Department of Environmental Biology, Laboratory of Bioresources and Environmental Biotechnology, University of Delhi, Delhi, 110 007, India.
Curr Microbiol. 2011 Jul;63(1):81-6. doi: 10.1007/s00284-011-9946-9. Epub 2011 May 15.
Outer-membrane characteristics may determine the survivability of rhizobia under diverse abiotic and biotic stresses. Therefore, the role of lipopolysaccharides (LPS) and membrane proteins of two stem-nodulating bacteria of Sesbania rostrata (Azorhizobium caulinodans ORS571 and Rhizobium sp. WE7) in determining tolerance towards abiotic and biotic stresses (hydrophobics and phages) was investigated. Outer-membrane characteristics (LPS and membrane-protein profiles) of ORS571, WE7 and thirteen standard strains were distinct. ORS571 and WE7 also showed susceptibility towards morphologically distinct phages, i.e., ACSR16 (short-tailed) and WESR29 (long-tailed), respectively. ORS571 and WE7 were tolerant to hydrophobic compounds (triton X-100, rifampicin, crystal violet and deoxycholate). To ascertain the role of outer membrane characteristics in stress tolerance, phage-resistant transconjugant mutants of ORS571 (ORS571-M8 and ORS571-M20) and WE7 (WE7-M9) were developed. LPS- and membrane-protein profiles of mutants differed from that of respective wild types (ORS571 and WE7). In in vitro assay, phages got adsorbed onto purified LPS-membrane protein fractions of wild types. Phages did not adsorb onto membrane fraction of mutants and standard strains. Mutant with reduced expression of LPS (ORS571-M20 and WE7-M9) showed reduced tolerance towards hydrophobics. However, the tolerance was unaffected in mutant (ORS571-M8) where expression of LPS was not reduced but pattern was different. The tolerance level of mutants towards hydrophobics varied with the expression of LPS, whereas the specificity towards phages is correlated with the specific LPS pattern.
外膜特性可能决定根瘤菌在不同的非生物和生物胁迫下的生存能力。因此，研究了两种Sesbania rostrata 结瘤菌（Azorhizobium caulinodans ORS571 和 Rhizobium sp. WE7）的脂多糖（LPS）和膜蛋白在决定对非生物和生物胁迫（疏水性和噬菌体）的耐受性中的作用。ORS571、WE7 和 13 个标准菌株的外膜特性（LPS 和膜蛋白图谱）明显不同。ORS571 和 WE7 也对形态上不同的噬菌体敏感，即 ACSR16（短尾）和 WESR29（长尾）。ORS571 和 WE7 耐受疏水性化合物（曲通 X-100、利福平、结晶紫和脱氧胆酸钠）。为了确定外膜特征在应激耐受性中的作用，开发了 ORS571（ORS571-M8 和 ORS571-M20）和 WE7（WE7-M9）的噬菌体抗性转导突变体。突变体的 LPS 和膜蛋白图谱与相应的野生型不同。在体外试验中，噬菌体吸附到野生型的纯化 LPS-膜蛋白部分。噬菌体不吸附到突变体和标准菌株的膜部分。LPS 表达减少的突变体（ORS571-M20 和 WE7-M9）对疏水性的耐受性降低。然而，在 LPS 表达没有减少但模式不同的突变体（ORS571-M8）中，耐受性不受影响。突变体对疏水性的耐受性水平随 LPS 的表达而变化，而对噬菌体的特异性与特定的 LPS 模式相关。
