Bacterial DNA Synthesis Research Articles

Inhibiting Dihydrofolate Reductase as a Treatment for Tuberculosis

One‐third of the world's population is infected by Mycobacterium tuberculosis (M.tb). Two million people die each year from tuberculosis (TB), the disease caused by this bacterium. TB primarily affects the lungs and is easily transmitted. One way to kill M. tb might be to inhibit the enzyme dihydrofolate reductase (DHFR). DHFR catalyzes the production of tetrahydrofolate by transferring a hydrogen ion (H−) from NADPH to dihydrofolate, thereby releasing tetrahydrofolate and NADP+. Tetrahydrofolate is essential to the bacteria's survival, and is a cofactor that is needed for the synthesis of the DNA base thymine. Isoniazid is one antibiotic already used to treat TB by targeting several TB proteins that are necessary for building M. tb cell walls and inhibiting DHFR. Unfortunately, strains of M. tb are evolving resistance to isoniazid, so next generation antibiotics are needed. A variation of isoniazid could be designed to avoid resistance, and to inhibit DHFR, thereby targeting bacterial DNA synthesis. The Valders SMART Team (Students Modeling A Research Topic), using 3D printing technology, created a physical model of DHFR and a possible inhibitor of tetrahydrofolate production. Supported by a grant from NIH‐NCRR‐SEPA.

Antibacterial Peptides - A Bright Future or a False Hope

The increasing number of antibiotic resistant bacterial strains presents an emerging world health problem that demands continued effort to develop new antibacterial compounds. Endogenous antibacterial peptides (ABPs) that are constitutively and/or inducibly produced in tissues exposed to external surroundings represent new candidates for devel- opment of such compounds. Most ABPs target bacterial membranes initially by electrostatic interactions between posi- tively charged amino acids and negatively charged molecules present on bacterial walls, followed by compromise of the permeability barrier of bacterial membranes through the formation of pores, leading to rapid cell death and efficient bacte- rial elimination. Other mechanisms, such as the inhibition of bacterial protein and DNA synthesis or receptor-mediated stimulation of host defense mechanisms are also ascribed to these molecules. The activities of ABPs correlate positively with a gradient of hydrophobicity along the peptide backbone, net positive charge at neutral pH, and secondary structure. More than 850 sequences with antibacterial activity have been described, and this number continues to grow with the ad- dition of newly discovered, as well as synthetic, peptides. Many strategies, including increasing net positive charge, in- creasing net hydrophobicity, conjugation of peptides with lipophilic acids, incorporation of carbonate bonds, and synthesis of their hybrids and truncated sequences that omit hemolytic regions, have been proposed to increase efficiency of syn- thetic ABPs. Additionally peptide-mimicking molecules such as cationic steroid antibiotics (CSAs) may be useful alterna- tives to natural ABPs. Current challenges for practical application of ABPs are the high cost of synthesis/isolation, inacti- vation by blood plasma, confinement by anionic polyelectrolytes, and possible unknown toxicity.

Aminoacyl-tRNA synthetases: essential and still promising targets for new anti-infective agents

The emergence of resistance to existing antibiotics demands the development of novel antimicrobial agents directed against novel targets. Historically, bacterial cell wall synthesis, protein, and DNA and RNA synthesis have been major targets of very successful classes of antibiotics such as β-lactams, glycopeptides, macrolides, aminoglycosides, tetracyclines, rifampicins and quinolones. Recently, efforts have been made to develop novel agents against validated targets in these pathways but also against new, previously unexploited targets. The era of genomics has provided insights into novel targets in microbial pathogens. Among the less exploited – but still promising – targets is the family of 20 aminoacyl-tRNA synthetases (aaRSs), which are essential for protein synthesis. These targets have been validated in nature as aaRS inhibition has been shown as the specific mode of action for many natural antimicrobial agents synthesized by bacteria and fungi. Therefore, aaRSs have the potential to be targeted by novel agents either from synthetic or natural sources to yield specific and selective anti-infectives. Numerous high-throughput screening programs aimed at identifying aaRS inhibitors have been performed over the last 20 years. A large number of promising lead compounds have been identified but only a few agents have moved forward into clinical development. This review provides an update on the present strategies to develop novel aaRS inhibitors as anti-infective drugs.

