Differential expression of enzyme activities initiating anoxic metabolism of various aromatic compounds via benzoyl-CoA

The regulation of the expression of enzyme activities catalyzing initial reactions in the anoxic metabolism of various aromatic compounds was studied at the whole cell level in the denitrifying Pseudomonas strain K 172. The specific enzyme activities were determined after growth on six different aromatic substrates (phenol, 4-hydroxybenzoate, benzoate, p-cresol, phenylacetate, 4-hydroxyphenylacetate) all being proposed to be metabolized anaerobically via benzoyl-CoA. As a control cells were grown on acetate, or aerobically on benzoate. The expression of the following enzyme activities was determined.Phenol carboxylase, as studied by the isotope exchange between ¹⁴CO₂ and the carboxyl group of 4-hydroxybenzoate; 4-hydroxybenzoyl-CoA reductase (dehydroxylating); p-cresol methylhydroxylase; 4-hydroxybenzyl alcohol dehydrogenase; 4-hydroxybenzaldehyde dehydrogenase; coenzymeA ligases for the aromatic acids benzoate, 4-hydroxybenzoate, phenylacetate, and 4-hydroxyphenylacetate; phenylglyoxylate: acceptor oxidoreductase and 4-hydroxyphenylglyoxylate: acceptor oxidoreductase; aromatic alcohol and aldehyde dehydrogenases.The formation of most active enzymes is strictly regulated; they were only induced when required, the basic activities being almost zero. The observed whole cell regulation pattern supports the postulate that the enzyme activities play a role in anoxic aromatic metabolism and that the compounds are degraded via the following intermediates: Phenol 4-hydroxybenzoate 4-hydroxybenzoyl-CoA benzoyl-CoA; 4-hydroxybenzoate 4-hydroxybenzoyl-CoA benzoyl-CoA; benzoate benzoyl-CoA; p-cresol 4-hydroxybenzaldehyde 4-hydroxybenzoate 4-hydroxybenzoyl-CoA benzoyl-CoA; phenylacetate phenylacetyl-CoA phenylglyoxylate benzoyl-CoA plus CO₂; 4-hydroxyphenylacetate 4-hydroxyphenylacetyl-CoA 4-hydroxyphenylglyoxylate 4-hydroxybenzoyl-CoA plus CO₂ benzoyl-CoA.     

α-Isopropylmalate synthase from Alcaligenes eutrophus H 16

The purified isopropylmalate synthase of Alcaligenes eutrophus H 16 reacted with the following -keto acids and acyl-coenzyme A derivatives (in the sequence of decreasing affinities): -ketoisovalerate, -keto-n-valerate, -ketobutyrate and pyruvate; acetyl-CoA, propionyl-CoA, butyryl-CoA. malonyl-CoA, valeryl-CoA, and crotonyl-CoA. -Ketoisocaproate, however, is a strong inhibitor of the enzyme. All reactions catalyzed by isopropylmalate synthase were inhibited to the same extent by the endproduct l-leucine. the substrate saturation curves of -ketoisovalerate or other -keto acids and of acetyl-coenzyme A or other acyl-CoA derivatives had intermediary plateau regions; the Hill coefficient alternated between n _H -values higher and lower than 1.0, indicating changes from positive to negative and from negative to positive cooperativity for the substrates. The products, isopropylmalate and free coenzyme A, showed competitive inhibition patterns against both substrates (-ketoisovalerate and acetyl-CoA). Free coenzyme A (1 M) inactivated the enzyme irreversibly. The 3-phosphate of coenzyme A and the free carboxyl group of -ketoisovalerate were involved in optimal binding of these substrates, but 3-dephospho-acetyl-coenzyme A and the methylester of -ketoisovalerate were also converted by this enzyme. A CH₃–CH₂-grouping of the -keto acids seemed to be necessary for binding this substrate.Abbreviations Used CoA Coenzyme A - Tris Tris(hydroxymethyl)aminomethane hydrochloride - DTNB 5,5-dithiobis-(2-nitrobenzoic acid) - IPM -Isopropylmalate - KIV -Ketoisovalerate Prepared from doctoral thesis of the University of Göttingen 1973     

