An extracellular polysaccharide is involved in the aluminum tolerance of Pullulanibacillus sp. CA42, a newly isolated strain from the Chinese water chestnut growing in an actual acid sulfate soil area in Vietnam.

A novel aluminum-tolerant bacterial strain CA42 was isolated from the aquatic plant Eleocharis dulcis, which grows in a highly acidic swamp in Vietnam. Inoculation with CA42 allowed Oryza sativa to grow in the presence of 300 µM AlCl3 at pH 3.5, and biofilms were observed around the roots. Using 16S rRNA gene sequencing analysis, the strain was identified as Pullulanibacillus sp. CA42. This strain secreted large amounts of an extracellular polysaccharide (CA42 EPS). Results from structural analyses on CA42 EPS, namely methylation analysis and nuclear magnetic resonance (NMR), indicated that the chemical structure of CA42 EPS was a glycogen-like α-glucan. Purified CA42 EPS and the commercially available oyster glycogen adsorbed aluminum ions up to 15-30 µmol/g dry weight. Digestion treatments with α-amylase and pullulanase completely attenuated the aluminum ion-adsorbing activity of purified CA42 EPS and oyster glycogen, suggesting that the glycogen-like structure adsorbed aluminum ions and that its branching structure played an important role in its aluminum adsorbing activity. Furthermore, the aluminum tolerance of CA42 cells was attenuated by pullulanase treatment directly on the live CA42 cells. These results suggest that CA42 EPS adsorbs aluminum ions and is involved in the aluminum tolerance mechanism of Pullulanibacillus sp. CA42. Thus, this strain may be a potential plant growth-promoting bacterium in acidic soils. In addition, this study is the first to report a glycogen-like polysaccharide that adsorbs aluminum ions.

Evaporation and drying kinetics of water-NaCl droplets via acoustic levitation.

The acoustic levitation method (ALM) is expected to be applied as a container-less processing technology in the material science, analytical chemistry, biomedical technology, and food science domains because this method can be used to levitate any sample in mid-air and prevent nucleation and contamination due to the container wall. However, this approach can lead to nonlinear behavior, such as acoustic streaming, which promotes the evaporation of a levitated droplet. This study aims to understand the evaporation and precipitation kinetics of an acoustically levitated multicomponent droplet. An experimental investigation of the evaporation process of a salt solution droplet was performed, and the experimental results were compared with those of the d 2-law. The droplet was noted to evaporate in two stages owing to the precipitation of the salt. Because of the vapor pressure depression, the experimental data did not agree with the classical prediction obtained using the d 2-law. However, the experimental results were in partial agreement with those of the d 2-law when the vapor pressure depression was considered by using the concentration estimate at each time, as obtained from the experimental results. In addition, it was observed that the time when the salt completely precipitated could be estimated by using the extended theory. These findings provide physical and practical insights into the droplet evaporation mid-air for potential lab-in-a-drop applications.