B. pseudomallei and B. thailandensis form biofilms under different temperatures
We assessed the ability of Burkholderia to form a biofilm under a scanning electron microscope (SEM) using B. pseudomallei JW270 strain. We depict that the biofilm formation process inBurkholderia follows the same pattern as most Gram-negative bacteria (Fig 1a). We see single cells adhere to each other (Fig 1a, step 1). The adherence is followed by colony aggregation (Fig 1a, step 2) and export of the biofilm components (Fig 1a, steps 3-4). Export of biofilm components progresses until most cells are covered/protected to form a mature biofilm (Fig 1a, step 5). Cells are dispersed from a matured biofilm to continue the cycle (Fig 1a, step 6). A visual and microscopic observation shows that all four strains used for the composition study: B. pseudomallei strains (Bp1026b Δasd , Bp82, and JW270) and B. thailandensis E264 are all able to form both an adherent biofilm at the bottom of the plate and a pellicle; a biofilm formed at the air-liquid interface (Fig 1b). We observed that pellicle morphologies differed between strains. Bp82 and JW270 present wrinkled and cloudy pellicles while 1026b Δasd and E264 have a thin, smooth layer (Fig. 1b). Fig 1c shows an image of a processed JW270 pellicle. There was no difference in the SEM images between all pellicles.
B. pseudomallei is not fastidious and can grow under diverse environmental conditions [41], such as soil and rice paddy field water at temperatures between 21°C and 37°C [42, 43]. B. pseudomallei in the lab is commonly grown at 37°C, a temperature that corresponds to human body temperature [44]. To compare biofilm capabilities under varying temperatures, B. pseudomallei was grown statically for 72 hours either at room temperature (22°C) to represent rice paddy fields or at 37°C in an incubator to represent human host temperature. Fig. 1d shows that at the end of the experiment, there is no significant difference between the same strains grown at different temperatures (Student’s t-test, P > 0.05). However, we observed that in earlier time points, cells grown at RT lagged behind 37°C cells but ultimately forms the same amount of biofilm by 72 hours. For comparison between groups at the end of the experiment (e.g. 1026b Δasd vs. Bp82 at 37°C), student t-tests show that there was no significant difference between biofilms formed between all strains (Fig 1e, P >0.05). We also observed that cultures grown at both temperatures formed surface adherent biofilms, but cultures grown at 37°C are capable of forming both surface adherent biofilms and pellicles.