Soil Biology and Biotechnology Department, University of Tabriz, P.O. Box 51664, Tabriz, Iran.
Curr Microbiol. 2010 Jul;61(1):37-43. doi: 10.1007/s00284-009-9573-x. Epub 2010 Jan 5.
In addition to the characterized mechanisms responsible for many direct effects of plant growth promoting bacteria (PGPB) on plants, it has been suggested that a number of PGPB contain the enzyme ACC deaminase that catalyzes degradation of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene, into alpha-ketobutyrate and ammonia. As part of an effort to obtain an ACC deaminase encoding gene from a collection of soil samples, only one bacterial isolate, Pseudomonas fluorescens FY32 was capable of growing on ACC as a sole source of nitrogen. The ACC deaminase gene was amplified from the above isolate by polymerase chain reaction (PCR) giving an expected DNA fragment, 1017 bp. Sequence analysis of the fragment showed that it was highly homologous (94% and 98% identities at nucleotide and amino acid levels, respectively) to the previously characterized acdS gene from Pseudomonas sp. 6G5. Furthermore, fusion of the ACC deaminase ORF with lacZ gene resulted in the expression of active enzyme in Escherichia coli. In addition, further analyses revealed that the acdS gene was plasmid-encoded so that a large plasmid (pFY32) with almost 50 kb in size was identified from this bacterium. Furthermore, transfer of pFY32 into E. coli DH5alpha proved its ACC deaminase activity. This result was in accordance with previous reports suggesting horizontal transfer of the acdS gene. However, it needs more investigation to identify whether this pFY32 plasmid has undergone lateral gene transfer during the evolutionary process.
除了许多植物促生细菌 (PGPB) 对植物产生直接影响的特征机制外，还发现一些 PGPB 含有 ACC 脱氨酶，该酶可催化 1-氨基环丙烷-1-羧酸 (ACC) 的降解，ACC 是乙烯的直接前体，生成 α-酮丁酸和氨。作为从土壤样本中获得 ACC 脱氨酶编码基因的努力的一部分，只有一种细菌分离株，荧光假单胞菌 FY32 能够以 ACC 作为唯一氮源生长。通过聚合酶链反应 (PCR) 从上述分离株中扩增出 ACC 脱氨酶基因，得到预期的 DNA 片段，1017bp。该片段的序列分析表明，它与先前从假单胞菌 6G5 中鉴定的 acdS 基因高度同源（核苷酸和氨基酸水平的同一性分别为 94%和 98%）。此外，将 ACC 脱氨酶 ORF 与 lacZ 基因融合导致在大肠杆菌中表达活性酶。此外，进一步分析表明，acdS 基因是质粒编码的，因此从该细菌中鉴定出一个大小约为 50kb 的大质粒 (pFY32)。此外，将 pFY32 转移到大肠杆菌 DH5alpha 中证明了其 ACC 脱氨酶活性。这一结果与先前的报告一致，表明 acdS 基因发生了水平转移。然而，需要进一步的研究来确定这种 pFY32 质粒在进化过程中是否发生了横向基因转移。
