Importance of host cell arginine uptake in Francisella phagosomal escape and ribosomal protein amounts.

Upon entry into mammalian host cells, the pathogenic bacterium Francisella must import host cell arginine to multiply actively in the host cytoplasm. We identified and functionally characterized an arginine transporter (hereafter designated ArgP) whose inactivation considerably delayed bacterial phagosomal escape and intracellular multiplication. Intramacrophagic growth of the ΔargP mutant was fully restored upon supplementation of the growth medium with excess arginine, in both F. tularensis subsp. novicida and F. tularensis subsp. holarctica LVS, demonstrating the importance of arginine acquisition in these two subspecies. High-resolution mass spectrometry revealed that arginine limitation reduced the amount of most of the ribosomal proteins in the ΔargP mutant. In response to stresses such as nutritional limitation, repression of ribosomal protein synthesis has been observed in all kingdoms of life. Arginine availability may thus contribute to the sensing of the intracellular stage of the pathogen and to trigger phagosomal egress. All MS data have been deposited in the ProteomeXchange database with identifier PXD001584 (http://proteomecentral.proteomexchange.org/dataset/PXD001584).

[Identification and characterization of the Francisella sp. strain 08HL01032 isolated in air condition systems].

OBJECTIVE: To identify and characterize the strain 08H101032 was isolated from air condition systems in the routine investigations of Legionella in Guangzhou, China, in 2008. METHODS: We adopted several phenotypic and genotypical methods, such as the growth status on various media, morphological, physical and biochemical characteristics, animal test, antibiotic susceptivities, PCR identification, sequence analysis of 16S RNA and RNA polymerase beta-subunit (ropB) gene etc, to determinate the phylogenetic position and outline the basic biological characteristics. RESULTS: Strain 08H101032 was Gram-negative with polymorphic short rods or coccobacillus; with no flagella; devoid of spores; well growth on buffered charcoal yeast extraction (BCYE) agar and BCYE supplemented with glycine (3 g/L), polymyxin B sulfate (80000 iu/L), vancomycin (1 mg/L) and cycloheximide (80 mg/L) (GVPC medium) within 2 days, but delayed growth on ordinary sheep blood agar untill 5 - 7 days; catalase positive; oxidase negative; no reduction of nitrate; no hydrolysis of urea; delayed fermention of glucose to produce acid; which was primarily considered as Legionella. It was lastly identified to the genus Fransicella, characterized by a variety of biochemical and molecular phylogenetic tests, which shared the highest similarities to F. Philomiragia with 95.3% to 16S rRNA gene of 1377 oligo nucleotides and 87.3% to ropB gene of 367 oligo nucleotides (GenBank accession number: FJ591095, FJ939309). Growth were observed after a treatment for 10 minutes with the KCl-HCl buffer of pH 2.2, 20 degrees C, and at 25 degrees C, 37 degrees C (optimum 25 degrees C - 28 degrees C), but not at 42 degrees C. The cells had capsule-like construction by transmission electron microscopy, however no virulence found to mice. CONCLUSIONS: Strain 08H101032 was a potential new species of the genus Fransicella with a typical characteristic of L-cysteine growth stimulating activity, distinguishingly to Legionella with L-cysteine growth dependent activity.