Response of the Biocontrol Agent Pseudomonas pseudoalcaligenes AVO110 to Rosellinia necatrix Exudate

Abstract

Diseases associated with fungal root invasion cause a significant loss of fruit tree production worldwide. The bacterium Pseudomonas pseudoalcaligenes AVO110 controls avocado white root rot disease caused by Rosellinia necatrix by using mechanisms involving competition for nutrients and niches. Here, a functional genomics approach was conducted to identify the bacterial traits involved in the interaction with this fungal pathogen. Our results contribute to a better understanding of the multitrophic interactions established among bacterial biocontrol agents, the plant rhizosphere, and the mycelia of soilborne pathogens.

The Rhizobacterium Pseudomonas alcaligenes AVO110 Induces the Expression of Biofilm-Related Genes in Response to Rosellinia necatrix Exudates

“…Manual curing of COG categories related to cell motility, locomotion, cellular component assembly, and signal transduction (6.8% of the total number of annotated products) revealed that P. alcaligenes AVO110 singletons encode 115 genes related to bacterial lifestyle transitions, such as those involved in flagellar motility, chemotaxis, adhesion, biofilm formation, and colonization of host surfaces, 25 of which encode GDEEF and/or EAL domain proteins (Table S2). We also found that 3 of the 21 P. alcaligenes AVO110 genes previously identified as required for growth in fungal exudates [28] were singletons, i.e., the GGDEF-EAL domain gene cmpA and two genes potentially involved in the metabolism of fatty acids, fadE and fadD.…”

“…Pseudomonas and Escherichia coli strains were grown in lysogeny broth (LB) medium [40] or super optimal broth (SOB) [41] at 28 and 37 • C, respectively. BM minimal medium [42] was used for growth of R. necatrix Rn400 mycelia to obtain fungal exudate-containing medium (BM-RE, pH 7.1), as previously described [1,28]. When necessary, solid and liquid media were supplemented with antibiotics as follows: for E. coli, ampicillin (Ap) 100 µg mL −1 , kanamycin (Km) 50 µg mL −1 , and gentamicin (Gm) 50 µg mL −1 final concentration; for P. alcaligenes Microorganisms 2021, 9, 1388 3 of 17 AVO110, Ap 300 µg mL −1 , Km 25 µg mL −1 , and Gm 10 µg mL −1 ; and for P. putida KT2440, Km 50 µg mL −1 and Gm 50 µg mL −1 .…”

“…Downregulated genes encode two glutamine synthetases, a potassium transporter, a metallohydrolase, and an alanine racemase (Table 4). Previously, we reported that the P. alcaligenes AVO110 cmpA gene encodes a GGDEF/EAL domain protein [28]. Here, we conducted a detailed domain analysis of CmpA using the Pfam database.…”

“…In this sense, a recent study identified several molecular mechanisms linked to the mycophagous behavior of P. alcaligenes AVO110 toward R. necatrix exudates [ 28 ]. Using signature-tagged mutagenesis (STM) [ 29 ], these authors identified a collection of AVO110 genes required for growth and survival in R. necatrix exudates, several of which are biofilm related.…”

“…This gene was shown to be involved in the colonization of both the avocado rhizosphere and fungal hyphae. Among other genes, transcription of cmpA has been shown to be induced in response to R. necatrix exudates [ 28 ]. GGDEF and EAL (or HY-GYP) protein domains are involved in the turnover of c-di-GMP, a universal intracellular second messenger mediating phenotypic changes related to the transition between sessility and motility, such as the production of extracellular matrix components (EPSs and proteins), biofilm formation, and bacterial motility.…”