Effects of an EPS Biosynthesis Gene Cluster of Paenibacillus polymyxa WLY78 on Biofilm Formation and Nitrogen Fixation under Aerobic Conditions

Xiaojuan He,Qin Li,Sanfeng Chen,Nan Wang

doi:10.3390/microorganisms9020289

Abstract

Exopolysaccharides (EPS) are of high significance in bacterial biofilm formation. However, the effects of EPS cluster(s) on biofilm formation in Paenibacillus species are little known. In this study, we have shown that Paenibacillus polymyxa WLY78, a N2-fixing bacterium, can form biofilm. EPS is the major component of the extracellular matrix. The genome of P. polymyxa WLY78 contains two putative gene clusters (designated pep-1 cluster and pep-2 cluster). The pep-1 cluster is composed of 12 putative genes (pepO-lytR) co-located in a 13 kb region. The pep-2 cluster contains 17 putative genes (pepA-pepN) organized as an operon in a 20 kb region. Mutation analysis reveals that the pep-2 cluster is involved in EPS biosynthesis and biofilm formation. Disruption of the pep-2 cluster also leads to the enhancement of motility and change of the colony morphology. In contrast, disruption of the pep-1 cluster does not affect EPS synthesis or biofilm formation. More importantly, the biofilm allowed P. polymyxa WLY78 to fix nitrogen in aerobic conditions, suggesting that biofilm may provide a microaerobic environment for nitrogenase synthesis and activity.

Highlights

Bacteria can obtain many survival benefits by forming biofilm
Our results revealed that the pep-2 cluster is responsible for EPS biosynthesis and biofilm formation and the biofilm provides a microaerobic environment for nitrogen fixation
The highest amount of biofilm was produced when 200 mM glucose was used (Figure 1E). These results suggested that sufficient carbon sources and nitrogen sources were critical for the P. polymyxa WLY78 biofilm formation

Summary

Introduction

Biofilms are architecturally complex communities of microorganisms in which the cells are held together by an extracellular matrix [1,2]. Recent reports have highlighted the biofilm formation of the beneficial bacteria in agriculture, such as the plant growth-promoting bacteria Bacillus subtilis, Azospirillum brasilense, Rhizobia, etc [7,8,9,10]. Many studies showed that EPS play a critical role in biofilm formation [12]. The extracellular polysaccharides of rhizobacteria (e.g. Sinorhizobium meliloti and Azospirillum brasilense Sp7) play an important role in biofilm formation and the interactions between bacterium and plant roots [17,18,19]. Some species of the Paenibacillus genus are the important plant growth-promoting rhizobacteria (PGPR). Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations

Methods

Results

Conclusion