Antibacterial Activity and Mechanism of Action of a Novel Anilinouracil-Fluoroquinolone Hybrid Compound

The anilinouracils (AUs) such as 6-(3-ethyl-4-methylanilino)uracil (EMAU) are a novel class of gram-positive, selective, bactericidal antibacterials which inhibit pol IIIC, the gram-positive-specific replicative DNA polymerase. We have linked various fluoroquinolones (FQs) to the N-3 position of EMAU to generate a variety of AU-FQ "hybrids" offering the potential for targeting two distinct steps in DNA replication. In this study, the properties of a hybrid, "251D," were compared with those of representative AUs and FQs in a variety of in vitro assays, including pol IIIC and topoisomerase/gyrase enzyme assays, antibacterial, bactericidal, and mammalian cytotoxicity assays. Compound 251D potently inhibited pol IIIC and topoisomerase/gyrase, displayed gram-positive antibacterial potency at least 15 times that of the corresponding AU compound, and as expected, acted selectively on bacterial DNA synthesis. Compound 251D was active against a broad panel of antibiotic-resistant gram-positive pathogens as well as several gram-negative organisms and was also active against both AU- and FQ-resistant gram-positive organisms, demonstrating its capacity for attacking both of its potential targets in the bacterium. 251D also was bactericidal for gram-positive organisms and lacked toxicity in vitro. Although we obtained strains of Staphylococcus aureus resistant to the individual parent compounds, spontaneous resistance to 251D was not observed. We obtained 251D resistance in multiple-passage experiments, but resistance developed at a pace comparable to those for the parent compounds. This class of AU-FQ hybrids provides a promising new pharmacophore with an unusual dual mechanism of action and potent activity against antibiotic-sensitive and -resistant gram-positive pathogens.

Changing bacterioplankton growth characteristics on a large spatial scale: oligotrophic versus mesotrophic ocean

This study deals with large spatial scale differences in the ratios between bacterial leucine incorporation (TLi: protein synthesis) and thymidine incorporation (TTi: DNA synthesis) in oligotrophic offshore and comparatively more mesotrophic inshore (sub)tropical regions of the Atlantic Ocean. Observations were derived from 2 RV ‘Polarstern’ cruises, one of which traversed a meridional mid-ocean transect while the other followed the African coast line. Average values (from 42°N to 35°S) of TLi, TTi and chlorophyll a (chl a) concentration were 40.3 pmol leucine l–1 h–1, 1.32 pmol thymidine l–1 h–1 and 0.18 µg chl a l–1 along the offshore transect, compared to 51.8 pmol leucine l–1 h–1, 2.72 pmol thymidine l–1 h–1 and 0.29 µg chl a l–1 along the inshore transect. Mean values of the TLi:TTi ratio (which defines bacterial growth characteristics) were 32.4 in offshore waters and 20.5 in inshore waters. Offshore ratios of TLi:chl a or TTi:chl a (proxy for bacterial substrate) were 274.1 and 8.5, compared to inshore ratios of 198.7 and 10.0, respectively. This means that, per unit of chl a, considerably higher bacterial protein synthesis was supported in water farther from the coast than near the coast, whereas bacterial DNA synthesis per unit chl a was slightly higher in the latter. Because temperature variability along the cruise tracts was rather similar (except in the Benguela upwelling region), we assume that substrate supply was mainly responsible for the observed significant differences in bacterial growth characteristics. In addition, the potential different contributions of picocyanobacteria to leucine uptake (TLi) must be considered. We conclude that the different TLi:TTi ratios in (sub)tropical offshore and inshore waters reflect reactions of the relevant bacterial communities to prevailing environmental conditions. Therefore, we did not interpret our results in the context of the currently used terms ‘balanced’ or ‘unbalanced’ growth. Bacterial community growth may be balanced in both regions of study, but at different levels of the TLi:TTi ratio.

