- Volume 138, Issue 1, 1992

Summary: In order to provide a profile of the plasmid gene pool in Salmonella prior to the clinical use of antibiotics, a molecular genetic analysis was made of plasmids in strains collected by E. D. G. Murray between 1917 and 1954. These pre-antibiotic era (PAE) salmonellae contain conjugative plasmids of the same incompatibility groups as contemporary enterobacterial plasmids. Upon analysis of total plasmid content, 42 plasmids, sized between 23 and 72 MDa, were found. We defined and investigated six groups of these PAE Salmonella plasmids in terms of three groups of genes; those involved in plasmid maintenance and incompatibility, DNA repair and virulence. Of the five groups, three were replicon-typed to groups IncI1, IncX and IncFII; one group exhibited no homology to contemporary Inc/Rep probes, and one group represented virulence plasmids containing a common plasmid-partitioning locus. The results indicated that most of the PAE groups were progenitors of contemporary R-plasmids, except for the virulence plasmids, which have generally not evolved as vectors of antibiotic resistance.

Summary: Streptococcus pneumoniae requires 0·15 mm-Ca2+ in the medium for optimal growth. Increasing the Ca2+ concentration to 1 mm triggers either a differentiative state, competence for genetic transformation during exponential growth, or partial lysis as soon as the cultures enter stationary phase. Genetic and physiological data both suggest that these responses are under the control of activator(s), excreted in the presence of high Ca2+ concentrations. 45Ca2+ transport is also stimulated by the activator(s). The amiloride derivative 2”,4′-dimethylbenzamil (DMB) inhibits 45Ca2+ transport and prevents lysis and competence development. This provides evidence in favour of the involvement of Ca2+ transport in competence and culture lysis. On the other hand, addition of DNA to a competent culture prevents lysis of wild-type bacteria while a mutant, defective for DNA uptake, is not protected from lysis by exogenous DNA. An hypothesis is proposed for competence induction as a global metabolic response to Ca2+, under the control of competence factor.

Summary: Resting suspensions of cells of Saccharomyces cerevisiae grown in iron-rich or iron-deficient conditions were studied by following the fluorescence emission changes (λem 400-460 nm, λexc. 300-340 nm) occurring in these suspensions upon addition of glucose and ferric iron. The results show that, in addition to NAD(P)H, metabolites of the aromatic amino acid pathway interfere with the fluorescence measurements, and that they could be involved in ferric iron reduction. Wild-type strains of S. cerevisiae are known to excrete anthranilic acid and 3-hydroxyanthranilic acid in response to glucose. The major fluorescing compound excreted by a chorismate-mutase-deficient mutant strain of S. cerevisiae was identified as anthranilic acid. The excretion of anthranilic and 3-hydroxyanthranilic acids was correlated with the ferric-reducing capacity of the extracellular medium. Excretion during growth was much greater by cells cultured in iron-rich medium than by cells grown in iron-deficient medium. The possibility was examined that a link could exist between the biosynthesis of aromatics and the ferri-reductase activity of the cells, via chorismate synthase and its putative diaphorase-associated activity. Two ferri-reductase-deficient mutants excreted much less 3-hydroxyanthranilate than did the parental wild-type strains. However, the ferri-reductase activity of a chorismate-synthase-deficient mutant was comparable to that of the parental strain.

Summary: When the salt-tolerant yeast Zygosaccharomyces rouxii was grown in YPD medium containing 15% (w/v) NaCl, the relative amounts of C16:1 and C18:1 fatty acids in acyl lipids increased and those of C18:0 and C18:2 acids decreased both in whole cells and in crude plasma membrane preparations, as compared with cells grown in YPD medium alone. The proportions of C12:0 and C14:0 acids, which are minor components of yeast lipids, decreased in whole cells and markedly increased in plasma membranes when 15% NaCl was included in the growth medium. The degree of unsaturation of fatty acids in the membranes and in whole cells decreased in the presence of 15% NaCl in the culture medium. The amount of free ergosterol in the membranes of cells grown in 15% NaCl increased to 2·9 times that of control cells. The ratio of ergosterol to phospholipid increased to 5 times that of control cells, whereas the ratio of phospholipid to protein in the membranes of cells grown in 15% NaCl decreased to less than half that of control cells. The fluorescence polarization value of DPH (1,6-diphenyl-1,3,5-hexatriene) in membranes of cells grown in 15% NaCl was 1·2 times higher than that for membranes from control cells, indicating a decrease in membrane fluidity in the presence of a high concentration of NaCl.

Summary: Previous results [E. Cabib, A. Sburlati, B. Bowers & S. J. Silverman (1989) Journal of Cell Biology 108, 1665-1672] strongly suggested that the lysis observed in daughter cells of Saccharomyces cerevisiae defective in chitin synthase 1 (Chs1) was caused by a chitinase that partially degrades the chitin septum in the process of cell separation. Consequently, it was proposed that in wild-type cells, Chs1 acts as a repair enzyme by replenishing chitin during cytokinesis. The chitinase requirement for lysis has been confirmed in two different ways: (a) demethylallosamidin, a more powerful chitinase inhibitor than the previously used allosamidin, is also a much better protector against lysis and (b) disruption of the chitinase gene in chs1 cells eliminates lysis. Reintroduction of a normal chitinase gene, by transformation of those cells with a suitable plasmid, restores lysis. The percentage of lysed cells in strains lacking Chs1 was not increased by elevating the chitinase level with high-copy-number plasmids carrying the hydrolase gene. Furthermore, the degree of lysis varied in different chs1 strains; lysis was abolished in chs1 mutants containing the scs1 suppressor. These results indicate that, in addition to chitinase, lysis requires other gene products that may become limiting.

