Fig. 2.

A. Bacterial biofilm lifecycle. B. Mechanisms involved in the secretion of the large adhesion proteins LapA and LapF and in the regulation of the expression of their biosynthetic genes in P. putida. LapA is produced at the beginning of biofilm formation to promote cell-surface attachment. It is released from the outer membrane through the action of LapG in response to nutrient deficiency or other stresses. LapF is synthetized later in the process, allowing cell–cell attachment. Regulation is especially mediated by transcription factors such as FleQ, Fis and RpoS. Many aspects of LapF structure and secretion remain to be deciphered. The lapA and lapF genes are distant from each other in Pseudomonas putida genomes. Cyclic-di-GMP: cyclic dimeric guanosine monophosphate; EPS: extracellular polymeric substances; RTX: repeats-in-toxin; T1SS: type I secretion system.