Hot topic: effects of frequent milking in early lactation on milk yield and udder health.

A field study was conducted to evaluate the influence of milking frequency (3 or 6 times/d [3x or 6x, respectively]) during the initial 21 d of lactation on milk and milk component yield and mammary gland health as indicated by somatic cell count. During 2 seasons, spring and fall, multiparous cows were milked 6 times/d until d 21 of lactation and then returned to the 3 times/d frequency for the remainder of lactation (6x; n = 9). Multiparous cows milked 3 times/d from the beginning of lactation served as a control group (3x; n = 17). With the exception of milking frequency, all other aspects of management, including housing, milk harvesting, and feeding, were identical between the groups and were consistent with industry norms. Retrospective analysis of Dairy Herd Improvement Association records was used to evaluate milk yield, milk component yield, and somatic cell scores. As expected, 6x cows produced more milk on the first test day than 3x cows. Compared with 3x cows, higher milk yields persisted for 6x cows from test day 2 through 6, indicating a persistent effect of early lactation milking frequency on milk yield potential for that lactation. Milk component yield followed a similar pattern: 6x cows produced significantly more protein, fat, and total solids than did control cows throughout the study. With regard to udder health, 6x cows had lower somatic cell counts at the first test day relative to 3x cows and had reduced somatic cell scores for the first 3 mo of lactation, which suggests that early lactation milking frequency influences the mammary gland capacity to resist infection in addition to improving milk production efficiency.

Naphthalene uptake by a Pseudomonas fluorescens isolate.

The uptake of naphthalene has been investigated in the metabolizing cells of Pseudomonas fluorescens utilizing [1-14C]naphthalene. The uptake displayed an affinity constant (Kt) of 11 microM and a maximal velocity (Vmax) of 17 nmol.h-1.mg-1 cellular dry weight. Naphthalene uptake was not observed in a mutant strain, TG-5, which was unable to utilize naphthalene as a sole source of carbon for growth. Uptake was significantly inhibited (approximately 90%) by the presence of growth-inhibiting levels of either azide or 2,4-dinitrophenol and was sensitive to the presence of structural analogues of naphthalene. The intracellular levels of ATP were not significantly reduced by the presence of either azide or 2,4-dinitrophenol. The presence of alpha-naphthol was found to noncompetitively inhibit naphthalene uptake, displaying a Ki of 0.041 microM. It is concluded that the first step in the utilization of naphthalene by Pseudomonas fluorescens is its transport into the cell by a specific energy-linked transport system.

Growth and Maintenance of Thiobacillus ferrooxidans Cells.

A rapid and sensitive spectrophotometric procedure was developed for monitoring the growth of Thiobacillus ferrooxidans in liquid culture. Values determined for the optical densities at 500 nm of washed T. ferrooxidans cell suspensions were directly proportional to both total cell number and total cell protein concentration and provided an accurate measurement of culture growth rate. The utility of this procedure was demonstrated by conducting physiological studies on the influence of CO(2) and FeSO(4) availability on the growth of T. ferrooxidans. In addition, we describe a procedure for the long-term maintenance of cells T. ferrooxidans that ensures culture purity and genetic stability.

Purification and characterization of Rhodobacter sphaeroides acyl carrier protein.

