Neudorf Kara D, Vanderlinde Elizabeth M, Tambalo Dinah D, Yost Christopher K
Department of Biology, University of Regina, Regina, Saskatchewan S4S 0A2, Canada.
Department of Microbiology and Immunology, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5A2, Canada.
Microbiology (Reading). 2015 Jan;161(Pt 1):148-157. doi: 10.1099/mic.0.082420-0. Epub 2014 Nov 4.
Rhizobium leguminosarum is a soil bacterium that is an intracellular symbiont of leguminous plants through the formation of nitrogen-fixing root nodules. Due to the changing environments that rhizobia encounter, the cell is often faced with a variety of cell altering stressors that can compromise the cell envelope integrity. A previously uncharacterized operon (RL3499-RL3502) has been linked to proper cell envelope function, and mutants display pleiotropic phenotypes including an inability to grow on peptide-rich media. In order to identify functional partners to the operon, suppressor mutants capable of growth on complex, peptide-rich media were isolated. A suppressor mutant of a non-polar mutation to RL3500 was chosen for further characterization. Transposon mutagenesis, screening for loss of the suppressor phenotype, led to the identification of a Tn5 insertion in an uncharacterized tetratricopeptide-repeat-containing protein RL0936. Furthermore, RL0936 had a 3.5-fold increase in gene expression in the suppressor strain when compared with the WT and a 1.5-fold increase in the original RL3500 mutant. Mutation of RL0936 decreased desiccation tolerance and lowered the ability to form biofilms when compared with the WT strain. This work has identified a potential interaction between RL0936 and the RL3499-RL3502 operon that is involved in cell envelope development in R. leguminosarum, and has described phenotypic activities to a previously uncharacterized conserved hypothetical gene.
豌豆根瘤菌是一种土壤细菌，通过形成固氮根瘤成为豆科植物的细胞内共生体。由于根瘤菌所面临的环境不断变化，细胞常常会遇到各种能够破坏细胞包膜完整性的细胞改变应激源。一个先前未被表征的操纵子（RL3499 - RL3502）与细胞包膜的正常功能有关，其突变体表现出多效性表型，包括无法在富含肽的培养基上生长。为了鉴定该操纵子的功能伙伴，分离出了能够在复杂的、富含肽的培养基上生长的抑制突变体。选择了一个对RL3500的非极性突变的抑制突变体进行进一步表征。通过转座子诱变，筛选抑制表型的丧失，从而鉴定出在一个未被表征的含四肽重复序列的蛋白RL0936中有一个Tn5插入。此外，与野生型相比，抑制菌株中RL0936的基因表达增加了3.5倍，而在原始的RL3500突变体中增加了1.5倍。与野生型菌株相比，RL0936的突变降低了耐干燥性并降低了形成生物膜的能力。这项工作确定了RL0936与RL3499 - RL3502操纵子之间潜在的相互作用，该相互作用参与了豌豆根瘤菌细胞包膜的发育，并描述了一个先前未被表征的保守假设基因的表型活性。
