Effects of the Bradyrhizobium japonicum waaL (rfaL) Gene on Hydrophobicity, Motility, Stress Tolerance, and Symbiotic Relationship with Soybeans

Abstract

We cloned and sequenced the waaL (rfaL) gene from Bradyrhizobium japonicum, which infects soybean and forms nitrogen-fixing nodules on soybean roots. waaL has been extensively studied in the lipopolysaccharide (LPS) biosynthesis of enteric bacteria, but little is known about its function in (brady)rhizobial LPS architecture. To characterize its role as O-antigen ligase in the LPS biosynthesis pathway, we constructed a waaL knock-out mutant and its complemented strain named JS015 and CS015, respectively. LPS analysis showed that an LPS structure of JS015 is deficient in O-antigen as compared to that of the wild type and complemented strain CS015, suggesting that WaaL ligates the O-antigen to lipid A-core oligosaccharide to form a complete LPS. JS015 also revealed increased cell surface hydrophobicity, but it showed decreased motility in soft agar plates. In addition to the alteration in cell surface properties, disruption of the waaL gene caused increased sensitivity of JS015 to hydrogen peroxide, osmotic pressure, and novobiocin. Specifically, plant tests revealed that JS015 failed to nodulate the host plant soybean, indicating that the rhizobial waaL gene is responsible for the establishment of a symbiotic relationship between soybean and B. japonicum.

The Role of Pseudomonas aeruginosa Lipopolysaccharide in Bacterial Pathogenesis and Physiology

“…O antigen is necessary for effective swimming and swarming motility in many bacteria [110][111][112][113][114][115][116][117][118][119][120], which has been demonstrated in genetic studies that investigated the effect on motility when genes involved in various steps of the O antigen synthesis and assembly pathway are deleted. Our group reported the phenotypes of several such mutants in P. aeruginosa.…”

Struktura lipopolisacharydów rizobiowych i ich znaczenie w procesie symbiozy

“…Przeprowadzone doświadczenia dodatkowo wykazały, że soja zakażona mutantem B. japonicum zupełnie nie tworzyła brodawek korzeniowych. Rezultaty tych badań pokazują, że O-PS ma kluczowe znaczenie w inicjacji i podtrzymywaniu relacji symbiotycznych pomiędzy bakteriami, a roślinnym gospodarzem [86].…”

Structure of the Lipopolysaccharide from the Bradyrhizobium sp. ORS285 rfaL Mutant Strain

“…[13] This in contrast to many rhizobials pecies, such as B. japonicum, Rhizobium etli or R. phaseoli,f or which the absence of the O-chain is reportedt oc ause ad ramatic decrease in symbiotic capacity. [15][16][17] Thus, the ability of the O-antigen-lacking ORS285 mutants to retain nodulation-promoting properties is not yetf ully understood.…”