Corrigendum: Diversity of Weissella confusa in Pozol and Its Carbohydrate Metabolism.

[This corrects the article DOI: 10.3389/fmicb.2021.629449.].

Diversity of Weissella confusa in Pozol and Its Carbohydrate Metabolism.

The genus Weissella is composed of a group of Gram-positive facultative anaerobe bacteria with fermentative metabolism. Strains of this genus have been isolated from various ecological niches, including a wide variety of fermented cereal foods. The present study aimed to determine the relative abundance and fermentation capabilities of Weissella species isolated from pozol, a traditional maya product made of lime-cooked (nixtamalized) fermented maize. We sequenced the V3-V4 regions of 16S rDNA; Weissella was detected early in the fermentation process and reached its highest relative abundance (3.89%) after 3 h of culture. In addition, we evaluated five Weissella strains previously isolated from pozol but reported as non-amylolytic, to define alternative carbon sources such as xylan, xylooligosaccharides, and sucrose. While no growth was observed on birch xylan, growth did occur on xylooligosaccharides and sucrose. Strains WcL17 and WCP-3A were selected for genomic sequencing, as the former shows efficient growth on xylooligosaccharides and the latter displays high glycosyltransferase (GTF) activity. Genomes of both strains were assembled and recorded, with a total of 2.3 Mb in 30 contigs for WcL17 and 2.2 Mb in 45 contigs for WCP-3a. Both strains were taxonomically assigned to Weissella confusa and genomic analyses were performed to evaluate the gene products encoding active carbohydrate enzymes (CAZy). Both strains have the gene content needed to metabolize sucrose, hemicellulose, cellulose, and starch residues, all available in pozol. Our results suggest that the range of secondary enzymatic activity in Weissella confusa strains confer them with wide capabilities to participate in fermentative processes of natural products with heterogeneous carbon sources.

Biochemical characterization of a bacteriocin-like inhibitory substance produced by Enterococcus faecium MXVK29, isolated from Mexican traditional sausage.

BACKGROUND: Enterococci are lactic acid bacteria that can produce bacteriocins, which may offer an additional hurdle to control the growth of food-borne pathogens; moreover, these bacteriocins may have great potential as natural biopreservatives. The aim of this work was to characterize a bacteriocin-like inhibitory substance (BLIS) with antilisterial activity produced by an enterococcal strain. RESULTS: The bacteriogenic strain was isolated from Mexican fermented sausages and identified as Enterococcus faecium with 99% sequence similarity. Maximal activity was detected at 16 h, where bacterial growth was in middle of the stationary phase. The producer strain was not inhibited by its own antimicrobial peptide. BLIS showed a strong anti-Listeria activity and was inactivated by proteinase K. Heating (121 °C for 15 min) induced some inactivation, but thermotolerance was higher at acid pH values. The yield obtained with a pH-mediated purification process was 32.7%, showing a band with an estimated molecular weight of 3.5 kDa. Automated N-terminal Edman degradation showed the following sequence: YYGNGVTCGSHHCSVD. CONCLUSION: Biochemical characteristics of BLIS produced by E. faecium MXVK29 suggested that it belongs to Class IIa of the Klaenhammer classification and could be considered as a natural food preservative, although further studies need to be performed.

[Methods for the study of microbial communities in fermented foods]. / Métodos para el estudio de comunidades microbianas en alimentos fermentados.

The importance of ecological concepts to understand the presence and growth of microorganisms in foods is presently recognized. The production of fermented foods under controlled conditions and its safety assurance depend on the knowledge and control of their microbiota. Traditional fermented foods are obtained by natural fermentations (in which no inoculum is added) and contain complex microbiotas, which are difficult to describe through the use of traditional microbiological methods. The microbial structure of these foods can be studied with different approaches. One of them consists on the typification of isolated microorganisms with methods based on DNA as RFLP, ribotyping, AFLP, ARDRA and RAPD. In order to detect non-culturable or not yet cultured microorganisms, nucleic acids are directly extracted from foods and the microbial diversity is determined from them. Examples of these techniques are the construction of 16S rDNA clone libraries and fingerprinting techniques, such as DGGE and TGGE. Recent advances on the application of these techniques on the study of fermented foods are presented.