Lactobacillus curtus sp. nov., isolated from beer in Finland.

A Gram-stain-positive, catalase-negative and short-rod-shaped organism, designated VTT E-94560, was isolated from beer in Finland and deposited in the VTT culture collection as a strain of Lactobacillus rossiae. However, the results of 16S rRNA gene sequence analysis showed that VTT E-94560 was only related to Lactobacillus rossiae JCM 16176T with 97.0 % sequence similarity, lower than the 98.7 % regarded as the boundary for the species differentiation. Additional phylogenetic studies on the pheS gene, rpoA gene and 16S-23S rRNA internally transcribed spacer region further reinforced the taxonomically independent status of VTT E-94560 and its related Lactobacillus species including L. rossiae and Lactobacillus siliginis. Strain VTT E-94560 also exhibited several differences in its carbohydrate fermentation profiles from those related Lactobacillus species. In addition, DNA-DNA relatedness between VTT E-94560 and these two type strains was 4 % (L. rossiae JCM 16176T) and 12 % (L. siliginins JCM 16155T), respectively, which were lower than the 70 % cut-off for general species delineation, indicating that these three strains are not taxonomically identical at the species level. These studies revealed that VTT E-94560 represents a novel species, for which the name Lactobacillus curtus sp. nov. is proposed. The type strain is VTT E-94560T (=JCM 31185T).

HorC, a hop-resistance related protein, presumably functions in homodimer form.

To determine whether two HorC molecules coordinately form a single unit, the functional properties of covalently linked dimers of HorC encoded by tandemly fused horC genes were studied. Lactobacillus brevis introduced with the fused horC genes and a single horC gene exhibited same degree of resistance to hop compounds and cetyltrimethylammonium bromide. This suggests that HorC functions as a homodimer.

Rapid detection and identification of beer-spoilage lactic acid bacteria by microcolony method.

We evaluated a microcolony method for the detection and identification of beer-spoilage lactic acid bacteria (LAB). In this approach, bacterial cells were trapped on a polycarbonate membrane filter and cultured on ABD medium, a medium that allows highly specific detection of beer-spoilage LAB strains. After short-time incubation, viable cells forming microcolonies were stained with carboxyfluorescein diacetate (CFDA) and counted with muFinder Inspection System. In our study, we first investigated the growth behavior of various beer-spoilage LAB by traditional culture method, and Lactobacillus lindneri and several L. paracollinoides strains were selected as slow growers on ABD medium. Then the detection speeds were evaluated by microcolony method, using these slowly growing strains. As a result, all of the slowly growing beer-spoilage LAB strains were detected within 3 days of incubation. The specificity of this method was found to be exceptionally high and even discriminated intra-species differences in beer-spoilage ability of LAB strains upon detection. These results indicate that our microcolony approach allows rapid and specific detection of beer-spoilage LAB strains with inexpensive CFDA staining. For further confirmation of species status of detected strains, subsequent treatment with species-specific fluorescence in situ hybridization (FISH) probes was shown as effective for identifying the CFDA-detected microcolonies to the species level. In addition, no false-positive results arising from noise signals were recognized for CFDA staining and FISH methods. Taken together, the developed microcolony method was demonstrated as a rapid and highly specific countermeasure against beer-spoilage LAB, and compared favorably with the conventional culture methods.

Modified multiplex PCR methods for comprehensive detection of Pectinatus and beer-spoilage cocci.

Specific PCR primers were designed based on the 16S rRNA genes of recently proposed beer-spoilage species, Pectinatus haikarae, Megasphaera sueciensis, and M. paucivorans, and two sets of our previously reported multiplex PCR methods for Pectinatus spp. and beer-spoilage cocci were reconstructed. Each modified multiplex PCR method was found specifically to detect beer-spoilage species of Pectinatus and cocci, including new species.

Effects of morphological changes in beer-spoilage lactic acid bacteria on membrane filtration in breweries.

Membrane filter performance was investigated using beer-spoilage lactic acid bacteria (LAB). As a result, beer-adapted LAB strains showed considerably increased penetration rate through filters, as compared with non-adapted strains. Further statistical analyses demonstrated the significant shifts in cell size distribution towards shorter rods, when Lactobacillus brevis and L. lindneri strains were precultured in beer. These results indicate that diminished cell size is responsible for the deteriorated filter performance and, therefore, beer-adapted lactic acid bacteria are regarded as a serious threat to the production of unpasteurized beers. In addition, the selection of test strains and preculture conditions are suggested to be important for the rigorous and standardized evaluation of membrane filter performance in the brewing industry.

Isolation of a hop-sensitive variant of Lactobacillus lindneri and identification of genetic markers for beer spoilage ability of lactic acid bacteria.

We have isolated a hop-sensitive variant of the beer spoilage bacterium Lactobacillus lindneri DSM 20692. The variant lost a plasmid carrying two contiguous open reading frames (ORF s) designated horB(L) and horC(L) that encode a putative regulator and multidrug transporter presumably belonging to the resistance-nodulation-cell division superfamily. The loss of hop resistance ability occurred with the loss of resistance to other drugs, including ethidium bromide, novobiocin, and cetyltrimethylammonium bromide. PCR and Southern blot analysis using 51 beer spoilage strains of various species of lactic acid bacteria (LAB) revealed that 49 strains possessed homologs of horB and horC. No false-positive results have been observed for nonspoilage LAB or frequently encountered brewery isolates. These features are superior to those of horA and ORF 5, previously reported genetic markers for determining the beer spoilage ability of LAB. It was further shown that the combined use of horB/horC and horA is able to detect all 51 beer spoilage strains examined in this study. Furthermore sequence comparison of horB and horC homologs identified in four different beer spoilage species indicates these homologs are 96.6 to 99.5% identical, which is not typical of distinct species. The wide and exclusive distribution of horB and horC homologs among beer spoilage LAB and their sequence identities suggest that the hop resistance ability of beer spoilage LAB has been acquired through horizontal gene transfer. These insights provide a foundation for applying trans-species genetic markers to differentiating beer spoilage LAB including previously unencountered species.