Self-preservation strategies during bacterial biomineralization with reference to hydrozincite and implications for fossilization of bacteria.

The induction of mineralization by microbes has been widely demonstrated but whether induced biomineralization leads to distinct morphologies indicative of microbial involvement remains an open question. For calcium carbonate, evidence suggests that microbial induction enhances sphere formation, but the mechanisms involved and the role of microbial surfaces are unknown. Here, we describe hydrozincite biominerals from Sardinia, Italy, which apparently start life as smooth globules on cyanobacterial filaments, and evolve to spheroidal aggregates consisting of nanoplates. Complementary laboratory experiments suggest that organic compounds are critical to produce this morphology, possibly by inducing aggregation of nanoscopic crystals or nucleation within organic globules produced by metabolizing cells. These observations suggest that production of extracellular polymeric substances by microbes may constitute an effective mechanism to enhance formation of porous spheroids that minimize cell entombment while also maintaining metabolite exchange. However, the high porosity arising from aggregation-based crystal growth probably facilitates rapid oxidation of entombed cells, reducing their potential to be fossilized.

Discrete site surface complexation constants for lanthanide adsorption to bacteria as determined by experiments and linear free energy relationships.

Bacteria are abundant in many natural and engineered environments where they are thought to exert important controls on the cycling, mobility, bioavailability, and toxicity of metal contaminants. In order to probe their role in moderating the behavior of lanthanides, pH-dependent adsorption edges of 13 individual lanthanides and yttrium to the Gram-negative bacterium Pantoea agglomerans were used to generate discrete site surface complexation constants. The calculated surface complexation constants were compared with stability constants estimated using linear free energy relationships based on a number of hydroxyl-containing ligands. The experimental data suggests that lanthanide adsorption edges below pH 6.5 are consistent with adsorption to phosphate groups for the light and some of the middle lanthanides (La to Gd), whereas some of the middle and heavy lanthanides appear to favor carboxyl co-ordination (Tb to Yb), although exceptions occur in each grouping. The experimentally derived surface complexation constants for carboxyl coordination were of similar magnitude to stability constants estimated from linear free energy correlations using fulvic acid stability constants. The implication is that the adsorption of lanthanides to bacterial surfaces could be modeled reasonably well using lanthanide stability constants for natural organic matter, except perhaps at low pH where phosphate binding dominates.

Physical and chemical effects of extracellular polymers (EPS) on Zn adsorption to Bacillus licheniformis S-86.

This study investigated Zn adsorption to an extracellular polymeric substance (EPS)-producing bacterial strain, Bacillus licheniformis S-86. Batch metal adsorption experiments and spectroscopic (EXAFS) analysis were conducted using both native (EPS-covered) cells and EPS-free cells in order to assess the contribution made by EPS to metal adsorption by this strain. Thermodynamic modelling of the macroscopic adsorption data indicated that Zn complexation to both native and EPS-free cells was predominantly to carboxyl (pK(a)5.3-5.4) and phosphate (pK(a)7.4-7.5) functional groups, but with some adsorption to phosphodiester (pK(a)3.3-3.4) groups also evident. EXAFS analysis shows Zn-carboxyl complexation, but possibly with a significant contribution from a second, phosphate functional group. Apparently, EPS removal does not affect the metal adsorption capacity at the metal: biomass ratios used here. As the concentration of carboxyl and phosphate functional groups is only slightly affected by EPS extraction, complexation to these functional groups explains why EPS removal does not reduce the amount of Zn adsorbed by the cells. It was also observed that EPS production induces aggregation of cells in suspension. This may reduce the cell surface area available for metal adsorption, thus counteracting any greater availability of metal-complexing ligands in the EPS layer compared to an EPS-free cell surface. Furthermore, the EPS layer appears to be the major source of dissolved organic carbon (DOC) released to solution during the metal adsorption experiments. This DOC may reduce metal binding to the cell surfaces by acting as a competing complexing ligand. These observations have implications for industrial application of biofilms and suggest that over-production of EPS in bio-reactors may reduce the metal removal efficiency of the biomass.

Quantitative appraisal of murine filariasis confirms host strain differences but reveals that BALB/c females are more susceptible than males to Litomosoides sigmodontis.

Litomosoides sigmodontis, a rodent filarial nematode, can infect inbred laboratory mice, with full development to patency in the BALB/c strain. Strains such as C57BL/6 are considered resistant, because although filarial development can occur, circulating microfilariae are never detected. This model system has, for the first time, allowed the power of murine immunology to be applied to fundamental questions regarding susceptibility to filarial nematode infection. As this is a relatively new model, many aspects of the biology remain to be discovered or more clearly defined. We undertook a major analysis of 85 experiments, to quantitatively assess differences in filarial survival and reproduction in male versus female and BALB/c versus C57BL/6 mice over the full course of infection. This large dataset provided hard statistical support for previous qualitative reviews, including observations that the resistant phenotype of C57BL/6 mice is detectable as early as 10 days postinfection (dpi). An unexpected finding, however, was that filarial survival was reduced in male BALB/c mice compared to their female counterparts. Worm recovery as well as the prevalence and density of microfilariae were higher in female compared with male BALB/c mice. Therefore, L. sigmodontis bucks the filarial trend of increased susceptibility in males. This could be partially explained by the different anatomical locations of adult L. sigmodontis versus lymphatic filariae. Interestingly, the effects of BALB/c sex upon microfilaremia were independent of worm number. In summary, this study has significantly refined our understanding of the host-L. sigmodontis relationship and, critically, has challenged the dogma that males are more susceptible to filarial infection.