No abstract

Escherichia coli in shear flow near a surface are shown to exhibit a steady propensity to swim towards the left (within the relative coordinate system) of that surface. This phenomenon depends solely on the local shear rate on the surface, and leads to cells eventually aligning and swimming upstream preferentially along a left sidewall or crevice in a wide range of flow conditions. The results indicate that flow-assisted translation and upstream swimming along surfaces might be relevant in various models of bacterial transport, such as in pyelonephritis and bacterial migration in wet soil and aquatic environments in general.

Pseudomonads sense changes in the concentration of chemicals in their environment and exhibit a behavioral response mediated by flagella or pili coupled with a chemosensory system. The two known chemotaxis pathways, a flagella-mediated pathway and a putative pili-mediated system, are described in this review. Pseudomonas shows chemotaxis response toward a wide range of chemicals, and this review includes a summary of them organized by chemical structure. The assays used to measure positive and negative chemotaxis swimming and twitching Pseudomonas as well as improvements to those assays and new assays are also described. This review demonstrates that there is ample research and intellectual space for future investigators to elucidate the role of chemotaxis in important processes such as pathogenesis, bioremediation, and the bioprotection of plants and animals.

Phytate, the most abundant organic phosphorus compound in soil, dominates the biotic phosphorus input from terrestrial runoffs into aquatic systems. Microbial mineralization of phytate by phytases is a key process for recycling phosphorus in the biosphere. Bioinformatic studies were carried out on microbial genomes and environmental metagenomes in the NCBI and the CAMERA databases to determine the distribution of the four known classes of phytase in the microbial world. The b-propeller phytase is the only phytase family that can be found in aquatic environments and it is also distributed in soil and plant bacteria. The b-propeller phytase-like genes can be classified into several subgroups based on their domain structure and the positions of their conserved cysteine residues. Analysis of the genetic contexts of these subgroups showed that b-propeller phytase genes exist either as an independent gene or are closely associated with a TonB-dependent receptor-like gene in operons, suggesting that these two genes are functionally linked and thus may play an important role in the cycles of phosphorus and iron. Our work suggests that b-propeller phytases play a major role in phytate-phosphorus cycling in both soil and aquatic microbial communities.

The influence of bacterial growth stage and the evolution of surface macromolecules on cell adhesion have been examined by using a mutant of Escherichia coli K-12. To better understand the adhesion kinetics of bacteria in the mid-exponential and stationary growth phases under flow conditions, deposition experiments were conducted in a well-controlled radial stagnation point flow (RSPF) system. Complementary cell characterization techniques were conducted in combination with the RSPF experiments to evaluate the hydrophobicity, electrophoretic mobility, size, and titratable surface charge of the cells in the two growth phases considered. It was observed that cells in stationary phase were notably more adhesive than those in mid-exponential phase. This behavior is attributed to the high degree of local charge heterogeneity on the outer membranes of stationary-phase cells, which results in decreased electrostatic repulsion between the cells and a quartz surface. The mid-exponential-phase cells, on the other hand, have a more uniform charge distribution on the outer membrane, resulting in greater electrostatic repulsion and, subsequently, less adhesion. Our results suggest that the macromolecules responsible for this phenomenon are outer membrane-bound proteins and lipopolysaccharide-associated functional groups.