplant (HSCT) patients. We applied this approach to CMV viral loads measured at least weekly in 122 patients in the 3 months posttransplant. Viral growth rates were estimated by using a modeling approach that accounts for the viral load and the time since the last negative reading. Viral growth rates decreased rapidly within the first week, from 0.72/day (doubling time, 0.96 day) at the point of reactivation to 0.22/day (doubling time, 3.1 days) at 1 week. Results from this method correlated closely with a two-point regression analysis of a subset of 58 patients with detectable subthreshold viral loads immediately prior to overt reactivation. Patients with lymphocyte counts of ≥0.5 × 10⁹/liter had significantly slower viral growth than patients with low lymphocyte counts (0.612/day versus 0.325/day, P < 0.0001). Thus, our novel method of estimating pathogen growth rates reveals a rapid slowing of CMV growth during reactivation in HSCT patients and a significant impact of the lymphocyte count on CMV growth.     

Revisiting the Estimation of Dinosaur Growth Rates

Previous growth-rate studies covering 14 dinosaur taxa, as represented by 31 data sets, are critically examined and reanalyzed by using improved statistical techniques. The examination reveals that some previously reported results cannot be replicated by using the methods originally reported; results from new methods are in many cases different, in both the quantitative rates and the qualitative nature of the growth, from results in the prior literature. Asymptotic growth curves, which have been hypothesized to be ubiquitous, are shown to provide best fits for only four of the 14 taxa. Possible reasons for non-asymptotic growth patterns are discussed; they include systematic errors in the age-estimation process and, more likely, a bias toward younger ages among the specimens analyzed. Analysis of the data sets finds that only three taxa include specimens that could be considered skeletally mature (i.e., having attained 90% of maximum body size predicted by asymptotic curve fits), and eleven taxa are quite immature, with the largest specimen having attained less than 62% of predicted asymptotic size. The three taxa that include skeletally mature specimens are included in the four taxa that are best fit by asymptotic curves. The totality of results presented here suggests that previous estimates of both maximum dinosaur growth rates and maximum dinosaur sizes have little statistical support. Suggestions for future research are presented.     

Ribosome Patterns in Escherichia coli Growing at Various Rates

The distribution of ribosomes, 30 and 50S subunits and polysomes, at three different growth rates of Escherichia coli strains B and K-12 has been studied. The usual percentage of subunits is about 20%. However, at the lowest growth rate (mu = generations/hour), mu = 0.45 at 30C, the proportion of subunits is about 30%. An exceptional situation exists in K-12 strains growing at maximum growth rate, mu = 1.35, where the percentage of subunits is 45%. Several points of control over ribosome production are thus indicated. It is suggested that "subunit pool" is essentially a reserve. Furthermore, the polysome content when related to deoxyribonucleic acid content varies directly with the growth rate, which indicates the average efficiency of polysomes in protein synthesis does not vary over the range of growth rates tested.     

Quantitative Physiology of Saccharomyces cerevisiae at Near-Zero Specific Growth Rates