Haemophilus parasuis invades porcine brain microvascular endothelial cells

Haemophilus parasuis, an important swine pathogen, is the aetiological agent of Glässer's disease. It is responsible for cases of polyserositis, meningitis and pneumonia in young pigs. To date, 15 serotypes have been described, although several non-typable isolates are frequently recovered from diseased animals. The pathogenesis of H. parasuis infection is poorly understood. To cause meningitis, H. parasuis would have to cross the blood-brain barrier (BBB), composed of brain microvascular endothelial cells (BMEC). The objective of this study was to investigate the ability of H. parasuis to interact with porcine brain microvascular endothelial cells (PBMEC). It was demonstrated that the serotype 5 reference strain of H. parasuis, Nagasaki (originally recovered from a case of meningitis), was able to adhere at very high levels to and, most importantly, invade PBMEC. These capacities were confirmed by electron microscopy. Actinobacillus pleuropnemoniae serotype 7 (strain WF 83), used as negative control, was not able to adhere to or invade PBMEC. Comparisons of the levels of adhesion and invasion by several H. parasuis field strains from different serotypes isolated from cases of either meningitis or pneumonia showed that isolates of serotypes 4 and 5 had a higher invasion capacity than isolates belonging to other serotypes. Inhibition studies demonstrated that PBMEC invasion by H. parasuis required rearrangement of actin microfilaments and microtubular cytoskeletal elements but not active bacterial DNA, RNA or protein synthesis. Characterization studies demonstrated that proteinaceous invasin(s) does not seem to play a major role in entry of H. parasuis into PBMEC. Intracellular viable H. parasuis were found in PBMEC up to 6 h after antibiotic treatment. Even at high bacterial doses, H. parasuis was not toxic to PBMEC. In swine, the invasion of endothelial cells of the BBB may play an important role in the pathogenesis of meningitis caused by H. parasuis.

In Vitro and In Vivo Potency of Moxifloxacin and Moxifloxacin Ophthalmic Solution 0.5%, A New Topical Fluoroquinolone

Fluoroquinolones are a class of synthetic antibacterial agents that were approved for ocular therapy in 1991 and have become popular therapy for the treatment and prevention of various ocular infections. These agents are synthetic, broad-spectrum, rapidly bactericidal, and have good penetration into ocular tissues. Their main mechanism of action is the inhibition of bacterial enzymes needed for bacterial DNA synthesis. However, antibiotic resistance occurred swiftly to the earlier fluoroquinolones and better fluoroquinolones were needed. The fourth-generation fluoroquinolones, such as moxifloxacin and gatifloxacin, have enhanced activity against gram-positive bacteria while retaining potent activity against most gram-negative bacteria. These fourth-generation fluoroquinolones have improved penetration into the anterior chamber and have also demonstrated increased in vivo efficacy in several animal models of ocular infections. In addition, topical ophthalmic antibiotic products can deliver antibiotic concentrations directly to the eye that are thousands of times higher than their MICs. This article reviews published data describing the in vitro potency of moxifloxacin and its in vivo activity for treating and preventing experimental ocular infections.

Discovery of Bicyclic Thymidine Analogues as Selective and High-Affinity Inhibitors of Mycobacterium tuberculosis Thymidine Monophosphate Kinase

Thymidine monophosphate kinase of Mycobacterium tuberculosis (TMPKmt) represents an attractive target for selectively blocking bacterial DNA synthesis. Hereby, we report on the discovery of a novel class of bicyclic nucleosides (10 and 11) and one dinucleoside (12), belonging to the most selective inhibitors of TMPKmt discovered so far.

Antimicrobial drug discovery through bacteriophage genomics.

