Bacterial cooperative organization under antibiotic stress

Bacteria have developed sophisticated modes of cooperative behavior to cope with unfavorable environmental conditions. Here we report the effect of an tibiotic stress on the colonial development of Paenibacillus dendritiformis and P. vortex. We focus on the effect of co-trimoxazole on the colonial or ganization of P. dendritiformis. We find that the exposure to non-lethal co ncentrations of antibiotic leads to dramatic changes in the colonial growth patterns. Branching, tip-splitting patterns are affected by reduction in t he colonial fractal dimension from D-f = 2.0 to 1.7, appearance of pronounc ed weak chirality and pronounced radial orientation of the growth. We combi ne the experimental observations with numerical studies of both discrete an d continuous generic models to reveal the causes for the modifications in t he patterns. We conclude that the bacteria adjust their chemotactic signali ng together with variations in the bacteria length and increase in the meta bolic load. (C) 2000 Elsevier Science B.V. All rights reserved.