Starvation-Induced Multiresistance in Enterococcus faecalis JH2-2

Compared with growing bacteria, carbohydrate-starved cells of Enterococcus faecalis show development of a multiresistance state against heat, H₂O₂, acid, and ethanol, but not against UV irradiation. The kinetics of acquisition of resistance is different according to the stress. Three hours of starvation provide maximal resistance against ethanol, while the tolerance to heat, H₂O₂, and acid increases progressively with the duration of starvation. Chloramphenicol treatment does not abolish the ethanol tolerance. Protein synthesis inhibition during the transitional growth phase and the first hours of starvation partially inhibit the acquisition of heat and oxidative resistances. Antibiotic treatment after 3 h of starvation does not affect the increase of these resistances. We suggest that synthesis of specific proteins revealed by 2-D gel analysis in the first 3 h of starvation, followed by a second mechanism related to protein degradation or alteration, is necessary for acquisition of maximal resistance towards heat and oxidative stresses.     

Plasmid Transfer by Electroporation and Conjugation in Tetragenococcus and Pediococcus Genera and Evidence of Plasmid-Linked Metabolic Traits

Various strains of Pediococcus genus were successfully transformed by electroporation using the broad host-range plasmid pSA3 and the lactococcal Rep22 based-replicon pUCB304. Failure to transform Tetragenococcus strains by electroporation have led to use conjugation as an alternative plasmid DNA transfer mechanism. Intergeneric matings conducted with the broad host-range conjugative plasmid pVA797 from Lactococcus lactis subsp. lactis SL2/797A to Tetragenococcus halophilus and Pediococcus pentosaceus strains have shown that Tetragenococcus strains are not impervious to plasmid DNA transfer. Plasmid and metabolic profiles of wild and mutant strains of Pediococcus pentosaceus NCDO990 have shown that many metabolic traits including lactose utilization are plasmid linked.     

The Lactic Acid Stress Response of Lactococcus lactis subsp. lactis

The lactic acid tolerance response (LATR) of the lactic acid bacterium Lactococcus lactis subsp. lactis has been studied. A dramatic increase in survival to a severe acid stress (pH 3.9) was obtained by preexposing the cells for 30 min to a mildly acid shock at pH 5.5. Whole-cell protein extract analysis revealed that during the acid tolerance response 33 polypeptides are induced over the level of naive cells. Among these are the major heat shock proteins DnaK and GroEL. In conjunction with a previous report (Hartke et al. 1994), the results establish that L. lactis can adapt to lactic acid exposure in two different ways: a logarithmic phase LATR, which may be activated by protons, and a stationary-phase LATR, which needs no activation by protons. Both systems are independent of de novo protein synthesis. Received: 8 February 1996 / Accepted: 11 March 1996