Quelas Juan Ignacio, López-García Silvina L, Casabuono Adriana, Althabegoiti M Julia, Mongiardini Elías J, Pérez-Giménez Julieta, Couto Alicia, Lodeiro Aníbal R
Instituto de Bioquímica y Biología Molecular (IBBM), Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Calles 47 y 115, 1900 La Plata, Argentina.
Arch Microbiol. 2006 Aug;186(2):119-28. doi: 10.1007/s00203-006-0127-3. Epub 2006 Jun 21.
The exopolysaccharide (EPS) is an extracellular molecule that in Bradyrhizobium japonicum affects bacterial efficiency to nodulate soybean. Culture conditions such as N availability, type of C-source, or culture age can modify the amount and composition of EPS. To better understand the relationship among these conditions for EPS production, we analyzed their influence on EPS in B. japonicum USDA 110 and its derived mutant DeltaP22. This mutant has a deletion including the 3' region of exoP, exoT, and the 5' region of exoB, and produces a shorter EPS devoid of galactose. The studies were carried out in minimal media with the N-source at starving or sufficient levels, and mannitol or malate as the only C-source. Under N-starvation there was a net EPS accumulation, the levels being similar in the wild type and the mutant with malate as the C-source. By contrast, the amount of EPS diminished in N-sufficient conditions, being poyhydroxybutyrate accumulated with culture age. Hexoses composition was the same in both N-situations, either with mannitol or malate as the only C-source, in contrast to previous observations made with different strains. This result suggests that the change in EPS composition in response to the environment is not general in B. japonicum. The wild type EPS composition was 1 glucose:0.5 galactose:0.5 galacturonic acid:0.17 mannose. In DeltaP22 the EPS had no galactose but had galacturonic acid, thus indicating that it was not produced from oxidation of UDP-galactose. Infectivity was lower in DeltaP22 than in USDA 110. When the mutant infectivity was compared between N-starved or N-sufficient cultures, the N-starved were not less infective, despite the fact that the amounts of altered EPS produced by this mutant under N-starvation were higher than in N-sufficiency. Since this altered EPS does not bind soybean lectin, the interaction of EPS with this protein was not involved in increasing DeltaP22 infectivity under N-starvation.
胞外多糖（EPS）是一种胞外分子，在日本慢生根瘤菌中，它会影响细菌对大豆进行结瘤的效率。诸如氮素有效性、碳源类型或培养时间等培养条件会改变EPS的数量和组成。为了更好地理解这些条件与EPS产生之间的关系，我们分析了它们对日本慢生根瘤菌USDA 110及其衍生突变体DeltaP22中EPS的影响。该突变体有一个缺失区域，包括exoP的3'区域、exoT以及exoB的5'区域，并且产生的EPS较短，不含半乳糖。研究在基本培养基中进行，氮源处于饥饿或充足水平，以甘露醇或苹果酸作为唯一碳源。在氮饥饿条件下有EPS的净积累，以苹果酸作为碳源时，野生型和突变体中的EPS水平相似。相比之下，在氮充足条件下EPS的量减少，随着培养时间的推移聚羟基丁酸酯会积累。在两种氮条件下，无论以甘露醇还是苹果酸作为唯一碳源，己糖组成都是相同的，这与之前对不同菌株的观察结果不同。这一结果表明，日本慢生根瘤菌中EPS组成对环境的响应变化并非普遍现象。野生型EPS的组成是1份葡萄糖：0.5份半乳糖：0.5份半乳糖醛酸：0.17份甘露糖。在DeltaP22中，EPS不含半乳糖但含有半乳糖醛酸，因此表明它不是由UDP - 半乳糖氧化产生的。DeltaP22的感染性低于USDA 110。当比较突变体在氮饥饿或氮充足培养条件下的感染性时，尽管该突变体在氮饥饿条件下产生的改变后的EPS量高于氮充足条件下，但氮饥饿条件下的感染性并不更低。由于这种改变后的EPS不与大豆凝集素结合，因此在氮饥饿条件下EPS与该蛋白的相互作用并不参与提高DeltaP22的感染性。
