1. Free-living nitrogen-fixing bacteria in Egyptian soils and their possible contribution to soil fertility;Abd-el-Malek;Plant and Soil, Special volume,1971
2. Abundance of Azotobacter in Egyptian soils;Abd-el-Malek,1962
3. Introduction to Soil Microbiology;Alexander,1961
4. The structure and development of Azotobacter;Bachinskaya;Bul. State Inst. Agr. Microbiol.,1935
5. Über oligonitrophile Mikroben;Beijerink;Zbl. Bakt. II,1901