- Volume 135, Issue 3, 1989

The placenta is the primary site of infection of Chlamydia psittaci and is also intimately involved in the control of parturition. Changes in the pattern of placental hormone secretion were investigated in ewes infected with C. psittaci and in saline-injected controls. The concentration of progesterone in peripheral plasma of infected sheep was significantly lower than in control sheep (P < 0·01). A gradual decline in plasma progesterone occurred in Chlamydia-infected sheep, beginning on day 125 of gestation, in comparison with the sharper decline commencing on day 139 of gestation in the control population. The release of oestradiol 17β, which was greatest on the day of parturition in control sheep, was significantly (P < 0·02) increased on the day before parturition in Chlamydia-infected sheep. The concentrations of prostaglandin E2 in amniotic and allantoic fluids were low during late pregnancy in 12 control sheep, but were significantly raised (P < 0·05) in four out of 12 samples obtained from Chlamydia-infected sheep over the same period. The changes in progesterone and prostaglandin E2 were temporally related to the morphological and histochemical changes characteristic of trophoblast infection. These findings suggest that C. psittaci infection may precipitate premature labour by altering placental steroid and prostaglandin release.

Strains of Escherichia coli can be isolated that require erythromycin for growth. With one strain, AM, a range of antibiotics, including chloramphenicol, tetracycline, spectinomycin, kasugamy-cin and rifampicin, will substitute for erythromycin on solid and in liquid media; nalidixic acid supports growth in liquid but not on solid media. With a second strain, 103, chloramphenicol, tetracycline and spectinomycin support growth in liquid media but on solid medium only chloramphenicol substitutes for erythromycin. In media of higher than normal ionic strength, strain AM, but not strain 103, can grow in the absence of antibiotics. Possible reasons for these complex phenotypes are discussed.

The obligate aerobe yeast Rhodotorula gracilis was grown in batch culture on a chemically defined, pH-controlled medium containing glucose or d-alanine as carbon sources, ammonium or d-alanine as nitrogen sources, and d-alanine as a sole carbon and nitrogen source. Under these conditions, d-alanine induced the synthesis of d-amino-acid oxidase (EC 1.4.3.3) to an extent depending on the nutrients, the highest specific activity of the enzyme [up to 0·6 U (mg protein)−1] being detected when both d-alanine and glucose were present in the growth medium. In contrast, enzyme activity was negligible when both ammonium and glucose were present in the growth medium, even in the presence of d-alanine. The racemic mixture dl-alanine was also utilized as a source of both carbon and nitrogen for the growth of R. gracilis, but the enzyme activity appeared only after the depletion of l-alanine from the medium. Data on transmembrane transport of d-alanine in the presence of different nutrients clearly indicated that the l-isomer prevented induction by d-alanine through inhibition of the transport of the d-amino acid into cells. However, such an effect was not exerted by ammonium, indicating that this compound probably acts at the level of enzyme synthesis.

Ammonia assimilation in Rhizobium leguminosarum biovar viceae strain RCR1001 (hereafter called R. leguminosarum) appears to take place only through the glutamine synthetase/glutamate synthase pathway since (a) no glutamate dehydrogenase was detected in crude extracts of bacteria grown in different nitrogen sources, and (b) the growth rate on glutamine as a nitrogen source was faster than that observed on NH4Cl. In contrast to reports for other Rhizobium species, R. leguminosarum can definitely utilize NH4C1 for growth. R. leguminosarum contains two glutamine synthetase isoenzymes, GSI and GSII, which can be detected in the presence of each other by differential heat stability, or separated by affinity chromatography or immunoabsorption with an antiserum raised against pure GSI. GSII does not cross-react with an anti-GSI antiserum. GSI was shown to be reversibly adenylylated and it was also shown that adenylylation inhibits the biosynthetic activity of this enzyme, in a similar way to that reported for Escherichia coli glutamine synthetase and in contrast to that observed for glutamine synthetase of Rhizobium sp. strain ANU289. The apparent adenylylation level in different growth conditions changes from 21% to 99%, indicating a physiological role of this post-translational modification in the in vivo regulation of GSI activity. The intracellular concentration of GSI varies very little when R. leguminosarum is grown on different nitrogen sources (twofold when measured by the transferase assay, or fourfold when measured by ELISA). In addition, the concentration of mRNA specific for GSI in different nitrogen sources does not show appreciable differences. The intracellular concentration of GSII varies from a specific activity value higher than 1000 when R. leguminosarum is grown on glutamate or nitrate, to an undetectabie level when grown on NH4C1. When NH4C1 is added to a culture growing in glutamate, GSII activity is rapidly diluted out, suggesting a post-translational mechanism of enzyme inhibition or inactivation. Chloramphenicol prevents the disappearance of GSII activity, thus suggesting that protein synthesis is required for this process.

