A total of 31 bacterial isolates that have potential Alexandrium cyst formation-promoting activity (Alex-CFPB) were isolated from Hiroshima Bay (Japan), which is characterized by seasonal blooms of the toxic dinoflagellate Alexandrium tamarense. The population structure of Alex-CFPB was analyzed by means of restriction fragment length polymorphism analysis of the 16S rRNA genes (16S rDNA). Fourteen ribotypes, A to N, were observed among the 31 isolates of Alex-CFPB by using four restriction enzymes, MboI, HhaI, RsaI and BstUI. Among them, seven isolates, which were obtained from the seawater samples taken during the peak and termination periods of the A. tamarense bloom in 1998, belonged to ribotype A. This result suggests that bacterial strains of ribotype A may be dominant in the Alex-CFPB assemblages during these periods. The partial 16S rDNA-based phylogenetic tree of 10 ribotypes studied showed that nine of them fell into the Rhodobacter group of the ␣ subclass of the Proteobacteria. Eight of nine ribotypes of the Rhodobacter group fell into the lineage of the Roseobacter subgroup, and one fell into the Rhodobacter subgroup. The non-Rhodobacter group type fell into the Marinobacterium-Neptunomonas-Pseudomonas group of the ␥-Proteobacteria. Isolates of Alex-CFPB ribotypes A and C do not have clear growth-promoting activities but have strong cyst formationpromoting activities (CFPAs) under our laboratory conditions. These results show that the Alex-CFPB assemblage may consist of various bacteria that belong mainly to the Roseobacter group and have strong CFPAs. These results suggest that not only the Alexandrium cyst formation-inhibiting bacteria (Alex-CFIB) reported previously but also Alex-CFPB, especially bacteria of ribotype A, may play significant roles in the process of encystment and bloom dynamics of Alexandrium in the natural environment.
ABSTRACT:The relationship between the abundance of the toxic marine dinoflagellate Alexandrium tamarense (Lebour) Balech and cyst formation-inhibiting bacteria (Alex-CFIB) was investigated in samples taken from the water column in Hiroshima Bay (Japan) in 1999. The cell density of A. tamarense peaked in the middle of April and blooms declined in May. Alex-CFIB were detected during the bloom period as well as the non-bloom period in 1999 by means of the most probable number (MPN) bioassay as well as the colony counting method. A total of 32 strains that had potential Alexandrium cyst formation-inhibiting activities (CFIB) were isolated from the seawater samples from Hiroshima Bay throughout the year. The population structure and genetic diversity of Alex-CFIB were analyzed by means of restriction fragment length polymorphism (RFLP) of the 16S ribosomal RNA genes (16S rDNA). Five ribotypes, Ia to Id and II types, were determined among the 32 strains of Alex-CFIB. Most of the strains belonged to ribotype I, suggesting that bacteria of ribotype I may be dominant in the Alex-CFIB assemblages in the field seawater. Almost the entire 16S rDNAbased phylogenetic tree showed that ribotypes I and II fell into the class Proteobacteria γ-subdivision Alteromonas group and theVibrio group, respectively. The 6-well microplate approach clarified that Alex-CFIB obtained in this study do not have growth-inhibiting activities, and Alex-CFIB of ribotype I (Alteromonas group) have strong activities of encystment inhibition among these ribotypes. The existence not only of Alexandrium cyst formation-promoting bacteria (Alex-CFPB) reported previously but also of Alex-CFIB in Hiroshima Bay throughout the year suggests that Alex-CFPB, as well as Alex-CFIB, especially bacteria of ribotype I, may play significant roles in the process of encystment and bloom dynamics of Alexandrium in the natural environment.KEY WORDS: Alexandrium · Dinoflagellate · Bacteria · Cyst Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 26: [223][224][225][226][227][228][229][230][231][232][233] 2001 It is important to elucidate the environmental factors that affect cyst formation in these toxic dinoflagellates in considering the production of cysts in their natural habitats. In laboratory cultures, sexuality of dinoflagellates has been reported to occur in response to stress following nitrogen and/or phosphorus depletion (Pfiester & Anderson 1987). There are, however, field reports of encystment under seemingly favorable nutrient conditions for growth. Anderson & Morel (1979), Anderson et al. (1983) and Perez et al. (1998) reported cyst formation for natural populations of Alexandrium tamarense in the presence of relatively high levels of nitrate and phosphate capable of supporting vegetative growth.Recently, we have focused on one of the possible biological factors, bacteria, that interact with toxic dinoflagellate Alexandrium. We clarified the existence of Alexandrium cyst formation-promoting bacteria (Alex-CFPB...
Jannaschia cystaugens sp. nov., an Alexandrium (Dinophyceae) cyst formation-promoting bacterium from Hiroshima Bay, Japan Heterotrophic bacteria isolated from water samples taken from Hiroshima Bay, Japan, and referred to as Alexandrium (Dinophyceae) cyst formation-promoting bacteria, were assigned to the Roseobacter-Sulfitobacter-Silicibacter group within the a-Proteobacteria on the basis of nearly complete 16S rRNA gene sequences. Phylogenetic analyses showed that two strains, CFPB-A9 T and CFPB-A5, are closely related to each other and that their closest relative was Jannaschia helgolandensis (95?9 % sequence similarity). These strains were Gram-negative, motile, obligately aerobic rods that required sodium ions and 2-7 % sea salts for growth and did not produce bacteriochlorophyll a. Their optimal growth temperature was 25-30 6C. The strains had Q-10 as the dominant respiratory quinone. Primary cellular fatty acid in both strains was 18 : 1v7c. The DNA G+C contents of strains CFPB-A9 T and CFPB-A5 were 59?1 and 59?2 mol%, respectively. Based on physiological, biological, chemotaxonomic and phylogenetic data, the strains are considered to represent a novel species, Jannaschia cystaugens sp. nov., with type strain CFPB-A9 T (=LMG 22015 T =NBRC 100362 T ).
Clostridium difficile (C. difficile)-associated diarrhea (CDAD) is a challenging nosocomial infectious disease. C. DIFF Quik Chek Complete assay is widely used to detect glutamate dehydrogenase (GDH) antigen and toxin A/B of C. difficile simultaneously. However, the interpretation of GDH positive/toxin negative results is problematic. We performed a retrospective study of patients with GDH positive/toxin negative results to determine the probability of detecting toxigenic C. difficile and its risk factors. Between April 2012 and March 2017, we investigated cultures of fecal specimens followed by toxin detection tests. The clinical histories of patients with and without toxigenic C. difficile were compared using univariate- and multivariate-analyses. In total, 2675 patients were examined using C. Diff Quik Chek Complete assay. Among 356 GDH positive/toxin negative patients, cultures were performed in 220 cases and toxigenic C. difficile was recovered from 139 (63.2%) specimens. Patients with toxigenic C. difficile had significantly lower body mass index than those without. Over half the GDH positive/toxin negative patients were infected with toxigenic C. difficile. Lower BMI was a CDAD risk factor in this patient population. These data can be utilized to initiate isolation and clinical interventions before confirmatory test results are available. J. Med. Invest. 65:131-135, February, 2018.
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