The role of nitric-oxide-synthase-derived nitric oxide in multicellular traits of Bacillus subtilis 3610: biofilm formation, swarming, and dispersal
1 Max-Planck-Institute for Marine Microbiology, Celsiusstrasse 1, D-28359 Bremen, Germany
2 bionsys GmbH, Fahrenheitstrasse 1, D-28359, Bremen, Germany
3 Instituto Nacional de Téchnica Aeroespecial, Centro de Astrobiologia (INTA-CSIC), Madrid 28850, Spain
4 Eawag - Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133-P.O. Box 611-8600 Dübendorf-Switzerland
BMC Microbiology 2011, 11:111 doi:10.1186/1471-2180-11-111Published: 20 May 2011
Bacillus subtilis 3610 displays multicellular traits as it forms structurally complex biofilms and swarms on solid surfaces. In addition, B. subtilis encodes and expresses nitric oxide synthase (NOS), an enzyme that is known to enable NO-mediated intercellular signalling in multicellular eukaryotes. In this study, we tested the hypothesis that NOS-derived NO is involved in the coordination of multicellularity in B. subtilis 3610.
We show that B. subtilis 3610 produces intracellular NO via NOS activity by combining Confocal Laser Scanning Microscopy with the NO sensitive dye copper fluorescein (CuFL). We further investigated the influence of NOS-derived NO and exogenously supplied NO on the formation of biofilms, swarming motility and biofilm dispersal. These experiments showed that neither the suppression of NO formation with specific NOS inhibitors, NO scavengers or deletion of the nos gene, nor the exogenous addition of NO with NO donors affected (i) biofilm development, (ii) mature biofilm structure, and (iii) swarming motility in a qualitative and quantitative manner. In contrast, the nos knock-out and wild-type cells with inhibited NOS displayed strongly enhanced biofilm dispersal.
The results suggest that biofilm formation and swarming motility in B. subtilis represent complex multicellular processes that do not employ NO signalling and are remarkably robust against interference of NO. Rather, the function of NOS-derived NO in B. subtilis might be specific for cytoprotection against oxidative stress as has been proposed earlier. The influence of NOS-derived NO on dispersal of B. subtilis from biofilms might be associated to its well-known function in coordinating the transition from oxic to anoxic conditions. Here, NOS-derived NO might be involved in fine-tuning the cellular decision-making between adaptation of the metabolism to (anoxic) conditions in the biofilm or dispersal from the biofilm.