Is there a common water-activity limit for the three domains of life?

Archaea and Bacteria constitute a majority of life systems on Earth but have long been considered inferior to Eukarya in terms of solute tolerance. Whereas the most halophilic prokaryotes are known for an ability to multiply at saturated NaCl (water activity (a(w)) 0.755) some xerophilic fungi can germinate, usually at high-sugar concentrations, at values as low as 0.650-0.605 a(w). Here, we present evidence that halophilic prokayotes can grow down to water activities of <0.755 for Halanaerobium lacusrosei (0.748), Halobacterium strain 004.1 (0.728), Halobacterium sp. NRC-1 and Halococcus morrhuae (0.717), Haloquadratum walsbyi (0.709), Halococcus salifodinae (0.693), Halobacterium noricense (0.687), Natrinema pallidum (0.681) and haloarchaeal strains GN-2 and GN-5 (0.635 a(w)). Furthermore, extrapolation of growth curves (prone to giving conservative estimates) indicated theoretical minima down to 0.611 aw for extreme, obligately halophilic Archaea and Bacteria. These were compared with minima for the most solute-tolerant Bacteria in high-sugar (or other non-saline) media (Mycobacterium spp., Tetragenococcus halophilus, Saccharibacter floricola, Staphylococcus aureus and so on) and eukaryotic microbes in saline (Wallemia spp., Basipetospora halophila, Dunaliella spp. and so on) and high-sugar substrates (for example, Xeromyces bisporus, Zygosaccharomyces rouxii, Aspergillus and Eurotium spp.). We also manipulated the balance of chaotropic and kosmotropic stressors for the extreme, xerophilic fungi Aspergillus penicilloides and X. bisporus and, via this approach, their established water-activity limits for mycelial growth (∼0.65) were reduced to 0.640. Furthermore, extrapolations indicated theoretical limits of 0.632 and 0.636 a(w) for A. penicilloides and X. bisporus, respectively. Collectively, these findings suggest that there is a common water-activity limit that is determined by physicochemical constraints for the three domains of life.

Asynchronous emergence by loggerhead turtle (Caretta caretta) hatchlings

For many decades it has been accepted that marine turtle hatchlings from the same nest generally emerge from the sand together. However, for loggerhead turtles (Caretta caretta) nesting on the Greek Island of Kefalonia, a more asynchronous pattern of emergence has been documented. By placing temperature loggers at the top and bottom of nests laid on Kefalonia during 1998, we examined whether this asynchronous emergence was related to the thermal conditions within nests. Pronounced thermal variation existed not only between, but also within, individual nests. These within-nest temperature differences were related to the patterns of hatchling emergence, with hatchlings from nests displaying large thermal ranges emerging over a longer time-scale than those characterised by more uniform temperatures. In many egg-laying animals, parental care of the offspring may continue while the eggs are incubating and also after they have hatched. Consequently, the importance of the nest site for determining incubation conditions may be reduced since the parents themselves may alter the local environment. By contrast, in marine turtles, parental care ceases once the eggs have been laid and the nest site covered. The positioning of the nest site, in both space and time, may therefore have profound effects for marine turtles by affecting, for example, the survival of the eggs and hatchlings as well as their sex (Janzen and Paukstis 1991). During incubation, sea turtle embryos grow from a few cells at oviposition to a self-sufficient organism at hatching some 50-80 days later (Ackerman 1997). After hatching, the young turtles dig up through the sand and emerge typically en masse at the surface 1-7 nights later, with a number of stragglers following over the next few nights (Christens 1990). This contrasts with the frequently observed pattern of hatching asynchrony in birds. It has been suggested that the cause of mass emergence in turtles is that eggs within a clutch are fertilised within a short period of time and then, when thermal conditions within the nest are uniform, develop at very similar rates and hence hatch and emerge together (Porter 1972). As a corollary of this idea, it would be predicted that when there are pronounced within-nest thermal gradients, development rates of siblings will be different and hence asynchronous hatching and emergence might occur. While it may be energetically beneficial for hatchlings to emerge in a group (Carr and Hirth 1961), if the extent of hatching asynchrony is marked then there may be severe costs for individuals if they wait for all their siblings to hatch before attempting to dig out of the sand (Hays and Speakman 1992). Under such conditions, the protracted emergence of small groups of hatchlings over several nights may be favoured. Examination of the literature suggests that emergence asynchrony may be more widespread than generally considered. For example, Witherington et al. (1990) described loggerhead turtle hatchlings (Caretta caretta) emerging over 4 days in Florida; for green turtles (Chelonia mydas), Hendrickson (1958) documented that nests in Malaysia and Sarawak produced hatchlings for up to 8 days; whilst Diamond (1976) found that hawksbill (Eretmochelys imbricata) nests on Cousin Island, Seychelles, were active for up to 4 days. Similarly, on the Greek Island of Kefalonia, we have shown that emergence from individual loggerhead turtle nests may occur on up to 11 nights (Hays and Speakman 1992). It is logical to suppose that asynchronous emergence relates to thermal gradients within nests, since the incubation duration of sea turtle eggs is related to temperature, with eggs hatching quicker when the temperature is higher. Here we test this hypothesis by measuring thermal variations within loggerhead turtle nests and comparing these variations to the patterns of hatchling emergence.

