Current data from bacterial pathogens of animals and from bacterial symbionts of plants support some of the more general proposed functions for lipopolysaccharides (LPS) and underline the importance of LPS structural versatility and adaptability. Most of the structural heterogeneity of LPS molecules is found in the O-antigen polysaccharide. In this review, the role and mechanisms of this striking flexibility in molecular structure of the O-antigen in bacterial pathogens and symbionts are illustrated by some recent findings. The variation in O-antigen that gives rise to an enormous structural diversity of O-antigens lies in the sugar composition and the linkages between monosaccharides. The chemical composition and structure of the O-antigen is strain-specific (interstrain LPS heterogeneity) but can also vary within one bacterial strain (intrastrain LPS heterogeneity). Both LPS heterogeneities can be achieved through variations at different levels. First of all, O-polysaccharides can be modified non-stoichiometrically with sugar moieties, such as glucosyl and fucosyl residues. The addition of non-carbohydrate substituents, i.e. acetyl or methyl groups, to the O-antigen can also occur with regularity, but in most cases these modifications are again non-stoichiometric. Understanding LPS structural variation in bacterial pathogens is important because several studies have indicated that the composition or size of the O-antigen might be a reliable indicator of virulence potential and that these important features often differ within the same bacterial strain. In general, O-antigen modifications seem to play an important role at several (at least two) stages of the infection process, including the colonization (adherence) step and the ability to bypass or overcome host defense mechanisms. There are many reports of modifications of O-antigen in bacterial pathogens, resulting either from altered gene expression, from lysogenic conversion or from lateral gene transfer followed by recombination. In most cases, the mechanisms underlying these changes have not been resolved. However, in recent studies some progress in understanding has been made. Changes in O-antigen structure mediated by lateral gene transfer, O-antigen conversion and phase variation, including fucosylation, glucosylation, acetylation and changes in O-antigen size, will be discussed. In addition to the observed LPS heterogeneity in bacterial pathogens, the structure of LPS is also altered in bacterial symbionts in response to signals from the plant during symbiosis. It appears to be part of a molecular communication between bacterium and host plant. Experiments ex planta suggest that the bacterium in the rhizosphere prepares its LPS for its roles in symbiosis by refining the LPS structure in response to seed and root compounds and the lower pH at the root surface. Moreover, modifications in LPS induced by conditions associated with infection are another indication that specific structures are important. Also during the differentiation from bacterium to bact...

This document presents the Bonn PRINTEGER Consensus Statement: Working with Research Integrity—Guidance for research performing organisations. The aim of the statement is to complement existing instruments by focusing specifically on institutional responsibilities for strengthening integrity. It takes into account the daily challenges and organisational contexts of most researchers. The statement intends to make research integrity challenges recognisable from the work-floor perspective, providing concrete advice on organisational measures to strengthen integrity. The statement, which was concluded February 7th 2018, provides guidance on the following key issues: Providing information about research integrityProviding education, training and mentoringStrengthening a research integrity cultureFacilitating open dialogueWise incentive managementImplementing quality assurance proceduresImproving the work environment and work satisfactionIncreasing transparency of misconduct casesOpening up researchImplementing safe and effective whistle-blowing channelsProtecting the alleged perpetratorsEstablishing a research integrity committee and appointing an ombudspersonMaking explicit the applicable standards for research integrity

Rhizobiaceae are Gram-negative bacteria that are able to induce the formation of nitrogen-fixing nodules on roots of leguminous plants. For infection and differentiation of nodules, bacterial determinants including surface polysaccharides are required. LPS 1 is the major structural component of a Gramnegative bacterial outer membrane, and evidence for its importance in plant-microbe interactions is appealing. Various Rhizobium mutants with alterations in LPS are defective in the symbiotic association at different stages of infection and nodule development (1).LPS consists of lipid A, which anchors it to the outer membrane, and a polysaccharide portion that extends into the environment. The polysaccharide portion contains an inner core region, conserved among related strains, and an O-antigen region, whose structure varies in a strain-dependent manner. The O-antigen region consists of the repeating unit and a non-repeating sequence, also referred to as the O-chain attachment region or outer core region (2-5). LPS II (or rough LPS) refers to lipid A and the inner core, whereas LPS I (or smooth LPS) refers to the complete structure. The recent elucidation of the glycosyl sequence of the Rhizobium etli CE3 LPS O-antigen completed the glycosyl sequence of the R. etli CE3 LPS (2-5). The O-antigenic polysaccharide was found to be a unique, relatively low molecular weight glycan of a fairly discrete size, with surprisingly little variation in the number of repeating units (degree of polymerization ϭ 5). Each trisaccharide repeating unit consists of glucuronic acid, fucose, and 3-O-methyl-6-deoxytalose (2).No specific information on the biosynthetic mechanism leading to the assembly of the O-chain polysaccharide in R. etli CE3 is available. Nevertheless, despite the diversity in structures of O-antigens, the mechanisms involved in their synthesis seem to be conserved in those bacteria that have been studied to date (6). In general, the activated sugar precursors are not transferred directly to a growing LPS molecule. Instead, O-antigens are synthesized separately on a lipid carrier, termed bactoprenyl phosphate. This polymerization step can occur either in the cytoplasm or in the periplasm depending on the assembly pathway. In each case, translocation of the O-antigen across the inner plasma membrane is required. So far, three assembly pathways are known for the polymerization and export of Oantigens. These processes are designated the "Wzy-dependent" pathway, the "ABC transporter-dependent" pathway, and the "synthase-dependent" pathway based on the proteins that are involved in the pathways and the components involved in export across the plasma membrane (7). Once completed, the O-antigen is covalently ligated to a preformed acceptor composed of lipid A and the inner core at the periplasmic face of the plasma membrane. After ligation, the completed LPS molecule is translocated to the cell surface by an unknown mechanism.The genes involved in saccharide processing, including export, polymerization, and assembly of comple...

The Bradyrhizobium japonicum hupT gene was sequenced, and its gene product was found to be homologous to NtrB-like histidine kinases. A hupT mutant expresses higher levels of hydrogenase activity than the wild-type strain under hydrogenase-inducing conditions (i.e., microaerobiosis plus hydrogen, or symbiosis), whereas in noninduced hupT cells,hupSL expression is derepressed but does not lead to hydrogenase activity. We conclude that HupT is involved in the repression of HupSL synthesis at the transcriptional level but that enzymatic activation requires inducing conditions.