INTRODUCTION

The growth and activity of microorganisms affect our lives in both positive and negative ways. We have, since early times, tried to combat unwanted microbes and utilize those expressing useful traits. Microorganisms can cause diseases and chronic infections in humans, animals, and plants. In medicine, agriculture and fish farming, treatment scenarios are based on antimicrobial compounds such as antibiotics, with toxic and growth-inhibitory properties. Control of growth by eradication of bacteria is one of the most important scientific achievements. Unfortunately, bacteria have become gradually more and more resistant to antibiotics, and infections caused by resistant bacteria are on a dramatic increase. It has recently become apparent that the bacterial lifestyle also contributes significantly to this problem. The traditional way of culturing bacteria as planktonic, liquid cultures imprinted the view that bacteria live as unicellular organisms. Although it must be emphasized that such test-tube studies have led to fundamental insights into basic life processes and have unraveled complex intracellular regulatory networks, it is now clear that in nature microbial activity is mainly associated with surfaces and we as scientists must therefore turn our attention to this sessile mode of growth (33). It appears that the ability to form surface-associated, structured and cooperative consortia (referred to as biofilms) is one of the most remarkable and ubiquitous characteristics of bacteria (12). In this sessile life form, bacteria can cause various problems in industrial settings, ranging from corrosion and biofouling to food contamination.