Variations in exopolysaccharide production by Rhizobium tropici.

Rhizobium tropici, a legume-symbiont soil bacterium, is known for its copious production of exopolysaccharide (EPS). Many aspects of this organism's growth and EPS production, however, remain uncharacterized, including the influence of environment and culturing conditions upon EPS. Here, we demonstrate that R. tropici EPS chemical composition and yield differ when grown with different substrates in a defined minimal medium in batch culture. Exopolysaccharide was quantified from R. tropici grown using arabinose, glucose, sucrose, mannitol, fructose, or glutamate as a sole carbon source. All tested substrates produced plenteous amounts of exopolysaccharide material. Variations in pH and carbon-to-nitrogen (C/N) ratio also resulted in assorted cell growth and exopolysaccharide production differences. We found that optimizing the C/N ratio has a greater impact upon R. tropici EPS production than upon R. tropici growth. A maximum EPS yield of 4.08 g/L was realized under optimized conditions, which is large even in comparison with other known rhizobia. We provide evidence that the chemical composition of R. tropici EPS can vary with changes to the growth environment. The composition of glucose-grown EPS contained rhamnose-linked residues that were not present in arabinose-grown EPS.

Imaging and analysis of Pseudomonas aeruginosa swarming and rhamnolipid production.

Many bacteria spread over surfaces by "swarming" in groups. A problem for scientists who study swarming is the acquisition of statistically significant data that distinguish two observations or detail the temporal patterns and two-dimensional heterogeneities that occur. It is currently difficult to quantify differences between observed swarm phenotypes. Here, we present a method for acquisition of temporal surface motility data using time-lapse fluorescence and bioluminescence imaging. We specifically demonstrate three applications of our technique with the bacterium Pseudomonas aeruginosa. First, we quantify the temporal distribution of P. aeruginosa cells tagged with green fluorescent protein (GFP) and the surfactant rhamnolipid stained with the lipid dye Nile red. Second, we distinguish swarming of P. aeruginosa and Salmonella enterica serovar Typhimurium in a coswarming experiment. Lastly, we quantify differences in swarming and rhamnolipid production of several P. aeruginosa strains. While the best swarming strains produced the most rhamnolipid on surfaces, planktonic culture rhamnolipid production did not correlate with surface growth rhamnolipid production.

Copper doping improves hydroxyapatite sorption for arsenate in simulated groundwaters.

Hydroxyapatite (HAP) has been widely used to immobilize many cationic heavy metals in water and soils. Compared with its strong sorption for metal cations, the abilities of HAP to sorb metal anions, such as arsenic, are less significant. Improving HAP sorption for anionic arsenic species is important for expanding its application potential because the presence of arsenic in the environment has raised serious health concerns and there is need for cost-effective remediation methods. In this work, we report an innovative method of copper doping to improve a synthetic HAP sorption for arsenate, which is a primary aqueous arsenic species, in simulated groundwaters. The undoped HAP and copper doped HAP (CuHAP) were characterized with XRD, FTIR, N(2) adsorption, and SEM, and then evaluated as sorbents for arsenate removal tests. The experimental results suggest that copper doping changed the morphology and increased the surface area of HAP. The CuHAP sorbed 1.6-9.1x more arsenate than the undoped HAP did in a simulated groundwater at pH of 7.7-8.0. The improved arsenate sorption is presumably due to the increase in surface area of HAP as a result of copper doping. In addition to the copper doping level, the arsenate sorption to HAP and CuHAP can also be increased with increasing water pH and calcium concentration. The experimental data indicate that sorbent dissolution is an important factor governing arsenate sorption to HAP and CuHAP.