A homolog of methionine γ-lyase is required for biofilm development in the cyanobacterium Synechococcus elongatus

Bacterial type IV pilus assembly systems are involved in diverse functions including motility, adhesion and DNA uptake. Studies of the cyanobacterium Synechococcus elongatus sp. PCC7942 revealed that this machinery is also involved in suppression of biofilm formation: inactivation of components of this complex results in robust biofilm development. EbsA, a unique component of cyanobacterial type IV pilus assembly complexes, immunoprecipitates with a homolog of methionine γ-lyase (MGL). Here we demonstrate that MGL is required for biofilm development. Based on immunoprecipitation experiments using MGL as a bait, we suggest that this enzyme associates with a large enzymatic hub and with the translation machinery. Inactivation of mgl in the biofilm-forming mutant pilBΩ abrogates biofilm formation. However, assessment of expression of the ebfG-operon, which encodes proteins that comprise the biofilm matrix, using yellow fluorescent protein reporter strains, indicated high induction in the double mutant pilB/mgl similar to the biofilm-forming pilB-mutant. Thus, induction of the ebfG-operon is insufficient to promote biofilm development when a downstream step in which MGL participates is blocked. Overall, data suggest that MGL activity or an enzymatic activity of its interactor(s) is required to promote biofilm formation.