Structure, production characteristics and fungal antagonism of tensin - a new antifungal cyclic lipopeptide from Pseudomonas fluorescens strain 96.578

Abstract

Aim: To study the antagonistic activity by Pseudomonas¯uorescens strain 96.578 on the plant pathogenic fungus Rhizoctonia solani. Methods and Results: Strain 96.578 produced a new cyclic lipopeptide, tensin. High tensin production per cell was detected in liquid media with glucose, mannitol or glutamate as growth substrate while fructose, sucrose and asparagine supported low production. Tensin production was nearly constant in media with different initial C levels, while low initial N contents reduced production. When applied to sugar beet seeds, strain 96.578 produced tensin during seed germination. When challenged with strain 96.578 or puri®ed tensin, Rhizoctonia solani reduced radial mycelium extension but increased branching and rosette formation. Conclusion: The antagonistic activity of strain 96.578 towards Rhizoctonia solani was caused by tensin. Signi®cance and Impact of the Study: When coated onto sugar beet seeds, tensin production by strain 96.578 could be of signi®cant importance for inhibition of mycelial growth and seed infection by Rhizoctonia solani.

Production of Cyclic Lipopeptides byPseudomonas fluorescensStrains in Bulk Soil and in the Sugar Beet Rhizosphere

“…When P. fluorescens strains 96.578 and DSS73 were added to bulk soil, the CFU counts were nearly constant over a 1-week period, as shown in Fig. 3B and C. Unlike viscosinamide, the tensin and amphisin compounds produced by these strains show only limited binding to the producing cells (17), and washing the inocula before adding them to the soil therefore results in very low initial CLP concentrations. The calculated initial tensin concentration was thus 8 ng g of dry soil Ϫ1 on day zero, which was below the detection limit in the soil (ϳ60 ng g of dry soil Ϫ1 ).…”

“…All three P. fluorescens strains, DR54, 96.578, and DSS73, were initially selected as being capable of antagonizing P. ultimum and R. solani on plates and during the early seed germination and root development of sugar beets (13,15,16,17,23,24). When looking for antibiotics involved in this antagonistic activity in vitro, it has been shown that purified CLPs from these three strains have inhibitory activity toward both P. ultimum and R. solani (15,16,17). A prerequisite for CLP production to be involved in fungal inhibition in soils is that the P. fluorescens strains be active and produce the CLP compounds after sugar beet seeds are coated with the bacteria.…”

“…isolated from the sugar beet rhizosphere in certain soils (16) and that all of the CLPs identified here contained either 9 or 11 amino acids in the peptide ring structure and a C 10 fatty acid moiety at one of the amino acids (16). The P. fluorescens strains DR54, 96.578, and DSS73 studied in the present work produce three different CLPs, viscosinamide (16), tensin (5), and amphisin (21), all showing antagonistic activities against the important plant-pathogenic microfungi Pythium ultimum (13,15,23) and Rhizoctonia solani (16,17). In other studies, it was shown that viscosinamide production is coupled to primary metabolism and cell proliferation in the producing bacteria and thus is controlled by growth substrate and nutrient conditions (14,15).…”

“…Purified viscosinamide, tensin, and amphisin were extracted from cultures of P. fluorescens DR54, 96.578, and DSS73 as described earlier (15,17,21). The extraction efficacy (recovery) for viscosinamide in soil was tested by adding 0.05, 0.08, 0.1, 0.5, and 1 g of purified viscosinamide (ϳ90% purity) g of soil…”

Inoculation of Sugar Beet Seed with Bacteria P. fluorescens, B. subtilis and B. megaterium – Chemical Fungicides Alternative

“…For the capacity to synthesize toxic cyclic lipopeptides (Andersen et al, 2003;Koch et al, 2002;Thrane et al, 2000) they are used as effective biological control agents (Sorensen et al, 2001). Many authors have reported that these purified lipopeptides show an antagonistic activity against certain fungi pathogenic on sugar beet roots such as Rhizoctonia solani (Andersen et al, 2003;Nielsen et al, 2000Nielsen et al, , 2002, Aphanomyces cochlioides (Raaijmakers et al, 2010;Sorensen et al, 2001), Pythium ultimum and Pythium debarianum (Andersen et al, 2003;Gorlach-Lira & Stefaniak, 2009;Lee et al, 2000;Nielsen et al, 2000;Thrane et al, 2000). This suggests that bacteria producing lipopeptides could have a potential role in the biocontrol of fungal diseases, which was approved in both laboratory and field trials (Thrane et al, , 2001.…”