Acyl carrier protein (ACP) has been purified from the facultative phototrophic bacterium Rhodobacter sphaeroides. The ACP preparation was greater than 95% homogeneous as determined by native and disodium dodecyl sulfate (Na2DodSO4)-polyacrylamide gel electrophoreses and N-terminal amino acid analysis. Amino acid compositional analysis revealed that the protein contains approximately 75 amino acids, has a calculated minimum molecular weight of 8700, and lacks the amino acids tyrosine and tryptophan. The presence of the characteristic 4'-phosphopantetheine prosthetic group was indicated by the occurrence of equimolar quantities of beta-alanine and taurine in amino acid hydrolysates and was confirmed by independent chemical analysis. The protein displayed a pI of 3.8 and had a calculated partial specific volume of 0.732 mL/g. The primary structure of the protein has been determined for the first 46 amino acid residues from the N terminus of the molecule, and the region of the molecule encompassing the amino acids from residues 31 to 44 was found to have 100% homology with the identical residues in Escherichia coli ACP. In contrast to E. coli ACP, R. sphaeroides ACP migrated according to its molecular weight during Na2DodSO4 gel electrophoresis, was resistant to pH-induced denaturation, and comigrated with the cis-vaccenoyl-ACP derivative during native gel electrophoresis. It is proposed that the basis for these properties is the enhanced hydrophobic character of the protein.

Stringency in the absence of ppGpp accumulation in Rhodobacter sphaeroides.

Leucine deprivation of either phototrophically or chemotrophically growing cells of Rhodobacter sphaeroides resulted in a restriction in the continued accumulations of cellular RNA, phospholipids, and protein. Phototrophically growing cells also displayed restrictions in the accumulations of cellular carotenoids and bacteriochlorophyll. Leucine deprivation, however, did not provoke the accumulation of cellular ppGpp or alter the steady-state levels of ppGpp, ATP, or GTP in cells of R. sphaeroides.

Purification and properties of acyl coenzyme A thioesterase II from Rhodopseudomonas sphaeroides.

A high molecular weight acyl coenzyme A (acyl-CoA) thioesterase, designated thioesterase II, has been purified 5300-fold from photoheterotrophically grown cells of Rhodopseudomonas sphaeroides. In contrast to R. sphaeroides acyl-CoA thioesterase I [Boyce, S.G., & Lueking, D.R. (1984) Biochemistry 23, 141-147], thioesterase II has a native molecular mass (Mr) of 120,000, is capable of hydrolyzing saturated and unsaturated acyl-CoA substrates with acyl chain lengths ranging from C4 to C18, and is completely insensitive to the serine esterase inhibitor diisopropyl fluorophosphate. Palmitoyl-CoA and stearoyl-CoA are the preferred (lowest Km) saturated acyl-CoA substrates and vaccenoyl-CoA is the preferred unsaturated substrate. However, comparable Vmax values were obtained with a variety of acyl-CoA substrates. Unlike a similar thioesterase present in cells of Escherichia coli [Bonner, W.M., & Bloch, K. (1972) J. Biol. Chem. 247, 3123-3133], R. sphaeroides thioesterase II displays a high ratio of decanoyl-CoA to palmitoyl-CoA activities and exhibits little ability to hydrolyze 3-hydroxyacyl-CoA substrates. Only 3-hydroxydodecanoyl-CoA supported a measurable rate of enzyme activity. With the purification of thioesterase II, the enzymes responsible for greater than 90% of the acyl-CoA thioesterase activity present in cell-free extracts of R. sphaeroides have now been identified.

Localization and characterization of the sn-glycerol-3-phosphate acyltransferase in Rhodopseudomonas sphaeroides.

The membrane localization and properties of the Rhodopseudomonas sphaeroides sn-glycerol-3-phosphate acyltransferase have been examined utilizing enzymatically prepared acyl-acyl carrier protein (acyl-ACP) substrates as acyl donors for sn-glycerol-3-phosphate acylation. Studies conducted with membranes prepared from chemotrophically and phototrophically grown cells show that sn-glycerol-3-phosphate acyltransferase activity is predominantly (greater than 80%) associated with the cell's cytoplasmic membrane. Enzyme activity associated with the intracytoplasmic membranes present in phototrophically grown R. sphaeroides was within the range attributable to cytoplasmic membrane contamination of this membrane fraction. Enzyme activity was optimal at 40 degrees C and pH 7.0 to 7.5, and required the presence of magnesium. No enzyme activity was observed with any of the long-chain acyl-CoA substrates examined. Vaccenoyl-ACP was the preferred acyl-ACP substrate and vaccenoyl-ACP and palmitoyl-ACP were independently utilized to produce lysophosphatidic and phosphatidic acids. With either vaccenoyl-ACP or palmitoyl-ACP as sole acyl donor substrate, the lysophosphatidic acid formed was primarily 1-acylglycerol-3-phosphate and the Km(app) for sn-glycerol-3-phosphate utilization was 96 microM. The implications of these results to the mode and regulation of phospholipid synthesis in R. sphaeroides are discussed.

