Chemotactic responses in Vibrio alginolyticus, which has lateral and polar flagellar systems in one cell, were investigated. A lateral-flagella-defective (Pof- Laf-) mutant, which has only a polar flagellum, usually swam forward by the pushing action of its flagellum and occasionally changed direction by backward swimming. When the repellent phenol was added, Pof+ Laf- cells moved frequently forward and backward (tumbling state). The tumbling was derived from the frequent changing between counter-clockwise and clockwise (CW) rotation of the flagellar motor, as was confirmed by the tethered-cell method. Furthermore, we found that the tumbling cells did not adapt to the phenol stimulus. When the attractant serine was added, the phenol-treated cells ceased tumbling and swam smoothly, adapting to the attractant stimulus after several minutes. We isolated chemotaxis-defective (Che-) mutants from the Pof+ Laf- mutant; the tumbling mutants were not isolated. One interesting mutant swam backwards continuously, with its flagellum leading the cell and its flagellar motor rotating CW continuously. A polar-flagella-defective mutant (Pof- Laf+) stopped swimming after phenol addition and then recovered swimming ability within 10 min, indicating that lateral flagella can adapt to the repellent stimulus. This may represent a functional difference between the two flagellar systems in Vibrio cells, and between the chemotaxis systems affecting the two types of flagella.
The response of Pseudomonas putida to the electrophile N-ethylmaleimide (NEM) has been investigated. Treatment with low levels of NEM (20-30 µM) led to transient growth inhibition followed by recovery of normal growth. Stationary phase cells acquired resistance to NEM; one component of this tolerance was a more rapid metabolism of NEM. In exponential phase cells, the period of growth inhibition was associated with detoxification of NEM. Detoxification was biphasic and cells lost the ability to form colonies on minimal agar plates during the first phase of detoxification. Full viability was retained on MacConkey agar. Peptones are the active components in MacConkey medium. Addition of peptones to minimal agar restored colony-forming ability, but each peptone source had a different efficiency. These data suggest that a deficiency in the ability to assimilate nitrogen is a consequence of NEM treatment.
The role of phospholipid synthesis in peptidoglycan metabolism during growth of Escherichia coli was determined. The inhibition of phospholipid synthesis, achieved by inhibiting fatty acid synthesis with cerulenin or by glycerol deprivation of gpsA mutant strains, resulted in the concomitant inhibition of peptidoglycan synthesis. These effects on peptidoglycan synthesis were relatively specific in that the treatments did not cause a general inhibition of macromolecular synthesis. Furthermore, the inhibition of phospholipid synthesis also resulted in the rapid development of penicillin tolerance. It was unlikely that penicillin tolerance in these cases were simply due to the inhibition of growth caused by cerulenin treatment or glycerol deprivation because treatments with more effective growth inhibitors, e.g. chloramphenicol or norfloxacin, did not confer penicillin tolerance. Penicillin tolerance was shown to be a direct consequence of the inhibition of phospholipid synthesis and not due to the possible accumulation of guanosine-3′,5′-bispyrophosphate (ppGpp), the starvation stress signal molecule known to be responsible for the development of penicillin tolerance in amino-acid-deprived bacteria. Therefore, peptidoglycan metabolism is coupled to phospholipid synthesis during growth of E. coli, and this may represent an important means to ensure the coordination of cell envelope synthesis in growing bacteria.
Extracts from Escherichia coli K-12 contained two distinct enzymes capable of catalysing the phosphorylation of hydroxymethylpyrimidine (HMP) to HMP monophosphate: pyridoxine kinase (EC 188.8.131.52) and an enzyme that has not previously been genetically analysed, HMP kinase (EC 184.108.40.206). Two distinct genes, pdxL and thiJ, specify the activities of the former and latter enzymes, respectively. The inactivation of both genes by independent mutations in the same cell resulted in the complete loss of HMP kinase activity. Experiments with a series of strains that carry mutations in thiC, thiC pdxB, thiC pdxB pdxL and thiC pdxB pdxL thiJ revealed that the ability of the double mutant (pdxL thiJ) to utilize HMP in thiamin pyrophosphate biosynthesis was restored by introducing the wild-type allele corresponding to the thiJ mutation. The thiJ locus was mapped on the chromosome near the thiD and thiM loci, which govern the activities of phosphomethylpyrimidine kinase (EC 220.127.116.11) and hydroxyethylthiazole kinase (EC 18.104.22.168), respectively.
Listeria monocytogenes acquired increased acid tolerance during exponential growth upon exposure to sublethal acid stress, a response designated the acid tolerance response (ATR). Maximal acid resistance was seen when the organism was exposed to pH 5.0 for 1 h prior to challenge at pH 3.0, although intermediate levels of protection were afforded by exposure to pH values ranging from 4.0 to 6.0. A 60 min adaptive period was required for the development of maximal acid tolerance; during this period the level of acid tolerance increased gradually. Full expression of the ATR required de novo protein synthesis; chloramphenicol, a protein synthesis inhibitor, prevented full induction of acid tolerance. Analysis of protein expression during the adaptive period by two-dimensional gel electrophoresis revealed a change in the expression of at least 23 proteins compared to the non-adapted culture. Eleven proteins showed induced expression while 12 were repressed, implying that the ATR is a complex response involving a modulation in the expression of a large number of genes. In addition to the exponential phase ATR, L. monocytogenes also developed increased acid resistance upon entry into the stationary phase; this response appeared to be independent of the pH-dependent ATR seen during exponential growth.