Effect of thefloury-2 locus on protein body formation during maize endosperm development

Summary The seed storage proteins of maize (Zea mays L.) are synthesized during endosperm development on membrane-bound polyribosomes. These proteins, collectively called zeins, are translocated into the lumen of the rough endoplasmic reticulum, where they assemble into protein bodies. Protein body formation in normal genotypes occurs via an ordered deposition of the various types of zeins, and leads to the formation of spherical structures with a diameter of about 1 m. These structures consist of a central core that contains predominantly -zein; this central region is surrounded by a peripheral layer of - and -zeins, and the entire structure is bounded by rough endoplasmic reticulum.In the endosperm mutant floury-2 the levels of all classes of zeins are reduced; these kernels exhibit an opaque phenotype instead of the vitreous phenotype observed in normal genotypes. In contrast to the discrete, spherical protein bodies which are formed in normal maize endosperm, the protein bodies within floury-2 endosperm are irregular and the zeins are disorganized; patches of - and -zeins occur within irregularly lobed clusters of -zein within the lumen of the rough endoplasmic reticulum. The implications of this aberrant distribution are discussed, both with respect to protein body development and kernel characteristics.Abbreviations BSA bovine serum albumin - DAP days after pollination - IgG immunoglobulin G     

Holling's “hungry mantid” model for the invertebrate functional response considered as a Markov process. Part II: Negligible handling time

In this paper we analyse a stochastic model for invertebrate predation taking account of the predator's satiation. This model approximates Holling's hungry mantid model when handling time is negligible (see Part I). For this model we derive equations from which we can calculate the functional response and the variance of the total catch. Moreover we study a number of approximations which can be used to calculate these quantities in practical cases in a relatively simple manner.List of Notation a rate constant of digestion - b maximum of rate constant of prey encounter in the mantid - c satiation threshold for search - c satiation threshold for pursuit in the mantid - c _i (w^1/2(N- N)ⁱ) - expectation operator - f rate of change of satiation during search - F functional response: mean number of prey eaten per unit of time - g rate constant of prey capture - h probability generating function of N conditional on S = s times p - H probability generating function of N - m_i ¹ - n, N number of prey caught - p probability density of S - p_n simultaneous probability (density) of N and S - q probability of strike success - r dummy variable in generating function - s, S satiation - T _s search time - T _d digestion time - v asymptotic rate of increase of var v - V asymptotic rate of increase of var N - w weight of edible part of prey - W standard Wiener process - x prey density - z (N{S = s}-N)p - rate constant of prey escape time maximum pursuit time - (v{S = + w ^1/2}-v) - present time as a fraction of the time from the start to the end of the experiment - hazard rate of T _s - mean time between (downward) passages of S through c - v w_–1/2(N-) - edible prey biomass density - probability density of , number pi - parameter of Weibull distribution of T _s = (1/2acx(-g(c)))_1/2 - w_–1/2(S -) - satiation in the guzzler approximation: solution to d/dt = f() + g(), (0)=S(0). - biomass functional response: wF - total biomass catch in the guzzler approximation: solution to d/dt = g(), (0) = 0     

