Affiliation:
1. Department of Biological Sciences, Virginia Tech , Blacksburg, Virginia, USA
Abstract
ABSTRACT
The regulation of biofilm and motile states as alternate bacterial lifestyles has been studied extensively in flagellated bacteria, where the second messenger cyclic-di-GMP (cdG) plays a crucial role. However, much less is known about the mechanisms of such regulation in motile bacteria without flagella. The bacterial type IV pilus (T4P) serves as a motility apparatus that enables
Myxococcus xanthus
to move on solid surfaces. PilB, the T4P assembly ATPase, is, therefore, required for T4P-dependent motility in
M. xanthus
. Interestingly, T4P is also involved in the regulation of exopolysaccharide as the biofilm matrix material in this bacterium. A newly discovered cdG-binding domain, MshE
N
, is conserved in the N-terminus of PilB (PilB
N
) in
M. xanthus
and other bacteria. This suggests that cdG may bind to PilB to control the respective outputs that regulate biofilm development and T4P-powered motility. In this study, we aimed to validate
M. xanthus
PilB as a cdG effector protein. We performed a systematic mutational analysis of its cdG-binding domain to investigate its relationship with motility, piliation, and biofilm formation. Excluding those resulting in low levels of PilB protein, all other substitution mutations in PilB
N
resulted in
pilB
mutants with distinct and differential phenotypes in piliation and biofilm levels in
M. xanthus
. This suggests that the PilB
N
domain plays dual roles in modulating motility and biofilm levels, and these two functions of PilB can be dependent on and independent of each other in
M. xanthus
.
IMPORTANCE
The regulation of motility and biofilm by cyclic-di-GMP in flagellated bacteria has been extensively investigated. However, our knowledge regarding this regulation in motile bacteria without flagella remains limited. Here, we aimed to address this gap by investigating a non-flagellated bacterium with motility powered by bacterial type-IV pilus (T4P). Previous studies hinted at the possibility of
Myxococcus xanthus
PilB, the T4P assembly ATPase, serving as a cyclic-di-GMP effector involved in regulating both motility and biofilm. Our findings strongly support the hypothesis that PilB directly interacts with cyclic-di-GMP to act as a potential switch to promote biofilm formation or T4P-dependent motility. These results shed light on the bifurcation of PilB functions and its pivotal role in coordinating biofilm formation and T4P-mediated motility.
Funder
National Science Foundation
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
1 articles.
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