Purification and identification of apophycocyanin alpha and beta subunits from soluble protein extracts of the red alga Cyanidium caldarium. Light exposure is not a prerequisite for biosynthesis of the protein moiety of this photosynthetic accessory pigment

Much controversy exists as to the level at which light exerts control over the biosynthesis of the photosynthetic apparatus in higher plants and other organisms. The eukaryotic red alga Cyanidium caldarium, like higher plants, undergoes light induction of chlorophyll synthesis. In addition to chlorophyll a the alga also synthesises the linear tetrapyrrole phycocyanobilin, which is combined with alpha or beta apobiliproteins to form phycocyanin, the major light-harvesting pigment in this organism. We have previously shown that the tetrapyrrole precursor 5-aminolaevulinic acid (ALA) can substitute for light in inducing the biosynthesis of the phycocyanobilin moiety of this protein. We have also described the appearance of a protein of similar isoelectric point and molecular weight to phycocyanin in ALA-fed cells (Turner et al., 1992, Plant Physiol Biochem 30: 309-314). We now report on the protein's immunological and sequence identity with phycocyanin alpha and beta subunits, and provide further evidence that bilin-apoprotein ligation is light dependent.

Out-of-district attenders: the passing trade of an accident and emergency department

The resources of accident and emergency (A&E) departments are often required to treat patients who are not within the catchment population of the local health authority. An assessment of workload caused by this particular group was carried out over a 2-month period at Northampton General Hospital which serves a population of 318,000. Details were collected and analysed on the patients' reason for attendance, investigations and treatment.

Biosynthesis of phycobilins. Formation of the chromophore of phytochrome, phycocyanin and phycoerythrin

Phycobiliproteins play important roles in photomorphogenesis and photosynthesis. The light-absorbing chromophores of the phycobiliproteins are linear tetrapyrroles (bilins) very similar in structure to the mammalian bile pigments. 5-Aminolaevulinate (5-ALA) is the first committed intermediate in phycobilin synthesis. The biosynthesis of 5-ALA, destined for phycobilins, occurs via the five-carbon pathway, now well established for tetrapyrrole synthesis in plants and distinct from the mammalian pathway. The phycobilins are formed by reduction of biliverdin which results from the synthesis and degradation of haem. This haem is an essential intermediate in the biosynthesis of phycobilins. Phycocyanobilin, the blue-green pigment found in certain algae and cyanobacteria, is formed from biliverdin via phytochromobilin, the chromophore of phytochrome. This leads to the likelihood that phytochromobilin is formed as an end product, or intermediate, in the synthesis of all phycobilins.