Regulation ofN-acetylglucosaminyltransferase V by protein kinases

When 7721 human hepatocarcinoma cells were treated with 100nm phorbol-12-myristate-13-acetate (PMA), the activity ofN-acetylglucosaminyltransferase V(GnT-V) in the cells varied in accordance with the activity of membranous protein kinase C (PKC), but not with that of cytosolic PKC. Quercetin, a non-specific inhibitor of Ser/Thr protein kinase, andd-sphingosine and staurosporine, two specific inhibitors of PKC, blocked the activation of membranous PKC and GnT-V by PMA. Among the three inhibitors, quercetin was least effective. The inhibitory rates of quercetin and staurosporine toward membranous PKC and GnT V were proportional to the concentrations of the two inhibitors. The activities of GnT V and membranous protein kinase A (PKA) were also induced in parallel by dibutyryl cAMP (db-cAMP) and this induction was blocked by a specific PKA inhibitor. When cell free preparations of 7721 cells and human kidney were treated with alkaline phosphatase (ALP) to remove the phosphate groups, the GnT V activities were decreased. These results suggest that GnT V may be activated by membranous PKC or PKA, indirectly or directly, via phosphorylation of Ser/Thr residues.Abbreviations UDP uridine diphospho- - GnT N-acetylglucosaminyltransferase - GlcNAc Gn N-acetylglucosamine - M mannose - PMA phorbol-12-myristate-13-acetate - PKC protein kinase C - PKA protein kinase A - cAMP adenosine 3, 5-cyclic monophosphate - db-cAMP dibutyryl cAMP - TPK tyrosine protein kinase - MES 2-[N-morpholino]ethanesulfonic acid - DTT dithiothreitol - PMSF phenylmethylsulfonyl fluoride - EDTA ethylene diamine tetraacetic acid - EGTA glycol-bis-(-aminoethyl) etherN,N,N,N-tetraacetic acid - PA 2-aminopyridine - ALP alkaline phosphatase - C₂C₂ GlcNAc1-2 Man1-6(GlcNAc1-2Man1-3)ManR - C_2,4C₂ GlcNAc1-2Man1-6(GlcNAc1-4[GlcNAc1-2]Man1-3)ManR - C₂C_2,6 GlcNAc1-6[GlcNAc1-2]Man1-6(GlcNAc1-2Man1-3)ManR - C_2,4C_2,6 GlcNAc1-6[GlcNAc1-2]Man1-6(GlcNAc1-4[GlcNAc1-2]Man1-3)ManR where R=1-4GlcNAc1-4GlcNAcAsnX - Gn₂M₃Gn₂-PA C₂C₂ where R=1-4GlcNAc1-4GlcNAc-PA - Gn₃M₃Gn₂-PA C₂C_2,6 where R=1-4GlcNAc1-4GlcNAc-PA     

A structural model for elongation factor 1 (EF-1) and phosphorylation by protein kinase CKII

EF-1a binds aminoacyl-tRNA to the ribosome with the hydrolysis of GTP; the complex facilitates the exchange of GDP for GTP to initiate another round of elongation. To examine the subunit structure of EF-1 and phosphorylation by protein kinase CKII, recombinant , , and subunits from rabbit were expressed in E. coli and the subunits were reconstituted into partial and complete complexes and analyzed by gel filtration. To determine the availability of the and subunits for phosphorylation by CKII, the subunits and the reconstituted complexes were examined as substrates for CKII. Formation of the nucleotide exchange complex increased the rate of phosphorylation of the subunit and reduced the Km, while addition of to or the complex inhibited phosphorylation by CKII. However, a had little effect on phosphorylation of . Thus, the and subunits in EF-1 were differentially phosphorylated by CKII, in that phosphorylation of was altered by association with other subunits, while the site on was always available for phosphorylation by CKII. From the availability of the subunits for phosphorylation by CKII and the composition of the reconstituted partial and complete complexes, a model for the subunit structure of EF-1 consisting of (22)2 is proposed and discussed.     

Enzymic synthesis of lacto-N-triose II and its positional analogues

N-acetylhexosaminidase fromNocardia orientalis catalysed the synthesis of lacto-N-triose II glycoside (-d-GlcNAc-(1-3)--d-Gal-(1-4)--d-Glc-OMe,3) with its isomers -d-GlcNAc-(1-6)--d-Gal-(1-4)--d-Glc-OMe (4) and -d-Gal-(1-4)-[-d-GlcNAc-(1-6)]--d-Glc-OMe (5) throughN-acetylglucosaminyl transfer fromN,N-diacetylchitobiose (GlcNAc₂) to methyl -lactoside. The enzyme formed the mixture of trisac-charides3, 4 and5 in 17% overall yield based on GlcNAc₂, in a ratio of 20:21:59. Withp-nitrophenyl -lactoside as an acceptor, the enzyme also producedp-nitrophenyl -lacto-N-trioside II (-d-GlcNAc-(1-3)--d-Gal-(1-4)--d-Glc-OC₆H₄NO₂-p,6) with its isomers -d-GlcNAc-(1-6)--d-Gal-(1-4)--d-Glc-OC₆H₄NO₂-p (7) and -d-Gal-(1-4)-[-d-GlcNAc-(1-6)]--d-Glc-OC₆H₄NO₂-p (8). In this case, when an inclusion complex ofp-nitrophenyl lactoside acceptor with -cyclodextrin was used, the regioselectivity of glycosidase-catalysed formation of trisaccharide glycoside was substantially changed. It resulted not only in a significant increase of the overall yield of transfer products, but also in the proportion of the desired compound6.Abbreviations GlcNAc₂ 2-acetamido-2-deoxy--d-glucopyranosyl-(1-4)-2-acetamido-2-deoxy-d-glucose - NAHase N-acetylhexosaminidase - -CD -cyclodextrin     

