The ionizing-radiation-resistant fractions of two soil bacterial communities were investigated by exposing an arid soil from the Sonoran Desert and a nonarid soil from a Louisiana forest to various doses of ionizing radiation using a 60 Co source. The numbers of surviving bacteria decreased as the dose of gamma radiation to which the soils were exposed increased. Bacterial isolates surviving doses of 30 kGy were recovered from the Sonoran Desert soil, while no isolates were recovered from the nonarid forest soil after exposure to doses greater than 13 kGy. The phylogenetic diversities of the surviving culturable bacteria were compared for the two soils using 16S rRNA gene sequence analysis. In addition to a bacterial population that was more resistant to higher doses of ionizing radiation, the diversity of the isolates was greater in the arid soil. The taxonomic diversity of the isolates recovered was found to decrease as the level of ionizing-radiation exposure increased. Bacterial isolates of the genera Deinococcus, Geodermatophilus, and Hymenobacter were still recovered from the arid soil after exposure to doses of 17 to 30 kGy. The recovery of large numbers of extremely ionizing-radiationresistant bacteria from an arid soil and not from a nonarid soil provides further ecological support for the hypothesis that the ionizing-radiation resistance phenotype is a consequence of the evolution of other DNA repair systems that protect cells against commonly encountered environmental stressors, such as desiccation. The diverse group of bacterial strains isolated from the arid soil sample included 60 Deinococcus strains, the characterization of which revealed nine novel species of this genus.Extreme ionizing-radiation resistance has been observed in several members of the domains Bacteria and Archaea. Of the genera containing ionizing-radiation-resistant organisms, Deinococcus and Rubrobacter show the highest levels of resistance, and all species of these genera have been shown to be

SummaryWe used DNA macroarray analysis to identify genes that respond to the status of the intracellular acetyl phosphate (acP) pool. Genes whose expression correlated negatively with the ability to synthesize acP (i.e. negatively regulated genes) function primarily in flagella biosynthesis, a result consistent with observations that we published previously (Prüß and Wolfe, 1994, Mol Microbiol 12: 973-984). In contrast, genes whose expression correlated positively with the ability to synthesize acP (i.e. positively regulated genes) include those for type 1 pilus assembly, colanic acid (capsule) biosynthesis and certain stress effectors. To our knowledge, this constitutes the first report that these genes may respond to the status of the intracellular acP pool. Previously, other researchers have implicated flagella, type 1 pili, capsule and diverse stress effectors in the formation of biofilms. We therefore tested whether cells altered in their ability to metabolize acP could construct normal biofilms, and found that they could not. Cells defective for the production of acP and cells defective for the degradation of acP could both form biofilms, but these biofilms exhibited characteristics substantially different from each other and from biofilms formed by their wild-type parent. We confirmed the role of individual cell surface structures, the expression of which appears to correlate with acP levels, in fim or fli mutants that cannot assemble type 1 pili or flagella respectively. Thus, the information gained by expression profiling of cells with altered acP metabolism indicates that acP may help to co-ordinate the expression of surface structures and cellular processes involved in the initial stages of wild-type biofilm development.

Ludox density gradients were used to enrich for Escherichia coli mutants with conditional growth defects and alterations in membrane composition. A temperature-sensitive mutant named Lud135 was isolated with mutations in two related, nonessential genes: yghB and yqjA. yghB harbors a single missense mutation (G203D) and yqjA contains a nonsense mutation (W92TGA) in Lud135. Both mutations are required for the temperature-sensitive phenotype: targeted deletion of both genes in a wild-type background results in a strain with a similar phenotype and expression of either gene from a plasmid restores growth at elevated temperatures. The mutant has altered membrane phospholipid levels, with elevated levels of acidic phospholipids, when grown under permissive conditions. Growth of Lud135 under nonpermissive conditions is restored by the presence of millimolar concentrations of divalent cations Ca 2؉ , Ba 2؉ , Sr 2؉ , or Mg 2؉ or 300 to 500 mM NaCl but not 400 mM sucrose. Microscopic analysis of Lud135 demonstrates a dramatic defect at a late stage of cell division when cells are grown under permissive conditions. yghB and yqjA belong to the conserved and widely distributed dedA gene family, for which no function has been reported. The two open reading frames encode predicted polytopic inner membrane proteins with 61% amino acid identity. It is likely that YghB and YqjA play redundant but critical roles in membrane biology that are essential for completion of cell division in E. coli.

Abstract. The pyrenoid is a prominent proteinaceous structure found in the stroma of the chloroplast in unicellular eukaryotic algae, most multicellular algae, and some hornworts. The pyrenoid contains the enzyme ribulose-l,5-bisphosphate carboxylase/oxygenase and is sometimes surrounded by a carbohydrate sheath. We have observed in the unicellular green alga Chlamydomonas reinhardtii Dangeard that the pyrenoid starch sheath is formed rapidly in response to a decrease in the CO2 concentration in the environment. This formation of the starch sheath occurs coincidentally with the induction of the CO2-concentrating mechanism. Pyrenoid starch-sheath formation is partly inhibited by the presence of acetate in the growth medium under light and low-CO2 conditions. These growth conditions also partly inhibit the induction of the CO2-concentrating mechanism. When cells are grown with acetate in the dark, the CO2-concentrating mechanism is not induced and the pyrenoid starch sheath is not formed even though there is a large accumulation of starch in the chloroplast stroma. These observations indicate that pyrenoid starch-sheath formation correlates with induction of the CO2-concentrating mechanism under low-CO 2 conditions. We suggest that this ultrastructural reorganization under low-CO 2 conditions plays a role in the CO2-concentrating mechanism C. reinhardtii as well as in other eukaryotic algae.

