Sourdough bacterial dynamics revealed by metagenomic analysis in Brazil.

This study dealt with the influence of the temperature on the bacterial dynamics of two spontaneously fermented wheat sourdoughs, propagated at 21 ± 1 °C (SD1) and 30 ± 1 °C (SD2), during nine backslopping steps (BS1 to BS9). Proteobacteria was the only phylum found in flour. Escherichia hermannii was predominant, followed by Kosakonia cowanii, besides species belonging to the genera Pantoea and Pseudomonas. After one step of propagation, Clostridium and Bacillus cereus group became predominant. Lactobacillus curvatus was found at low relative abundance. For the second backslopping step, Clostridium was flanked by L. curvatus and Lactobacillus farciminis. From BS4 (6th day) onward, lactic acid bacteria (LAB) became predominant. L. farciminis overcame L. curvatus and remained dominant until the end of propagations for both sourdoughs. At 21 °C, Bacillus, Clostridium, Pseudomonas, and Enterobacteriaceae were gradually inhibited. At the end of propagation, SD1 harbored only LAB. Otherwise, the temperature of 30 °C favored the persistence of atypical bacteria in SD2, as Pseudomonas and Enterobacteriaceae. Therefore, the temperature of 21 °C was more suitable for sourdough propagation in Brazil. This study enhanced the knowledge of temperature's influence on microbial assembly and contributed to the elucidation of sourdough microbial communities in Brazil

Study of the bacterial diversity of foods: PCR-DGGE versus LH-PCR

The present study compared two culture-independent methods, polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) and length-heterogeneity polymerase chain reaction (LH-PCR), for their ability to reveal food bacterial microbiota. Total microbial DNA and RNA were extracted directly from fourteen fermented and unfermented foods, and domain A of the variable regions V1 and V2 of the 16S rRNA gene was analyzed through LH-PCR and PCR-DGGE. Finally, the outline of these analyses was compared with bacterial viable counts obtained after bacterial growth on suitable selective media. For the majority of the samples, RNA-based PCR-DGGE revealed species that the DNA-based PCR-DGGE was not able to highlight. When analyzing either DNA or RNA, LH-PCR identified several lactic acid bacteria (LAB) and coagulase negative cocci (CCN) species that were not identified by PCR-DGGE. This phenomenon was particularly evident in food samples with viable loads b 5.0 Log cfu g−1 . Furthermore, LH-PCR was able to detect a higher number of peaks in the analyzed food matrices relative to species identified by PCR-DGGE. In light of these findings, it may be suggested that LH-PCR shows greater sensitivity than PCR-DGGE. However, PCR-DGGE detected some other species (LAB included) that were not detected by LH-PCR. Therefore, certain LH-PCR peaks not attributed to known species within the LH-PCR database could be solved by comparing them with species identified by PCR-DGGE. Overall, this study also showed that LH-PCR is a promising method for use in the food microbiology field, indicating the necessity to expand the LH-PCR database, which is based, up to now, mainly on LAB isolates from dairy produc

Characterization of a repertoire of tomato fruit genetic variants in the San Marzano genetic background

[EN] San Marzano (SM) is a worldwide famous tomato Italian traditional landrace characterized by elongated fruits with a dual-purpose use in the fresh and processing market. A repertoire of mutations affecting the fruit and of interest for commercial breeding were introduced into the SM genetic background following backcross schemes. The lines generated included 13 genotypes each carrying a single mutation in genes controlling a) the content of all pigments (hp-1, hp-2, pd), b) of carotenoids (r, t, at, B, B_mo(B)), c) of chlorophyll (gf), d) of flavonoids (y) or e) the ripening process (Nr, rin, Gr). Five lines carrying a combination of two mutations were also included. Analysis of SNP polymorphisms showed that the genetic distance of the lines from the recurrent parent was very variable and not well predicted by the number of backcrosses because it was also a function of the dissimilarity of the donor parent. All the genotypes, together with an SM control, were grown in two consecutive years and characterized for vegetative, reproductive and fruit quality traits. Overall, the studied lines reproduced the SM typical phenotypes, but several differences also emerged as both possible negative or advantageous pleiotropic traits for fresh or processing uses and peeling. High pigment mutations confirmed the negative pleiotropic effects on plant fertility and fruit development described earlier and also negatively affected fruit post-harvest life. These latter defects were also reported in the carotenoid mutant tangerine. In contrast, absence of peel pigmentation in the y mutant was associated with positive postharvest properties as those fruit presented higher resistance to wrinkling and dehydration. Delayed ripening mutants showed positive post-harvest phenotypes, as expected. In conclusion, the study of the present repertoire of fruit variations in an elongated tomato genotype represents a contribution to expand the study of fruit physiology to unusual fruit types and to breed innovative tomato lines with valuable nutritional and technological properties.This work was supported by the Latium Region FILAS project "MIGLIORA", by the Italian Ministry of Agriculture (MiPAAF) under the AGROENER project (D.D. n. 26329, 1 april 2016) - http://agroener.crea.gov.it/and by the European Commission through-H2020 SFS-7a-2014 TRADITOM (634561).Dono, G.; Picarella, ME.; Pons Puig, C.; Santangelo, E.; Monforte Gilabert, AJ.; Granell Richart, A.; Mazzucato, A. (2020). Characterization of a repertoire of tomato fruit genetic variants in the San Marzano genetic background. Scientia horticulturae (Online). 261:1-10. https://doi.org/10.1016/j.scienta.2019.108927S11026

The effect of silicon on the uptake and translocation of arsenic in tomato (Solanum lycopersicum L.)

Measuring tomato seed germination on a medium containing either arsenite or arsenate showed that the presence of 0.5 mM NaH2AsO4·7H2O reduced germination by between 20% and 40%, depending on cultivar. The inhibitory effect was mitigated by the addition of CaSiO3. However, the presence of both forms of As had a drastic negative effect on seedling shoot elongation, which was not mitigated by the presence of CaSiO3. In a subsequent soil-based pot trial, damage due to the presence of As was visible by 15 days after the initiation of the treatment, and the provision of CaSiO3 was significantly ameliorative; again, the severity of the effects was cultivar-dependent. Analysis of the accumulation and distribution of As showed that some of the cultivars are As excluders, and others accumulators. As was taken up by the latter cultivars whether or not CaSiO3 supplementation was provided. The extent of As entry into the fruit varied from cultivar to cultivar, but never rose above the safety threshold. A survey of stress response-associated genes showed that LeGR was strongly up-regulated by exposure to As