Abstract
We investigated the effect of temperature on the biofilm formation of Pseudomonas aeruginosa and revealed that the biofilm formation increased rapidly at temperatures lower than 25°C. P. aeruginosa formed the most robust biofilm of a conspicuous mushroom-like structure at 20°C. However, when the temperature increased to 25°C, the biofilm formation rapidly decreased. Above 25°C, as the temperature rose, the biofilm formation increased again little by little despite its less-structured form, indicating that 25°C is the low point of biofilm formation. The intracellular 3',5'-cyclic diguanylate (c-di-GMP) levels also decreased rapidly as the temperature rose from 20 to 25°C. The expression levels of pelA, algD, and pslA encoding Pel, alginate, and Psl, respectively, were also dramatically affected by temperature, with pelA being regulated in a pattern similar to that of the intracellular c-di-GMP levels, and the pattern seen for algD regulation was the most similar to the actual biofilm formation pattern. Total exopolysaccharide production was thermoregulated and followed the regulation pattern of c-di-GMP. Interestingly, the thermoregulation patterns in biofilm formation were different depending on the strain of P. aeruginosa Unlike PAO1, another strain, PA14, showed a gradual decrease in biofilm formation and c-di-GMP in the range of 20 to 37°C, and P. aeruginosa clinical isolates also showed slightly different patterns in biofilm formation in conjunction with temperature change, suggesting that different strains may sense different temperature ranges for biofilm formation. However, it is obvious that P. aeruginosa forms more biofilms at lower temperatures and that temperature is an important factor in determining the biofilm formation.IMPORTANCE Biofilm formation is an important protection mechanism used by most microorganisms and provides cells with many advantages, like high infectivity, antibiotic resistance, and strong survivability. Since most persistent bacterial infections are believed to be associated with biofilms, biofilm control is an important issue in medicine, environmental engineering, and industry. Biofilm formation is influenced by various environmental factors. Temperature is the most direct environmental cue encountered by microorganisms. Here, we investigated the effect of temperature on the biofilm formation of P. aeruginosa, a notorious pathogen, and found that temperature is an important factor determining the amount and structure of biofilms. Low temperatures greatly increase biofilm formation and give biofilms a highly conspicuous structure. Although thermoregulation of biofilm formation is mainly mediated by c-di-GMP, some c-di-GMP-independent regulations were also observed. This study shows how biofilms are formed at various temperatures and provides new insights to control biofilms using temperature.
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