Bacteria

About: Bacteria is a research topic. Over the lifetime, 23676 publications have been published within this topic receiving 715990 citations. The topic is also known as: eubacteria.

Intracellular Growth of Legionella pneumophila Gives Rise to a Differentiated Form Dissimilar to Stationary-Phase Forms

Abstract: The genus Legionella is one of the most successful of all aquatic bacteria, consisting of over 40 named species, their numerous serogroups (7), and a collection of Legionella-like amoebal pathogens that usually exhibit an obligate intracellular lifestyle requiring a particular protozoan host (3). An obligate requirement for the amino acid cysteine (38), which cannot be substituted for by cystine (the oxidized form most commonly found in aerobic environments), conceivably limits members of the Legionella genus to an intracellular lifestyle (25, 46) or to life in association with other microorganisms (46, 56, 63, 66) that may constitute a source of cysteine. However, in a biofilm coculture model, persistence but not multiplication of legionellae could be strictly demonstrated, suggesting that natural growth may indeed require the intracellular environment of a protozoan host (52). Thus, the natural life cycle of Legionella most likely alternates between periods of intracellular replication in protozoan hosts and planktonic survival, after death and lysis of spent hosts. In environments where suitable hosts are plentiful (e.g., cooling towers, hot tubs, and biofilms) the period between hosts would be shorter than that in environments of low host density, where planktonic survival for extended periods, even years, might be required. Several lines of evidence (reviewed in reference 2) suggest that Legionella pneumophila, the best-studied species of this genus and the one most commonly associated with Legionnaires' disease in humans, must have evolved an exit strategy from protozoan hosts that not only prepares the bacteria for planktonic survival but also ensures a favorable outcome in ensuing encounters with suitable hosts. In fact, early studies have shown that L. pneumophila is capable of surviving for up to 14 months in water with only a modest loss in viability in the first few months (46, 60, 61). Long-term survival may be associated with the formation of viable but nonculturable forms (55) that remain infectious for amoebae (62). With respect to ensuring a successful infection of new hosts, Cirillo et al. (20, 21) and others (29, 58) have demonstrated that intracellular growth enhances the ability of L. pneumophila to infect amoebae or mammalian cells. This increase in infectivity is accompanied by changes in (i) bacterial morphology, (ii) cell wall composition or structure, as indicated by Gimenez staining, and (iii) the route of entry into macrophages, all in relation to those for bacteria grown in vitro (20, 21, 29). Furthermore, studies in which mice were challenged with L. pneumophila, either alone or in various combinations with amoebae, also indicated that growth of L. pneumophila in amoebae always results in a more severe pneumonia (13, 14, 15), as well as increased replication in the lungs of mice (20). Collectively, these findings suggest that L. pneumophila has evolved a developmental program that enables the bacteria to shift from a replicative phase to one of maturation that produces a resilient, highly infectious form (39), perhaps analogous to the shift from reticulate bodies to elementary bodies (EBs) so well characterized in the developmental cycle of Chlamydia spp. (35, 50). In this respect, we have identified two well-defined, morphologically distinct forms of L. pneumophila in HeLa cells: (i) a replicative form (RF), found inside a specialized cell compartment known as the replicative endosome, and (ii) a cyst-like, mature intracellular form (MIF), observed late in infection of HeLa cells (26, 27, 29). RFs appear as slender rods and display a typical gram-negative cell envelope that is ultrastructurally similar to that of agar-grown bacteria. In contrast, MIFs appear as short, stubby rods containing cytoplasmic inclusions of poly-β-hydroxybutyrate (PHBA) and display a unique electron-dense layer associated with the outer membrane and/or multiple layers of intracytoplasmic membranes (29). We have recently shown that RFs and MIFs alternate in every intracellular growth cycle and have suggested that MIFs are the in vivo equivalent of stationary-phase (SP) bacteria grown in vitro (27). Interestingly, the entry of exponentially growing L. pneumophila into SP in vitro is accompanied by activation of the stringent response regulator RelA (33), which together with the SP sigma factor RpoS coordinates the activation of virulence traits (flagellum synthesis and increased osmotic resistance, cytotoxicity, and infectivity for macrophages) (18, 32, 33, 34). At issue, and the subject of this report, is whether MIFs are distinct from in vitro SP bacteria, which have been proposed to be the transmissible infectious forms associated with disease (34). We took advantage of our ability to purify MIFs (29) to directly compare them with SP forms obtained from broth cultures in vitro. Here we show that MIFs purified from HeLa cells exhibit a lower respiration rate, increased resistance to antibiotics and detergent-mediated lysis, and increased levels of surface-associated Hsp60 and display a unique pattern of proteins compared with SP bacteria. We conclude that the MIF is a unique form with cyst-like properties that enables L. pneumophila to persist as a highly infectious particle in the environment when between hosts.

