Antibiotic and Biosurfactant Properties of Cyclic Lipopeptides Produced by Fluorescent Pseudomonas spp. from the Sugar Beet Rhizosphere

Abstract

Cyclic lipopeptides (CLPs) with antibiotic and biosurfactant properties are produced by a number of soil bacteria, including fluorescent Pseudomonas spp. To provide new and efficient strains for the biological control of root-pathogenic fungi in agricultural crops, we isolated approximately 600 fluorescent Pseudomonas spp. from two different agricultural soils by using three different growth media. CLP production was observed in a large proportion of the strains (approximately 60%) inhabiting the sandy soil, compared to a low proportion (approximately 6%) in the loamy soil. Chemical structure analysis revealed that all CLPs could be clustered into two major groups, each consisting of four subgroups. The two major groups varied primarily in the number of amino acids in the cyclic peptide moiety, while each of the subgroups could be differentiated by substitutions of specific amino acids in the peptide moiety. Production of specific CLPs could be affiliated with Pseudomonas fluorescens strain groups belonging to biotype I, V, or VI. In vitro analysis using both purified CLPs and whole-cell P. fluorescens preparations demonstrated that all CLPs exhibited strong biosurfactant properties and that some also had antibiotic properties towards root-pathogenic microfungi. The CLPproducing P. fluorescens strains provide a useful resource for selection of biological control agents, whether a single strain or a consortium of strains was used to maximize the synergistic effect of multiple antagonistic traits in the inoculum.Cyclic lipopeptides (CLPs) are produced by distinctively different groups of bacteria, both gram-positive (20) and gramnegative (28). The high diversity of CLP-producing microorganisms (28) and differences in chemical structure suggest that the CLP compounds may serve different, and possibly multiple, purposes. This may explain why the specific role of CLP production is often unclear (28,40). For a limited number of CLPs (28), the reported functions include promotion of bacterial swarming (12, 26) and biosurfactant properties (19,24,41). In many cases, CLP compounds are also known to exert a role in antagonistic interactions with other organisms (28), e.g., plant pathogenicity (5) and antifungal (19,30,31,38,44), antibacterial (11), antiviral (49), or cytotoxic (16) activity.Synthesis of CLPs is nonribosomal and catalyzed by large peptide synthetase complexes (27). Various environmental stimuli may affect CLP production, i.e., carbon substrate (36), limitation by C, N, or P (15, 37), Fe limitation (15), growth phase conditions (15), and interaction with interfaces (32). Little information is available on production rates and regulating factors for the compounds in natural environments. Asaka and Shoda (2) detected surfactin and iturine production by Bacillus subtilis RB14 in a sterilized vermiculite-soil system, and Nakayama et al. (31) detected xanthobaccin A production by a Stenotrophomonas sp. strain, SB-K88, in a hydroponic sugar beet rhizosphere system, but documentation for in situ production of CLPs...

Surface motility in Pseudomonas sp. DSS73 is required for efficient biological containment of the root-pathogenic microfungi Rhizoctonia solani and Pythium ultimum

“…Among the great variety of antifungal metabolites produced by fluorescent Pseudomonas spp., our attention has been focused on the cyclic lipopeptides (Kochi et al, 1951;Nielsen et al, 1998Nielsen et al, , 1999Nielsen et al, , 2000Nielsen et al, , 2002. In addition, there are several examples of a close correlation between the production of cyclic lipopeptides and the ability to carry out surface motility on low-agar nutrient plates .…”

Cyclic Lipopeptide Surfactant Production by Pseudomonas fluorescens SS101 Is Not Required for Suppression of Complex Pythium spp. Populations

“…CLPs have been shown to possess a role in antagonistic interactions between producing strains and other organisms, including bacteria, fungi, and viruses (28). Numerous reports have proposed a functional role for CLPs in the capacity of certain soil-dwelling bacteria to provide biological control of plant root pathogenic fungi and oomycetes (9,25). In most of these studies, however, the antimicrobial effects of the CLPs were tested in vitro only and most biocontrol assays with plants did not include mutants deficient in CLP biosynthesis.…”

“…The efficacy of soilborne disease control brought about through the application of CLP-producing bacteria most typically is attributed to the biosurfactant properties of these compounds (9,25). The zoosporicidal property of various bacterial biosurfactants has been shown to limit the spread and incidence of diseases incited by oomycete plant pathogens (32).…”

“…Exposure to CLPs and other biosurfactants such as rhamnolipids can render zoospores of oomycete pathogens immotile and induce subsequent cell lysis (7)(8)(9). However, CLPs also have been reported to exhibit antibiotic properties toward fungal root pathogens, resulting in suppression of spore germination and inhibition of hyphal growth (15,25,26).…”

Workability Tests on Fresh Concrete Formulated with Eco-friendly Admixture

“…It is an eco-friendly product, which was used as BA (bio-admixture) in this study. Bio-admixtures described in the literature can have different possible natures, such as viscosin, viscosinamide and amphisin lipopeptides [8], the rhamnolipid glycolipids [9] or the AP6 protein-like polymer [10]. The BA should complete simultaneously two functions: limit the biocontamination of surface of concrete, as well as inhibit the rebars corrosion of reinforced concrete.…”