Department of Molecular, Microbial and Structural Biology, University of Connecticut Health Center, Farmington, Connecticut, USA.
J Bacteriol. 2012 Nov;194(21):5749-58. doi: 10.1128/JB.01276-12. Epub 2012 Aug 17.
As previously reported, gerP Bacillus subtilis spores were defective in nutrient germination triggered via various germinant receptors (GRs), and the defect was eliminated by severe spore coat defects. The gerP spores' GR-dependent germination had a longer lag time between addition of germinants and initiation of rapid release of spores' dipicolinic acid (DPA), but times for release of >90% of DPA from individual spores were identical for wild-type and gerP spores. The gerP spores were also defective in GR-independent germination by DPA with its associated Ca(2+) divalent cation (CaDPA) but germinated better than wild-type spores with the GR-independent germinant dodecylamine. The gerP spores exhibited no increased sensitivity to hypochlorite, suggesting that these spores have no significant coat defect. Overexpression of GRs in gerP spores did lead to faster germination via the overexpressed GR, but this was still slower than germination of comparable gerP(+) spores. Unlike wild-type spores, for which maximal nutrient germinant concentrations were between 500 μM and 2 mM for l-alanine and ≤10 mM for l-valine, rates of gerP spore germination increased up to between 200 mM and 1 M l-alanine and 100 mM l-valine, and at 1 M l-alanine, the rates of germination of wild-type and gerP spores with or without all alanine racemases were almost identical. A high pressure of 150 MPa that triggers spore germination by activating GRs also triggered germination of wild-type and gerP spores identically. All these results support the suggestion that GerP proteins facilitate access of nutrient germinants to their cognate GRs in spores' inner membrane.
如前所述，gerP 枯草芽孢杆菌孢子在各种发芽受体 (GR) 触发的营养发芽中存在缺陷，并且该缺陷通过严重的孢子外壳缺陷消除。gerP 孢子的 GR 依赖性发芽在添加发芽剂和开始快速释放孢子二吡啶酸 (DPA) 之间有更长的滞后时间，但野生型和 gerP 孢子释放>90%的 DPA 的时间相同。gerP 孢子在 GR 独立的 DPA 发芽中也存在缺陷，其与相关的 Ca(2+) 二价阳离子 (CaDPA)，但与 GR 独立的发芽剂十二胺相比，gerP 孢子发芽更好。gerP 孢子对次氯酸盐没有增加的敏感性，这表明这些孢子没有明显的外壳缺陷。在 gerP 孢子中过度表达 GR 确实导致通过过度表达的 GR 更快地发芽，但这仍然比可比的 gerP(+)孢子的发芽慢。与野生型孢子不同，对于 l-丙氨酸，最大营养发芽浓度在 500 μM 和 2 mM 之间，对于 l-缬氨酸，浓度在≤10 mM 之间，gerP 孢子的发芽率增加到 l-丙氨酸之间的 200 mM 和 1 M 之间，并且在 1 M l-丙氨酸时，具有或不具有所有丙氨酸消旋酶的野生型和 gerP 孢子的发芽率几乎相同。压力为 150 MPa 的高压通过激活 GR 触发孢子发芽，也相同地触发野生型和 gerP 孢子的发芽。所有这些结果都支持这样的观点，即 GerP 蛋白有助于营养发芽剂进入孢子内膜中它们的同源 GR。
