Newbold C J, Wallace R J, Watt N D
Rowett Research Institute, Bucksburn, Aberdeen, UK.
J Appl Bacteriol. 1992 Jan;72(1):65-70. doi: 10.1111/j.1365-2672.1992.tb04883.x.
Bacteroides ruminicola M384 was grown in the presence of increasing concentrations of tetronasin, an ionophore that has been developed as a feed additive for ruminants. The resulting culture, B. ruminicola M384/TnR, was then maintained in medium containing 0.1 microgram tetronasin/ml. Growth of the parent strain was eliminated by the addition of 0.1 micrograms tetronasin/ml, but the growth rate of B. ruminicola M384/TnR, which grew more slowly than the parent strain, was unaffected by adding tetronasin. Bacteroides ruminicola M384/TnR retained its resistance to tetronasin even after repeated subculture in the absence of the ionophore, suggesting that a mutation had occurred. The absence of plasmids in individual colonies of B. ruminicola M384/TnR implied that the mutation was chromosomal. Bacteroides ruminicola M384/TnR was also more resistant to the ionophores monensin and lasalocid and, to a lesser degree, to the antibiotic avoparcin than B. ruminicola M384. Binding of [14C]tetronasin to B. ruminicola M384/TnR was lower than binding of the ionophore to the parent stain, and this difference was eliminated by washing cells with EDTA. The peptidolytic activity of B. ruminicola M384 towards triphenylalanine (Mr = 460) was unaffected in B. ruminicola M384/TnR, but the rate of breakdown tetraphenylalanine (Mr = 607) was decreased. This difference was also abolished by EDTA. It was concluded that growth of B. ruminicola in the presence of tetronasin resulted in a mutation affecting the permeability of the cell envelope, such that permeation of tetronasin and molecules of a similar size (Mr = 628) was decreased.
将反刍拟杆菌M384在浓度不断增加的四球霉素（一种已被开发用作反刍动物饲料添加剂的离子载体）存在的条件下培养。随后，将所得培养物反刍拟杆菌M384/TnR保存在含有0.1微克四球霉素/毫升的培养基中。添加0.1微克四球霉素/毫升可消除亲本菌株的生长，但生长速度比亲本菌株慢的反刍拟杆菌M384/TnR的生长速度不受添加四球霉素的影响。即使在没有离子载体的情况下反复传代培养，反刍拟杆菌M384/TnR仍保持对四球霉素的抗性，这表明发生了突变。反刍拟杆菌M384/TnR单个菌落中不存在质粒，这意味着该突变是染色体突变。与反刍拟杆菌M384相比，反刍拟杆菌M384/TnR对离子载体莫能菌素和拉沙里菌素也更具抗性，对抗生素阿伏帕星的抗性程度稍低。[14C]四球霉素与反刍拟杆菌M384/TnR的结合低于离子载体与亲本菌株的结合，用EDTA洗涤细胞可消除这种差异。反刍拟杆菌M384对三苯丙氨酸（Mr = 460）的肽水解活性在反刍拟杆菌M384/TnR中未受影响，但四苯丙氨酸（Mr = 607）的分解速率降低。EDTA也消除了这种差异。得出的结论是，反刍拟杆菌在四球霉素存在的情况下生长导致影响细胞膜通透性的突变，从而使四球霉素和类似大小（Mr = 628）的分子的渗透减少。