Existence and uniqueness of a sharp travelling wave in degenerate non-linear diffusion Fisher-KPP equations

In this paper we use a dynamical systems approach to prove the existence of a unique critical value c ^* of the speed c for which the degenerate density-dependent diffusion equation u _ct = [D(u)u _x ] _x + g(u) has: 1. no travelling wave solutions for 0 < c < c ^*, 2. a travelling wave solution u(x, t) = (x - c ^* t) of sharp type satisfying (– ) = 1, () = 0 ^*; '(^*–) = – c ^*/D'(0), '(^*+) = 0 and 3. a continuum of travelling wave solutions of monotone decreasing front type for each c > c ^*. These fronts satisfy the boundary conditions (– ) = 1, '(– ) = (+ ) = '(+ ) = 0. We illustrate our analytical results with some numerical solutions.     

Pyrococcus furiosus sp. nov. represents a novel genus of marine heterotrophic archaebacteria growing optimally at 100°C

Ten strains representing a novel genus of marine thermophilic archaebacteria growing at between 70 and 103°C with an optimal growth temperature of 100°C and a doubling time of only 37 min were isolated from geothermally heated marine sediments at the beach of Porto di Levante, Vulcano, Italy. The organisms are spherical-shaped, 0.8 to 2.5 m in width and exhibit monopolar polytrichous flagellation. They are strictly anaerobic heterotrophs, growing on starch, maltose, peptone and complex organic substrates. Only CO₂ and H₂ could be detected as metabolic products, the latter being inhibitory to growth at high concentrations. Hydrogen inhibition can be prevented by the addition of S^o, whereupon H₂S is formed in addition, most likely as the result of a detoxification reaction. The GC-content of the DNA of isolate Vc 1 is 38 mol%. The new genus is named Pyrococcus, the fireball. Type species and strain is Pyrococcus furiosus Vc 1 (DSM 3638).     

sym 18. A novel gene conditioning altered strain specificity in Pisum sativum cv. ‘Sparkle’

An induced mutant of pea Pisum sativum cv. Sparkle forms few nodules with R. leguminosarum bv. viciea from temperate regions, exemplified by strain PRE, but nodulates normally with some rhizobia from Middle East soils, exemplified by strain TOM. The mutant gene is not an allele of sym2, found in the primitive cultivar Afghanistan. Mutant line E54 has a specificity similar to Afghanistan but forms more nodules with temperate strains, especially PF₂ which nodulates Afghanistan only poorly. The new phenotype is conditioned by gene sym18, which can act as recessive or semi-dominant depending on the rhizobial strain. Also sym18 is distinguished from sym 2 by its location on a different linkage group. Sym18 was mapped 9cM from k on linkage group II.     

Decreases in Plasma Aβ1-40 Levels with Aging in Non-Demented Elderly with ApoE-ε4 Allele

This report examines plasma amyloid proteins A40 and A42 and apolipoprotein E (apoE) levels and their relationships with age in non-demented older adults with (N = 32) or without the apoE-4 allele (N = 94). A levels did not differ between the groups whereas the 4 allele was associated with a significant reduction in plasma apoE. In subjects with the 4 allele, increasing age was associated with significant reduction in plasma A40. Subjects without the 4 allele showed a significant positive correlation between A40 and A42 levels. There was also a significant correlation between plasma A40 and apoE levels in all subjects.     

