Catabolism of arginine byCarnobacterium spp. isolated from vacuum-packed sugar-salted fish

The ability ofCarnobacterium spp. originally isolated from vacuum-packed, sugar-salted fish to catabolize arginine was examined. All strains were able to produce citrulline, ornithine, and NH₃ from arginine, presumably by the arginine deiminase pathway. The metabolism of arginine was concurrent with acid production from glucose for one strain ofCarnobacterium sp. but delayed for one strain ofCarnobacterium piscicola. The arginine catabolism was not inhibited in the presence of 2% glucose for three strains of carnobacteria during growth in test broth and/or shrimp extract. Growth as well as arginine catabolism was delayed for two strains of carnobacteria by lowering the temperature from 9°C to 4°C. A similar result was obtained by incubating one strain ofC. piscicola in CO₂. None of the compoundsl-citrulline,l-ornithine hydrochloride, and (NH₄)₂SO₄ had any effect on growth or arginine catabolism of this strain. Neither did pH of the medium affect the time for initiation of arginine catabolism.     

Evidence for two newVibrio anguillarum K antigens

Surface polysaccharides from five strains ofVibrio anguillarum were studied by means of immunoelectrophoretic procedures. The study suggested existence of two new K antigens, displaying cross-reactivity, in strains derived from diseased feral fish. The importance of a detailed serologic characterization of isolates for ecologic and epidemiologic studies ofV. anguillarum is considered.     

Aroma production by spores ofPenicillium roqueforti on a synthetic medium

Summary The synthesis of 2-heptanone from the sodium salt of octanoic acid by spores of five strains ofPenicillium roqueforti was studied. The strains showed a high disparity in kinetic behavior. The one selected, which was originally isolated from blue cheese, had a good resistance to substrate inhibition along with a good apparent biotransformation yield (close to 60%). An activator was needed in the incubation medium. The loss of activity of aging spores was reduced by the activator compounds; ethanol exhibited the highest efficiency. When spores were produced on buckwheat seeds with a solid state fermentation technique, the medium itself was an activator source. When the biotransformation reaction was carried out in a stirred aerated fermentor, the volatile loss by air-stream stripping had to be taken into account. No ketone metabolism occurred with the strain used.     

Detection and identification ofListeria monocytogenes from milk and cheese by a single-step PCR

Primers ofiap gene were used as a target to develop a PCR technique for detectingListeria monocytogenes in milk and cheese. The PCR technique gives good results in the detection ofListeria monocytogenes either in artificially or naturally contaminated foodstuffs and has a high sensitivity and specificity. Application of this rapid diagnostic tool could provide further information about the spread ofL. monocytogenes in milk and cheese.     

Production of butyric acid by batch fermentation of cheese whey withClostridium beijerinckii

Summary The effect of pH on the fermentation of butyric acid byClostridium beijerinckii using cheese whey as a substrate was studied. Maximum concentrations of the acid were produced when the pH was controlled at 5.5. Raising or lowering of pH was found to reduce the total acid formation. This particular strain ofC. beijerinckii produced insignificant amounts of butanol in all the pure culture cases investigated. A comparative study of the fermentation in a synthetic glucose medium and in cheese whey showed the whey to produce more butyric acid.     

Cultural and serological comparison of ten strains of Aspergillus fumigatus Fresenius

Ten strains ofAspergillus fumigatus Fresenius, isolated from human or animal sources, were compared for cultural and serologic characteristics when grown on neopeptone dialysate medium. All strains grew well and antigenic similarities were noted among the strains. Best antigen production occurred after 6 weeks' incubation.     

