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Bacteria growing as surface-adherent biofilms are better able to withstand chemical and physical stresses than their unattached, planktonic counterparts. Using transcriptional profiling and quantitative PCR, we observed a previously uncharacterized gene, yjfO to be upregulated during Escherichia coli MG1655 biofilm growth in a chemostat on serine-limited defined medium. A yjfQ mutant, developed through targeted-insertion mutagenesis, and a yjfQ-complemented strain, were obtained for further characterization. While bacterial surface colonization levels (c.f.u. [cm.sup.-2]) were similar in all three strains, the mutant strain exhibited reduced microcolony formation when observed in flow cells, and greatly enhanced flagellar motility on soft (0.3%) agar. Complementation of yjfO restored microcolony formation and flagellar motility to wild-type levels. Cell surface hydrophobicity and twitching motility were unaffected by the presence or absence of yjfO. In contrast to the parent strain, biofilms from the mutant strain were less able to resist acid and peroxide stresses. yjfO had no significant effect on E. coli biofilm susceptibility to alkali or heat stress. Planktonic cultures from all three strains showed similar responses to these stresses. Regardless of the presence of yjfQ, planktonic E. coli withstood alkali stress better than biofilm populations. Complementation of yjfO restored viability following exposure to peroxide stress, but did not restore acid resistance. Based on its influence on biofilm maturation and stress response, and effects on motility, we propose renaming the uncharacterized gene, yjfO, as bsmA (biofilm stress and motility). DOI 10.1099/mic.0.031468-0

More than 40 calcite-precipitation experiments were performed under sterile conditions in order to investigate the origins of 25-300 nm spherical-, rod-, and ovoid-shaped objects that have been widely interpreted as evidence of nanometer-scale life (i.e., nannobacteria). Individual experiments included the addition of soluble organic compounds, common species of eubacteria, or phage-induced eubacterial lysates. These experiments indicate that many of the nanometer-scale objects have inorganic or nonnannobacterial origins. In the precipitation experiments, calcite formed euhedral crystals 50-800 nm in diameter and smaller (< 50 nm) anhedral or rounded particles or protocrystals. The small anhedral or rounded solids resembled nannobacteria. The relative amount of anhedral or rounded calcite was greatest in experiments with a dissolved organic component. These controlled experiments are in accord with observations that rounded nanometerscale objects are more common in minerals formed in organic-rich environments. Bacterial fragments occur as rounded to irregularly shaped particles that included cell-wall fragments, expulsed cytoplasm, and relict capsules that also closely resembled nannobacteria. Acid etching of the large euhedral crystals produced in the precipitation experiments also resulted in the formation of nanometer-scale features that resembled nannobacteria in natural carbonates. The shapes of the etching artifacts vary as a function of the strength of the acid and the duration of etching. Much caution is advisable in interpreting the origin of rounded features < 50 nm.

Research was conducted to examine the hypothesis that biofilms on indwelling urethral catheters produce quorum-sensing signal molecules in situ and in vitro. The Pseudomonas aeruginosa biofilms produced strongly positive reaction that were generated on catheters. Sections of the catheters from which biofilm had been taken also gave positive responses in the assay. Results along with negative reactions seen in unused catheters reveal that the quorum-sensing signal molecules may have been generated by the biofilm during its development in the catheter.

The effect of the oxidation states on iron binding by the gamma-glutamyl capsule polymer of Bacillus lichensis was discussed. The methodlogy involved anaerobic suspension of lyophilized capsule in ferric acid solution and addition of reducing agent. The solutions were incubated for one week, unbound metal were removed by dialysis and then prepared for trace metal anaylis. Results showed that less Fe2+ was bound than Fe3+. In addition, Fe3+ bound to the anionic bacterial polymers can released by reduction.

Research was conducted to examine the effect of rpoS deletion on Escherichia coli biofilms. It was hypothesized that slow growth is an essential aspect of bacterial physiology within biofilms. Two strains of Escherichia coli and its isogeic derivvative were used to test the hypothesis. Results indicate that deletion of rpoS greatly reduces the ability of E coli to grow in biofilms but has little impact on the growth of planktonic bacteria.

Leaf fossils commonly form through authigenic preservation in which the leaf surface is encrusted with a mineral film, typically iron oxides. The exact mechanism of mineral precipitation is unclear because largely hydrophobic leaf surfaces do not readily bind metal ions; however, previous workers have suggested precipitation of minerals in sediment pore space, at the leaf surface by decay-produced CO2, or on the leaf surface by iron-sheathed bacteria. A 3 by 2 experiment was conducted to determine the role of non-iron bacteria in precipitating metal ions and enhancing fossilization potential in leaves of Platanus and Taxodium, two genera common in the Tertiary fossil record. Leaves of Platanus and Taxodium were separated into two groups, one of which was inoculated for 5 days in river water and the other of which consisted of fresh leaves that served as a control. Leaves of these two groups were placed in solutions of iron chloride, silica, and distilled water to determine mineralization potential. Leaves inoculated in river water developed an anionic bacterial biofilm of diverse bacteria, which rapidly adsorbed [Fe.sup.3+] ions to form ferrihydrite. In contrast, leaves with no biofilm did not mineralize, even after weeks in a solution of iron chloride or silica. Decay was arrested in leaves placed in the iron chloride solution but not distilled water, high levels of iron can inhibit microbial metabolism. These results imply that bacterial colonization of leaves during their first 1-2 weeks in a stream environment may be an essential pre-requisite for authigenic preservation and that precipitation of iron by bacterial biofilms enhances leaf preservation potential by inhibiting the process of decay.