Growth at near-zero specific growth rates is a largely unexplored area of yeast physiology. To investigate the physiology of Saccharomyces cerevisiae under these conditions, the effluent removal pipe of anaerobic, glucose-limited chemostat culture (dilution rate, 0.025 h⁻¹) was fitted with a 0.22-μm-pore-size polypropylene filter unit. This setup enabled prolonged cultivation with complete cell retention. After 22 days of cultivation, specific growth rates had decreased below 0.001 h⁻¹ (doubling time of >700 h). Over this period, viability of the retentostat cultures decreased to ca. 80%. The viable biomass concentration in the retentostats could be accurately predicted by a maintenance coefficient of 0.50 mmol of glucose g⁻¹ of biomass h⁻¹ calculated from anaerobic, glucose-limited chemostat cultures grown at dilution rates of 0.025 to 0.20 h⁻¹. This indicated that, in contrast to the situation in several prokaryotes, maintenance energy requirements in S. cerevisiae do not substantially change at near-zero specific growth rates. After 22 days of retentostat cultivation, glucose metabolism was predominantly geared toward alcoholic fermentation to meet maintenance energy requirements. The strict correlation between glycerol production and biomass formation observed at higher specific growth rates was not maintained at the near-zero growth rates reached in the retentostat cultures. In addition to glycerol, the organic acids acetate, d-lactate, and succinate were produced at low rates during prolonged retentostat cultivation. This study identifies robustness and by-product formation as key issues in attempts to uncouple growth and product formation in S. cerevisiae.Laboratory studies on microorganisms are often performed in batch cultures. During the initial phase of batch cultivation, all nutrients are usually present in excess. As a consequence, the initial specific growth rate, μ, of the microorganism in such cultures equals the maximum specific growth rate, μ_max. In natural environments, the specific growth rate of microorganisms is likely to be constrained by the limited availability of one or more growth-limiting nutrients, resulting in specific growth rates far below μ_max (8, 24). In chemostat cultures fed with a medium containing a single growth-limiting nutrient, the dilution rate determines the specific growth rate. Chemostat cultivation therefore offers the possibility to study microbial physiology at carefully controlled, submaximal specific growth rates and to investigate the effect of specific growth rate on cellular physiology (20). Chemostat cultivation of the yeast Saccharomyces cerevisiae has demonstrated strong effects of specific growth rate on biomass composition (26, 51), product formation (5, 37), and cell size (23). Moreover, during energy-limited growth at low specific growth rates, a relatively large fraction of the energy substrate has to be dissimilated for maintenance-related processes such as maintenance of chemi-osmotic gradients and turnover of cellular components (34). Not surprisingly, recent genome-wide studies have shown strong effects of specific growth rate on levels of mRNAs and proteins (9, 14, 38).In chemostat studies on S. cerevisiae, the steady-state specific growth rate is usually between 0.03 h⁻¹ and 0.40 h⁻¹. While this range is relevant for many industrial applications, there are several incentives to study growth of this yeast at even lower specific growth rates. In many natural environments, growth at a μ of 0.03 h⁻¹, corresponding to a doubling time of 23.1 h, probably still represents extremely fast growth. Furthermore, in industrial applications, S. cerevisiae and other microorganisms can be considered as self-replicating catalysts, and, unless biomass is the desired product, growth can be considered as undesirable by-product formation leading to nonproductive substrate consumption. This problem is further augmented when the excess yeast biomass cannot be valorized because it is genetically modified or has been used for the production of compounds that are not compatible with use as, for example, cattle feed. A third incentive for exploring the physiology of S. cerevisiae at near-zero growth rates is related to the increasing interest in this yeast as a systems biology model for human cells (16, 27, 33). At near-zero growth rates, the age of individual yeast cells becomes much higher than can be achieved in conventional batch or chemostat cultures. Studies on extremely slow growth of S. cerevisiae under defined conditions may therefore provide an interesting model for ageing of human cells.Retentostat cultivation, first proposed by Herbert (18), is a modification of chemostat cultivation that has been specifically designed to study microbial physiology at near-zero specific growth rates. In a retentostat, sometimes referred to as recycling fermentor or recyclostat, the growth-limiting energy substrate is fed at a constant rate, and biomass is retained in the fermentor by an internal filter probe connected to the effluent line or by an external filter module. Prolonged retentostat cultivation should, in theory, result in a situation where the specific growth rate becomes zero and where the specific rate of substrate consumption equals the maintenance energy requirement. This situation is fundamentally different from starvation, which involves deterioration of physiological processes, and from resting states typified by spores, which have little or no metabolic activity. Retentostat cultivation has been applied to several bacterial systems including Escherichia coli (11), Paracoccus denitrificans, and Bacillus licheniformis (49) and the autotrophs Nitrosomonas europaea and Nitrobacter winogradskyi (46, 47). These studies demonstrated that the physiology of these prokaryotes at extremely low specific growth rates could not be accurately predicted by a simple extrapolation of results obtained at higher specific growth rates. In particular, near-zero specific growth rates coincided with increased levels of ppGpp (2), which induces the stringent response, a regulatory program that diverts cellular resources from growth to amino acid biosynthesis (10, 21). Furthermore, it was concluded that extremely slow growth led to a reduction of the maintenance energy requirement of prokaryotes. A recent quantitative analysis on cell retention cultures of S. cerevisiae was performed under severely nitrogen-limited growth conditions and used incomplete cell retention (7), which precluded a quantitative comparison with maintenance energy requirements calculated from energy-limited chemostat cultures.The goal of the present study was to quantitatively analyze the physiology of S. cerevisiae at extremely low specific growth rates in glucose-limited retentostat cultures. To this end, an internal filter probe was introduced in the effluent line of standard laboratory chemostat fermentors and used in long-term cultivation runs with complete cell retention. Anaerobic conditions were chosen to facilitate quantification of catabolic fluxes and growth energetics.     