Over evolutionary time bacteriophages have developed unique proteins that arrest critical cellular processes to commit bacterial host metabolism to phage reproduction. Here, we apply this concept of phage-mediated bacterial growth inhibition to antibiotic discovery. We sequenced 26 Staphylococcus aureus phages and identified 31 novel polypeptide families that inhibited growth upon expression in S. aureus. The cellular targets for some of these polypeptides were identified and several were shown to be essential components of the host DNA replication and transcription machineries. The interaction between a prototypic pair, ORF104 of phage 77 and DnaI, the putative helicase loader of S. aureus, was then used to screen for small molecule inhibitors. Several compounds were subsequently found to inhibit both bacterial growth and DNA synthesis. Our results suggest that mimicking the growth-inhibitory effect of phage polypeptides by a chemical compound, coupled with the plethora of phages on earth, will yield new antibiotics to combat infectious diseases.

Bacterial numbers and growth in surficial deep-sea sediments and phytodetritus in the NE Atlantic: Relationships with particulate organic carbon and total nitrogen

Bacteria in deep-sea sediments constitute the largest global fraction of total benthic bacteria, and play a major role in most biogeochemical cycles. However, as yet the relationship between bacterial production and substrate availability (particulate organic carbon and nitrogen) in deep-sea sediments is not well understood. Therefore the aim of this study was to explore the relationships between bacterial numbers and DNA synthesis (a measure of bacterial growth) and the concentration of bulk POC and total nitrogen in surficial deep-sea sediments and recently deposited phytodetritus, at three sites in the NE Atlantic. We found statistically significant positive exponential relationships between bacterial numbers and [ 3H]-thymidine incorporation rates (DNA synthesis) and sediment and phytodetritus % particulate organic carbon (POC) and % total nitrogen (%TN) from samples collected in the deep NE Atlantic at three different times at 3 contrasting sites. Mean bacterial numbers were in the range 5.6–53.2×10 10 cell l −1 in surficial sediments and 9.2–12.9×10 10 cells l −1 in the phytodetritus; [ 3H]-thymidine incorporation rates were 14.8–593.7 pmol l −1 h −1 in the sediment and 395.8–491.4 pmol l −1 h −1 in the phytodetritus. POC concentrations were 0.22–0.61% in the sediment and 0.92–0.99% in the phytodetritus; TN was 0.04–0.09% in the sediment and 0.13–0.14% in the phytodetritus. The C:N ratio was 6.7–9.0 in sediment and 7.6–7.9 in phytodetritus. In addition, a positive exponential relationship was still evident with the inclusion of other data from the NE Atlantic and Solomon and Coral Sea. The logarithmic regression for this combined relationship was not statistically different from the one derived from the current data alone. However, the relationship failed with the inclusion of data from the highly eutrophic Arabian Sea, which has a mid-water oxygen minimum zone that may inhibit heterotrophic bacterial production. This implies that such a relationship is not generic to all ocean systems, and additional research is required to further test the relationship between bacterial [ 3H]-thymidine incorporation rates and % POC from other oceanic deep-sea surficial sediments.

Bacterial activity in South Pole snow.

Large populations (200 to 5,000 cells ml(-1) in snowmelt) of bacteria were present in surface snow and firn from the south pole sampled in January 1999 and 2000. DNA isolated from this snow yielded ribosomal DNA sequences similar to those of several psychrophilic bacteria and a bacterium which aligns closely with members of the genus Deinococcus, an ionizing-radiation- and desiccation-resistant genus. We also obtained evidence of low rates of bacterial DNA and protein synthesis which indicates that the organisms were metabolizing at ambient subzero temperatures (-12 to -17 degrees C).

Effects of antibiotics on the early infection process of a macronuclear endosymbiotic bacterium Holospora obtusa of Paramecium caudatum

We examined the effects of antibiotics involved in bacterial DNA, RNA and protein synthesis and host protein synthesis on the early infection process of the bacterium Holospora obtusa, a macronucleus-specific symbiont of the ciliate Paramecium caudatum. Infection of the host macronucleus by the bacterium was not inhibited by mitomycin C, rifampicin and chloramphenicol. However, ingestion of the bacterium into the host digestive vacuoles and escape of the bacterium from the vacuoles to the host cytoplasm were significantly arrested with emetine. The results suggest that newly synthesized host proteins play an important role in the early infection process.

