B) Colony spread is limited by 500 μg/L CR, but wetting agent spreads as above. C) Drop collapse assay using dilute methylene blue solution showing the reduced surface tension in the wetting agent zone (left of the black line). Impact of humidity on find more swarming When the incubation of the plates was performed in a humidified chamber, the swarming rate under all permissive conditions was reduced (Fig 2B). The physiology of the swarm was significantly altered by humid
incubation (Fig 3). For morphological analysis of humidified colonies, magnified images were used, which are not directly comparable in size to the non-humidified samples. In the absence of CR, the gross morphology buy BI 2536 of the swarms (Fig 3A, I) differed markedly. Swarming on CR in the humidified incubator was characterized by macroscopic tendrils at low concentrations (Fig 3J), which were not seen during swarming under non-humidified conditions (Fig 3B). At higher CR CB-839 concentrations, the gross morphology did not differ due to humidification (Fig 3C, D, K, L), but the edges viewed microscopically were sharply altered, with a pronounced branching pattern evident that increased with CR dose (Fig 3M–P). No branching of this sort was observed at any concentration of CR under non-humidified conditions (Fig 3E–H). No wetting agent was observed preceding the swarms on humidified plates,
regardless of CR treatment (not shown). Swarming motility on different carbon sources Experiments were undertaken to determine what carbon sources could induce swarming on two different basal media (Table 1) containing NH4Cl as sole nitrogen
source. On the FW base medium, only casamino acids (as sole C and N) and succinate supported robust swarming, with a minimal level of swarming observed on d-sorbitol and very delayed minimal swarming on malic acid (Table 2). When 2 mM sodium phosphate buffer (pH 7) was added to FW glucose media, growth in liquid media was restored (not shown), and swarming was similar to M9 glucose (Fig 5A). On M9 based media, however, all carbon sources except maleic acid and sodium benzoate supported swarming motility DNA ligase (Table 2). Over a 48 h period, rapid swarming on d-sorbitol, malic acid, and succinate was observed (Fig 5A). Swarming was slower on glucose and sucrose, and slowest on maltose (Fig 5A). Swarming on maltose was characterized by long branches that failed to merge over long distances (Fig 6C). Swarming on other carbon sources on M9 resulted in similar edge phenotypes to the succinate edges. When multiple swarms were developing on a single plate, a repulsion effect was observed, such that the two growing swarms did not merge (Fig 7G). Cultures grown on either basal medium with CAA as sole C-source were strikingly disorganized (Fig 7B), and merged together on the plate (not shown).