Uptake of sewage derived nitrogen by<Emphasis Type="Italic"> Ulva rigida</Emphasis> (Chlorophyceae) in Bahía Nueva (Golfo Nuevo,Patagonia, Argentine)

Uptake kinetics of nitrogen derived from sewage–seawater mixtures (2.5–20% v/v effluent) were determined in the laboratory for Ulva rigida (Chlorophyceae) native from Bahía Nueva (Golfo Nuevo, Patagonia, Argentine). In terms of nitrogen concentration, experimental enrichment levels varied between 53.7 and 362.3M of ammonium and between 0.77 and 6.21M of nitrate+nitrite. Uptake rates were fitted to the Michaelis–Menten equation, with the following kinetic parameters: ammonium: V_max = 591.2molg^–1h^–1, K _s=262.3M, nitrate+nitrite: V _max=12.9molg^–1h^–1, K _s=3.5M). Both nutrients were taken up simultaneously, but ammonium incorporation was faster in all cases. The results show a high capability of Ulva rigida to remove sewage-derived nitrogen from culture media. In the field, most of the nitrogen provided by the effluent would be tied up in algal biomass, supporting low nitrogen levels found at a short distance away from the source.     

The carotenoids of Flavobacterium strain R1560

The main carotenoid of Flavobacterium strain R1560 has been identified as (3R,3R)-zeaxanthin. Also present were small amounts of 15-cis-phytoene, phytofluene, -carotene (7,8,7,8-tetrahydro-, -carotene plus 7,8,11,12-tetrahydro-, -carotene), neurosporene, lycopene, -zeacarotene, -carotene, -carotene, -cryptoxanthin, rubixanthin, 3-hydroxy--zeacarotene and several apo-carotenals. Zeaxanthin production was inhibited by nicotine (10 mM), and lycopene and rubixanthin accumulated. The biosynthesis of zeaxanthin is discussed in terms of pathways and also of half-molecule reaction sequences. The presence of zeaxanthin may be a characteristic of a group of Flavobacterium species, and may thus be useful in the taxonomic classification of these organisms.     

Against “Revolution” and “Evolution”

Those standard historiographic themes of evolution and revolution need replacing. They perpetuate mid-Victorian scientists history of science. Historians history of science does well to take in the long run from the Greek and Hebrew heritages on, and to work at avoiding misleading anachronism and teleology. As an alternative to the usual evo-revo themes, a historiography of origins and species, of cosmologies (including microcosmogonies and macrocosmogonies) and ontologies, is developed here. The advantages of such a historiography are illustrated by looking briefly at a number of transitions the transition from Greek and Hebrew doctrines to their integrations by medieval authors; the transition from the Platonist, Aristotelian, Christian Aquinas to the Newtonian Buffon and to the no less Newtonian Lamarck; the departures the early Darwin made away from Lamarcks and from Lyells views. Issues concerning historical thinking about nature, concerning essentialism and concerning classification are addressed in an attempt to challenge customary stereotypes. Questions about originality and influence are raised, especially concerning Darwins tree of life scheme. The broader historiography of Darwinian science as a social ideology, and as a worldview, is examined and the scope for revisions emphasised. Throughout, graduate students are encouraged to see this topic area not as worked out, but as full of opportunities for fresh contributions.     

Coral growth in high-nutrient,low-pH seawater: a case study of corals cultured at the Waikiki Aquarium,Honolulu, Hawaii

