Plant-Associated Symbiotic Burkholderia Species Lack Hallmark Strategies Required in Mammalian Pathogenesis

Abstract

Burkholderia is a diverse and dynamic genus, containing pathogenic species as well as species that form complex interactions with plants. Pathogenic strains, such as B. pseudomallei and B. mallei, can cause serious disease in mammals, while other Burkholderia strains are opportunistic pathogens, infecting humans or animals with a compromised immune system. Although some of the opportunistic Burkholderia pathogens are known to promote plant growth and even fix nitrogen, the risk of infection to infants, the elderly, and people who are immunocompromised has not only resulted in a restriction on their use, but has also limited the application of non-pathogenic, symbiotic species, several of which nodulate legume roots or have positive effects on plant growth. However, recent phylogenetic analyses have demonstrated that Burkholderia species separate into distinct lineages, suggesting the possibility for safe use of certain symbiotic species in agricultural contexts. A number of environmental strains that promote plant growth or degrade xenobiotics are also included in the symbiotic lineage. Many of these species have the potential to enhance agriculture in areas where fertilizers are not readily available and may serve in the future as inocula for crops growing in soils impacted by climate change. Here we address the pathogenic potential of several of the symbiotic Burkholderia strains using bioinformatics and functional tests. A series of infection experiments using Caenorhabditis elegans and HeLa cells, as well as genomic characterization of pathogenic loci, show that the risk of opportunistic infection by symbiotic strains such as B. tuberum is extremely low.

To split or not to split: an opinion on dividing the genus Burkholderia

“…Similarly, Angus et al (2014) analyzed the genomes of several Burkholderia species using functional and genomic methods to determine whether virulence determinants could be found in Group A species. Their genomics analysis showed that many of the Group A strains lack the Type 3 secretion system, especially T3SS-3, which is responsible for B. pseudomallei virulence in mammalian hosts.…”

Transfer of eleven species of the genus Burkholderia to the genus Paraburkholderia and proposal of Caballeronia gen. nov. to accommodate twelve species of the genera Burkholderia and Paraburkholderia

“…To address the safety concerns, a study of the pathogenic potential of plant-associated symbiotic species of the genus Burkholderia was conducted, resulting in the conclusion that it is highly unlikely that they can infect mammals (Angus et al, 2014), but the study results did not seem to be sufficiently convincing . It was argued that strains of some species from the second group, such as strains of Burkholderia fungorum isolated from various human and veterinary clinical samples, might be opportunistic pathogens.…”

Choline Catabolism in Burkholderia thailandensis Is Regulated by Multiple Glutamine Amidotransferase 1-Containing AraC Family Transcriptional Regulators

“…B. thailandensis is used as a less virulent model for the select agents B. pseudomallei and B. mallei, the causative agents of melioidosis and glanders, respectively. The reduced virulence of B. thailandensis is due primarily to the absence of the major capsule locus, important for B. pseudomallei virulence in mammals (4), although it is used to study the effect of type III secretion systems on phagocytic escape and retains other genes associated with virulence (5,6). Despite virulence differences, a great deal of the core genome is shared between B. thailandensis and its relatives, including many pathways for accessory metabolism.…”