Hydrophobic membrane thickness and lipid-protein interactions of the leucine transport system of Lactococcus lactis

The effect of the phospholipid acyl chain carbon number on the activity of the branched-chain amino acid transport system of Lactococcus lactis has been investigated. Major fatty acids identified in a total lipid extract of L. lactis membranes are palmitic acid (16:0), oleic acid (18:1) and the cyclopropane-ring containing lactobacillic acid (19 delta). L. lactis membrane vesicles were fused with liposomes prepared from equimolar mixtures of synthetic phosphatidylethanolamine (PE) and phosphatidylcholine (PC) with cis mono-unsaturated acyl chains. The activity of the branched-chain amino acid carrier is determined by the bulk properties of the membrane (Driessen, A.J.M., Zheng, T., In 't Veld, G., Op den Kamp, J.A.F. and Konings, W.N. (1988) Biochemistry 27, 865-872). PE acts as an activator and PC is ineffective. Counterflow and protonmotive-force driven transport of leucine is sensitive to changes in the acyl chain carbon number of both phospholipids and maximal with dioleoyl-PE/dioleoyl-PC. Above the gel to liquid-crystalline phase transition temperature of the lipid species, membrane fluidity decreased with increasing acyl chain carbon number. Our data suggest that the carbon number of the acyl chains of PE and PC determine to a large extent the activity of the transport system. This might be relevant for the interaction of PE with the transport protein. Variations in the acyl chain composition of PC exert a more general effect on transport activity. The acyl chain composition of phospholipids determines the membrane thickness (Lewis, B.A. and Engelman, D.M. (1983) J. Mol. Biol. 166, 211-217). We therefore propose that the degree of matching between the lipid-bilayer and the hydrophobic thickness of the branched-chain amino acid carrier is an important parameter in lipid-protein interactions.     

Comparison of growth characteristics of anaerobic fungi isolated from ruminant and non-ruminant herbivores during cultivation in a defined medium

Anaerobic fungi were isolated from rumen fluid of a domestic sheep (Ovis aries; a ruminant) and from faeces of five non-ruminants: African elephant (Loxodonta africana), black rhinoceros (Diceros bicornis), Indian rhinoceros (Rhinoceros unicornis), Indian elephant (Elephas maximus) and mara (Dolichotis patagonum). The anaerobic fungus isolated from the sheep was a Neocallimastix species and the isolates from non-ruminants were all species similar to Piromyces spp. A defined medium is described which supported growth of all the isolates, and was used to examine growth characteristics of the different strains. For each fungus the lipid phosphate content was determined after growth on cellobiose and the resulting values were used to estimate fungal biomass after growth on solid substrates. The ability of isolates from ruminants and non-ruminants to digest both wheat straw and cellulose was comparable. More than 90% and 60%, respectively, of filter paper cellulose and wheat straw were digested by most strains within 60-78 h. Growth of two fungi, isolated from rumen fluid of a sheep (Neocallimastix strain N1) and from faeces of an Indian rhinoceros (Piromyces strain R1), on cellobiose was studied in detail. Fungal growth yields on cellobiose were 64.1 g (mol substrate)-1 for N1 and 34.2 g mol-1 for R1. The major fermentation products of both strains were formate, lactate, acetate, ethanol and hydrogen.     

Treatment of hypertension with ketanserin,a new selective 5-HT2 receptor antagonist.

The new selective 5-HT2 receptor blocking agent ketanserin was given in a dose of 10 mg intravenously to 12 patients with essential hypertension. It caused a distinct fall in supine systemic arterial, right atrial, pulmonary artery, and pulmonary capillary "wedge" pressures. Cardiac output, renal blood flow, and glomerular filtration rate showed no persistent changes. Thus 5-HT2 receptor blockade caused dilatation of both resistance and capacitance vessels and of the renal vascular bed. Heart rate and plasma concentrations of renin and noradrenaline rose after ketanserin. These data suggest that 5-HT may have a role in maintaining high blood pressure.     

The transmission of campylobacter in piggeries; an epidemiological study

The campylobacter infection of 10 sows and their piglets was monitored. These pigs werekept on two multiplier farms. Rectal faeces samples were taken from the sows shortly beforelittering and at different intervals after littering. Swab samples of rectal content were taken fromsix piglets per sow at different intervals after birth. Nine sows were shown to be infected withcampylobacter before litter and all sows after litter, with an average colony count of 4·1in log N g^–1 of faeces. Half of the piglets became infected withcampylobacter during the first week of life and 85%, after four weeks. Two genetic subtypingmethods (ERIC-PCR and RFLP) were used to study the relationships between campylobacterisolates from sows and piglets. A large diversity of campylobacter subtypes was found.Nevertheless, piglets and their mothers often harboured campylobacter isolates with identicalgenetic subtyping profiles, suggesting that piglets become infected via their mothers. However,observed similarities in genetic subtyping profiles between campylobacters isolated on differentfarms made this difficult to prove.     