Comparison of growth characteristics and roquefortin C production of<Emphasis Type="Italic">Penicillium roqueforti</Emphasis> from blue-veined cheese

The properties of 21 isolates ofPenicillium roqueforti from just as many commercial blue-veined cheeses, purchased from the Argentinean market (domestic and imported products) were comparatively examined. Isolates were investigated for their ability to grow at different temperatures, pH values and concentration of NaCl, as well as for their proteolytic and lipolytic activities, respectively. The potential of these strains to produce roquefortin in vitro, and the actual levels of roquefortin in 10 of these cheeses were analysed by TLC. All strains showed similar growth properties in aspects of salt concentration and pH-value of the medium, and all grew well at 10 °C. Only four strains showed proteolytic activity on casein agar, while all strains were lipolytic on trybutirin agar. After incubation at 25 °C for 16 days, all strains produced roquefortin in Yeast Extract Sucrose (25.6–426.7 μg/g) and in reconstituted (10%) sterile skim milk (26.9–488 μg/g). Roquefortin at >0.1 μg/g was also found in 9 out of 10 analysed samples of blue-veined cheeses (8 from Argentine, 1 from Spain), with a maximum value 3.6 μg/g. During the ripening process of blueveined cheese, production of roquefortin seems to be unavoidable. Care should be taken to select strains with low toxin production characteristics, to minimize potential health risks. Roquefortin C production byP. roqueforti in vitro was not correlated with roquefortin C levels found in cheese. Financial support: Research grants from the National University of Quilmes, Argentina     

A vitamin-free minimal synthetic medium forCryptococcus neoformans

The use of a simple synthetic medium is essential for study on the growth and physiology ofCryptococcus neoformans. In the present study, a minimal synthetic liquid medium (MSM) was tested for the growth of 23C. neoformans strains. This medium contained a low concentration of glucose, ammonium sulphate and inorganic salts with a pH value of 4.5, but no amino acids or vitamins. The strains were starved for 4 days to eliminate nutrients which might have been carried over from their pre-culture medium. Then, they were inoculated in the MSM at an initial OD of 0.020 at 550 nm and incubated at 37 °C for 20 days. Cell growth was generally monitored daily by measuring the absorbance at 550 nm. The medium supported the growth of the strains tested and gave an average final OD of 0.500. The results obtained indicate thatC. neoformans may be autotrophic with respect to vitamins and in particular to thiamine. The MSM medium is easy to prepare and store. It is highly reproducible and useful for studies on the growth and physiology ofC. neoformans.     

Adaptation of Listeria monocytogenes in a simulated cheese medium: effects on virulence using the Galleria mellonella infection model

The aim of this study was to evaluate the effect of the acid and salt adaptation in a cheese‐based medium on the virulence potential of Listeria monocytogenes strains isolated from cheese and dairy processing environment using the Galleria mellonella model. Four L. monocytogenes strains were exposed to a cheese‐based medium in conditions of induction of an acid tolerance response and osmotolerance response (pH 5·5 and 3·5% w/v NaCl) and injected in G. mellonella insects. The survival of insects and the L. monocytogenes growth kinetics in insects were evaluated. The gene expression of hly, actA and inlA genes was determined by real‐time PCR. The adapted cells of two dairy strains showed reduced insect mortality (P < 0·05) in comparison with nonadapted cells. Listeria monocytogenes Scott A was the least virulent, whereas the cheese isolate C882 caused the highest insect mortality, and no differences (P > 0·05) was found between adapted and nonadapted cells. The gene expression results evidenced an overexpression of virulence genes in cheese‐based medium, but not in simulated insect‐induced conditions. Our results suggest that adaptation to low pH and salt in a cheese‐based medium can affect the virulence of L. monocytogenes, but this effect is strain dependent.

Significance and Impact of the Study

In this study, the impact of adaptation to low pH and salt in a cheese‐based medium on L. monocytogenes virulence was tested using the Wax Moth G. mellonella model. This model allowed the differentiation of the virulence potential between the L. monocytogenes strains. The effect of adaptation on virulence is strain dependent. The G. mellonella model revealed to be a prompt method to test food‐related factors on L. monocytogenes virulence.     