Rates of Cell Division in the Shoot Apical Meristem of Pisum

The relative rates of cell division in different regions ofthe pea shoot apical meristem were obtained by measuring theincrease in the numbers of metaphases following applicationof colchicine to the plants. Absolute values for the rates ofcell division could be calculated since the average rate ofcell division for the whole apex was known. Measurements ofthe rates of cell division were obtained at defined intervalsduring the course of a single plastochron. Within each regionof the apex the rate of cell division did not change more thanabout two-fold throughout the plastochron. There was very littleor no increase in the rate of cell division associated withleaf initiation. The formation of a leaf primordium and thesubsequent growth of the apical dome apparently result fromchanges in the direction of growth rather than changes in therates of growth. Three main regions were discernible withinthe apical meristem: a region with a slow rate of cell divisionin the apical dome, a region of a faster rate of cell divisionat the base of the apical dome and at the site of initiationof procambial strands, and a region of an intermediate rateof cell division in the newly initiated leaf primordium andthe adjacent part of the shoot axis.     

The Relative Growth Rates of Three Plankton Diatoms in Relation to Underwater Radiation and Temperature

Relative growth rates of three freshwater plankton diatoms-Asterionellaformosa, Fragilaria crotonensis, and Tabellaria flocculosa var.asterionelloides-are described from cultures suspended at variousdepths and during several seasons in the lake Windermere. Seasonalvariation in rates recorded near the surface (i m. depth) isinterpreted in terms of seasonal changes in temperature anddaylength. Rates recorded for Asterionella and Fragilaria aregenerally similar, but are approximately twice the rates obtainedwith Tabellaria. Depth profiles of relative growth rates areof similar form in all species, and normally show lightsaturationnear the surface. The shape of profiles for Asterionella isin good agreement with estimates of photosynthesis integratedover the growth periods. The parallelism between photosyntheticand relative growth rates of Asterionella is further illustratedfrom laboratory experiments: an approximate interconversion,under certain conditions, is given.     

Grazing, Growth, and Ammonium Excretion Rates of a Heterotrophic Microflagellate Fed with Four Species of Bacteria

We studied aspects of the population growth of a microflagellate, Monas sp., isolated from Lake Kinneret, Israel. The protozoan growth rates, rates of ingestion of bacteria, and final population yields generally increased with increasing bacterial concentrations, although the exact relationship varied depending on the species of bacteria used as food. Grazing rates decreased hyperbolically with increasing food density. Gross growth efficiencies and ammonia excretion rates were similar over a range of food densities among the four species of bacteria. Population doubling times and ammonia excretion rates were lowest, and growth efficiencies were highest, at temperatures between 18 and 24°C. Under optimum conditions, the microflagellates had average population doubling times of 5.0 to 7.8 h, average growth efficiencies of 23.7 to 48.7%, and average ammonia excretion rates of 0.76 to 1.23 μmol of NH₄⁺ per mg (dry wt) per h.     

