The Effect Of Genetically-Modified Cotton On The Diversity Of Soil Bacteria And Cellulose-Degrading Microorganisms

Genetically-modified (GM) cotton brings a new revolution to the prevention of insect pests. It plays a vital role in the products promotion and makes enormous economical and social benefits in the world. However, the potential risk due to its complexity and unpredictability of the transgenic crops has aroused great concerns of the scientists all over the world. Most countries demand a careful assessment on the ecological safety before the release of the GM cottons.Soil microorganism is an indispensible component of soil, so it is necessary to make an assessment of the effect of the GM cotton on the soil microorganisms. Cellulose-degrading bacterium is a kind of essential microbial population, which plays key roles during both the process of straw decomposition and energy recycling. However, the effect of GM cotton on the soil microorganism (including the cellulose-degrading bacteria) is still not clear. It is urgent to construct a system of ecological safety assessment for the GM cotton.In this study, the diversity of soil bacteria in different cotton growth phases was analyzed by molecular technology of DGGE combined with statistical methods such as clustering and PCA analysis. The results indicated that, the diversity of soil bacteria changed along with the temperature and growth phase of cotton. During the blossoming and boll-forming phases, some particular bands occurred in the DGGE fingerprints. Statistical analysis showed a high similarity between the GM and traditional cottons, indicating that no significant influence of the GM cotton on the soil bacteria.In order to study the effect of GM cotton on the population of soil cellulose-degrading bacteria, we used the traditional plating method combined with CMC-Na congo-red sodium cultural method. It showed that the total number of cellulose-degrading bacteria of both GM and traditional cottons performed a basic law related to the corresponding growth phases. The population number began to rise at budding, quickly reached its peak during blossoming and boll-forming phases, then decreased slightly later in the wadding phase. SPSS analysis illustrated an acceleration of the cellulose-degrading bacteria population caused by the GM cotton at the same growing period, but it only showed a significant influence in some specific phases (P<0.05).We used PNPG method to detect the soil enzyme activity of β-glucosidase on purpose of exploring the effect of GM cotton on the soil cellulose enzyme activity. It showed a similar trend corresponding with the change of cellulose-degrading bacteria, but we also found particular bounce in the decaying phase. The GM cotton performed a significant influence on the soil enzyme activity of β-glucosidase during some specific periods, most of which were simulative while some were negative. The differences varied from breeds and regions.Three cellulose-degrading bacteria with high FPA enzyme activity, named XWS-3, XWS-9 and XWS-10 were isolated from soil of cotton fields. Based on the 16S rRNA sequence analysis, strains XWS-3, XWS-9 and XWS-10 were identified as Bacillus sp., Streptomyces sp. and Agromyces sp., respectively. We plan to use these strains as indicators and design specific primers based on their sequences relate with cellulose decomposition for the detection of genes via real-time PCR to establish a reasonable assessment system for GM cotton.