Effects of antibiotics on the early infection process of a macronuclear endosymbiotic bacterium Holospora obtusa of Paramecium caudatum.

We examined the effects of antibiotics involved in bacterial DNA, RNA and protein synthesis and host protein synthesis on the early infection process of the bacterium Holospora obtusa, a macronucleus-specific symbiont of the ciliate Paramecium caudatum. Infection of the host macronucleus by the bacterium was not inhibited by mitomycin C, rifampicin and chloramphenicol. However, ingestion of the bacterium into the host digestive vacuoles and escape of the bacterium from the vacuoles to the host cytoplasm were significantly arrested with emetine. The results suggest that newly synthesized host proteins play an important role in the early infection process.

Invasion of brain microvascular endothelial cells by group B streptococci.

Group B streptococci (GBS) are the leading cause of meningitis in newborns. Although meningitis develops following bacteremia, the precise mechanism or mechanisms whereby GBS leave the bloodstream and gain access to the central nervous system (CNS) are not known. We hypothesized that GBS produce meningitis because of a unique capacity to invade human brain microvascular endothelial cells (BMEC), the single-cell layer which constitutes the blood-brain barrier. In order to test this hypothesis, we developed an in vitro model with BMEC isolated from a human, immortalized by simian virus 40 transformation, and propagated in tissue culture monolayers. GBS invasion of BMEC monolayers was demonstrated by electron microscopy. Intracellular GBS were found within membrane-bound vacuoles, suggesting the organism induced its own endocytic uptake. GBS invasion of BMEC was quantified with a gentamicin protection assay. Serotype III strains, which account for the majority of CNS isolates, invaded BMEC more efficiently than strains from other common GBS serotypes. GBS survived within BMEC for up to 20 h without significant intracellular replication. GBS invasion of BMEC required active bacterial DNA, RNA, and protein synthesis, as well as microfilament and microtubule elements of the eukaryotic cytoskeleton. The polysaccharide capsule of GBS attenuated the invasive ability of the organism. At high bacterial densities, GBS invasion of BMEC was accompanied by evidence of cellular injury; this cytotoxicity was correlated to beta-hemolysin production by the bacterium. Finally, GBS demonstrated transcytosis across intact, polar BMEC monolayers grown on Transwell membranes. GBS invasion of BMEC may be a primary step in the pathogenesis of meningitis, allowing bacteria access to the CNS by transcytosis or by injury and disruption of the endothelial blood-brain barrier.

Levofloxacin and trovafloxacin: the next generation of fluoroquinolones?

The pharmacology, spectrum of activity, pharmacokinetics, clinical efficacy, and adverse effects of levofloxacin, recently approved by FDA, and trovafloxacin, currently undergoing clinical trials, are reviewed. Compared with quinolones in current use, levofloxacin is more potent against gram-negative bacteria and exhibits better antipseudomonal activity as well as greater oral bioavailability. Trovafloxacin is more potent than existing quinolones against gram-positive bacteria. Both agents exert their antibacterial effects by inhibiting bacterial DNA synthesis. Compared with other quinolones, levofloxacin and trovafloxacin both demonstrate superior activity against the Bacteroides fragilis group, Chlamydia spp., Mycoplasma pneumoniae, and Mycobacterium spp. The half-life (t1/2) of levofloxacin is nearly eight hours. Levofloxacin can therefore be administered once daily for mild to moderate infections and twice daily for more serious infections. The recommended daily dose is 500 mg. Trovafloxacin has a t1/2 of 12 hours, which allows for single daily doses, and is extensively metabolized. Levofloxacin has demonstrated clinical efficacy in the treatment of community-acquired respiratory-tract infections, genitourinary infections, skin and skin-structure infections, acute bacterial sinusitis, and infections of the head and neck. Trovafloxacin may have a role in treating skin and skin-structure or soft-tissue infections respiratory-tract infections, sexually transmitted diseases, and meningitis. Both agents are well tolerated, with central-nervous-system and gastrointestinal adverse effects reported most frequently. Concomitant administration of antacids or compounds containing meal cations decreases absorption of these quinolones. Levofloxacin and trovafloxacin have favorable antimicrobial and pharmacokinetic profiles, offering the advantages of once-daily doses as well as superior potency and spectrum of activity compared with currently available quinolones.

