| In order to meet massive demands of the lactic acid especially L- lactic acid, it is very important to continuously explore the fine strain in the natural microorganism resources and optimize it . In this paper ,The L-lactic acid producing condition of Rhizopus chinensis was optimized. Then through 10kev N+ implanting into Rhizopus chinensis to obtain high-yield mutant. Simultaneously in order to compare differences between the original strain and the mutain strain in the molecular level, 108 primers were examined to clarify the genetic background by using randomly amplified polymorphic DNA (RAPD) analysis.The results were as follows:1. The optimal production medium and fermentation consisted of following: C6H12O6 90‰,(NH4)2SO4 2‰,KH2PO4 0.6‰,MgSO4·7H2O 0.25‰,ZnSO4·7H2O 0.05‰,CaCO3 50.0‰,5% volume of seeds, 34℃, 200rpm. The final concentration of L-lactic acid reached to 28.8g/L.2. Use 10keV, 0.26×1015 ions/cm2～2.86×1015 ions/cm2 doses, N+ dealing with the the original strain Rhizopus chinensis.The strain shows"saddle type"dose surivial curve. The best ion implatation dose is 1.30×1015 ions/cm2. After several screens, a high-yield mutant strain RC-H13 was obtained. Its lactic acid was increased by 17% than that of original. The genetic of high-yield mutant strain is stable.3. Using 108 amplified primers to examinate the genetic background between the original strain and the mutain strain , 83 primers have amplified productions in two pools. 3 polymorphic primers were screened from 108 primers between the two near-isogenic lines. The frequency of polymorphic primers is 2.78%.4. 2 differentially expressed fragments were extracted and sequenced. The result of alignment in NCBI showed that the sequence of S271 primer amplified had 86% homology with Magnaporthe grisea hypothetical protein.,had 79% homology with Aspergillus fumigatus Af293 DNA replication licensing factor. The sequence of S193 primer amplified had not homology sequence.
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