Fifty-seven species of hermatypic corals have been maintained and grown in high-nutrient seawater at the Waikiki Aquarium, Honolulu, Hawaii. In this study we document the chemical conditions of aquarium water in terms of dissolved nutrients and carbon. Aquarium water is characterized by concentrations of inorganic nutrients that are high relative to most natural reef ecosystems: SiO₃ 200 M; PO₄ 0.6 M; NO₃ 5 M; NH₄ 2 M. In contrast, concentrations of organic nutrients are lower than most tropical surface ocean waters: DOP 0.1 M and DON 4 M. The incoming well-water servicing the facility has low pH, crating over-saturation of carbon dioxide. The coral communities in aquaria took up inorganic nutrients and released organic nutrients. Rates of nutrient uptake into aquaria coral communities were similar to nutrient uptake by natural reef communities. Coral growth rates were near the upper rates reported from the field, demonstrating corals can and do flourish in relatively high-nutrient water. The growth of corals does not appear to be inhibited at concentrations of nitrogen up to 5 M. Statements implying that corals can only grow in low nutrient oligotrophic seawater are therefore oversimplifications of processes that govern growth of these organisms. Some basic guidelines are given for maintenance of coral communities in aquaria.     

Diversity of amyloid beta protein fragment [1-40]-formed channels

1. The lipid bilayer technique was used to characterize the biophysical and pharmacological properties of several ion channels formed by incorporating amyloid beta protein fragment (AP) 1–40 into lipid membranes. Based on the conductance, kinetics, selectivity, and pharmacological properties, the following AP[1–40]-formed ion channels have been identified: (i) The AP[1–40]-formed bursting fast cation channel was characterized by (a) a single channel conductance of 63 pS (250/50 mM KCl cis/trans) at +140 mV, 17 pS (250/50 mM KCl cis/trans) at –160 mV, and the nonlinear current–voltage relationship drawn to a third-order polynomial, (b) selectivity sequence P _K > P _Na > P _Li = 1.0:0.60:0.47, (c) P_o of 0.22 at 0 mV and 0.55 at +120 mV, and (d) Zn²⁺-induced reduction in current amplitude, a typical property of a slow block mechanism. (ii) The AP[1–40]-formed spiky fast cation channel was characterized by (a) a similar kinetics to the bursting fast channel with exception for the absence of the long intraburst closures, (b) single channel conductance of 63 pS (250/50 KCl) at +140 mV 17 pS (250/50 KCl) at –160 mV, the current–voltage relationship nonlinear drawn to a third-order polynomial fit, and (c) selectivity sequence P _Rb > P _K > P _Cs > P _Na > P _Li = 1.3:1.0:0.46:0.40:0.27. (iii) The AP[1–40]-formed medium conductance channel was charcterized by (a) 275 pS (250/50 mM KCl cis/trans) at +140 mV and 19 pS (250/50 mM KCl cis/trans) at –160 mV and (b) inactivation at V_ms more negative than –120 and more positive than +120 mV. (iv) The AP[1–40]-formed inactivating large conductance channel was characterized by (a) fast and slow modes of opening to seven multilevel conductances ranging between 0–589 pS (in 250/50 mM KCl) at +140 mV and 0–704 pS (in 250/50 mM KCl) at –160 mV, (b) The fast mode which had a conductance of <250 pS was voltage dependent. The inactivation was described by a bell-shaped curve with a peak lag time of 7.2 s at +36 mV. The slow mode which had a conductance of >250 pS was also voltage dependent. The inactivation was described by a bell-shaped curve with a peak lag time of 7.0 s at –76 mV, (c) the value of P _K/P _choline for the fast mode was 3.9 and selectivity sequence P _K > P _Cs > P _Na > P _Li = 1.0:0.94:0.87:0.59. The value of P _K/P _choline for the slow mode was 2.7 and selectivity sequence P _K > P _Na > P _Li > P _Cs = 1.0:0.59:0.49:0.21, and (d) asymmetric blockade with 10 mM Zn²⁺-induced reduction in the large conductance state of the slow mode mediated via slow block mechanism. The fast mode of the large conductance channel was not affected by 10 mM Zn²⁺.2. It has been suggested that, although the bursting fast channel, the spiky fast channel and the inactivating medium conductance channel are distinct, it is possible that they are intermediate configurations of yet another configuration underlying the inactivating large conductance channel. It is proposed that this heterogeneity is one of the most common features of these positively-charged cytotoxic amyloid-formed channels reflecting these channels ability to modify multiple cellular functions.3. Furthermore, the formation of -sheet based oligomers could be an important common step in the formation of cytotoxic amyloid channels.     