Summary: Ten species of fungi were isolated from floating leaves cut from plants of Nymphaea alba in various initial stages of decay, which were collected from an acidic moorland pool. None of the fungal species isolated belonged to the aquatic Hyphomycetes sensu Ingold or the aero-aquatic fungi sensu Van Beverwijk. Growth experiments were conducted with five of the species on media containing glucose, polysaccharide or isolated cell walls of N. alba, each at three pH values. The fungi investigated were capable of growth on a variety of structural polysaccharides, indicating their potential importance in leaf degradation. Low pH inhibited growth on media containing glucose, pectin or cell wall fraction. Utilization of carboxymethylcellulose and crystalline cellulose did not differ much within the pH range studied. The fungi isolated were grown on N. alba leaf strips at three pH values to study the influence of pH on leaf maceration. All the fungi investigated could develop at low pH (4·0), but maceration was only observed at pH 5·5 or 7·5. It is likely that inhibition of pectin degradation is an important factor causing suppression of leaf fragmentation at low pH. This may contribute to the inhibition of the decomposition of macrophyte remains in acid aquatic systems.

Summary: The mechanism of unsaturated fatty acid biosynthesis in two estuarine strains of Flexibacter was investigated. Addition of cyclic AMP (cAMP) inhibited the incorporation of radiolabeled acetate into fatty acids of lateexponential phase cultures of strain Inp2. Cerulenin selectively inhibited the incorporation of radioactive acetate into the major fatty acid, 16:1. When Flexibacter strain Inp3 was grown in a medium of high osmotic strength, polyunsaturated fatty acids were present, but they were absent from cultures grown in media with an osmotic strength close to that of sea water. Addition of cAMP to cultures growing at high osmotic strength suppressed the formation of polyunsaturated fatty acids; the uncoupler 2,4-dinitrophenol had a similar effect. The findings are discussed in the context of the suggestion made by Intriago and Floodgate (Journal of General Microbiology 137, 1503–1509, 1991) that Flexibacter strains possess both the anaerobic and aerobic pathways for unsaturated fatty acid biosynthesis, the activity of the latter being modulated by the intracellular concentration of cAMP.

Summary: The marine luminous bacterium Vibrio fischeri, the species-specific light-organ symbiont of monocentrid (pinecone) fish, grew on 3′:5′-cyclic adenosine monophosphate (cAMP) as a sole source of carbon and energy, a capability not previously described in bacteria. In a minimal, chemically defined medium containing cAMP as the sole source of carbon and energy, V. fischeri cells grew more slowly than on glucose or ribose, but as quickly as on 5′-AMP. Expression of luminescence, which is dependent on cAMP in V. fischeri, was stimulated in cells grown on cAMP compared to cells grown on glucose or ribose. All strains of V. fischeri tested (MJ-1, B-61, ATCC 7744, MJ-A1, CG-A1) grew on cAMP, as did strains of two other marine luminous bacteria, V. logei and Photobacterium phosphoreum, and strains of the terrestrial enteric bacterium Serratia marcescens. Other tested species of marine luminous bacteria (P. leiognathi, Shewanella [Alteromonas] hanedai, V. harveyi, V. orientalis, V. splendidus) and terrestrial enteric bacteria (Escherichia coli, Salmonella typhimurium), which grew on 5′-AMP or ribose, did not grow on cAMP. Assays on intact cells and periplasmic extracts revealed that V. fischeri MJ-1 produced a periplasmic 3′:5′-cAMP phosphodiesterase (cAMP phosphodiesterase) of very high specific activity [9·0 μmol phosphate released (mg protein)−1 min−1] and narrow substrate specificity (3′:5′-cAMP and 3′:5′-cGMP were attacked). The novel periplasmic location and unusually high activity of cAMP phosphodiesterase appear to account for the ability of this species to grow on cAMP. The periplasmic cAMP phosphodiesterase of V. fischeri night play a role in degrading free cAMP in seawater or in a cAMP-mediated aspect of the light organ symbiosis with monocentrid fish.

Summary: The expression of Bacillus stearothermophilus genes complementing arginine auxotrophs of Escherichia coli was studied. The activity responsible for the formation of ornithine in B. stearothermophilus was identified as a repressible ornithine acetyltransferase (genetic symbol argJ) encoded by the same DNA fragment as the argC, orgA and argB genes. Bacillus subtilis and Bacillus licheniformis displayed the same pattern of enzyme activities as B. stearothermophilus. In contrast to previous reports, these organisms consequently use the cyclic pathway of ornithine biosynthesis. B. stearothermophilus also possesses a broad specificity aminoacylase which exhibits low affinity towards N 2-acetyl-l-ornithine.

Summary: Methyl mercaptan (MM)-oxidase was purified to near homogeneity from Thiobacillus thioparus TK-m grown on dimethyl sulphide. The enzyme was a monomer with an M r value of approximately 40000. It oxidized MM stoichiometrically to formaldehyde, S2- and H2O2. The enzyme had a K m of 31·3 μM for MM. It was also shown to oxidize ethyl mercaptan. MM-oxidase from T. thioparus was shown to have some different characteristics from MM-oxidase of Hyphomicrobium EG, such as a higher K m, the absence of inhibition by S2- and the inability to catalyse the oxidation of S2-.