Light-mediated regulation of phospholipid synthesis in Rhodopseudomonas sphaeroides.

The relationship between the culture levels of guanosine-5'-diphosphate-3'-diphosphate (ppGpp) and the rates of synthesis and accumulation of cellular phospholipids was examined in cultures of Rhodopseudomonas sphaeroides that had been subjected to immediate decreases in incident light intensity. After a high-to-low light transition of high-light-adapted cells, an immediate inhibition of total cellular phospholipid production occurred coincident with a rapid accumulation of culture ppGpp. The inhibition of phospholipid accumulation occurred at the level of phospholipid synthesis rather than turnover, and both the extent of ppGpp accumulation and the degree of inhibition of phospholipid synthesis were directly dependent upon the magnitude of the light transition. Maximum inhibition (greater than 90%) of the rate of cellular phospholipid synthesis occurred after transitions from 5,350 to 268 1x and lower, including transitions to the dark, with comparable inhibition being exerted upon the rates of synthesis of individual species of phospholipids. Reinitiation of culture phospholipid accumulation in cultures shifted from 5,350 to 1,070 1x and lower occurred 65 to 70 min subsequent to the downshift in light intensity, apparently irrespective of the culture level of ppGpp.

Long-chain fatty acid assimilation By rhodopseudomonas sphaeroides.

Exogenously supplied long-chain fatty acids have been shown to markedly alleviate the inhibition of phototrophic growth of cultures of Rhodopseudomonas sphaeroides caused by the antibiotic cerulenin. Monounsaturated and polyunsaturated C18 fatty acids were most effective in relieving growth inhibition mediated by cerulenin. Medium supplementation with saturated fatty acids (C14 to C18) failed to influence the inhibitory effect of cerulenin. The addition of mixtures of unsaturated and saturated fatty acids to the growth medium did not enhance the growth of cerulenin-inhibited cultures above that obtained with individual unsaturated fatty acids as supplements. Resolution and fatty acid analysis of the extractable lipids of R. sphaeroides revealed that exogenously supplied fatty acids were directly incorporated into cellular phospholipids. Cells treated with cerulenin displayed an enrichment in their percentage of total saturated fatty acids irrespective of the presence of exogenous fatty acids. Cerulenin produced comparable inhibitions of the rates of both fatty acid and phospholipid synthesis and was further found to preferentially inhibit unsaturated fatty acid synthesis.

Light-induced division and genomic synchrony in phototrophically growing cultures of Rhodopseudomonas sphaeroides.

An experimental procedure for rapidly obtaining cell populations of phototrophically growing Rhodopseudomonas sphaeroides which display division and genomic synchrony has been developed. The basis of the procedure resides with the normal physiological response displayed by cells of R. sphaeroides that have been subjected to an immediate decrease in incident light intensity. After an abrupt high- to low-light transition of an asynchronously dividing cell population, an immediate cessation of increases in culture turbidity, total cell number, and net accumulations of culture deoxyribonucleic acid and phospholipid occurs. Total cell number remains constant for 2.5 h after the transition to low light, after which time, it undergoes a sharp increase. Reinitiation of high-light conditions of growth 1 h subsequent to this increase in total cell number results in a cell population possessing a high degree of division and genomic synchrony. A characterization of this procedure, together with a demonstration of its utility for studies on intracytoplasmic membrane assembly, is presented.

