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United States Department of Agriculture

Agricultural Research Service


Location: National Soil Erosion Research Lab

Title: Isolation and characterization of Chilembwe and Sinda Rock Phosphate solubilizing soil microorganisms

item Mweetwa, Alice -
item Eckhardt, Elizabeth -
item Stott, Diane
item Schulze, Darrell -
item Chilembo, Gwen -
item Armstrong, Arthur -
item Nakatsu, Cindy -

Submitted to: African Journal of Microbiology Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 20, 2014
Publication Date: N/A

Interpretive Summary: In many parts of Africa, crops yields are suppressed due to insufficient soil phosphorus. Local deposits of rock phosphate would provide an inexpensive source of phosphorus fertilizer for farmers, but rock phosphate is notoriously insoluble. Recently, there has been several research papers reporting on several genera of bacteria that are capable of solubilizing rock phosphate. Our study reports on over 80 isolates capable of solubilizing the rock phosphate, including some from two bacterial genera not previously reported to have P-solubilizing capabilities, Dyella and Curtobacterium. Some isolates P-dissolving capability only worked with one of the two rock phosphates that were mined locally in Zambia. While most isolates were capable of obtaining P from organic sources as well as the inorganic rock phosphate, some could not obtain P from both sources. This work will be useful in developing appropriate seed inocula that can enhance rock phosphate dissolution and increased plant available P for crop production in Zambia and other parts of Africa.

Technical Abstract: This study was conducted to isolate and characterize soil microorganisms capable of solubilizing Chilembwe and Sinda rock phosphates readily available in Zambia. Single isolates were obtained by direct plating and enrichment cultures with succinate, cellulose and glucose as the carbon sources. Isolates were differentiated using colony morphology (form, margin, elevation and colour) and a subset of 20 was chosen for identification using the 16S rRNA gene sequences. After being cultured in nutrient broth and defined medium with tricalcium phosphate as the sole phosphate source, ten isolates were characterized for acid phosphatase enzyme activity. Over 80 isolates were obtained from different rock phosphate-sugar combinations. Isolates had varying morphological characteristics and the 20 strains identified showed a large diversity of organisms belonging to the genera Enterobacter, Burkholderia, Arthrobacter, Bacillus, Beijerinckia and two genera not previously reported to have P-solubilizing capabilities, Dyella and Curtobacterium. Both the observed growth and genera to which isolates belonged were dependent on the type of rock phosphate. Almost all isolates tested showed acid phosphatase activity that were similar to previously reported levels, ranging from 0.62 to 4.8 µg p-nitrophenol per 108 cells per hr. This work will be useful as the basis for the development of appropriate seed inocula that can enhance Sinda and Chilembwe rock phosphate dissolution and increased plant available P for crop production.

Last Modified: 10/21/2014
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