Cell Plasticity of Pseudomonas Putida KT2440 During Biofilm Mode of Growth in Response to Environmental Cues

Abstract

In a natural environment, bacteria frequently encounter a variety of environmental cues, including mechanical, oxidative, reductive, nitrosative, osmotic and thermal stresses. To cope up these dynamic environments, bacteria possess different adaptation mechanisms. These include production of latent endospores, decrease in metabolic rate, alteration in cell shape, gene expression, and protein synthesis. The present study aimed to understand the effect of nutrient limitation and alternation in pH on the phenotypic changes in the cell shape and size of Pseudomonas putida KT2440 during biofilm mode of growth. The phase contrast microscopic-based analysis of Pseudomonas putida KT2440 revealed that the outer layer of the colonies consists mostly of rod-shaped cells, whereas the inner layers consist of coccoid-shaped cells. The nutrient limitation experiment revealed that the cell size decreased over time. The rod-shaped cells were predominant during the initial growth phase, which further converted into coccoid-shaped cells with decreasing nutrient concentration. Further, the effects of H+ ion concentration on bacterial morphology were carried out in a pH-limiting medium with synchronously declining order of 0.5 pH from pH 7 to pH 5. The cell size of Pseudomonas putida KT2440 showed significant reduction as the concentration of H+ ions increased, and the rod-shaped planktonic cells were observed during the early growth phase changed into coccoid-shaped cells as the time interval increased. The current study depicted that Pseudomonas putida KT2440 have two vegetative phenotypes. Depending on the favourable and stressful conditions of the biofilm, the bacteria can move from motile rods to non-motile cocci and vice versa.