The Flagellar Gene Regulates Biofilm Formation and Mussel Larval Settlement and Metamorphosis.

Xiao Liang,Asami Yoshida,Li-Hua Peng,Xiu-Kun Zhang,Kiyoshi Osatomi,Jin-Long Yang,You-Ting Zhu

doi:10.3390/ijms21030710

Abstract

Biofilms are critical components of most marine systems and provide biochemical cues that can significantly impact overall community composition. Although progress has been made in the bacteria–animal interaction, the molecular basis of modulation of settlement and metamorphosis in most marine animals by bacteria is poorly understood. Here, Pseudoalteromonas marina showing inducing activity on mussel settlement and metamorphosis was chosen as a model to clarify the mechanism that regulates the bacteria–mussel interaction. We constructed a flagellin synthetic protein gene fliP deletion mutant of P. marina and checked whether deficiency of fliP gene will impact inducing activity, motility, and extracellular polymeric substances of biofilms. Furthermore, we examined the effect of flagellar proteins extracted from bacteria on larval settlement and metamorphosis. The deletion of the fliP gene caused the loss of the flagella structure and motility of the ΔfliP strain. Deficiency of the fliP gene promoted the biofilm formation and changed biofilm matrix by reducing β-polysaccharides and increasing extracellular proteins and finally reduced biofilm-inducing activities. Flagellar protein extract promoted mussel metamorphosis, and ΔfliP biofilms combined with additional flagellar proteins induced similar settlement and metamorphosis rate compared to that of the wild-type strain. These findings provide novel insight on the molecular interactions between bacteria and mussels.

Highlights

In the marine environment, biofilms are critical components of most marine systems and provide biochemical cues that can significantly impact overall community composition [1,2]
In order to test that the impact of deficiency of fliP gene on the mussel settlement-inducing activity, we constructed a flagellin synthetic protein gene fliP deletion mutant of P. marina (Figure 1) and compared the inducing activity of biofilms formed by wild-type and ∆fliP strains on the larvae of M. coruscus (Figure 2)
At an initial concentration of 5 × 108 colony-forming units (CFU)/mL, larval settlement and metamorphosis rate in biofilms formed by ∆fliP strain was only 8.33%, a 75.01% reduction compared with the wild-type strain (Figure 2A)

Summary

Introduction

Biofilms are critical components of most marine systems and provide biochemical cues that can significantly impact overall community composition [1,2]. Biofilm development has been known to be mediated by cellular and environmental factors, and the production of settlement-inducing cues of biofilms varies due to the space-time change in biofilm characteristics including cell density and structure [6,7,8]. Marine bacteria dominate in the natural biofilms developed in ocean conditions [9,10,11]. Pseudoalteromonas is widely distributed in marine environments [12], and biofilms formed by Pseudoalteromonas mediate settlement and metamorphosis of many typical macrofouling organisms, including mussel, barnacle, and tubeworm [13,14,15,16]. Some progress has been made in the specific animal Hydroides elegans [15,16,17,18], the molecular basis of modulation of settlement and metamorphosis in most marine animals by bacteria is poorly understood

Methods

Results

Discussion

Conclusion