Molecular cloning of a putative divalent-cation transporter gene as a new genetic marker for the identification of Lactobacillus brevis strains capable of growing in beer
N. Hayashi et al., Molecular cloning of a putative divalent-cation transporter gene as a new genetic marker for the identification of Lactobacillus brevis strains capable of growing in beer, APPL MICR B, 55(5), 2001, pp. 596-603
Random amplified polymorphic DNA (RAPD) PCR analysis of Lactobacillus brevi
s isolates from breweries revealed that one of the random primers could dis
tinguish beer-spoilage strains of L. brevis from non-spoilage strains. The
1.1-kb DNA fragment amplified from all beer-spoilers included one open read
ing frame, termed hitA (hop-inducible cation transporter), which encodes an
integral membrane protein with 11 putative trans-membrane domains and a bi
nding protein-dependent transport signature of a non-ATP binding membrane t
ransporter common to several prokaryotic and eukaryotic transporters. The h
itA polypeptide is homologous to the natural resistance-associated macropha
ge protein (Nramp) family characterized as divalent-cation transport protei
ns in many prokaryotic and eukaryotic organisms. Northern blot analysis ind
icated that the hitA transcripts are expressed in cells cultivated in MRS b
roth supplemented with hop bitter compounds, which act as mobile-carrier io
nophores, dissipating the trans-membrane pH gradient in bacteria sensitive
to the hop bitter compounds by exchanging Hf for cellular divalent cations
such as Mn2+. This suggests that the hitA gene products may play an importa
nt role in making the bacteria resistant to hop bitter compounds in beer by
transporting metal ions such as Mn2+ into cells that no longer maintain th
e proton gradient.