Growth and Grazing Rates of the Heterotrophic Dinoflagellate Polykrikos kofoidii on Red-Tide and Toxic Dinoflagellates

We investigated growth rates, grazing rates, and prey selection of Polykrikos kofoidii when feeding on several species of red-tide and/or toxic dinoflagellates. Polykrikos kofoidii ingested all prey species used in this study, exhibiting positive growth on Lingulodinium polyedrum, Scrippsiella trochoidea, Ceratium furca, Gymnodinium catenatum, Gyrodinium impudicum, Prorocentrum micans, and the toxic dinoflagellate Amphidinium carterae, but not on P. minimum. Specific growth rates of P. kofoidii increased rapidly with increasing density of L. polyedrum, S. trochoidea, C. furca, and G. catenatum before saturating between 500-2,000 ng C ml(-1). Specific growth rates increased continuously when P. kofoidii was fed the other prey species. Maximum specific growth rates of P. kofoidii on G. catenatum (1.12 d(-1)), S. trochoidea (0.97 d(-1)), and L. polyedrum (0.83 d(-1)) were higher than those on C. furca (0.35 d(-1)), A. carterae (0.10 d(-1)), P. micans (0.06 d(-1)), G. impudicum (0.06 d(-1)), and P. minimum (-0.03 d(-1)). Threshold prey concentrations (where net growth = 0) were 54-288 ng C ml(-1). Maximum ingestion and clearance rates of P. kofoidii on these dinoflagellates were 5-24 ng C pseudocolony(-1) d(-1) and 1.0-5.9 microl pseudocolony(-1) h(-1), respectively. Polykrikos kofoidii strongly selected L. polyedrum over S. trochoidea in prey mixtures. Polykrikos kofoidii exhibited higher maximum growth, ingestion, and clearance rates than previously reported for the mixotrophic dinoflagellate Fragilidium cf. mexicanum or the heterotrophic dinoflagellates Protoperidinium cf. divergens and P. crassipes, when grown on the same prey species. Grazing coefficients calculated by combining field data on abundances of Polykrikos spp. and co-occurring red-tide dinoflagellate prey with laboratory data on ingestion rates obtained in the present study suggest that Polykrikos spp. sometimes have a considerable grazing impact on prey populations.     

Plant Growth-Promoting Rhizobacteria Allow Reduced Application Rates of Chemical Fertilizers

The search for microorganisms that improve soil fertility and enhance plant nutrition has continued to attract attention due to the increasing cost of fertilizers and some of their negative environmental impacts. The objectives of this greenhouse study with tomato were to determine (1) if reduced rates of inorganic fertilizer coupled with microbial inoculants will produce plant growth, yield, and nutrient uptake levels equivalent to those with full rates of the fertilizer and (2) the minimum level to which fertilizer could be reduced when inoculants were used. The microbial inoculants used in the study were a mixture of plant growth-promoting rhizobacteria (PGPR) strains Bacillus amyloliquefaciens IN937a and Bacillus pumilus T4, a formulated PGPR product, and the arbuscular mycorrhiza fungus (AMF), Glomus intraradices. Results showed that supplementing 75% of the recommended fertilizer rate with inoculants produced plant growth, yield, and nutrient (nitrogen and phosphorus) uptake that were statistically equivalent to the full fertilizer rate without inoculants. When inoculants were used with rates of fertilizer below 75% of the recommended rate, the beneficial effects were usually not consistent; however, inoculation with the mixture of PGPR and AMF at 70% fertility consistently produced the same yield as the full fertility rate without inoculants. Without inoculants, use of fertilizer rates lower than the recommended resulted in significantly less plant growth, yield, and nutrient uptake or inconsistent impacts. The results suggest that PGPR-based inoculants can be used and should be further evaluated as components of integrated nutrient management strategies.     

Effect of Oxygen-Supply Rates on Growth of Escherichia coli: I. Studies in Unbaffled and Baffled Shake Flasks

The effect of oxygen-supply rates on bacterial growth was studied in commercially available unbaffled and baffled flasks with the use of Escherichia coli in a synthetic medium as a test system. The amount of growth obtained depended on the oxygen-supply rate. Based on oxygen-absorption rates (OAR) measured by the rate of sulfite oxidation, equal OAR values in different types of flasks did not give equal amounts of growth. However, growth was essentially equal at the equal sulfite-oxidation rates when these were determined in the presence of killed whole cultures. Specific growth rates were reduced only at oxygen-supply rates much lower than those at which the total amount of growth was reduced. For the physical set-up used in this work and with the biological system employed, Bellco 598 flasks and flasks fitted with Biotech stainless-steel baffles gave satisfactory results at workable broth volumes; unbaffled and Bellco 600 flasks did not.     