Some cultural characteristics of mycelia of a mycorrhizal fungus,Lyophyllum shimeji

Cultural characteristics of 45 strains ofLyophyllum shimeji and 10 strains of three related species were determined. The average optimum temperature for mycelial growth ofL. shimeji on a medium consisting of rye grains was 24.9°C, slightly higher than those forL. fumosum andL. decastes. The average mycelial growth rate of theL. shimeji strains, each at its optimum temperature, was 2.0 mm/day, almost the same as that ofL. decastes and 2 times greater than those ofL. semitale andL. fumosum. All strains ofL. shimeji could grow on beech and pine sawdust, but none could significantly decompose beech wood blocks. Of the 45 strains ofL. shimeji, 3 strains had ability to form primordia on the rye grain medium without the host plant.This study was supported in part by the Forestry Agency, Japan.     

Production and characterization of the milk-clotting protease of<Emphasis Type="Italic"> Myxococcus xanthus</Emphasis> strain 422

The cheese industry is seeking novel sources of enzymes for cheese production. Microbial rennets have several advantages over animal rennets. (1) They are easy to generate and purify and do not rely on the availability of animal material. (2) The production of microbial clotting enzymes may be improved by biotechnological techniques. In this work, the biochemical characterization of a novel milk-clotting extracellular enzyme from Myxococcus xanthus strain 422 and a preliminary evaluation of its cheese-producing ability are reported. Strain 422 was selected from four M. xanthus strains as the best producer of extracellular milk-clotting activity, based on both its enzyme yield and specific milk-clotting activity, which also afforded lower titration values than enzymes from the three other M. xanthus strains. The active milk-clotting enzyme from M. xanthus strain 422 is a true milk-clotting enzyme with a molecular mass of 40 kDa and a pI of 5.0. Highest milk-clotting activity was at pH 6 and 37 °C. The enzyme was completely inactivated by heating for 12 min at 65 °C. The crude enzyme preparation was resolved by anion-exchange chromatography into two active fractions that were tested in cheese production assays of compositional (dry matter, fat content, fat content/dry-matter ratio, and moisture-non-fat content) and physicochemical properties (firmness, tensile strength, pH and Aw) of the milk curds obtained. Purified protein fraction II exhibited a significantly higher milk-clotting ability than either protein fraction I or a total protein extract, underlining the potential usefulness of M. xanthus strain 422 as a source of rennet for cheese production.     

Growth factor requirements of two strains ofSphaerotilus discophorus

The relatively complex growth-factor requirements of two strains ofSphaerotilus discophorus, strains 31 and 32, have been elucidated. In addition to thiamin and biotin which are required by other strains ofS. discophorus, the two strains must be supplied also with adenine or guanine and with cyanocobalamin for growth in a glucose — Casamino Acids — mineral salts medium. The cyanocobalamin can be replaced by methionine but only if relatively large amounts of this amino acid, 100 µg or more per ml, are added to the medium. The methionine requirement of the two strains is approximately 3 times greater than that of otherS. discophorus strains.     

Amino acid fermentation byBacteroides melaninogenicus

Each of four strains ofBacteroides melaninogenicus grew well in a trypticaseyeast extract medium, without carbohydrate. Addition of glucose did not increase growth, and the sugar was fermented to only a limited extent. However, growth decreased when the trypticase concentration of the medium was reduced. These observations suggest that amino acid fermentation is of major importance in the energy metabolism ofB. melaninogenicus. Acetic, butyric and isovaleric acids were produced by all four strains. Two of the strains also formed propionic and isobutyric acids. Experiments using media containing either labeled glucose or labeled protein indicated that these acids are primarily derived from the proteinaceous substrates in the medium, rather than from glucose, indicating that amino acid fermentation byB. melaninogenicus is not subject to glucose repression. Resting-cell suspensions ofB. melaninogenicus possessed a limited ability to ferment free acids, as judged by the liberation of ammonia. However the organisms readily fermented amino acids when present as peptides, suggesting that peptides are more readily transported into the cell. Three of the 4 strains studied grew well when incubated under an atmosphere containing 2 to 4 % oxygen in cultures possessing a high surface to volume ratio. Hence not all strains ofB. melaninogenicus can be considered strict anaerobes.This investigation was supported in part by grant DE-02847 from the National Institute of Dental Research, and in part by a grant from the Colgate-Palmolive Co.     

