Interactions between ectomycorrhizal symbiosis and fluorescent pseudomonads on Acacia holosericea: isolation of mycorrhiza helper bacteria (MHB) from a Soudano-Sahelian soil

Abstract

Acacia holosericea seedlings were planted in 1-l pots filled with a soil collected from an Australian Acacia plantation in Southern Senegal. After 6 months of culture, mycorrhizosphere soil, roots, galls induced by root-knot nematodes and Rhizobium nodules were sampled from each pot. The diversity of this bacterial group was characterized by siderotyping (pyoverdine IsoElectric Focusing (IEF) analysis) and by restriction fragment length polymorphism (RFLP). The effect of these isolates on the establishment of the ectomycorrhizal symbiosis between an Australian Acacia (A. holosericea) and Pisolithus sp. strain IR100 was studied. In the mycorrhizosphere soil, the population of fluorescent pseudomonads was represented by strains of two different siderovars (groups of bacterial strains presenting an identical pyoverdine-IEF pattern): siderovar 1 (74%) and siderovar 2 (26%). The siderotyping of the isolates around galls of the root-knot nematodes revealed three siderovars (40% from siderovar 1, 40% from siderovar 2 and about 15% from siderovar 3). RFLP of 16S rDNA divided the isolates into four different groups with MspI, two with HhaI and two with HaeIII endonucleases. The establishment of the ectomycorrhizal symbiosis with A. holosericea was promoted by 14 bacterial strains isolated from the mycorrhizosphere soil, three isolates from the roots and four from the galls. Shoot biomass of A. holosericea seedlings was stimulated by eight bacterial isolates from soil, six isolates from galls and seven from roots. These mycorrhiza helper bacteria could have a great ecological importance in tropical areas through the reforestation programs.

Pseudomonas fluorescens BBc6R8 type III secretion mutants no longer promote ectomycorrhizal symbiosis

“…The establishment of ectomycorrhizal symbiosis can be significantly improved by selected soil and mycorrhizosphere bacterial strains, called 'Mycorrhiza Helper Bacteria' (MHB; Frey-Klett et al, 2007). Despite this, direct effects of MHB on the pre-symbiotic survival and growth of ectomycorrhizal fungi in the soil have been well documented, highlighting the importance of fungal-bacterial interactions in the mycorrhiza helper process (Brule et al, 2001;Founoune et al, 2002;Schrey et al, 2005;Deveau et al, 2007). This has been demonstrated by the successful use of the controlled mycorrhization process for commercial reforestation in France.…”

Use of Bromodeoxyuridine Immunocapture To Identify Active Bacteria Associated with Arbuscular Mycorrhizal Hyphae

“…In recent years, several bacteria have been reported to be associated with the mycorrhizospheres of different host plants (3,4,14,16,17). The mycorrhizosphere, or more specifically the mycorrhizal hyphosphere, is the volume of soil influenced by the mycorrhizal hyphae, in contrast to the rhizosphere, which is the volume of soil influenced by plant roots (14).…”

Litter-forager termite mounds enhance the ectomycorrhizal symbiosis between Acacia holosericea A. Cunn. Ex G. Don and Scleroderma dictyosporum isolates

“…The phylogenetic analysis performed in this study showed that these fluorescent pseudomonads mostly belonged to Pseudomonas monteillii species. It has been demonstrated that one isolate of P. monteillii (isolate HR13) can stimulate the establishment of ectomycorrhizal symbiosis in tropical conditions (Founoune et al ., 2002b) and is considered as an MHB. This MHB effect has been recorded with different fungal isolates, such as S. dictyosporum , S. verrucosum , Pisolithus albus and P. tinctorius , on A. holosericea and other Australian Acacia species (Duponnois & Plenchette, 2003).…”