Physiological and Transcriptional Responses of Different Industrial Microbes at Near-Zero Specific Growth Rates

The current knowledge of the physiology and gene expression of industrially relevant microorganisms is largely based on laboratory studies under conditions of rapid growth and high metabolic activity. However, in natural ecosystems and industrial processes, microbes frequently encounter severe calorie restriction. As a consequence, microbial growth rates in such settings can be extremely slow and even approach zero. Furthermore, uncoupling microbial growth from product formation, while cellular integrity and activity are maintained, offers perspectives that are economically highly interesting. Retentostat cultures have been employed to investigate microbial physiology at (near-)zero growth rates. This minireview compares information from recent physiological and gene expression studies on retentostat cultures of the industrially relevant microorganisms Lactobacillus plantarum, Lactococcus lactis, Bacillus subtilis, Saccharomyces cerevisiae, and Aspergillus niger. Shared responses of these organisms to (near-)zero growth rates include increased stress tolerance and a downregulation of genes involved in protein synthesis. Other adaptations, such as changes in morphology and (secondary) metabolite production, were species specific. This comparison underlines the industrial and scientific significance of further research on microbial (near-)zero growth physiology.     

Radiographic studies of reef coral exoskeletons: Rates and patterns of coral growth

X-radiographs were made of vertical slices through the centers of 47 hermatypic coral colonies collected at Eniwetok Atoll, Marshall Islands. The image thus obtained are useful for the study of colony geometry, development, and response to damage.Comparison of radioactive inclusions of known age with previously reported cyclic skeletal density variations normal to the axis of growth confirms the annual nature of the density banding. Growth rates based on density bands and radioactivity inclusions are calculated for all 47 specimens, and measurements of the individual ‘growth bands’ are presented for 25 of them.Bulk densities measured by X-ray transmission ranged from 1.0 to 2.2 g/cm³, with an average range of 1.3–1.6 g/cm³. Intra-specimen skeletal densities typically vary by 10–30%; the period of high density skeletal deposition appears to coincide with the season of higher rainfall and warmer surface water at Eniwetok. Pigment residues left by boring algae are more commonly found in low density portions of the skeletons, but this distribution is believed to result from rather than cause the variations in the density of the deposited aragonite.Linear growth rates for the same specimen vary by factors of two or more from year to year, but the 25 specimens studied did not show a common pattern in the linear growth rate. Other than showing some general trends in growth as a function of species and depth, linear growth rates do not appear to be a particularly informative parameter.The density and growth rate variations are important factors in the measurement of coral growth and metabolism, and to the study of environmental controls of coral growth.     

Determination of In Situ Bacterial Growth Rates in Aquifers and Aquifer Sediments

Laboratory and field-scale studies with stained cells were performed to monitor cell growth in groundwater systems. During cell division, the fluorescence intensity of the protein stain 5-(and 6-)-carboxyfluorescein diacetate succinimidyl ester (CFDA/SE) for each cell is halved, and the intensity can be tracked with a flow cytometer. Two strains of bacteria, Comamonas sp. strain DA001 and Acidovorax sp. strain OY-107, both isolated from a shallow aquifer, were utilized in this study. The change in the average generation or the average fluorescence intensity of the CFDA/SE-stained cells could be used to obtain estimates of doubling times. In microcosm experiments, the CFDA/SE-based doubling times were similar to the values calculated by total cell counting and were independent of cell concentration. Intact and repacked sediment core experiments with the same bacteria indicated that changes in groundwater chemistry were just as important as growth rates in determining planktonic cell concentrations. The growth rates within the sediment cores were similar to those calculated in microcosm experiments, and preferential transport of the daughter cells was not observed. The experiments indicated that the growth rates could be determined in systems with cell losses due to other phenomena, such as attachment to sediment or predation. Application of this growth rate estimation method to data from a field-scale bacterial transport experiment indicated that the doubling time was approximately 15 days, which is the first known direct determination of an in situ growth rate for bacteria in an aquifer.     

