Abstract
Plants need phosphorus for many physiological activities in a form of phosphate anions. Three different bacterial strains (Bacillus subtilis PH, Serratia marcescens PH1, and Serratia marcescens PH2), recently isolated from tomato plant rhizosphere, have high phosphate solubilization index (SI from 2.8 to 3.2) on Pikovskaya agar medium (which contains calcium phosphate). Moreover, phosphate release from calcium in Pikovskaya broth over 5 days is increasing with cell growth for the different isolates. The most efficient phosphate solubilization case is the mixed culture of the 3 strains (OD475 is almost 1). On the other hand, pH values decreased dramatically with time due to organic acids secretion and the maximum acidification level is recoded for Serratia marcescens PH2 (pH = 1.94). Interestingly, the isolates are resistance to important pesticides (oxamyl, thiophanate methyl, and captan) that are commonly used in the sampling area. This resistance is very favorable and increases the persistence of the phosphate solubilizing bacteria in contaminated soils. The isolates are therefore plant symbionts and growth promoting agents.
Highlights
Phosphorus plays a key role for all life forms [1]
Predominant colonies in soil that is directly attached to tomato roots were selected and tested for production of halozones on Pikovskaya agar plates to detect phosphate solubilizing bacteria
The phosphate solubilization ability of the strains was qualified on Pikovskaya plates
Summary
Phosphorus plays a key role for all life forms [1]. It is essential for several plant physiological activities like photosynthesis, cell division, and others [2]. Phosphate solubilizing bacteria (PSB) which is associated with plant roots is one of the most significant alternatives for inorganic phosphate fertilizers [19] [20] [21] [22]. This group of bacteria is termed plant growth promoting rhizobacteria [23] [24] which includes many genera such as Serratia, Rhizobium, Pseudomonas, Paenibacillus, Flavobacterium, Erwinia, Enterobacter, Burkholderia, Bacillus, Azospirillum, Arthrobacter, Acinetobacter, and Alcaligenes [25] [26] [27]. The strains ability to release phosphate in Pikovskaya broth was tested as well as resistance against some commonly used pesticides
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