Biofilm formation assessment in Sinorhizobium meliloti reveals interlinked control with surface motility

Abstract

BackgroundSwarming motility and biofilm formation are opposite, but related surface-associated behaviors that allow various pathogenic bacteria to colonize and invade their hosts. In Sinorhizobium meliloti, the alfalfa endosymbiont, these bacterial processes and their relevance for host plant colonization are largely unexplored. Our previous work demonstrated distinct swarming abilities in two S. meliloti strains (Rm1021 and GR4) and revealed that both environmental cues (iron concentration) and bacterial genes (fadD, rhb, rirA) play crucial roles in the control of surface motility in this rhizobial species. In the current study, we investigate whether these factors have an impact on the ability of S. meliloti to establish biofilms and to colonize host roots.ResultsWe found that strain GR4, which is less prone to translocate on solid surfaces than strain Rm1021, is more efficient in developing biofilms on glass and plant root surfaces. High iron conditions, known to prevent surface motility in a wild-type strain of S. meliloti, promote biofilm development in Rm1021 and GR4 strains by inducing the formation of more structured and thicker biofilms than those formed under low iron levels. Moreover, three different S. meliloti mutants (fadD, rhb, and rirA) that exhibit an altered surface translocation behavior compared with the wild-type strain, establish reduced biofilms on both glass and alfalfa root surfaces. Iron-rich conditions neither rescue the defect in biofilm formation shown by the rhb mutant, which is unable to produce the siderophore rhizobactin 1021 (Rhb1021), nor have any impact on biofilms formed by the iron-response regulator rirA mutant. On the other hand, S. meliloti FadD loss-of-function mutants do not establish normal biofilms irrespective of iron levels.ConclusionsOur studies show that siderophore Rhb1021 is not only required for surface translocation, but also for biofilm formation on glass and root surfaces by strain Rm1021. In addition, we present evidence for the existence of control mechanisms that inversely regulate swarming and biofilm formation in S. meliloti, and that contribute to efficient plant root colonization. One of these mechanisms involves iron levels and the iron global regulator RirA. The other mechanism involves the participation of the fatty acid metabolism-related enzyme FadD.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-015-0390-z) contains supplementary material, which is available to authorized users.

2‐Tridecanone impacts surface‐associated bacterial behaviours and hinders plant–bacteria interactions

“…Next, we investigated whether 50 µM 2‐TDC could also impact the ability of S. meliloti to form surface‐attached communities. The defect shown by S. meliloti fadD mutants on biofilm development on glass surfaces has been shown previously (Amaya‐Gómez et al ., ) and was exhibited after long periods of incubation. Due to the volatile nature of 2‐TDC, its effect was analysed at earlier stages of biofilm formation (3 days).…”

Cyclophilin PpiB is involved in motility and biofilm formation via its functional association with certain proteins

“…; Amaya‐Gómez et al . ). As fatty acids and fatty acid‐related signals influence surface motility and biofilm formation in different bacteria (Tiaden et al .…”

Discrete Responses to Limitation for Iron and Manganese in Agrobacterium tumefaciens: Influence on Attachment and Biofilm Formation

“…Biofilm formation is a complex phenotype integrating numerous stimuli, metabolic pathways, regulatory networks, and bacterial behaviors to produce stable surface-associated communities (26). Nutrient levels have dramatic effects on the mode and extent of biofilm formation in numerous species (50,88,89). For example, biofilm formation by A. tumefaciens has been shown to be greatly stimulated by the limitation of inorganic phosphate (30).…”