Dr. Carsten Matz and colleagues looked at marine bacteria that face constant threats in their habitat from environmental phagocytes, the amoebae, which behave in a similar way in the sea as the immune cells in the human body.
The Braunschweig-based researcher says that these predators easily pick bacteria when they are swimming freely and separately in the water.
However, if they become attached to a surface and socialize with other bacteria, the amoebae can no longer successfully attack them, the researcher adds.
"The surprising thing was that the amoebae attacking the biofilms were de-activated or even killed. The bacteria are clearly not just building a fortress, they are also fighting back," says Carsten Matz.
The researchers say that their study shows that the bacteria utilise chemical weapons to achieve this result.
According to them, a widespread and highly effective molecule used by marine bacteria for the purpose is the pigment violacein that paralyses the attackers momentarily, and triggers a suicide mechanism in the amoebae.
The researchers said that the biofilm would shimmer a soft purple colour when the defence system was ready.
"I feel that these results could offer a change of perspective. Biofilms may no longer be seen just as a problem; they may also be a source of new bioactive agents. When organized in biofilms, bacteria produce highly effective substances which individual bacteria alone cannot produce," says Carsten Matz.
The researchers believe that such molecules may be helpful in combating a specific group of pathogens - human parasites that cause devastating infections such as sleeping illness and malaria.
An article on this study has been published in the journal PLoS ONE.