Incubation of pneumococci with d-alanine-containing peptides naturally occurrins in peptidoglycan protected cells against lysis and killing by β-lactam antibiotics near MIC. Such peptides caused decreased binding of the antibiotic to penicillin-binding proteins (PBPs), primarily PBP 2B. This provides direct evidence in vivo for the hypothesis that β-lactams act as substrate analogues and identifies PBP 2B as a killing target in pneumococci.

Uranyl actetate staining of thin sections allowed a distinction to be made between cell wall material that contains teichoic acid and that which contains teichuronic acid. The stain was used to study the pattern of wall assembly in Bacillus subtilis undergoing transitions between growth conditions leading to incorporation of the different anionic polymers. The results showed that new material is incorporated along the inner surface of the cylindrical region of the wall confirming, by a more direct method, results obtained earlier with teichoic acid specific phages. New material appears to be evenly distributed along the inner surface and no evidence was obtained for the presence of specific zones of incorporation.

The use of phage SP50 as marker for cell wall containing teichoic acid in Bacillus subtilis showed clear differences in the rates at which new wall material becomes exposed at polar and cylindrical regions of the wall, though the poles were not completely conserved. Following transition from phosphate limitation to conditions that permitted synthesis of teichoic acid, old polar caps fairly rapidly incorporated enough teichoic acid to permit phage binding. Electron microscopy suggested that the new receptor material spread towards the tip of the pole from cylindrical wall so that phages bound to an increasing proportion of the pole area until only the tip lacked receptor. Eventually, receptor was present over the whole polar surface. Direct electron microscopic staining of bacteria collected during transitions between magnesium and phosphorus limitations showed that new material was incorporated at the inner surface of polar wall and later became exposed at the outer surface by removal of overlying older wall. The apparent partial conservation of the pole reflected a slower degradation of the overlying outer wall at the pole than at the cylindrical surface, the rate being graded towards the tip of the pole. The relative proportions of the new wall material incorporated into polar and cylindrical regions differed in bacteria undergoing transitions that were accompanied by upshift or downshift in growth rate. These differences can be explained on the basis that growth rate affected the rate of synthesis of cylindrical but not septal wall.

Adsorption of bacteriophage SP50 to walls and heat-killed cells of Bacillus subtilis 168 appeared to be irreversible at both 37 and 0 °C. Few, if any, active phage were desorbed when phage-wall complexes, formed at either temperature, were suspended in fresh medium. Bacteria rich in wall teichoic acid (TA) bound phage rapidly at both 0 and 37 ¼C, binding at the higher temperature being approximately twice as fast. Bacteria containing diminished proportions of TA showed less rapid phage adsorption but the reduction in rate was greater at 37 than at 0 °C and bacteria containing only small proportions of TA bound phage more rapidly at 0 °C than they did at 37 °C. These findings show that at low phage receptor density the temperature affects some component(s) involved in the phage-bacterium interaction such that the collision efficiency is increased at the lower temperature. The possible effect of temperature on the organization of bacterial surface components is discussed.

The role of GTP and other ribonucleoside phosphates in the differentiation of Clostridium acetobutylicum and two sporulation-deficient mutants was investigated. The clostridial stage (cls-1) mutant was unable to produce the clostridial stage, solvents, granulose, capsules or endospores, whereas the sporulation-deficient (spo-1) mutant produced the clostridial stage, solvents, granulose and capsules, but did not form a forespore septum. The nucleoside triphosphate profiles of the wild-type and spo-1 mutant were similar and were characterized by a trough in nucleotide levels which occurred just prior to the pH break point, the onset of the stationary growth phase, clostridial stage formation and the transition from the acidogenic to the solventogenic phase. The nucleoside triphosphate concentrations during the exponential growth phase were much lower than those found during the stationary phase. The nucleotide levels in the cls-1 mutant during the exponential phase were comparable to those observed in the wild-type and spo-1 mutant. However, the nucleotide levels in the cls-1 mutant did not increase during the stationary growth phase. The involvement of nucleotide levels, particularly that of GTP, in the differentiation of C. acetobutylicum was indicated by the effect of inhibitors, which have been shown to decrease ribonucleotide levels in other organisms and cause an increase in sporulation.