Effects of 6,6-difluorocholestanol and 7,7-difluorocholestanol on hepatic enzymes of cholesterol metabolism

The effects of 6,6-difluorocholestanol and 7,7-difluorocholestanol on enzymes of hepatic liver cholesterol were examined. Neither compound affected the activity of 3-hydroxy-3-methylglutaryl-CoA reductase. 7,7-Diffluorocholestanol had no effect on the activity of acyl-CoA: cholesterol acyltransferase or cholesterol 7 alpha-hydroxylase. However, 6,6-difluorocholestanol was a competitive substrate for cholesterol in the esterification of cholesterol catalysed by the acyltransferase. 6,6-Difluorocholestanol also inhibited hydroxylation of cholesterol by cholesterol 7 alpha-hydroxylase but was not itself a substrate for this enzyme. These results show that substitutents in ring B of the sterol can have a significant effect on the binding of the sterol to enzymes and to the catalytic mechanism if the substituent is close to the groups in the molecule that participate.

The effect of gabaculine on tetrapyrrole biosynthesis and heterotrophic growth in Cyanidium caldarium

Pigment synthesis in four strains of the unicellular red alga Cyanidium caldarium with different pigment-synthesizing patterns was inhibited in the presence of gabaculine (3-amino-2,3-dihydrobenzoic acid). Parallel inhibition of light-induced chlorophyll and phycocyanin synthesis was observed in strain III-D-2, which only synthesizes pigments in the light. Similar parallel inhibition was observed in the dark in mutant CPD, which is able to synthesize chlorophyll and phycocyanin in the absence of light. Inhibition of pigment synthesis in all strains was overcome by addition of 5-aminolaevulinic acid. Inhibition of phycocyanin synthesis in mutant GGB (unable to synthesize chlorophyll) and inhibition of chlorophyll synthesis in mutant III-C (unable to synthesize phycocyanin) were also observed. Gabaculine also inhibited the heterotrophic growth of C. caldarium in the dark. However, inhibition was overcome after an extended lag period, following which cell growth proceeded at a similar rate to that of control cells not exposed to gabaculine. Heterotrophic growth in cells pre-exposed to gabaculine was not inhibited by subsequent exposure. Possible mechanisms for this adaptation are discussed.

The effects of 6-azacholest-4-en-3 beta-ol-7-one, an inhibitor of cholesterol 7 alpha-hydroxylase, on cholesterol metabolism and bile acid synthesis in primary cultures of rat hepatocytes

6-Azacholest-4-en-3 beta-ol-7-one (azacholesterol) was shown to be a specific inhibitor of cholesterol 7 alpha-hydroxylase. It inhibited cholesterol hydroxylation by a rat liver microsomal preparation with non-competitive kinetics and a Ki of 4 microM. No evidence was found for a time-dependent inhibition of activity. Azacholesterol did not inhibit acyl-CoA: cholesterol acyltransferase or 3-hydroxy-3-methylglutaryl coenzyme A reductase in rat liver microsomal preparations, or cholesterol esterification and synthesis in primary cultures of rat hepatocytes. The synthesis of bile acids was inhibited by azacholesterol in these cells in a dose-dependent way. When bile acid synthesis was inhibited by azacholesterol, newly-synthesized cholesterol from exogenous mevalonate was secreted by the hepatocyte cultures into the cell culture medium in several-fold excess over control incubations. No changes in the secretion of cholesteryl ester occurred in the presence of azacholesterol. This observation suggests that newly synthesised cholesterol that has entered the substrate pool for hydroxylation is no longer accessible to the substrate pool for esterification. This is further evidence for the compartmentation of cholesterol metabolism in the hepatocyte.

The role of acyl-CoA: cholesterol acyltransferase in the metabolism of free cholesterol to cholesteryl esters or bile acids in primary cultures of rat hepatocytes

Sandoz compound 58-035 has been shown to inhibit acyl-CoA: cholesterol acyltransferase activity in a variety of cell types. We have shown that it does not inhibit rat liver microsomal cholesterol 7 alpha-hydroxylase, the rate-limiting enzyme of bile-acid synthesis, but it does inhibit acyl-CoA: cholesterol acyltransferase in both the microsomal fraction and in rat hepatocyte monolayers. To test the role of acyl-CoA: cholesterol acyltransferase in these cells, monolayers were incubated over 5 h in the presence and absence of 58-035 and in the presence of increasing amounts of mevalonic acid to provide a source of cholesterol. The addition of mevalonic acid increased the secretion of bile acids by the cells, and this was further increased by the addition of 58-035. The secretion of cholesteryl esters was conversely inhibited by the addition of 58-035. The results help define the role of acyl-CoA: cholesterol acyltransferase in determining the fate of intracellular cholesterol.

