Laboratory of Soil Microbiology, Department of Agronomy, Cornell University, Ithaca, New York 14853.
Appl Environ Microbiol. 1986 Oct;52(4):807-11. doi: 10.1128/aem.52.4.807-811.1986.
The addition of streptomycin to nonsterile soil suppressed the numbers of bacterial cells in the rhizosphere of alfalfa (Medicago sativa L.) for several days, resulted in the enhanced growth of a streptomycin-resistant strain of Rhizobium meliloti, and increased the numbers of nodules on the alfalfa roots. A bacterial mixture inoculated into sterile soil inhibited the colonization of alfalfa roots by R. meliloti, caused a diminution in the number of nodules, and reduced plant growth. Enterobacter aerogenes, Pseudomonas marginalis, Acinetobacter sp., and Klebsiella pneumoniae suppressed the colonization by R. meliloti of roots grown on agar and reduced nodulation by R. meliloti, the suppression of nodulation being statistically significant for the first three species. Bradyrhizobium sp. and "Sarcina lutea" did not suppress root colonization nor nodulation by R. meliloti. The doubling times in the rhizosphere for E. aerogenes, P. marginalis, Acinetobacter sp., and K. pneumoniae were less and the doubling times for Bradyrhizobium sp. and "S. lutea" were greater than the doubling time of R. meliloti. Under the same conditions, Arthrobacter citreus injured alfalfa roots. We suggest that competition by soil bacteria reduces nodulation by rhizobia in soil and that the extent of inhibition is related to the growth rates of the rhizosphere bacteria.
链霉素添加到非无菌土壤中会抑制苜蓿（Medicago sativa L.）根际的细菌细胞数量数天，导致耐链霉素的根瘤菌（Rhizobium meliloti）的生长增强，并增加苜蓿根上的根瘤数量。接种到无菌土壤中的细菌混合物抑制了苜蓿根对根瘤菌的定植，导致根瘤数量减少，植物生长受到抑制。产气肠杆菌、边缘假单胞菌、不动杆菌和肺炎克雷伯菌抑制了根瘤菌在琼脂上的定植，并减少了根瘤菌的结瘤，对于前三种细菌，结瘤的抑制具有统计学意义。慢生根瘤菌和“黄色小球菌”（Sarcina lutea）既不抑制根瘤菌对根的定植，也不抑制根瘤菌的结瘤。产气肠杆菌、边缘假单胞菌、不动杆菌和肺炎克雷伯菌在根际的倍增时间较短，而慢生根瘤菌和“黄色小球菌”的倍增时间大于根瘤菌的倍增时间。在相同条件下，节杆菌（Arthrobacter citreus）损伤了苜蓿根。我们认为，土壤细菌的竞争减少了土壤中根瘤菌的结瘤，抑制的程度与根际细菌的生长速度有关。
