PHYSIOLOGY AND DEVELOPMENT OF PECTINATUS-CEREVISIIPHILUS AND PECTINATUS-FRISINGENSIS, 2 STRICT ANAEROBIC BEER SPOILAGE BACTERIA

The genus Pectinatus was isolated recently and the deposited strains w ere classified as beer spoilage bacteria producing propionate as a maj or fermentation product. A recent investigation of this genus demonstr ated the existence of two species: Pectinatus cerevisiiphilus, the typ e strain and Pectinatus frisingensis, a new species with a different p attern of growth substrates. Different culture media tested for both s pecies demonstrated a higher specific growth rate for P. cerevisiiphil us. However, final biomass production was in every case round 20% high er in P. frisingensis. A 400% decrease of final biomass production was measured when the species were cultivated on poor culture medium; thi s decrease was found to be broadly proportional to amounts of acetate excreted in the medium. Both species produced CO2 from glucose; howeve r, no significant modifications of biomass and volatile fatty acid pro duction were demonstrated when varying head space composition with reg ard to CO2 levels. Growth experiments on glucose with increasing amoun ts of ethanol added in the culture, revealed a higher sensitivity of P . cerevisiiphilus to ethanol inhibition. Ethanol concentrations over 1 .7 M resulted in a complete inhibition of growth for both Pectinatus s pecies. Combined effects of culture medium pH, lactate, and glucose co ncentrations, demonstrated the prevailing role of glucose in the devel opment of the bacteria. However, these three parameters had a differen t influence on growth characteristics of both Pectinatus species. P. c erevisiiphilus grew very poorly with a glucose concentration of 5 mM f or pH values below 4.1. This species had optimal pH for growth between 6 and 6.2 and it excreted increasing amounts of acetate with increase of pH, glucose or lactate in the culture medium. P. frisingensis show ed a wide range of pH allowing a good growth. For glucose concentratio ns below 20 mM, highest final biomass productions were measured in the culture for pH values round 4.9; this also corresponded to a minimum in acetate excretion. The above results pointed at P. frisingensis as the prevailing species of Pectinatus in beer spoilage. (C) 1997 Elsevi er Science B.V.