Intermembrane phospholipid transfer mediated by cell-free extracts of Rhodopseudomonas sphaeroides.

The transfer of phospholipids between two membrane substrates catalyzed by a soluble protein fraction from Rhodopseudomonas sphaeroides has been demonstrated. The assay employs purified intracytoplasmic membrane (ICM) vesicles derived from cells of R. sphaeroides grown on [3H]acetate as the phospholipid donor substrate and phosphatidylcholine (70%)/phosphatidylethanolamine (30%) unilamellar liposomes containing [14C]triolein, a nontransferable marker, as the acceptor substrate for transferred phospholipids. Incubation of these two membrane substrates with a 40 to 80% (NH4)2SO4 protein fraction from R. sphaeroides results in the transfer of tritium-labeled ICM phospholipids to the acceptor membrane substrate. Upon completion of the incubation period, the donor ICM vesicles are quantitatively separated from the acceptor liposomes by precipitation with antibody prepared against whole, purified ICM vesicles. Phospholipid transfer is linear with respect to time and protein concentration, is inhibited by trypsin and heat, and shows an absolute dependence upon the presence of acceptor liposomes and the 40 to 80% (NH4)2SO4 protein fraction. Control experiments indicate that no fusion of the donor and acceptor membrane occurs during the incubation period and that, following prolonged incubation there is no detectable degradation of the labeled lipid components. Preliminary data on the phospholipid specificity of the transfer reaction is also presented.

Synthesis of photopigments and electron transport components in synchronous phototrophic cultures of Rhodopseudomonas sphaeroides.

The kinetics of synthesis and incorporation of the photosynthetic pigments and several of the major oxidative and photosynthetic electron transport components of Rhodopseudomonas sphaeroides have been studied during synchronous and asynchronous phototrophic growth. The photosynthetic pigments and cytochromes c and b, measured spectroscopically, exhibited continuous patterns of synthesis and incorporation into the membrane particulate fraction in both synchronous and asynchronous cultures. Succinic dehydrogenase and NADH-oxidase activities, present at low levelnous growth. In a previous paper, Leuking, D.R., Fraley, R.T., and Kaplan, S. ((1978) J. Biol. Chem. 253, 451-457) have shown that total cellular phospholipid is also accumulated discontinuously during synchronous growth. A continuously incorporated membrane component is thus subject to a wide variation in the membrane protein/lipid ratio. The significance of this ratio in regulating the activity of membrane proteins is discussed and the distinction between protein incorporation and function is drawn with particular reference to the photosynthetic pigments and cytochrome components and the oxidative activities measured. It is suggested that a dependence of membrane protein activity on the membrane protein to lipid ratio in vivo is of possible significance in the control of membrane synthesis and cell division.

Intracytoplasmic membrane synthesis in synchronous cell populations of Rhodopseudomonas sphaeroides. Fate of "old" and "new" membrane.

A nonspecific density labeling technique has been employed to monitor the synthesis of intracytoplasmic membrane in synchronously dividing populations of Rhodopseudomonas sphaeroides. The intracytoplasmic membranes of cells synchronized in D2O-based medium were found to undergo discontinuous decreases in specific density during synchronous cell growth following transfer to H2O-based medium. These abrupt decreases in membrane specific density occurred immediately prior to cell division and were not observed with intracytoplasmic membranes prepared from asynchronously dividing cells (see also Kowakowski, H., and Kaplan, S. (1974) J. Bacteriol. 118, 1144-1157). Discontinuous increases in the net accumulation of cellular phospholipid were also observed during the synchronous growth of R. sphaeroides. This is to be contrasted to the continuous insertion of protein and the photopigment components of the photosynthetic apparatus into the intracytoplasmic membrane during the cell division cycle (Fraley, R.T., Lueking, D.R., and Kaplan, S. (1978) J. Biol. Chem. 253, 458-464; Wraight, C.A., Lueking, D.R., Fraley, R.T., and Kaplan, S. (1978) J. Biol. Chem. 253, 465-471). Further, examination of the protein/phospholipid ratios of purified intracytoplasmic membrane preparations revealed that this ratio undergoes cyclical changes of 35 to 40% during a normal cycle of cell division. In contrast to the results of Ferretti and Gray ((1968) J. Bacteriol, 95, 1400-1406), DNA synthesis was found to occur in a stepwise manner in synchronously dividing cell populations of R. sphaeroides.

