No abstract

Food-fermenting lactic acid bacteria (LAB) are generally considered to be non-toxic and non-pathogenic. Some species of LAB, however, can produce biogenic amines (BAs). BAs are organic, basic, nitrogenous compounds, mainly formed through decarboxylation of amino acids. BAs are present in a wide range of foods, including dairy products, and can occasionally accumulate in high concentrations. The consumption of food containing large amounts of these amines can have toxicological consequences. Although there is no specific legislation regarding BA content in many fermented products, it is generally assumed that they should not be allowed to accumulate. The ability of microorganisms to decarboxylate amino acids is highly variable, often being strain specific, and therefore the detection of bacteria possessing amino acid decarboxylase activity is important to estimate the likelihood that foods contain BA and to prevent their accumulation in food products. Moreover, improved knowledge of the factors involved in the synthesis and accumulation of BA should lead to a reduction in their incidence in foods.

Despite its importance in plant health and crop quality, the diversity of epiphytic bacteria on grape berries and other plant parts, like leaves and bark, remains poorly described, as does the role of telluric bacteria in plant colonization. In this study, we compare the bacterial community size and structure in vineyard soils, as well as on grapevine bark, leaves and berries. Analyses of culturable bacteria revealed differences in the size and structure of the populations in each ecosystem. The highest bacteria population counts and the greatest diversity of genera were found in soil samples, followed by bark, grapes and leaves. The identification of isolates revealed that some genera – Pseudomonas, Curtobacterium, and Bacillus – were present in all ecosystems, but in different amounts, while others were ecosystem-specific. About 50% of the genera were common to soil and bark, but absent from leaves and grapes. The opposite was also observed: grape and leaf samples presented 50% of genera in common that were absent from trunk and soil. The bacterial community structure analyzed by T-RFLP indicated similarities between the profiles of leaves and grapes, on the one hand, and bark and soil, on the other, reflecting the number of shared T-RFs. The results suggest an interaction between telluric bacterial communities and the epiphytic bacteria present on the different grapevine parts.

Histamine production from histidine in fermented food products by lactic acid bacteria results in food spoilage and is harmful to consumers. We have isolated a histamine-producing lactic acid bacterium, Lactobacillus hilgardii strain IOEB 0006, which could retain or lose the ability to produce histamine depending on culture conditions. The hdcA gene, coding for the histidine decarboxylase of L. hilgardii IOEB 0006, was located on an 80-kb plasmid that proved to be unstable. Sequencing of the hdcA locus disclosed a four-gene cluster encoding the histidine decarboxylase, a protein of unknown function, a histidyl-tRNA synthetase, and a protein, which we named HdcP, showing similarities to integral membrane transporters driving substrate/ product exchange. The gene coding for HdcP was cloned downstream of a sequence specifying a histidine tag and expressed in Lactococcus lactis. The recombinant HdcP could drive the uptake of histidine into the cell and the exchange of histidine and histamine. The combination of HdcP and the histidine decarboxylase forms a typical bacterial decarboxylation pathway that may generate metabolic energy or be involved in the acid stress response. Analyses of sequences present in databases suggest that the other two proteins have dispensable functions. These results describe for the first time the genes encoding a histamine-producing pathway and provide clues to the parsimonious distribution and the instability of histamine-producing lactic acid bacteria.

No abstract