The use of N-methylprotoporphyrin dimethyl ester to inhibit ferrochelatase in Rhodopseudomonas sphaeroides and its effect in promoting biosynthesis of magnesium tetrapyrroles

N-Methylprotoporphyrin dimethyl ester inhibits ferrochelatase in isolated membranes of Rhodopseudomonas sphaeroides at low concentrations (around 10 nm). Full inhibition developed after a short lag phase. The inhibition was non-competitive with porphyrin substrate. Addition of inhibitor to growing cultures of Rps. sphaeroides caused a decrease (near 40%) in cytochrome content and a severe inhibition of ferrochelatase; the excretion of haem into the medium by cell suspensions was also severely inhibited. The addition of N-methylprotoporphyrin dimethyl ester to suspensions of photosynthetically competent Rps. sphaeroides Ga caused excretion of Mg-protoporphyrin monomethyl ester. When added to mutants V3 and O1, magnesium divinylphaeoporphyrin a5 monomethyl ester and 2-devinyl-2-hydroxyethylphaeophorbide a were excreted, with maximum effect at around 3 microM-inhibitor in the medium. The results are interpreted to suggest that the inhibitor decreases concentration of intracellular haem, which normally controls the activity of 5-aminolaevulinate synthetase. Unregulated activity of this enzyme leads to overproduction of protoporphyrin, which is diverted to the bacteriochlorophyll pathway. Further control operates at magnesium protoporphyrin ester conversion in normal cells.

Light-dependent cytochrome P-450 changes in mung beans (Phaseolus aureus)

Maximum concentrations of microsomal cytochrome P-450 are present in 3-4 day-old mung beans (Phaseolus aureus). On illumination of dark-grown seedlings, cytochrome P-450 and later cytochrome P-450 undergo a rapid decrease in concentration in vivo, with an apparent half-time of about 6 h. Conversely light-grown seedlings, transferred to darkness, show a slow accumulation of cytochrome P-450, doubling time of about 30 h, with a later accumulation of cytochrome P-420. Microsomal cytochromes b559, b560.5 and b562.5 do not significantly alter on light-dark transitions. Possible functions for dark-induced cytochrome P-450 are discussed.

The cytochromes in microsomal fractions of germinating mung beans

Detailed studies of microsomal cytochromes from mung-bean radicles showed the presence of cytochrome P-420, particularly in dark-grown seedlings, accompanied by smaller quantities of cytochrome P-450. Similar proportions of cytochrome P-420 to cytochrome P-450 were found spectrophotometrically in vivo with whole radicles and hypocotyls. Assayed in vitro, maximum concentrations of both cytochromes were attained after 4 days of growth, before undergoing rapid degradation. Illumination of seedlings stabilized cytochrome P-450 and decreased the amount of cytochrome P-420. Three b cytochromes were present in the microsomal fraction, namely cytochromes b-562.5 (Em + 105 +/- 23 mV), b-560.5 (Em + 49 +/- 13 mV) and b5 (Em - 45 +/- 14 mV), all at pH 7.0. Of the b cytochromes, cytochrome b5 alone undergoes a rapid degradation after day 4, Changes in cytochrome b concentrations were confined to the microsomal fraction: mitochondrial b cytochrome concentrations were unaltered with age. Protohaem degradation (of exogenous methaemalbumin) was detected in microsomal fractions of mung beans. The rates of degradation were highest in extracts of young tissue and declined after day 4. The degradation mechanism and products did not resemble those of mammalian haem oxygenase.

Mediastinal Chorionepithelioma in a Male: A Case Report

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Malignant Teratoma of the Mediastinum: Report of a Case and Review of 24 Cases From the Literature

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