Jakobs Mareike, Hoffmann Kerstin, Grabke Anja, Neuber Stefania, Liesegang Heiko, Volland Sonja, Meinhardt Friedhelm
Westfälische Wilhelms-Universität Münster, Institut für Molekulare Mikrobiologie und Biotechnologie, Corrensstrasse 3, 48149 Münster, Germany.
Georg-August-University Goettingen, Department of Genomic and Applied Microbiology, Goettingen Genomics Laboratory, Grisebachstrasse 8, 37077 Göttingen, Germany.
Microbiology (Reading). 2014 Oct;160(Pt 10):2136-2147. doi: 10.1099/mic.0.079236-0. Epub 2014 Jul 9.
Bacterial natural genetic competence - well studied in Bacillus subtilis - enables cells to take up and integrate extracellularly supplied DNA into their own genome. However, little is known about competence development and its regulation in other members of the genus, although DNA uptake machineries are routinely encoded. Auxotrophic Bacillus licheniformis 9945A derivatives, obtained from repeated rounds of random mutagenesis, were long known to develop natural competence. Inspection of the colony morphology and extracellular enzyme secretion of two of these derivatives, M28 and M18, suggested that regulator genes are collaterally hit. M28 emerged as a 14 bp deletion mutant concomitantly displaying a shift in the reading frame of degS that encodes the sensor histidine kinase, which is part of the molecular switch that directs cells to genetic competence, the synthesis of extracellular enzymes or biofilm formation, while for M18, sequencing of the suspected gene revealed a 375 bp deletion in abrB, encoding the major transition state regulator. With respect to colony morphology, enzyme secretion and competence development, both of the mutations, when newly generated on the wild-type B. licheniformis 9945A genetic background, resulted in phenotypes resembling M28 and M18, respectively. All of the known naturally competent B. licheniformis representatives, hitherto thoroughly investigated in this regard, carry mutations in regulator genes, and hence genetic competence observed in domesticated strains supposedly results from deregulation.
细菌自然遗传转化能力——在枯草芽孢杆菌中已得到充分研究——使细胞能够摄取细胞外提供的DNA并将其整合到自身基因组中。然而，尽管DNA摄取机制通常是编码的，但对于该属其他成员中转化能力的发展及其调控知之甚少。从多轮随机诱变中获得的营养缺陷型地衣芽孢杆菌9945A衍生物，长期以来已知其具有自然转化能力。对其中两个衍生物M28和M18的菌落形态和细胞外酶分泌进行检查，表明调控基因受到了附带影响。M28是一个14 bp的缺失突变体，同时编码传感组氨酸激酶的degS的阅读框发生了移位，degS是指导细胞进行遗传转化、细胞外酶合成或生物膜形成的分子开关的一部分；而对于M18，对疑似基因进行测序发现abrB中有一个375 bp的缺失，abrB编码主要的过渡态调控因子。就菌落形态、酶分泌和转化能力发展而言，当在野生型地衣芽孢杆菌9945A遗传背景上新产生这两种突变时，分别导致了类似于M28和M18的表型。迄今为止，在这方面进行过深入研究的所有已知具有自然转化能力的地衣芽孢杆菌代表菌株，其调控基因都存在突变，因此，在驯化菌株中观察到的遗传转化能力可能是由于调控失调所致。
