Genes Required for the Anti-fungal Activity of a Bacterial Endophyte Isolated from a Corn Landrace Grown Continuously by Subsistence Farmers Since 1000 BC

Abstract

Endophytes are microbes that inhabit internal plant tissues without causing disease. Some endophytes are known to combat pathogens. The corn (maize) landrace Chapalote has been grown continuously by subsistence farmers in the Americas since 1000 BC, without the use of fungicides, and the crop remains highly valued by farmers, in part for its natural tolerance to pests. We hypothesized that the pathogen tolerance of Chapalote may, in part, be due to assistance from its endophytes. We previously identified a bacterial endophyte from Chapalote seeds, Burkholderia gladioli strain 3A12, for its ability to combat a diversity of crop pathogens, including Sclerotinia homoeocarpa, the most important fungal disease of creeping bentgrass, a relative of maize used here as a model system. Strain 3A12 represents a unique opportunity to understand the anti-fungal activities of an endophyte associated with a crop variety grown by subsistence farmers since ancient times. Here, microscopy combined with Tn5-mutagenesis demonstrates that the anti-fungal mode of action of 3A12 involves flagella-dependent swarming toward its pathogen target, attachment and biofilm-mediated microcolony formation. The mutant screen revealed that YajQ, a receptor for the secondary messenger c-di-GMP, is a critical signaling system that mediates this endophytic mobility-based defense for its host. Microbes from the traditional seeds of farmers may represent a new frontier in elucidating host–microbe mutualistic interactions.

Invasive Grass Dominance over Native Forbs Is Linked to Shifts in the Bacterial Rhizosphere Microbiome

“…Burkholderiaceae are considered keystone members in grasslands as endophytes or pathogens [83][84][85][86] and are known for their antimicrobial properties [87][88][89], nitrogen-fixing abilities [80,90], and competitive dominance, especially in N-limited environments [91]. Some members are even known to suppress fungal pathogens [92,93].…”

Burkholderia gladioli CGB10: A Novel Strain Biocontrolling the Sugarcane Smut Disease

“…We then reconstructed the phylogeny of the 22 bacterial species based on these 763 single-copy core genes, and the results showed that CGB10 was closest to B. gladioli, and together they clustered with B. glumae (Figure 1A). We further confirmed the taxonomic status of CGB10 by calculating the average nucleotide identity (ANI) [28] based on the whole genome of the CGB10 strain in comparison with another six B. gladioli strains, including established rice pathogen BSR3 [24], strains isolated from healthy plants and displaying antifungal activity [29][30][31], and strains isolated from a cystic fibrosis patient [32], as well as a B. glume strain BGR1 [24], which is also known as a rice pathogen (information of selected strains was detailed in Table 1). The identity between CGB10 and the six selected B. gladioli strains was all higher than 98%, yet the identity between CGB10 and the B. glumae strain BGR1 was 88.12%.…”

Invasive grass dominance over native forbs is linked to shifts in the bacterial rhizosphere microbiome

“…This family is considered a keystone member in grasslands and is often associated with plants as endophytes or pathogens [85][86][87][88]. Burkholderiaceae contains members known for their antimicrobial properties [89][90][91], nitrogen-fixing abilities [82,92], and competitive dominance, especially in N-limited environments [93] like serpentine. Some members of Burkholderiaceae are even known to suppress fungal pathogens including the turf grass pathogen Rhizoctonia (family Ceratobasidiaceae) [94,95].…”