Isolation and characterization of a Lactobacillus amylovorus mutant depleted in conjugated bile salt hydrolase activity: relation between activity and bile salt resistance
Jp. Grill et al., Isolation and characterization of a Lactobacillus amylovorus mutant depleted in conjugated bile salt hydrolase activity: relation between activity and bile salt resistance, J APPL MICR, 89(4), 2000, pp. 553-563
Growth experiments were conducted on Lactobacillus amylovorus DN-112 053 in
batch culture, with or without pH regulation. Conjugated bile salt hydrola
se (CBSH) activity was examined as a function of culture growth. The CBSH a
ctivity increased during growth but its course depended on bile salts type
and culture conditions. A Lact. amylovorus mutant was isolated from the wil
d-type strain of Lact. amylovorus DN-112 053 after mutagenesis with N-methy
l-N'-nitro-N-nitrosoguanidine. An agar plate assay was used to detect mutan
ts without CBSH activity. In resting cell experiments, the strain showed re
duced activity. Differences between growth parameters determined for wild-t
ype and mutant strains were not detected. Comparative native gel electropho
resis followed by CBSH activity staining demonstrated the loss of proteins
harbouring this activity in the mutant. Four protein bands corresponding to
CBSH were observed in the wild-type strain but only one was detected in th
e mutant. The specific growth rate of the mutant strain was affected more b
y bile salts than the wild-type strain. Nevertheless, bile was more toxic f
or the wild-type strain. In viability studies in the presence of nutrients,
it was demonstrated that glycodeoxycholic acid exerted a higher toxicity t
han taurodeoxycholic acid in a pH-dependent manner. No difference was appar
ent between the two strains. In the absence of nutrients, the wild-type str
ain died after 2 h whereas no effect was observed for the mutant. The de-en
ergization experiments performed using the ionophores nigericin and valinom
ycin suggested that the chemical potential of protons (Z Delta pH) was invo
lved in Lactobacillus bile salt resistance.