Capsular polysaccharide (CPS) is a major virulence factor in Vibrio vulnificus, and encapsulated strains have an opaque, smooth (OpS) colony morphology, while nonencapsulated strains have a translucent, smooth (TrS) colony morphology. Previously, we showed that OpS and TrS parental strains can yield a third colony type, rugose (R), and that the resulting strains, with the OpR and TrR phenotypes, respectively, form copious biofilms. Here we show that while OpR and TrR strains both produce three-dimensional biofilm structures that are indicative of rugose extracellular polysaccharide (rEPS) production, OpR strains also retain expression of CPS and are virulent in an iron-supplemented mouse model, while TrR strains lack CPS and are avirulent. Chlorine resistance assays further distinguished OpR and TrR isolates as exposure to 3 g/ml NaOCl eradicated both OpS and OpR strains, while both TrS and TrR strains survived, but at rates which were significantly different from one another. Taken together, these results further emphasize the importance of CPS for virulence of V. vulnificus and establish a correlation between CPS expression and chlorine sensitivity in this organism. Using reverse transcriptase PCR, we also identified a nine-gene cluster associated with both CPS and rEPS expression in V. vulnificus, designated the wcr (capsular and rugose polysaccharide) locus, with expression occurring primarily in R variants. The latter results set the stage for characterization of functional determinants which individually or collectively contribute to expression of multiple EPS forms in this pathogen.Vibrio vulnificus is a gram-negative marine and estuarine bacterium capable of causing severe disease in susceptible individuals. This bacterium is normally found in fish and shellfish, including oysters. Several medical conditions can predispose a person to being susceptible to infection by this organism, including diabetes, liver disease, hemachromatosis, and a compromised immune system. When people with such conditions consume raw oysters or other seafood containing V. vulnificus, they are at risk of developing a rapidly progressing primary septicemia that can be fatal within 24 to 48 h. In an otherwise healthy individual, if a break in the skin is exposed to seawater containing this organism, a severe wound infection may develop that could necessitate amputation if treatment is not begun soon after the onset of symptoms. V. vulnificus does not infect as many people as other members of the genus Vibrio, but it is the leading reported cause of death from the consumption of seafood in the United States (28, 48).V. vulnificus produces several virulence factors, including multiple enzymes, siderophores, RtxA toxin, and a polysaccharide capsule (for a review, see reference 15). While the other factors may assist in virulence, the capsular polysaccharide (CPS) is considered a major virulence factor and has been reported to protect the bacteria from phagocytosis and complement-mediated killing by the host immune system. When grown ...

The marine bacterium Vibrio vulnificus is a human pathogen that can spontaneously switch between virulent opaque and avirulent translucent phenotypes. Here, we document an additional form, the rugose variant, which produces copious biofilms and which may contribute both to pathogenicity of V. vulnificus and to its survival under adverse environmental conditions.Vibrio vulnificus is a marine bacterium that can cause human disease and has been implicated as the cause of over 95% of the deaths related to seafood consumption in the United States (13,25). Infection usually occurs through the ingestion of raw oysters or by contact of an open wound with contaminated seawater. Susceptible individuals include those with liver disease, immune dysfunction, or elevated serum iron levels. When a susceptible individual consumes raw oysters contaminated with V. vulnificus, the result can be a rapidly fulminating septicemia, with mortality occurring in over 50% of cases (13,25).Some V. vulnificus isolates produce a polysaccharide capsule (3) which gives the colonies a smooth, mucoid, opaque phenotype. It has been reported that the capsule is a major virulence factor, presumably protecting the bacterium from the host immune system (23, 32). In culture, many opaque (O) strains spontaneously produce translucent (T) variants (28, 35). Opaque strains have been shown to be virulent in a mouse model, while translucent strains were avirulent in this model (23,32,35). Several studies have shown that capsular polysaccharide (CPS) expression varies between opaque and translucent strains as well as among different translucent strains (i.e., suggesting there are different degrees of translucence) (28,29,32). Transposon insertions have been shown to produce completely acapsular translucent strains (28,29,35).Opaque strains of V. vulnificus have been reported to switch spontaneously to the translucent phenotype at frequencies of 10 Ϫ5 to 10 Ϫ4 when the cells were grown in rich medium (12,29,32). If grown in a peptone-based yet more-defined medium, the switch occurs at a higher frequency, with over 60% of the colonies exhibiting the translucent phenotype (23). The reverse switch, from translucent to opaque, has been reported to occur at frequencies of 9.2 ϫ 10 Ϫ3 (29), less than 10 Ϫ4 (32), or not at all (12, 23). We have previously observed that opaque strains will spontaneously yield translucent variants much more often than the reverse. However, the translucent-to-opaque switch did occur on rare occasions when strains were routinely subcultured in heart infusion broth at 37°C and then left to stand at room temperature for several days before plating and incubation of plates at 37°C (unpublished results).Vibrio cholerae, the etiological agent of cholera, is a close relative of V. vulnificus. Although the O1 strains of V. cholerae produce no CPS, they have been responsible for the first six pandemics of cholera. The current, seventh pandemic has been caused not only by O1 strains but also by O139 strains, which do produce CPS (19). In additio...

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