Tetraponera ants have gut symbionts related to nitrogen–fixing root–nodule bacteria

Abstract: Some Tetraponera ants (Formicidae, Pseudomyrmecinae) subsist almost entirely on amino acid deficient honeydew secretions of pseudococcids and harbour a dense aggregation of bacterial symbionts in a unique pouch-shaped organ at the junction of the midgut and the intestine. The organ is surrounded by a network of intruding tracheae and Malpighian tubules, suggesting that these bacteria are involved in the oxidative recycling of nitrogen-rich metabolic waste. We have examined the ultrastructure of these bacteria and have amplified, cloned and sequenced ribosomal RNA-encoding genes, showing that the ant pouch contains a series of close relatives of Flavobacteria and Rhizobium, Methylobacterium, Burkholderia and Pseudomonas nitrogen-fixing root-nodule bacteria. We argue that pouch bacteria have been repeatedly 'domesticated' by the ants as nitrogen-recycling endosymbionts. This ant-associated community of mutualists is, to our knowledge, the first finding of symbionts related to root-nodule bacteria in animals.

Biological systems for manufacture of polyhydroxyalkanoate polymers containing 4-hydroxyacids

Abstract: The gene encoding a 4-hydroxybutyryl-Co A transferase has been isolated from bacteria and integrated into the genome of bacteria also expressing a polyhydroxyalkanoate synthase, to yield an improved production process for 4HB-containing polyhydroxyalkanoates using transgenic organisms, including both bacteria and plants. The new pathways provide means for producing 4HB containing PHAs from cheap carbon sources such as sugars and fatty acids, in high yields, which are stable. Useful strains are obtaining by screening strains having integrated into their genomes a gene encoding a 4HB-CoA transferase and/or PHA synthase, for polymer production. Processes for polymer production use recombinant systems that can utilize cheap substrates. Systems are provided which can utilize amino acid degradation pathways, α-ketoglutarate, or succinate as substrate.

Bacillaene, a novel inhibitor of procaryotic protein synthesis produced by Bacillus subtilis: production, taxonomy, isolation, physico-chemical characterization and biological activity.

Abstract: Bacillaene, a novel polyene antibiotic, was discovered and isolated from fermentation broths of a strain of Bacillus subtilis. The novel antibiotic has a nominal molecular weight of 580 and an empirical formula of C35H48O7. Bacillaene is active against a broad spectrum of bacteria in agar-plate diffusion assays. Studies in vitro indicate that the antibiotic inhibits prokaryotic protein synthesis but not eukaryotic protein synthesis. Cell survival studies performed with strains of Escherichia coli indicate that the antibiotic is a bacteriostatic agent.

Xylem-residing bacteria in alfalfa roots

Abstract: Bacteria were consistently isolated from the root and crown xylem of symptomless field-grown alfalfa plants. Most of the plants tested contained more than one bacterial genus. Pseudomonas spp. accounted for 52% of the 387 isolates identified and the fluorescent pseudomonads were the most frequent bacteria isolated. About 23% of the isolates were Erwinia-like bacteria. Bacterial population ranged from 6.0 × 103 to 4.3 × 104 CFU/g of fresh xylem, and was not affected by plant age or cultivar or by the sampling locations. The surface-sterilized seeds of the cultivars Iroquois and Titan were bacteria free and only 3 and 5% of the seeds of the cultivars Apica and Saranac, respectively, contained bacteria. In a greenhouse experiment, double antibotic resistant bacteria were inoculated into the soil of artificially wounded and intact roots of alfalfa plants, and on the stubble. The highest incidence of bacteria in the root xylem occurred when the roots were wounded. The highest numbers of bacteria (CFU/g fresh w...