Microbial Resistance Mechanisms to the Antibiotic and Phytotoxin Fusaric Acid

Abstract

Fusaric acid (FA) produced by Fusarium oxysporum plays an important role in disease development in plants, including cotton. This non-specific toxin also has antibiotic effects on microorganisms. Thus, one expects a potential pool of diverse detoxification mechanisms of FA in nature. Bacteria and fungi from soils infested with Fusarium and from laboratory sources were evaluated for their ability to grow in the presence of FA and to alter the structure of FA into less toxic compounds. None of the bacterial strains were able to chemically modify FA. Highly FA-resistant strains were found only in Gram-negative bacteria, mainly in the genus of Pseudomonas. The FA resistance of the Gram-negative bacteria was positively correlated with the number of predicted genes for FA efflux pumps present in the genome. Phylogenetic analysis of predicted FA resistance proteins (FUSC, an inner membrane transporter component of the efflux pump) revealed that FUSC proteins having high sequence identities with the functionally characterized FA resistance protein FusC or Fdt might be the major contributors of FA resistance. In contrast, most fungi converted FA to less toxic compounds regardless of the level of FA resistance they exhibited. Five derivatives were detected, and the detoxification of FA involved either oxidative reactions on the butyl side chain or reductive reactions on the carboxylic acid group. The production of these metabolites from widely different phyla indicates that resistance to FA by altering its structure is highly conserved. A few FA resistant saprophytic or biocontrol strains of fungi were incapable of altering FA, indicating a possible involvement of efflux transporters. Deployment of both efflux and derivatization mechanisms may be a common feature of fungal FA resistance.

Genome sequencing and assessment of plant growth-promoting properties of a Serratia marcescens strain isolated from vermicompost

“…As part of the arms race between microorganisms, several Fusarium species produce fusaric acid, a mycotoxin reported to be toxic to some microorganisms, such as P. fluorescens [ 96 ]. We observed that S. marcescens UENF-22GI has a gene (AK961_08005) that encodes a multi-TM protein of the FUSC solute exporter family, which has been demonstrated to provide resistance against fusaric acid in other bacteria.…”

Illumina-MiSeq analysis of fungi in acid lime roots reveals dominance of Fusarium and variation in fungal taxa

“…This could be related to the fact that Fusarium growth rate is usually higher compared to several fungal species 35 , 36 . In addition, Fusarium species are well known to produce several toxic compounds which limit growth of other fungal species 37 , 38 , thus giving Fusarium a chance to dominate. However, a future study might be required to understand the reasons behind the dominance of Fusarium in acid lime roots.…”

MarR Family Transcription Factors from Burkholderia Species: Hidden Clues to Control of Virulence-Associated Genes

“…It has been reported that the ability of bacteria (with pseudomonads exhibiting the greatest resistance) to survive in the presence of fusaric acid correlates with the copy number of genes encoding FusC. Among the Burkholderia species analyzed in this particular survey were B. glumae and B. cepacia, both of which encode two FusC proteins; one of these FusC proteins is a homolog of B. cenocepacia BCAS0018 (95). Expression of the B. cepacia fusaric acid resistance locus in E. coli conferred resistance to fusaric acid, indicating that the enzyme is functional (98).…”

“…This operon is conserved in Bpc species, but it is absent from both B. cenocepacia and B. xenovorans. The fusaric acid resistance protein is involved in resistance to the nonspecific fungal toxin fusaric acid, which is produced by Fusarium species and considered a virulence factor in their interaction with susceptible plants (95). Resistance to fusaric acid would therefore benefit inhabitants of the rhizosphere.…”