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.

Community structure of ammonia-oxidizing bacteria within anoxic marine sediments.

Abstract: The potential for oxidation of ammonia in anoxic marine sediments exists through anaerobic oxidation by Nitrosomonas-like organisms, utilizing nitrogen dioxide, coupling of nitrification, manganese reduction, and anaerobic oxidation of ammonium by planctomycetes (the Anammox process). Here we describe the presence of microbial communities with the potential to carry out these processes in a natural marine sediment system (Loch Duich, Scotland). Natural microbial communities of Planctomycetales-Verrucomicrobia and beta- and gamma-proteobacterial ammonia-oxidizing bacteria were characterized by analysis of 16S rRNA genes amplified using group-specific primers by PCR- and reverse transcription-PCR amplification of 16S rDNA and RNA, respectively. Amplification products were analyzed by sequencing of clones and by denaturant gradient gel electrophoresis (DGGE). Amplification of primers specific for Planctomycetales-Verrucomicrobia and beta-proteobacterial ammonia-oxidizing bacteria generated products at all sampling sites and depths, but no product was generated using primers specific for gamma-proteobacterial ammonia-oxidizing bacteria. 16S rDNA DGGE banding patterns indicated complex communities of beta-proteobacterial ammonia-oxidizing bacteria in anoxic marine sediments. Phylogenetic analysis of sequences from clones and those excised from DGGE gels suggests dominance of Nitrosospira cluster 1-like organisms and of strains belonging to a novel cluster represented in dominant bands in 16S rRNA DGGE banding patterns. Their presence indicates a group of organisms closely related to recognized beta-proteobacterial ammonia-oxidizing bacteria that may be selected in anoxic environments and may be capable of anoxic ammonia oxidation. Sequence analysis of planctomycete clone libraries and sequences excised from DGGE gels also demonstrated a diverse microbial community and suggested the presence of new subdivisions, but no sequence related to recognized Anammox organisms was detected.

Pseudomonas aeruginosa invades corneal epithelial cells during experimental infection.

Abstract: Pseudomonas aeruginosa is considered an extracellular pathogen. Using assays to determine intracellular survival in the presence of gentamicin, we have demonstrated that some strains of P. aeruginosa are able to invade corneal cells during experimental bacterial keratitis in mice. Although intracellular bacteria were detectable 15 min after inoculation, the number of intracellular bacteria increased in a time-dependent manner over a 24-h period. Levels of invasion were similar when bacteria were grown as a biofilm on solid medium and when they were grown in suspension. Intracellular bacteria survived in vitro for at least 24 h, although only minimal bacterial multiplication within cells was observed. P. aeruginosa PAK and Escherichia coli HB101 did not cause disease in this model and were not isolated from corneas after 24 h even when an inoculum of 10(8) CFU was applied. Transmission electron microscopy of corneal epithelium from eyes infected for 8 h revealed that intracellular bacteria were present within membrane-bound vacuoles, which suggests that bacterial entry was an endocytic process. At 24 h, the observation of many bacteria free in the cytoplasm indicated that P. aeruginosa was able to escape the endocytic vacuole. The ability of some P. aeruginosa strains to invade corneal epithelial cells may contribute to the pathogenesis or to the progression of disease, since intracellular bacteria can evade host immune effectors and antibiotics commonly used to treat infection.

Formation of poly(3-hydroxyalkanoates) by phototrophic and chemolithotrophic bacteria

Abstract: The formation of poly(3-hydroxyalkanoic acid), PHA, by various strains of chemolithotrophic and phototrophic bacteria has been examined. Chemolithotrophic bacteria were grown aerobically under nitrogen-limiting conditions on various aliphatic organic acids. Phototrophic bacteria were grown anaerobically in the light on a nitrogen-rich medium and were subsequently transferred to a nitrogen-free medium containing acetate, propionate, valerate, heptanoate or octanoate as carbon source. All 41 strains investigated in this study were able to synthesize and accumulate PHA. All 11 strains of chemolithotrophic bacteria and all 15 strains belonging to the non-sulfur purple bacteria synthesized a polymer, which contained 3-hydroxy-valerate (3HV) beside 3-hydroxybutyrate (3HB), if the cells were cultivated in the presence of propionate, valerate or heptanoate. Many non-sulfur purple bacteria synthesized copolyesters of 3HB and 3HV even with acetate as carbon source. In contrast, most sulfur purple bacteria did not incorporate 3HV at all. Among 15 strains tested, only Chromatium vinosum strain 1611, C. purpuratum strain BN5500 and Lamprocystis roseopersicina strain 3112 were able to synthesize polyesters containing 3HV with propionate, valerate or heptanoate as carbon source.

Horizontal Genetic Exchange, Evolution, and Spread of Antibiotic Resistance in Bacteria

Abstract: Some transformable bacteria have acquired target-mediated antibiotic resistance by horizontal genetic exchange of fragments of chromosomal genes. The resistant strains express variants of the antibiotic target that are metabolically active but exhibit a lowered affinity for the antibiotic. The alleles encoding these resistant proteins are mosaics comprising DNA derived from the host and other bacteria, often members of a different species. Examples include penicillin-resistant penicillin-binding proteins (PBPs) in Streptococcus pneumoniae and the pathogenic Neisseria species and sulfonamide-resistant dihydropterate synthase in Neisseria meningitidis. Distinct mosaic alleles encoding antibiotic resistance have arisen on multiple occasions, indicating the mobility of chromosomal genes in these species. Mosaic genes can arise at any chromosomal locus, and S. pneumoniae organisms with high-level penicillin resistance have acquired mosaic PBP genes at three separate pbp loci. Furthermore, horizontal genetic exchange permits movement of alleles among bacterial lineages, increasing the opportunities for the spread of antibiotic resistance.