INVASION OF BRAIN MICROVASCULAR ENDOTHELIAL CELLS BY GROUP B STREPTOCOCCI• 1332

Group B streptococci (GBS) are the leading cause of meningitis in newborns. Although meningitis develops following bacteremia, the precise mechanism or mechanisms whereby GBS leave the bloodstream and gain access to the central nervous system (CNS) are not known. We hypothesized that GBS produce meningitis because of a unique capacity to invade human brain microvascular endothelial cells (BMEC), the single-cell layer which constitutes the blood-brain barrier. In order to test this hypothesis, we developed an in vitro model with BMEC isolated from a human, immortalized by simian virus 40 transformation, and propagated in tissue culture monolayers. GBS invasion of BMEC monolayers was demonstrated by electron microscopy. Intracellular GBS were found within membrane-bound vacuoles, suggesting the organism induced its own endocytic uptake. GBS invasion of BMEC was quantified with a gentamicin protection assay. Serotype III strains, which account for the majority of CNS isolates, invaded BMEC more efficiently than strains from other common GBS serotypes. GBS survived within BMEC for up to 20 h without significant intracellular replication. GBS invasion of BMEC required active bacterial DNA, RNA, and protein synthesis, as well as microfilament and microtubule elements of the eukaryotic cytoskeleton. The polysaccharide capsule of GBS attenuated the invasive ability of the organism. At high bacterial densities, GBS invasion of BMEC was accompanied by evidence of cellular injury; this cytotoxicity was correlated to beta-hemolysin production by the bacterium. Finally, GBS demonstrated transcytosis across intact, polar BMEC monolayers grown on Transwell membranes. GBS invasion of BMEC may be a primary step in the pathogenesis of meningitis, allowing bacteria access to the CNS by transcytosis or by injury and disruption of the endothelial blood-brain barrier.

Uptake of Streptococcus pneumoniae by respiratory epithelial cells.

Although Streptococcus pneumoniae is the leading cause of community-acquired pneumonia in humans, the mechanism whereby the organism penetrates lung tissue is poorly understood. In the present study we have examined the capacity of pneumococci to penetrate A549 cells, a human lung alveolar carcinoma (type II pneumocyte) cell line. Not all clinical S. pneumoniae isolates initially tested were capable of penetration of the cells, as judged by resistance to extracellular antibiotics. The presence of a polysaccharide capsule also significantly reduced the capacity to both adhere to and penetrate A549 cells. Electron micrographs showed the presence of pneumococci enclosed within vacuoles of intact A549 cells, but bacteria were also seen free in the cytoplasm of damaged cells. Ongoing bacterial DNA, RNA, or protein synthesis was not essential for uptake of pneumococci by A549 cells, and uptake was not diminished by pretreatment of the pneumococci with trypsin. However, inhibition of A549 microfilament assembly with cytochalasin D abolished the phenomenon.

