Isocitrate dehydrogenase of Bacillus cereus is involved in biofilm formation

A LysR-like Transcriptional Regulator DsfB Is Required for the Daughter Cell Separation in Bacillus cereus 0-9

Bacillus cereus 0-9 is a biocontrol strain isolated from a healthy wheat root, and studying cell separation after division in this strain will improve our understanding of its growth, environmental adaptation, and spread. In this work, we identified the deletion of dsfB resulted in a chaining phenotype. Four genes, lysM1, lysM2, lysM3, and lysM4, were associated with daughter cell separation in strain 0-9. Furthermore, DsfB bound to the promoter regions of lysM1 and lysM2 and induced their transcription. The peptidoglycan hydrolase activity of the lysM1 and lysM2 gene products was confirmed in vitro by site-directed mutagenesis and biochemical analyses. The addition of purified LysM1 or LysM2 proteins in vitro or the overexpression of their coding genes inhibited the chaining phenotype of ΔdsfB. Taken together, our data indicate that DsfB is involved in daughter cell separation via the positive regulation of lysM1 and lysM2 expression in B. cereus 0-9.

Phenanthrene degradation by Bacillus cereus strain Sneb1168 isolated from Reynosa, Mexico

Phenanthrene is classified as a priority environmental pollutant because of its impact on the environment and on human health as a mutagenic and carcinogenic agent. The aim of this study was isolated and identified new bacteria with the capability to degrade phenanthrene from Reynosa, Mexico. Achromobacter insolitus, Bacillus cereus, and Microbacterium thalassium had high tolerant to phenanthrene (250 mg L-1). Biodegradation experiments in liquid culture evidenced that Bacillus cereus strain Sneb1168 degraded 48.58% of phenanthrene at 500 mg L-1 after 32 days. Remarkably, in the soil system, B. cereus degraded 72.9% of phenanthrene at 250 mg kg-1 dw. These results highlight the potential of B. cereus strain Sneb1168 to be used as an agent for the remotion of phenanthrene from contaminated soils.

The cellular redox state in Bacillus amyloliquefaciens WH1 affects biofilm formation indirectly in a surfactant direct manner

Surfactin is a signal to trigger biofilm formation against harsh environments. Generally, harsh environments can result in change of the cellular redox state to induce biofilm formation, but we know little about whether the cellular redox state influences biofilm formation via surfactin. Here, the reductant glucose could reduce surfactin and enhance biofilm formation by a surfactin-indirect way. The oxidant H₂ O₂ led to a decrease of surfactin accompanying with weakened biofilm formation. Spx and PerR were both necessary for surfactin production and biofilm formation. H₂ O₂ improved surfactin production but inhibited biofilm formation by a surfactin-indirect manner in Δspx, while it reduced surfactin production without obvious influence on biofilm formation in ΔperR. The ability against H₂ O₂ stress was enhanced in Δspx, but weakened in ΔperR. Thereby, PerR was favorable for resisting oxidative stress, while Spx played a negative role in this action. Knockout and compensation of rex also supported that the cells could form biofilm by a surfactin-indirect way. Collectively, surfactin is not a unique signal to trigger biofilm formation, and the cellular redox state can influence biofilm formation by a surfactin-direct or -indirect way in Bacillus amyloliquefaciens WH1.

Comparative Proteomic Analysis of Protein Patterns of Stenotrophomonas maltophilia in Biofilm and Planktonic Lifestyles

Stenotrophomonas maltophilia is a clinically relevant bacterial pathogen, particularly in cystic fibrosis (CF) patients. Despite the well-known ability to form biofilms inherently resistant to antibiotics and host immunity, many aspects involved in S. maltophilia biofilm formation are yet to be elucidated. In the present study, a proteomic approach was used to elucidate the differential protein expression patterns observed during the planktonic-to-biofilm transition of S. maltophilia Sm126, a strong biofilm producer causing chronic infection in a CF patient, to identify determinants potentially associated with S. maltophilia biofilm formation. In all, 57 proteins were differentially (3-fold; p < 0.01) expressed in biofilm cells compared with planktonic counterparts: 38 were overexpressed, and 19 were down-expressed. It is worth noting that 34 proteins were exclusively found in biofilm, mainly associated with quorum sensing-mediated intercellular communication, augmented glycolysis, amino acid metabolism, biosynthesis of secondary metabolites, phosphate signaling, response to nutrient starvation, and general stress. Further work is warranted to evaluate if these proteins can be suitable targets for developing anti-biofilm strategies effective against S. maltophilia.

The quorum sensing system of Novosphingobium sp. ERN07 regulates aggregate formation that promotes cyanobacterial growth

Microbial aggregates play key roles in cyanobacterial blooms. Being a bacterial communication mechanism, quorum sensing (QS) synchronizes gene expression in a density-dependent manner and regulates bacterial physiological behavior. However, the regulatory role of QS in the formation of cyanobacteria-associated bacterial aggregates remains poorly understood. Here, we present insight into the role of QS in regulating bacterial aggregate formation in a representative bacterial strain, Novosphingobium sp. ERN07, which was isolated from Microcystis blooms in Lake Taihu. A biosensor assay showed that ERN07 exhibits significant AHL-producing capacity. Biochemical and microscopic analysis revealed that this strain possesses the ability to form aggregated communities. Gene knockout experiments indicated that the AHL-mediated QS system positively regulates bacterial aggregation. The aggregated communities possess the ability to enhance the production of extracellular polymeric substances (EPS), alter EPS composition ratios, and affect biofilm formation. The addition of aggregated substances also has a significant growth-promoting effect on M. aeruginosa. Transcriptomic analysis revealed that the aggregated substances positively regulate photosynthetic efficiency and energy metabolism of M. aeruginosa. These findings show that QS can mediate the aggregation phenotype and associated substrate spectrum composition, contributing to a better understanding of microalgal-bacterial interactions and mechanisms of Microcystis bloom maintenance in the natural environment.