Nasal hyperreactivity and inflammation in allergic rhinitis

The history of allergic disease goes back to 1819, when Bostock described his own 'periodical affection of the eyes and chest', which he called 'summer catarrh'. Since they thought it was produced by the effluvium of new hay, this condition was also called hay fever. Later, in 1873, Blackley established that pollen played an important role in the causation of hay fever. Nowadays, the definition of allergy is 'An untoward physiologic event mediated by a variety of different immunologic reactions'. In this review, the term allergy will be restricted to the IgE-dependent reactions. The most important clinical manifestations of IgE-dependent reactions are allergic conjunctivitis, allergic rhinitis, allergic asthma and atopic dermatitis. However, this review will be restricted to allergic rhinitis. The histopathological features of allergic inflammation involve an increase in blood flow and vascular permeability, leading to plasma exudation and the formation of oedema. In addition, a cascade of events occurs which involves a variety of inflammatory cells. These inflammatory cells migrate under the influence of chemotactic agents to the site of injury and induce the process of repair. Several types of inflammatory cells have been implicated in the pathogenesis of allergic rhinitis. After specific or nonspecific stimuli, inflammatory mediators are generated from cells normally found in the nose, such as mast cells, antigen-presenting cells and epithelial cells (primary effector cells) and from cells recruited into the nose, such as basophils, eosinophils, lymphocytes, platelets and neutrophils (secondary effector cells). This review describes the identification of each of the inflammatory cells and their mediators which play a role in the perennial allergic processes in the nose of rhinitis patients.     

Resistance of bacterial strains to dry conditions: use of anhydrous silica gel in a desiccation model system

The Viability of 18 bacterial strains desiccated on anhydrous silica gel and stored at a temperature of 22°C for at least 3 months was determined. According to their stability in the dried state, these strains could be classified into three typical groups. Group 1, containing Gram-positive strains and Salmonella serotypes, was marked by a very slow decrease of the concentration of culturable cells from day 14 on (respectively day 21 for Salmonella thompson . The rate of decrease expressed as regression coefficient (b) ranged from —0.000389 to —0.00521 log (cfp ml^-1) per d. The Group 2 strains Enterobacter cloacae and Escherichia coli did not reach a comparable slow decrease in the dry material within the indicated time period. Regression coefficients were respectively —0.04406 and —0.03412 log (cfp ml^-1) per d. The reciprocal values —(1/b) were respectively 23 d per log (cfp ml^-1) and 29 d per log (cfp ml^-1), indicating the time periods in which a reduction of 1 log unit of culturable cells occurred. Group 3 strains Pseudomonas aeruginosa, Aeromonas hydrophila and Aer. sobria were marked by a significant susceptibility to cell damage caused during desiccation and reconstitution. A high initial decrease (ID) of the concentration of culturable organisms seems to be a characteristic property of these bacterial strains: culturable organisms could not be detected after storage for 1 d ( Aer. hydrophila, Aer. sobria ) or 7 d ( Ps. aeruginosa ). The wide range of resistance of the different bacterial strains tested indicated that the silica gel model system is a suitable tool for microbiological challenge tests to investigate the survival of micro-organisms exposed to desiccation and their stability in dry materials.     

The immediate bactericidal effect of lactic acid on meat-borne pathogens

P. VAN NETTEN, J.H.J. HUIS IN'T VELD AND D.A.A. MOSSEL. 1994. The kinetics of the bactericidal effect of lactic acid decontamination (LAD) on meat-borne pathogens ( Salmonella spp., Campylobacter jejuni and Listeria monocytogenes ) was studied in an in-vitro model. The bactericidal effect was greatest on organisms in the lactic acid film that replaced the natural fluid on the meat surface during LAD. A stepwise increase in pH from 2.6 to 3.5 and 4.0 progressively reduced the bactericidal effect of decontamination. For treatment with 2% lactic acid for 30–90 s at 21C, the immediate death of Salmonella spp. decreased from about 0.5–2 log₁₀ cfu at pH 2.6 to an insignificant level at pH 4.0. The immediate death for Camp. jejuni decreased from 2.6 to >5.3 at pH 2.6 to 0.3–1.0 at pH 4.0. The decrease in bactericidal effect with increasing pH could, however, be countered by an increase in the temperature from 21C to 37C. It is suggested that 2% LAD at 37C for 30–90 s is suitable for elimination of salmonellas on meat but not for L. monocytogenes. Decontamination with 1% lactic acid at pH 3.0 and 21C for at least 30 s was effective for Camp. jejuni. Mesophilic Enterobacteriaceae were reliable indicators of the LAD-induced bactericidal effect on Salmonella spp. and Camp. jejuni.     

The stability and functional properties of proteoliposomes mixed with dextran derivatives bearing hydrophobic anchor groups.

Liposomes composed of Escherichia coli phospholipid were coated with polysaccharides bearing hydrophobic palmitoyl anchors. The effect on the stability of liposomes without or with integral membrane proteins was investigated. A high concentration of hydrophobized dextrans protected the liposomes against detergent degradation, decreased the fluidity of the membranes, prevented fusion of the liposomes and enhanced their stability. Proteoliposomes containing beef heart cytochrome-c oxidase and the lactose transport carrier of E. coli were similarly affected by coating with the dextrans. Under these conditions both membrane proteins were still active. Long-term stability of the coated liposomes was obtained only in the absence of the integral membrane proteins.