Flexibacter

Abstract: Little is known about bacteria associated with Lepidoptera, the large group of mostly phytophagous insects comprising the moths and butterflies. We inventoried the larval midgut bacteria of a polyphagous foliivore, the gypsy moth (Lymantria dispar L.), whose gut is highly alkaline, by using traditional culturing and culture-independent methods. We also examined the effects of diet on microbial composition. Analysis of individual third-instar larvae revealed a high degree of similarity of microbial composition among insects fed on the same diet. DNA sequence analysis indicated that most of the PCR-amplified 16S rRNA genes belong to the γ-Proteobacteria and low G+C gram-positive divisions and that the cultured members represented more than half of the phylotypes identified. Less frequently detected taxa included members of the α-Proteobacterium, Actinobacterium, and Cytophaga/Flexibacter/Bacteroides divisions. The 16S rRNA gene sequences from 7 of the 15 cultured organisms and 8 of the 9 sequences identified by PCR amplification diverged from previously reported bacterial sequences. The microbial composition of midguts differed substantially among larvae feeding on a sterilized artificial diet, aspen, larch, white oak, or willow. 16S rRNA analysis of cultured isolates indicated that an Enterococcus species and culture-independent analysis indicated that an Entbacter sp. were both present in all larvae, regardless of the feeding substrate; the sequences of these two phylotypes varied less than 1% among individual insects. These results provide the first comprehensive description of the microbial diversity of a lepidopteran midgut and demonstrate that the plant species in the diet influences the composition of the gut bacterial community.

Abstract: The endophytic bacterial diversity in the roots of rice (Oryza sativa L.) growing in the agricultural experimental station in Hebei Province, China was analyzed by 16S rDNA cloning, amplified ribosomal DNA restriction analysis (ARDRA), and sequence homology comparison. To effectively exclude the interference of chloroplast DNA and mitochondrial DNA of rice, a pair of bacterial PCR primers (799f–1492r) was selected to specifically amplify bacterial 16S rDNA sequences directly from rice root tissues. Among 192 positive clones in the 16S rDNA library of endophytes, 52 OTUs (Operational Taxonomic Units) were identified based on the similarity of the ARDRA banding profiles. Sequence analysis revealed diverse phyla of bacteria in the 16S rDNA library, which consisted of alpha, beta, gamma, delta, and epsilon subclasses of the Proteobacteria, Cytophaga/Flexibacter/Bacteroides (CFB) phylum, low G+C gram-positive bacteria, Deinococcus-Thermus, Acidobacteria, and archaea. The dominant group was Betaproteobacteria (27.08% of the total clones), and the most dominant genus was Stenotrophomonas. More than 14.58% of the total clones showed high similarity to uncultured bacteria, suggesting that nonculturable bacteria were detected in rice endophytic bacterial community. To our knowledge, this is the first report that archaea has been identified as endophytes associated with rice by the culture-independent approach. The results suggest that the diversity of endophytic bacteria is abundant in rice roots.

Abstract: Eight unidentified fish pathogens and 10 strains received as “Flexibacter columnaris,” “Cytophaga psychrophila,” and Flexibacter maritimus were compared with the type strains of all previously described species in the genera Cytophaga and Flexibacter and with seven Flavobacterium species by determining levels of deoxyribonucleic acid (DNA) relatedness (S1 nuclease method) and by performing phenotypic tests. The name Flexibacter columnaris sp. nov. is revived for a DNA relatedness group comprising eight strains that are 75 to 100% related to strain TG 39/87 and 0 to 8% related to all of the other species studied. These strains produce flat rhizoid colonies which adhere to agar, show strong gliding movement, absorb Congo red, reduce nitrate to nitrite, and produce H2S. The guanine-plus-cytosine content of the DNA is 32 mol%. The type strain is strain NCMB 2248 (= ATCC 23463). The name Flexibacter psychrophilus sp. nov. is revived for a DNA relatedness group comprising seven strains that are 90 to 100% related to strain NCMB 1947T (T = type strain) and 0 to 5% related to all of the other species studied. These strains produce circular, convex colonies that have regular or spreading margins and do not adhere to agar, show very slow gliding movement, do not absorb Congo red, do not reduce nitrate, and do not produce H2S. The guanine-plus-cytosine content of the DNA is 33 mol%. The type strain is strain NCMB 1947. Both F. columnaris and F. psychrophilus produce the flexirubin type of pigments, are strongly proteolytic, and do not hydrolyze (or produce acid from) any carbohydrate. Flexibacter maritimus (three strains) was shown to constitute a DNA relatedness group that is 0 to 8% related to all of the other species tested. Furthermore, this organism can be differentiated by phenotypic tests. The presence of F. maritimus in Europe is shown for the first time.

Abstract: Psychrophilic, yellow-pigmented, seawater-requiring bacteria isolated from the pycnocline of meromictic Burton Lake and from sea ice cores obtained in the Vestfold Hills (68 degrees S, 78 degrees E) in eastern Antarctica were characterized. Phenotypic analysis showed that the strains isolated formed two distinct taxa. The first taxon included nonmotile, nutritionally fastidious strains that were isolated from the pycnocline of Burton Lake. The cells of these strains were morphologically variant, ranging from vibrioid to ring shaped to coiled and filamentous; in addition, the strains were unable to metabolise carbohydrates or polysaccharides and had DNA G + C contents of 27 to 29 mol%. The strains of the second taxon, which were isolated from sea ice cores and from ice aigal biomass, were saccharolytic, exhibited rapid gliding motility, were rodlike to filamentous, and had DNA G + C contents of 36 to 38 mol%. A 16S ribosomal DNA (rDNA) sequence analysis revealed that the two Antarctic taxa formed related but distinct lineages within the [Flexibacter] maritimus rRNA branch of the family Flavobacteriacrae. The levels of 16S rDNA sequence similarity between the taxa were 90.5 to 91.3%, while the levels of similarity to other members of the [F.] maritimus rRNA branch were 85 to 90%. The whole-cell lipid profiles of the Antarctic strains were mainly comprised of branched and unbranched monounsaturated C15 to C17 fatty acids. The presence of significant levels of the lipids a 15:1 omega 10c and a17:1 omega 7c appeared to be useful biomarkers for the new Antarctic taxa and for differentiating these organisms from other members of the family Flavobacteriaceae. On the basis of polyphasic taxonomic data we propose that the new taxa are novel bacterial species designated Psychroserpens burtonensis gen. nov., sp. nov. (type strain, ACAM 188) and Gelidibacter algens gen. nov., sp. nov. (type strain, ACAM 536).