Casamino acids slow motility and stimulate surface growth in an extreme oligotroph

Environmental cues that regulate motility are poorly understood, but specific carbon and nitrogen sources, such as casamino acids (CAA), are known to stimulate motility in model organisms. However, natural environments are commonly more nutrient-limited than laboratory growth media, and the effect of energy-rich CAA on the motility of oligotrophic microorganisms is unknown. In this study, an extreme oligocarbotroph, Variovorax paradoxus YC1, was isolated from weathered shale rock within a disused mine level in North Yorkshire, UK. The addition of 0.1% CAA to minimal media significantly reduced the motility of YC1 after 72 h and inhibited swimming motility resulting in enhanced surface growth. We propose this response to CAA is a physiological adaptation to oligotrophy, facilitating the colonization of nutrient-rich environments.

Association Between Loss of Type IV Pilus Synthesis Ability and Phenotypic Variation in the Cucurbit Pathogenic Bacterium Acidovorax citrulli

Acidovorax citrulli is the causal agent of bacterial fruit blotch of cucurbits. We have shown that functional type IV pili (T4P) are required for full virulence of this bacterium. To identify A. citrulli genes required for T4P activity, we screened a library of about 10,000 transposon mutants of A. citrulli M6 for altered T4P-mediated twitching motility. This screen led to the identification of 50 mutants impaired in twitching ability due to transposon insertions into 20 different genes. Representative mutants with disruptions in these genes were further characterized. All mutants were compromised in their virulence in seed transmission and stem inoculation assays and had reduced biofilm formation ability relative to wild-type M6. When grown on nutrient agar, most mutants produced colonies with a translucent and fuzzy appearance, in contrast to the opaque and smooth appearance of wild-type colonies. The colony morphology of these mutants was identical to that of previously reported phenotypic variants of strain M6. The exceptions were M6 mutants disrupted in genes tonB, pilT, pilW, and pilX that exhibited typical wild-type colony morphology, although lacking twitching haloes surrounding the colony. Transmission electron microscopy revealed that most mutants lacked the ability to produce T4P. The exceptions were mutants with disruptions in tonB, pilT, pilW, and pilX genes that were shown to produce these appendages. These findings support the idea that colony phenotypic variation in A. citrulli is determined by the lack of ability to synthesize T4P but not by lack of T4P functionality.

Aerobic mineralization of nitroguanidine by Variovorax strain VC1 isolated from soil

Nitroguanidine (NQ) is an energetic material that is used as a key ingredient of triple-base propellants and is currently being considered as a TNT replacement in explosive formulations. NQ was efficiently degraded in aerobic microcosms when a carbon source was added. NQ persisted in unamended microcosms or under anaerobic conditions. An aerobic NQ-degrading bacterium, Variovorax strain VC1, was isolated from soil microcosms containing NQ as the sole nitrogen source. NQ degradation was inhibited in the presence of a more favorable source of nitrogen. Resting cells of VC1 degraded NQ effectively (54 μmol h(-1) g(-1) protein) giving NH(3) (50.0%), nitrous oxide (N(2)O) (48.5%) and CO(2) (100%). Disappearance of NQ was accompanied by the formation of a key intermediate product that we identified as nitrourea by comparison with a reference material. Nitrourea is unstable in water and suffered both biotic and abiotic decomposition to eventually give NH(3), N(2)O, and CO(2). However, we were unable to detect urea. Based on products distribution and reaction stoichiometry, we suggested that degradation of NQ, O(2)NN═C(NH(2))(2), might involve initial enzymatic hydroxylation of the imine, -C═N- bond, leading first to the formation of the unstable α-hydroxynitroamine intermediate, O(2)NNHC(OH)(NH(2))(2), whose decomposition in water should lead to the formation of NH(3), N(2)O, and CO(2). NQ biodegradation was induced by nitroguanidine itself, L-arginine, and creatinine, all being iminic compounds containing a guanidine group. This first description of NQ mineralization by a bacterial isolate demonstrates the potential for efficient microbial remediation of NQ in soil.

The cyst-dividing bacterium Ramlibacter tataouinensis TTB310 genome reveals a well-stocked toolbox for adaptation to a desert environment

Ramlibacter tataouinensis TTB310(T) (strain TTB310), a betaproteobacterium isolated from a semi-arid region of South Tunisia (Tataouine), is characterized by the presence of both spherical and rod-shaped cells in pure culture. Cell division of strain TTB310 occurs by the binary fission of spherical "cyst-like" cells ("cyst-cyst" division). The rod-shaped cells formed at the periphery of a colony (consisting mainly of cysts) are highly motile and colonize a new environment, where they form a new colony by reversion to cyst-like cells. This unique cell cycle of strain TTB310, with desiccation tolerant cyst-like cells capable of division and desiccation sensitive motile rods capable of dissemination, appears to be a novel adaptation for life in a hot and dry desert environment. In order to gain insights into strain TTB310's underlying genetic repertoire and possible mechanisms responsible for its unusual lifestyle, the genome of strain TTB310 was completely sequenced and subsequently annotated. The complete genome consists of a single circular chromosome of 4,070,194 bp with an average G+C content of 70.0%, the highest among the Betaproteobacteria sequenced to date, with total of 3,899 predicted coding sequences covering 92% of the genome. We found that strain TTB310 has developed a highly complex network of two-component systems, which may utilize responses to light and perhaps a rudimentary circadian hourglass to anticipate water availability at the dew time in the middle/end of the desert winter nights and thus direct the growth window to cyclic water availability times. Other interesting features of the strain TTB310 genome that appear to be important for desiccation tolerance, including intermediary metabolism compounds such as trehalose or polyhydroxyalkanoate, and signal transduction pathways, are presented and discussed.