A new mycobactin,mycobactin J,fromMycobacterium paratuberculosis

This paper reports the production, purification, and biological assay of a new mycobactin fromMycobacterium paratuberculosis. This new mycobactin, designated mycobactin J, is produced by a strain ofM. paratuberculosis adapted to growth on synthetic medium without exogenous mycobactin. Mycobactin J reduces the incubation period ofM. paratuberculosis in complex medium by 3 weeks when compared with medium containing mycobactin P, and a higher proportion of the organisms, in inocula from infected tissues or fecal specimens, produce colonies. Also, some strains ofM. paratuberculosis will grow on medium containing mycobactin J that will not grow on medium containing mycobactin P.     

Identification of the perfect state ofCryptococcus neoformans from 195 clinical isolates including 84 from AIDS patients

Filobasidiella neoformans is the teleomorphic state ofCryptococcus neoformans and it is a heterothalic. The purpose of this study was to establish the proportions of each mating types (a, ) from among 195 strains ofC. neoformans isolated from clinical material. The culture medium used was sunflower agar. Cultures were incubated at 20–22 °C for 15 days and observed periodically for one month. Non-reactive strains were mated several times with different reactive strains. Under these conditions 96.8% of the strains were found to be reactors. Among both varieties ofC. neoformans, mating type was found to have the highest frequency of 95% in the varietyneoformans and 84% in the varietygattii. These results showed a higher reactivity in comparison with other investigators. This difference could be due to the medium used or to repeated mating with different reactive tested strains.     

Isolation and purification of Australian isolates of the toxic cyanobacteriumMicrocystis aeruginosa Kütz

Isolation and laboratory culture ofMicrocystis aeruginosa Kütz. using a growth medium (MLA medium) suitable for both non-axenic and axenic cultures is described. Seventeen established strains ofM. aeruginosa were subjected to one or more of three purification methods: centrifugation cleaning, sulphide gradient selection, and antibiotic treatment (Imipenem^®). While each method purified only about half of the strains attempted, the selective application of each method, based on the morphological characteristics of the strains, succeeded in purifying 12 of the 17 strains. Three of the 5 strains not purified were contaminated with a sulphide-tolerant, Imipenem-resistant spirochaete,Spirochaeta cf.aurantia, which could not be detected on normal, broad spectrum bacterial test media. The presence of this bacterial species was detected only by phase contrast and DAPI (4,6-diamidino-2-phenylindole) stained fluorescence microscopy.Author for correspondence     

Development of a DNA probe using differential hybridization to detect the fish pathogenVibrio anguillarum

The fish pathogenVibrio anguillarum causes significant economic losses in commercially cultured fish species worldwide. At present, identification ofV. anguillarum requires conventional isolation and culturing techniques. Using differential hybridization, a 310 base pairV. anguillarum-specific DNA fragment was isolated for use as a probe. In specificity studies against 19 different bacterial species, including twoVibrio sp. and fish pathogens, and 223 marine bacterial isolates, the probe hybridized exclusively toV. anguillarum strains. The probe also strongly hybridizes to 7 of 9 serotypes tested, with serotype 09 giving a weak probe reaction and serotype O7 negative. The probe allows rapid and accurate detection of both pathogenic and environmental strains ofV. anguillarum.     

