Fructophilic lactic acid bacteria (FLAB) are a recently discovered group, consisting of a few and species. Because of their unique characteristics, including poor growth on glucose and preference of oxygen, they are regarded as "unconventional" lactic acid bacteria (LAB). Their unusual growth characteristics are due to an incomplete gene encoding a bifunctional alcohol/acetaldehyde dehydrogenase (). This results in the imbalance of NAD/NADH and the requirement of additional electron acceptors to metabolize glucose. Oxygen, fructose, and pyruvate are used as electron acceptors. FLAB have significantly fewer genes for carbohydrate metabolism than other LAB, especially due to the lack of complete phosphotransferase system (PTS) transporters. They have been isolated from fructose-rich environments, including flowers, fruits, fermented fruits, and the guts of insects that feed on plants rich in fructose, and are separated into two groups on the basis of their habitats. One group is associated with flowers, grapes, wines, and insects, and the second group is associated with ripe fruits and fruit fermentations. Species associated with insects may play a role in the health of their host and are regarded as suitable vectors for paratransgenesis in honey bees. Besides their impact on insect health, FLAB may be promising candidates for the promotion of human health. Further studies are required to explore their beneficial properties in animals and humans and their applications in the food industry.

BackgroundFructobacillus spp. in fructose-rich niches belong to the family Leuconostocaceae. They were originally classified as Leuconostoc spp., but were later grouped into a novel genus, Fructobacillus, based on their phylogenetic position, morphology and specific biochemical characteristics. The unique characters, so called fructophilic characteristics, had not been reported in the group of lactic acid bacteria, suggesting unique evolution at the genome level. Here we studied four draft genome sequences of Fructobacillus spp. and compared their metabolic properties against those of Leuconostoc spp.ResultsFructobacillus species possess significantly less protein coding sequences in their small genomes. The number of genes was significantly smaller in carbohydrate transport and metabolism. Several other metabolic pathways, including TCA cycle, ubiquinone and other terpenoid-quinone biosynthesis and phosphotransferase systems, were characterized as discriminative pathways between the two genera. The adhE gene for bifunctional acetaldehyde/alcohol dehydrogenase, and genes for subunits of the pyruvate dehydrogenase complex were absent in Fructobacillus spp. The two genera also show different levels of GC contents, which are mainly due to the different GC contents at the third codon position.ConclusionThe present genome characteristics in Fructobacillus spp. suggest reductive evolution that took place to adapt to specific niches.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2339-x) contains supplementary material, which is available to authorized users.

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Three strains, JCM 5343, JCM 5344 and JCM 1130, currently identified as Lactobacillus gasseri, were investigated using a polyphasic taxonomic approach. Although these strains shared high 16S rRNA gene sequence similarities with L. gasseri ATCC 33323 (99.9 %), they formed a clade clearly distinct from ATCC 33323 based on whole-genome relatedness. The average nucleotide identity and in silico DNA-DNA hybridization values of these three strains compared to L. gasseri ATCC 33323 were 93.4-93.7 and 53.1-54.1 %, respectively, and both were less than the widely accepted threshold to distinguish two species (95 and 70 %, respectively). The three strains were Gram-stain positive, non-motile, non-spore-forming, catalase-negative and rod-shaped bacteria. They grew at 25-45 °C and in the presence of 2.0 % (w/v) NaCl. The major fatty acids of the three strains were C16 : 0 and C18 : 1 ω9c. Based on phylogenetic analyses of the phenylalanyl-tRNA synthase alpha subunit and RNA polymerase alpha subunit genes, and on phenotypic and chemotaxonomic characteristics, strains JCM 5343, JCM 5344 and JCM 1130 represent a novel species distinct from L. gasseri, for which we propose the name Lactobacillusparagasseri sp. nov. In addition, a large portion of genomes currently labelled as L. gasseri in the public sequence database should be reclassified as L. paragasseri based on whole-genome relatedness.