Microbial and Physiological Characterization of Weakly Amylolytic but Fast-Growing Lactic Acid Bacteria: a Functional Role in Supporting Microbial Diversity in Pozol, a Mexican Fermented Maize Beverage

The lactic acid bacterial (LAB) community dynamics of two wheat and two spelt sourdough fermentations that were daily back-slopped were monitored during a period of 10 days by hybridizing time-related RNA samples, representing the metatranscriptome, to an LAB functional gene microarray. To indicate the species present in each hybridized sample, annotation information for the 2,269 oligonucleotides on the microarray was used. The overall hybridization data revealed that after a transition phase of 5 days, in which atypical sourdough LAB species, including Enterococcus species, were found, a stabilized ecosystem was established with Lactobacillus plantarum and Lactobacillus fermentum as the dominating LAB species. Compared with the combined outcome of culture-dependent and culture-independent identification techniques, the microarray data revealed a functional role for Lactococcus lactis in the early stage ecosystem and the dominance of Pediococcus pentosaceus in most of the fermentations, besides L. plantarum and L. fermentum. Consequently, metatranscriptome hybridization data obtained using an LAB functional gene microarray was shown to be an interesting alternative to microbiological analysis of the community dynamics of complex food ecosystems.

Section: Discussionmentioning

confidence: 85%

Community Dynamics of Bacteria in Sourdough Fermentations as Revealed by Their Metatranscriptome

Weckx

Meulen

Allemeersch

et al. 2010

“…This is of particular interest for at-risk populations such as pregnant women and young children in developing countries. For instance, the amylase activity of some LAB helps increase the energy content of gruels for the complementary feeding of young children through partial hydrolysis of starch in the food matrix (46,57) but also helps sustain the growth of the microbiota of starchy foods (15,62). Other functions-for example, folate and riboflavin synthesis-may improve the quality of the food matrix and may be beneficial for the host.…”

mentioning

confidence: 99%

Genetic Screening of Functional Properties of Lactic Acid Bacteria in a Fermented Pearl Millet Slurry and in the Metagenome of Fermented Starchy Foods

Turpin

Humblot

Guyot

2011

123

111

Lactic acid bacteria (LAB) (n ‫؍‬ 152) in African pearl millet slurries and in the metagenomes of amylaceous fermented foods were investigated by screening 33 genes involved in probiotic and nutritional functions. All isolates belonged to six species of the genera Pediococcus and Lactobacillus, and Lactobacillus fermentum was the dominant species. We screened the isolates for the abilities to survive passage through the gastrointestinal tract and to synthesize folate and riboflavin. The isolates were also tested in vitro for their abilities to survive exposure to bile salts and to survive at pH 2. Because the ability to hydrolyze starch confers an ecological advantage on LAB that grow in starchy matrixes as well as improving the nutritional properties of the gruels, we screened for genes involved in starch metabolism. The results showed that genes with the potential ability to survive passage through the gastrointestinal tract were widely distributed among isolates and metagenomes, whereas in vitro tests showed that only a limited set of isolates, mainly those belonging to L. fermentum, could tolerate a low pH. In contrast, the wide distribution of genes associated with bile salt tolerance, in particular bsh, is consistent with the high frequency of tolerance to bile salts observed. Genetic screening revealed a potential for folate and riboflavin synthesis in both isolates and metagenomes, as well as high variability among genes related to starch metabolism. Genetic screening of isolates and metagenomes from fermented foods is thus a promising approach for assessing the functional potential of food microbiotas.In Africa, many amylaceous fermented foods made from cassava and cereals are used as gruels for the complementary feeding of children under five during weaning. In Burkina Faso and Ghana, ben-saalga and koko gruels prepared from fermented pearl millet (Pennisetum glaucum) slurries are frequently consumed by young children (36,62). The microbiota of these fermented foods is dominated by lactic acid bacteria (LAB), which contribute to their nutritional and sanitary qualities (9, 47). We are currently studying pearl millet-based fermented slurries as a model ("ben-saalga model") for investigating the microbiota of this type of cereal-based food with the aim of developing strategies to improve nutritional quality (26,57,62). Many studies have focused on the phenotypic diversity of the LAB that compose the microbiota of tropical fermented foods. However, their functional diversity in isolates and in metagenomes remains to be described.Since niche-specific adaptation has played a central role in the evolution of LAB (41), the building of collections of bacteria from traditional fermented plant foods in tropical countries may enable the identification of a specific gene set that differs from those of LAB isolated from dairy or bakery products. LAB from microbiotas of plant origin that are found in traditional African foods may have probiotic characteristics (3,28,36). These bacteria first have to be selected for ...