Regional distribution of membrane-bound γ-glutamyl transpeptidase activity in mouse brain

Activity of membrane-bound -glutamyl transpeptidase (-GTP) was examined in various regions of mouse brain, in capillaries of the cerebral cortex and in telencephalic choroid plexuses. The level of activity in the capillaries was double and that of the choroid plexus nine times that of the -GTP activity found in the brain, septum, hippocampus, hypothalamus, thalamus, cerebellum, frontal cortex, pons, medulla oblongata, and amygdala. Histochemically the -GTP activity was demonstrated in the surface membranes of choroidal cells and in the endothelium of small capillaries.The activities of -GTP of cerebral cortex, choroid plexus, and capillaries from rabbit were 5–17 times greater than those from corresponding areas of mouse brain. While 30 mM methionine stimulated (in vitro) the enzyme from mouse brain, no such effect was observed with the enzyme activity from rabbit brain. The -GTP activity from the capillaries of cerebral cortex of both mouse and rabbit was not effected by the presence of methionine.These findings suggest existence of differences in the specificity of -GTP activity in these two species.     

Problems in estimating growth rates of marine phytoplankton from short-term14C assays

Growth rate estimates () of phytoplankton populations that were sampled from nitrogen-limited continuous cultures and then incubated for short durations in batch culture with added¹⁴C-HCO₃ ^– were significantly different than steady-state growth rates () for 3 of 5 marine phytoplankton species. Two diatoms,Thalassiosira weissflogii andChaetoceros simplex, displayed virtually identical growth rates (=) over a wide range of, whereas for a third diatom,Phaeodactylum tricornutum, was overestimated by an average of 40% compared to. In contrast, was underestimated by the¹⁴C technique for the two remaining species: up to 40% at a steady-state of 1.0 day^–1 for the chlorophyteDunaliella tertiolecta and up to 100% at of 1.4 day^–1 for the haptophytePavlova lutheri. For the latter two species the divergence between and appeared to increase with increasing steady-state. A simple model of labeled and total carbon flow between the aqueous phase and cellular biomass was constructed to demonstrate that respiration was negligible when=, but was significant when>. In the cases in which<, a rapid physiological alteration presumably took place once the steady state was disturbed and cells were placed in the incubation chambers, which perhaps was related to the nutritional state of the cultures at the time of sampling. Questions thus are raised regarding our ability to measure accurately primary productivity from shipboard experiments with confined samples of phytoplankton from nutrient-impoverished waters that probably are less hardy than the laboratory cultures used in these studies.     

Integration of bacteriophages lambda and phi 80 in wild-type Escherichia coli at secondary attachment sites. II. Genetic structure and mechanism of polylysogen formation for lambda, phi 80 and the lambda att80 hybrid

Summary The frequency of occurrence and the genetic structure of polylysogens were studied for phages , 80 and att80. In the case of , frequency of polylysogenization is high (0.20 to 0.41) with a tandem integration of prophages at the primary att site (att). With 80 and att80, this frequency is about 10 times lower, and usually one prophage becomes integrated at the primary att site (att80-I) while another (sometimes two others) integrates at one of the secondary sites. At least four secondary att80 sites have been found in wild-type Escherichia coli , two of which (near the his and tolC loci) are preferred. The frequency of secondary integration of 80 and att80 does not differ significantly in the wild-type host and in that deleted for the primary att site (0.041 and 0.045, respectively, among surviving cells at an MOI of 10).Homoimmune superinfection has revealed a constitutive cI-independent expression of the 80 int gene in the prophage state. The only 80 tandem detected proved to be unstable. With the 80int ^- mutant, we observed stabilization of 80 tandems; as a consequence, their frequency of occurrence during coinfection with 80int ⁺ was up to the level and no nontandem insertions were found. A model is proposed for the 80 and att80 nontandem integration.Abbreviations TP transducing phage(s) - PFU plaque-forming units - PC pink clear-resistant colonies on EMBO plates - MOI multiplicity of infection - O origin of Hfr transfer

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