Department of Environmental Protection, Consejo Superior de Investigaciones Científicas, C/Prof. Albareda, 1, E-18008 Granada, Spain.
Microb Biotechnol. 2008 Mar;1(2):158-69. doi: 10.1111/j.1751-7915.2007.00014.x.
Pseudomonas putida KT2440 exhibits two formaldehyde dehydrogenases and two formate dehydrogenase complexes that allow the strain to stoichiometrically convert formaldehyde into CO(2). The strain tolerated up to 1.5 mM formaldehyde and died in the presence of 10 mM. In the presence of 0.5 mM formaldehyde, a sublethal concentration of this chemical, the growth rate decreased by about 40% with respect to growth in the absence of the toxicant. Transcriptomic analysis revealed that in response to low formaldehyde concentrations, a limited number of genes (52) were upregulated. Based on the function of these genes it seems that sublethal concentrations of HCOH trigger responses to overcome DNA and protein damage, extrude this toxic compound, and detoxify it by converting the chemical to CO(2). In strains bearing mutations of the upregulated genes we analysed growth inhibition by 1.5 mM HCOH and killing rates by 10 mM HCOH. Mutants in the MexEF/OprN efflux pump and in the DNA repair genes recA and uvrB were hypersensitive to 10 mM HCOH, the killing rate being three to four orders of magnitude higher than those in the wild-type strain. Mutants in other upregulated genes died at slightly higher or at similar rates to the parental strain. Regarding growth inhibition, we found that mutants in glutathione biosynthesis, stress response mediated by 2-hydroxy acid dehydrogenases and two efflux pumps of the MSF family were unable to grow in the presence of 1.5 mM HCOH. In an independent screening test we searched for mutants which were hypersensitive to formaldehyde, but whose expression did not change in response to this chemical. Two mutants with insertions in recD and fhdA were found which were unable to grow in the presence of 1.5 mM HCOH. The recD mutant was hypersensitive to 10 mM HCOH and died at a higher rate than the parental strain.
恶臭假单胞菌 KT2440 具有两种甲醛脱氢酶和两种甲酸盐脱氢酶复合物，使该菌株能够将甲醛化学计量地转化为 CO2。该菌株可耐受高达 1.5mM 的甲醛，而在 10mM 时则会死亡。在存在 0.5mM 甲醛（这种化学物质的亚致死浓度）的情况下，相对于无毒性剂的生长，其生长速率降低了约 40%。转录组分析表明，对于低浓度的甲醛，只有少数基因（52 个）被上调。根据这些基因的功能，似乎低浓度的 HCOH 会引发响应，以克服 DNA 和蛋白质损伤，将这种有毒化合物排出体外，并通过将其转化为 CO2 来解毒。在分析了携带上调基因突变的菌株对 1.5mM HCOH 的生长抑制和 10mM HCOH 的致死率时，我们发现 MexEF/OprN 外排泵和 DNA 修复基因 recA 和 uvrB 的突变体能对 10mM HCOH 产生超敏反应，致死率比野生型菌株高出三到四个数量级。其他上调基因的突变体死亡速率略高于或与亲本菌株相似。关于生长抑制，我们发现谷胱甘肽生物合成、2-羟基酸脱氢酶介导的应激反应和 MSF 家族的两个外排泵突变体无法在 1.5mM HCOH 存在的情况下生长。在一个独立的筛选测试中，我们寻找对甲醛敏感的突变体，但这些突变体的表达不会因这种化学物质而改变。发现了两个带有 recD 和 fhdA 插入物的突变体，它们无法在 1.5mM HCOH 存在的情况下生长。recD 突变体对 10mM HCOH 敏感，死亡速率比亲本菌株高。