“…macedonicus was first isolated from traditional Greek Kasseri cheese (51), and since then it has been shown to participate in the fermenting floras of different traditional dairy products (10,18,43). S. macedonicus ACA-DC 198 exhibits antimicrobial activity against a number of important food spoilage and pathogenic bacteria, due to the production of a bacteriocin peptide named macedocin (23).…”

mentioning

confidence: 99%

Acid Tolerance of Streptococcus macedonicus as Assessed by Flow Cytometry and Single-Cell Sorting

Papadimitriou

Pratsinis

Nebe-von-Caron³

et al. 2007

An in situ flow cytometric viability assay employing carboxyfluorescein diacetate and propidium iodide was used to identify Streptococcus macedonicus acid tolerance phenotypes. The logarithmic-phase acid tolerance response (L-ATR) was evident when cells were (i) left to autoacidify unbuffered medium, (ii) transiently exposed to nonlethal acidic pH, or (iii) systematically grown under suboptimal acidic conditions (acid habituation). Stationary-phase ATR was also detected; this phenotype was gradually degenerated while cells resided at this phase. Single-cell analysis of S. macedonicus during induction of L-ATR revealed heterogeneity in both the ability and the rate of tolerance acquisition within clonal populations. L-ATR was found to be partially dependent on de novo protein synthesis and compositional changes of the cell envelope. Interestingly, acidhabituated cells were interlaced in lengthier chains and exhibited an irregular pattern of active peptidoglycan biosynthesis sites when probed with BODIPY FL vancomycin. L-ATR caused cells to retain their membrane potential after lethal challenge, as judged by ratiometric analysis with oxonol [DiBAC 4 (3)]. Furthermore, F-ATPase was important during the induction of L-ATR, but in the case of a fully launched response, inhibition of F-ATPase affected acid resistance only partially. Activities of both F-ATPase and the glucose-specific phosphoenolpyruvate-dependent phosphotransferase system were increased after L-ATR induction, distinguishing S. macedonicus from oral streptococci. Finally, the in situ viability assessment was compared to medium-based recovery after single-cell sorting, revealing that the culturability of subpopulations with identical fluorescence characteristics is dependent on the treatments imposed to the cells prior to acid challenge.The existence of common strategies employed by gram-positive bacteria, particularly lactic acid bacteria, in response to acid challenge has emerged only recently (14, 53). However, generalizations about specific mechanisms involved in such responses could prove premature, since it has been shown that these mechanisms can be species or even subspecies specific (14). A typical example relevant to this report is the current knowledge about streptococcal responses to acid stress. Linkages of acid production (acidogenicity) or tolerance (aciduricity) with pathogenicity have fueled recent interest in the basic physiology of oral streptococci (44). Today, Streptococcus mutans is probably the best-studied Streptococcus species in terms of acid stress physiology, but it is uncertain whether the behavior of this species is truly representative of the genus. For instance, a recent report on S. sobrinus revealed key differences from S. mutans concerning the involvement of F-ATPase and glucose-specific phosphoenolpyruvate-phosphotransferase system (PEP-PTS) activities in the manifestation of acid adaptation (35). Additionally, comparison of the recently completed genome sequence of S. thermophilus with those of other streptococci sh...