Proposal of Giesbergeria voronezhensis gen. nov., sp. nov. and G. kuznetsovii sp. nov. and reclassification of [Aquaspirillum] anulus, [A.] sinuosum and [A.] giesbergeri as Giesbergeria anulus comb. nov., G. sinuosa comb. nov. and G. giesbergeri comb. nov., and [Aquaspirillum] metamorphum and [A.] psychrophilum as Simplicispira metamorpha gen. nov., comb. nov. and S. psychrophila comb. nov

Five Gram-negative, motile, spiral-shaped strains were isolated from a sulfide spring (D-412T), active sludge of wastewater (D-419T, D-420, D-424) and industrial wastewater (D-416). Comparative 16S rRNA gene sequence analysis showed that the isolates belong to the family Comamonadaceae, within the class Betaproteobacteria, but fall into a distinct cluster. On the basis of phenotypic, chemotaxonomic and phylogenetic data, a new genus, Giesbergeria gen. nov., is proposed, including five species. The type species of the genus is Giesbergeria voronezhensis sp. nov. (type strain D-419T=DSM 12825T=CIP 107340T=VKM B-2350T) and other novel members of the genus are Giesbergeria kuznetsovii sp. nov. (type strain D-412T=DSM 12827T=VKM B-2352T), Giesbergeria giesbergeri comb. nov. (basonym Aquaspirillum giesbergeri), Giesbergeria sinuosa comb. nov. (basonym Aquaspirillum sinuosum) and Giesbergeria anulus comb. nov. (basonym Aquaspirillum anulus). Using the same criteria, isolate D-416 (=DSM 12826) was identified as a strain of [Aquaspirillum] metamorphum. Strain D-416, the type strain of [A.] metamorphum and the type strain of [Aquaspirillum] psychrophilum form a distinct cluster within the family Comamonadaceae (97–97·2 % 16S rRNA gene sequence similarity) and share phenotypic and chemotaxonomic properties. Therefore, it is proposed that these strains are reclassified as members of a new genus, Simplicispira gen. nov., as Simplicispira metamorpha comb. nov. (the type species) and Simplicispira psychrophila comb. nov., respectively.

Extracellular DNA in single- and multiple-species unsaturated biofilms

The extracellular polymeric substances (EPS) of bacterial biofilms form a hydrated barrier between cells and their external environment. Better characterization of EPS could be useful in understanding biofilm physiology. The EPS are chemically complex, changing with both bacterial strain and culture conditions. Previously, we reported that Pseudomonas aeruginosa unsaturated biofilm EPS contains large amounts of extracellular DNA (eDNA) (R. E. Steinberger, A. R. Allen, H. G. Hansma, and P. A. Holden, Microb. Ecol. 43:416-423, 2002). Here, we investigated the compositional similarity of eDNA to cellular DNA, the relative quantity of eDNA, and the terminal restriction fragment length polymorphism (TRFLP) community profile of eDNA in multiple-species biofilms. By randomly amplified polymorphic DNA analysis, cellular DNA and eDNA appear identical for P. aeruginosa biofilms. Significantly more eDNA was produced in P. aeruginosa and Pseudomonas putida biofilms than in Rhodococcus erythropolis or Variovorax paradoxus biofilms. While the amount of eDNA in dual-species biofilms was of the same order of magnitude as that of of single-species biofilms, the amounts were not predictable from single-strain measurements. By the Shannon diversity index and principle components analysis of TRFLP profiles generated from 16S rRNA genes, eDNA of four-species biofilms differed significantly from either cellular or total DNA of the same biofilm. However, total DNA- and cellular DNA-based TRFLP analyses of this biofilm community yielded identical results. We conclude that extracellular DNA production in unsaturated biofilms is species dependent and that the phylogenetic information contained in this DNA pool is quantifiable and distinct from either total or cellular DNA.

A gas vesiculate planktonic strain of the purple non-sulfur bacterium Rhodoferax antarcticus isolated from Lake Fryxell, Dry Valleys, Antarctica

A moderately psychrophilic purple non-sulfur bacterium, Rhodoferax antarcticus strain Fryx1, is described. Strain Fryx1 was isolated from the water column under the ice of the permanently frozen Lake Fryxell, Antarctica. Cells of Fryx1 are long thin rods and contain gas vesicles, the first report of such structures in purple non-sulfur bacteria. Gas vesicles are clustered at 2-4 sites per cell. Surprisingly, the 16S rRNA gene sequence of strain Fryx1 is nearly identical to that of Rfx. antarcticus strain AB, a short, vibrio-shaped phototroph isolated from an Antarctic microbial mat. Although showing physiological parallels, strains AB and Fryx1 differ distinctly in their morphology and absorption spectra. DNA-DNA hybridization shows that the genomes of strains AB and Fryx1 are highly related, yet distinct. We conclude that although strains AB and Fryx1 may indeed be the same species, their ecologies are quite different. Unlike strain AB, strain Fryx1 has adapted to a planktonic existence in the nearly freezing water column of Lake Fryxell.