北疆传统发酵生奶酪中乳酸菌的耐受性及益生特性测定

【背景】北疆乳制品中生奶酪作为发酵乳制品,其中有多种微生物的参与,是优质食品级微生物的宝贵来源,然而其中蕴含的丰富的微生物资源也面临着流失。【目的】研究已筛选出的41株乳酸菌的生长曲线变化规律,并对其在低pH环境的耐酸特性及益生特性进行分析。【方法】通过人工模拟胃肠液和含0.3%、0.5%、1.0%浓度牛胆盐溶液培养,对从生奶酪中分离鉴定的41株乳酸菌菌株进行人工胃肠液、牛胆盐耐受性试验。【结果】41株乳酸菌中有6株乳酸菌(编号为QM-5、QM-27、UM-12、UM-18、NM-11和NM-14)均能在pH值分别为2.0、2.5、3.0、3.5、4.0时生长较好,在pH 2.0的环境下也保持一定程度的生长。菌株存活率大于50%,乳酸菌含量为108 CFU/mL以上。从生奶酪分离的乳酸菌有极强的耐酸、耐胆盐特性,可以预测在胃肠道环境生存。41株菌对大肠杆菌(Escherichia coli)、金黄色葡萄球菌(Staphylococcus aureus)和枯草芽孢杆菌(Bacillus subtilis)均有抑制作用。【结论】通过比较耐酸性、胃肠道模拟、胆盐耐受性和抑菌特性等实验结果,初...     

Demographic and life history response of the cladoceranBosmina longirostris to variation in predator abundance

Population dynamics, demography and body size of the cladoceranBosmina longirostris were examined in an experimental study in which the abundance of its predator (the cyprind fishPhoxinus eos) was varied in an unproductive lake. Four densities of fish were used, encompassing the biomass of fish in the lake.Bosmina was most abundant at low and medium fish densities (1.06 and 2.12 g fish biomass · m^-3) and less abundant when fish were either absent or present at high density (3.71 g fish biomass · m^-3). The unimodal response to predator abundance resulted from effects on both birth and death rates.Bosmina birth rates increased as fish biomass increased, in response to increasing food (phytoplankton) biomass. Death rates were highest at high fish biomass (because of fish predation) and in the absence of fish (because of predation by the dipteranChaoborus, which was most abundant in the absence of fish). Size-frequency distributions revealed that fish eliminated the larger size classes ofBosmina, and mean carapace length ofBosmina populations was inversely proportional to fish biomass.Bosmina initiated reproduction at smaller size in the presence of fish than in their absence, and size at maturity was inversely proportional to fish biomass. Size at birth also tended to decrease with increasing fish biomass, but this trend was not as strong as that of size at maturity. Decreased size at maturity apparently allowedBosmina individuals to reproduce before becoming vulnerable to fish predation. Flexibility in size at maturity, together with low abundance of invertebrate predators and large herbivores (which were preyed upon by fish), allowedBosmina to become abundant in low and medium fish treatments. In the high fish treatment, mortality due to fish predation was too severe to be offset by decreased size at maturity, andBosmina population density was low. The net response ofBosmina populations to fish predation results from interactive effects of predation on mortality, natality, and life history traits.     

Iron-binding proteins and heme compounds as iron sources forVibrio anguillarum

Utilization of several iron sources available from the host was investigated in different strains ofVibrio anguillarum. We tested the ability to use transferrins, heme, hemoglobin, and haptoglobin-hemoglobin as iron sources in strains ofV. anguillarum possessing different iron uptake systems mediated by siderophores. Only the wild-type pathogenic strains with an intact siderophore-mediated iron transport system were able to obtain iron from transferrins. None of the low-virulence derivatives lacking siderophore production could grow in the presence of transferrins. However, all strains, wild-type and iron-deficient derivatives, could utilize heme, hemoglobin, and haptoglobin-hemoglobin as iron sources when added to iron-deficient media. The ability to grow in fish serum was also evaluated. Although only wild-type strains could grow in fresh serum, derivative strains lacking siderophore production also were able to grow when serum was heat inactivated or when a utilizable siderophore was present in serum. The results indicate that besides the siderophore-mediated mechanism,V. anguillarum can also obtain iron from other sources presumably available from the host, although its importance for growth in vivo is so far unknown.