Glycerol utilization by a mutant of Rhodopseudomonas capsulata.

The glycerol-catabolizing enzymes of a mutant of Rhodopseudomonas capsulata were found to be constitutive and modulated coordinately, although apparently not functional in the presence of malate. No difference in glycerol permeation was found between the mutant and wild type.

sn-Glycerol-3-phosphate acyltransferase activity in particulate preparations from anaerobic, light-grown cells of Rhodopseudomonas spheroides. Involvement of acyl thiolester derivatives of acyl carrier protein in the synthesis of complex lipids.

Crude particulate preparations obtained from anaerobic, light-grown cells of Rhodopseudomonas spheroides have been shown to possess a significant level of sn-glycerol-3-phosphate acyltransferase (EC 2.3.1.15) activity. In contrast to the enzyme from Escherichia coli, the R. spheroides glycerophosphate acyltransferase has a high specificity for acyl thiolester derivatives of acyl carrier protein (ACP) as acyl donors for the reaction. Only limited , nonlinear glycerophosphate incorporation into lipid occurs when acyl coenzyme A (CoA) derivatives are employed as acyl substrate. With oleyl-ACP as substrate, maximal enzyme activity was observed at 40 degrees, over a broad pH range (6.0 to 8.5) and did not require a divalent metal cation. The presence of dithiothreitol stimulated enzyme-activity 15 to 20%. When oleyl-ACP or palmityl-ACP was employed as sole acyl group donor, the major products recoverable from the reaction mixtures were lysophosphatidic acid, phosphatidic acid, and monoglyceride. Althouh oleyl-ACP and palmityl-ACP gave comparable maximal velocities in the initial acylation of glycerophosphate, the formation of phosphatidic acid occurred preferentially with the unsaturated acyl-ACP derivative.

The involvement of guanosine 5-diphosphate-3-diphosphate in the regulation of phospholipid biosynthesis in Escherichia coli. Lack of ppGpp inhibition of acyltransfer from acyl-ACP to sn-glycerol 3-phosphate.

The response of the Escherichia coli sn-glycerol-3-phosphate acyltransferase to guanosine 5-diphosphate-3-diphosphate (ppGpp) has been determined in vitro employing palmityl coenzyme A (CoA) and palmityl acyl carrier protein as acyl substrates. Levels of ppGpp which cause significant inhibition of enzyme activity with palmityl-CoA as substrate have no effect on enzyme activity when palmityl acyl carrier protein is employed as acyl donor. The inhibition of enzyme activity observed with palmityl-CoA as acyl substrate was dependent upon the relative concentrations of MgCl2 and ppGpp (MgCl2 to ppGpp ratio) employed. With palmityl-CoA as acyl donor, PPGpp inhibited the production of lysophosphatidic acid but not phosphatidic acid. With palmityl acyl carrier protein as acyl substrate, ppGpp had no influence upon the distribution of the reaction products.

Glycerol assimilation by a mutant of Rhodopseudomonas capsulata.

A spontaneous mutant of Rhodopseudomonas capsulata, capable of growth on glycerol, has been isolated. The mutant requires CO(2) or malate to assimilate glycerol photosynthetically. This requirement is not manifested aerobically. Glycerokinase (EC 2.7.1.30) and pyridine nucleotide-independent l-alpha-glycerophosphate dehydrogenase (EC 1.1.2.1) activities appear coincidently with the metabolism of glycerol, suggesting that this organism employs these enzymes for glycerol dissimilation.