Different patterns of bacterial DNA synthesis during postantibiotic effect

Studies on bacterial metabolism during the postantibiotic effect (PAE) period are limited but might provide insight into the nature of the PAE. We evaluated the rate of DNA synthesis in bacteria during the PAE period after a 1-h exposure of organisms in the logarithmic growth phase to various antibiotics. Staphylococcus aureus ATCC 25923 was exposed to vancomycin, dicloxacillin, rifampin, and ciprofloxacin; Escherichia coli ATCC 25922 was exposed to gentamicin, tobramycin, rifampin, imipenem, and ciprofloxacin; and Pseudomonas aeruginosa ATCC 25783 was exposed to imipenem, tobramycin, and ciprofloxacin. DNA synthesis was determined by measuring the rate of [3H]thymidine incorporation in S. aureus and E. coli and [3H]adenine incorporation in P. aeruginosa. DNA synthesis in S. aureus was suppressed during the PAE phase with vancomycin, dicloxacillin, and rifampin, it was suppressed in E. coli with rifampin, and it was suppressed in P. aeruginosa after exposure to tobramycin. Conversely, DNA synthesis was relatively enhanced in the gram-negative bacilli after exposure to imipenem and in all three species after exposure to ciprofloxacin. However, DNA synthesis in E. coli was only minimally affected after exposure to tobramycin and gentamicin. The differences in DNA synthesis observed after exposure to various antimicrobial agents suggest multiple mechanisms for the PAE.

Effects of a water-soluble ethylhydroxyethyl cellulose on gut physiology, bacteriology, and bacterial translocation in acute liver failure.

Bacterial infection and bacteremia are common complications in patients with acute liver failure. Bacterial translocation from the gut has been suggested to be a major cause of bacterial infections in experimental acute liver failure. In the present study, a water-soluble ethylhydroxyethyl cellulose (EHEC) was administered orally 1 and 24 hours prior to 90% hepatectomy in the rat in order to prevent bacterial translocation in experimental acute liver failure induced by subtotal liver resection in the rat. Ninety percent hepatectomy alone resulted in 80 to 100% translocation to mesenteric lymph nodes or blood 2 and 4 hours after operation. There was no translocation in rats undergoing sham operation or 90% hepatectomy with EHEC administration prior to operation (p < .01). Bacterial overgrowth, increased bacterial adherence onto the intestinal surface, and diminished intestinal and mucosal mass were also observed in animals with subtotal liver resection, but not in those administered EHEC. A delayed 2-hour intestinal transit time occurred in both groups receiving subtotal liver resection, with or without oral EHEC. EHEC inhibited bacterial growth and DNA synthesis and altered bacterial surface properties after 1-hour incubation with bacteria in vitro, an interaction that was not further influenced by time. These results imply that EHEC may alter enterobacterial capacities of metabolism, proliferation, and invasion by effects on the bacterial surface. Furthermore, EHEC seems to possess a trophic action on the intestine, though without enhancing the intestinal motility.

Organic carbon transport from the Southern Ocean and bacterial growth in the Antarctic intermediate Water masses of the Tasman Sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 119:291-297 (1995) - doi:10.3354/meps119291 Organic carbon transport from the Southern Ocean and bacterial growth in the Antarctic intermediate Water masses of the Tasman Sea Moriarty, D. J. W., O'Donohue, M. J. The concept that organic carbon is transported to the equatorial region at intermediate water depths from subantarctic frontal zones has been re-investigated using the tritiated thymidine method to determine rates of bacterial DNA synthesis in water masses of the Tasman Sea. There was a higher bacterial growth rate and thus a higher flux of organic carbon through bacteria in the Antarctic Intermediate Water (900 to 1000 m depth) than in the water masses immediately above or below in the Tasman Sea east and south of Tasmania. Values for bacterial production were 4 to 8 ug C m-3 d-1, which are equivalent to a consumption of about 3 to 6 ul O2 l-1 yr-1. In the deeper layer at 1200 to 1500 m, rates were 3 to 4 times lower. These rates are compatible with other data on oxygen utilisation. Our results support the concept that organic matter sinks with downwelling water in the zone between the Subtropical Convergence and the Polar Front in the Southern Ocean and is advected towards the equator below the photic zone. Oceanic carbon cycling . Southern Ocean . Pacific Ocean . Bacteria Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 119. Publication date: March 23, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.