Rates of Growth and Primordial Initiation During Flower Development in Silene at Different Temperatures

The growth of the flower and its constituent parts was measuredin Silene coeli-rosa plants, induced at 13, 20 and 27 °C,in order to try and identify those processes which consistentlyoccurred and would therefore be more likely to be essentialfor flower formation. The increased growth rate of the apical dome just before orabout the time of sepal initiation was not maintained in theflower, the growth rate of which was comparable to that of avegetative apex until all the carpels had been initiated, whenit decreased further. The primordia of the same whorl all hadsimilar growth rates so that the relative sizes of the primordiareflected their relative ages since their initiation. The relativegrowth rate of the stamens was the same (13 and 20 °C) orless (27 °C) than that of the sepals, but the relative growthrate of the petals was lower than either. The growth rate ofthe flower axis was least at the sepal node and increased bothdistally and proximally from this region. The plastochron during sepal initiation was shorter than forleaf initiation and tended to be shorter still during initiationof stamens and petals. Increasing temperature increased therate of primordial initiation but at 27 °C the growth ratesof the primordia were lowest although the rates of primordiainitiation were highest. The form of the flower, as exemplifiedby the relative sizes of the primordia at the moment when allcarpels had been initiated, was constant despite the differinggrowth rates and sizes of the primordia on initiation in differenttemperatures. It is concluded that neither the initiation ofthe primordia in the flower nor the form of the flower is determinedprimarily by the relative growth rates of its component parts. Silene coeli-rosa, flower development, primordia initiation, growth     

Protein Thermodynamics Can Be Predicted Directly from Biological Growth Rates

Life on Earth is capable of growing from temperatures well below freezing to above the boiling point of water, with some organisms preferring cooler and others hotter conditions. The growth rate of each organism ultimately depends on its intracellular chemical reactions. Here we show that a thermodynamic model based on a single, rate-limiting, enzyme-catalysed reaction accurately describes population growth rates in 230 diverse strains of unicellular and multicellular organisms. Collectively these represent all three domains of life, ranging from psychrophilic to hyperthermophilic, and including the highest temperature so far observed for growth (122°C). The results provide credible estimates of thermodynamic properties of proteins and obtain, purely from organism intrinsic growth rate data, relationships between parameters previously identified experimentally, thus bridging a gap between biochemistry and whole organism biology. We find that growth rates of both unicellular and multicellular life forms can be described by the same temperature dependence model. The model results provide strong support for a single highly-conserved reaction present in the last universal common ancestor (LUCA). This is remarkable in that it means that the growth rate dependence on temperature of unicellular and multicellular life forms that evolved over geological time spans can be explained by the same model.     

Rates of dissolution and biodegradation of water-insoluble organic compounds

We conducted a study of the relationship between the dissolution rates of organic compounds that are sparingly soluble in water and the biodegradation of these compounds by mixed cultures of bacteria. The rates of dissolution of naphthalene and 4-chlorobiphenyl were directly related to their surface areas. The bacteria caused a decline in the concentration of the soluble substrate. The rate of bacterial growth fell abruptly when 4-chlorobiphenyl or naphthalene was no longer detectable in solution. The population continued to increase in media with different surface areas of insoluble 4-chlorobiphenyl, but the final counts were higher in media in which the surface areas of the substrate were larger. The rates of dissolution of palmitic acid, octadecane, di(2-ethylhexyl) phthalate, and 1-naphthyl N-methylcarbamate were determined in the absence of microorganisms. A mixed culture of microorganisms mineralized palmitic acid, di(2-ethylhexyl) phthalate, and Sevin (1-naphthyl N-methylcarbamate) at a logarithmic rate, but octadecane mineralization was linear. The rates of mineralization at the end of the active phase of the biodegradation were lower than the rate of dissolution of palmitic acid but higher than the rate of dissolution of octadecane in the uninoculated medium. We suggest that spontaneous dissolution rates are only one of the factors that govern the rates of biodegradation.