Isolation and Characterization of Phosphate Solubilizing Streptomyces sp. Endemic from Sugar Beet Fields of the Beni-Mellal Region in Morocco

Abstract

In the course of our research, aimed at improving sugar beets phosphorus nutrition, we isolated and characterized Streptomyces sp. strains, endemic from sugar beet fields of the Beni-Mellal region, which are able to use natural rock phosphate (RP) and tricalcium phosphate (TCP) as sole phosphate sources. Ten Streptomyces sp. isolates yielded a comparable biomass in the presence of these two insoluble phosphate sources, indicating that they were able to extract similar amount of phosphorus (P) from the latter for their own growth. Interestingly, five strains released soluble P in large excess from TCP in their culture broth whereas only two strains, BP, related to Streptomyces bellus and BYC, related to Streptomyces enissocaesilis, released a higher or similar amount of soluble P from RP than from TCP, respectively. This indicated that the rate of P released from these insoluble phosphate sources exceeded its consumption rate for bacterial growth and that most strains solubilized TCP more efficiently than RP. Preliminary results suggested that the solubilization process of BYC, the most efficient RP and TCP solubilizing strain, involves both acidification of the medium and excretion of siderophores. Actinomycete strains possessing such interesting RP solubilizing abilities may constitute a novel kind of fertilizers beneficial for plant nutrition and more environmentally friendly than chemical fertilizers in current use.

Multiple Potential Plant Growth Promotion Activities of Endemic Streptomyces spp. from Moroccan Sugar Beet Fields with Their Inhibitory Activities against Fusarium spp.

“…In our previous research [ 40 ], we successfully isolated 10 Streptomyces spp. and revealed their phosphate solubilization capacities and siderophore production.…”

“…This indicated that the solubilization process might involve the excretion of organic acids. Interestingly, AI yielded much better biomass ( Figure 3 ) and was shown to excrete siderophores, but not the CYM strain [ 40 ], whereas BYC released a rather small amount (2-fold less, 61 mg/L). However, this strain produced siderophores and was selected as the best phosphate-solubilizing strain from both RP and TCP [ 40 ].…”

“…Ten selected Actinomycete strains used in this study were isolated from three different sugar beet rhizospheres that were previously selected for their abilities to solubilize insoluble phosphate forms (a Moroccan natural rock phosphate and a synthetic tricalcium phosphate) using the SMM medium and to produce siderophores [ 40 ]: AYD, AZ, AV and BX related to Streptomyces bellus ; BYC: Streptomyces enissocaesilis ; AI: Streptomyces tunisiensis ; BP: Streptomyces coerulescens ; CYM: Streptomyces cyaneofuscatus ; DE1: Streptomyces bellus and DE2: Streptomyces saprophyticus . Spores of the selected Actinomycete isolates were stored in 20% sterile glycerol at −20 °C for the next tests.…”

“…Briefly, disks of 10 mm in diameter from 5-day-old cultures of fungi were placed in the center of Sabouraud agar plates and the disks of tested Actinomycete strains were placed on either side of Sabouraud plates at a distance of 2.5 cm. After 5 days of incubation at 28 °C, the diameter of propagation of the fungi was recorded and the percentage of inhibition (PI) was calculated: PI = [(T − S)/T] × 100; where T represents the mycelial colony radius (mm) of a control culture and S represents the mycelial colony radius of the fungus in the presence of the Streptomyces strain [ 40 ].…”

“…Therefore, this research aimed to assess if the 10 strongly P-solubilizing strains of Streptomyces of the sugar beet rhizosphere in Beni-Mellal [ 40 ] possess multifaceted PGPR activities, and tested their abilities to solubilize K from insoluble orthoclase, produce auxins and inhibit sugar beet root pathogens in laboratory conditions. Through these experiments, we expected to identify the most effective strains of the collection for future field trials.…”