ABSTRACT
The microbial fermentation behind sourdough bread is among our oldest technologies, yet there are many opportunities for sourdough science to learn from traditional bakers. We analyzed 16S rRNA sequences in R to assess the bacterial community structure and performance of 40 starters grown from 10 types of flour over 14 days, and identified six distinct stages of succession. At each stage, bacterial taxa correlate with determinants of bread quality including pH, rise, and aromatic profile. Day 1 starter cultures were dominated by microorganisms commonly associated with plants and flour, and by aromas similar to toasted grain/cereal. Bacterial diversity peaked from days 2-6 as taxa shifted from opportunistic/generalist bacteria associated with flour inputs, toward specialized climax bacterial communities (days 10-14) characterized by acid-tolerant taxa and fruity (p < 3.03e-03), sour (p < 1.60e-01), and fermented (p < 1.47e-05) aromas. This collection of traits changes predictably through time, regardless of flour type, highlighting patterns of bacterial constraints and dynamics that are conserved across systems and scales. Yet, while sourdough climax communities exhibit similar markers of maturity (i.e., pH ≤ 4 and enriched in Lactobacillus (mean abundance 48.1%), Pediococcus (mean abundance 22.7%), and/or Gluconobacter (mean abundance 19.1%)), we also detected specific taxa and aromas associated with each type of flour. Our results address important ecological questions about the relationship between community structure and starter performance, and may enable bakers to deliberately select for specific sourdough starter and bread characteristics.
Subject(s)
Bacteria , Flour , Flour/microbiology , RNA, Ribosomal, 16S/genetics , Fermentation , Bacteria/genetics , Lactobacillus/geneticsABSTRACT
We have prepared CuO-derived electrocatalysts on a graphitic carbon nitride (g-C3N4) nanosheet support for the electrochemical carbon dioxide reduction reaction (CO2RR). Highly monodisperse CuO nanocrystals made by a modified colloidal synthesis method serve as the precatalysts. We use a two-stage thermal treatment to address the active site blockage issues caused by the residual C18 capping agents. The results show that the thermal treatment effectively removed the capping agents and increased the electrochemical surface area. During the process, the residual oleylamine molecules incompletely reduced CuO to a Cu2O/Cu mixed phase in the first stage of thermal treatment, and the following treatment in forming gas at 200 °C completed the reduction to metallic Cu. The CuO-derived electrocatalysts show different selectivities over CH4 and C2H4, and this might be due to the synergistic effects of Cu-g-C3N4 catalyst-support interaction, varied particle sizes, dominant surface facets, and catalyst ensemble. The two-stage thermal treatment enables sufficient capping agent removal, catalyst phase control, and CO2RR product selection, and with precise controls of the experimental parameters, we believe that this will help to design and fabricate g-C3N4-supported catalyst systems with narrower product distribution.
ABSTRACT
Over 15 years, with the support of a Canadian funding agency, the Universidad Mayor de San Simón, in Bolivia, undertook a large survey of aromatic plants of the South American country. More than a hundred species were studied under various aspects, including the production and characterization of essential oils. As part of this survey, the chemical composition of an essential oil sample obtained from Pentacalia herzogii (Asteraceae) growing wild in the High Valley region of the department of Cochabamba was determined by a combination of GC and GC-MS measurements. α-Pinene was the main constituent of this essential oil (34%), accompanied by limonene (22%) and germacrene D (7.5%) as well as an important fraction of methoxylated monoterpenoids. They were mainly isomers of thymol methyl ether, accounting for 13% of the chromatogram. A new quantitatively important compound (9%) was identified through NMR and chemical synthesis as 4-isopropyl-6-methylbenzo[d][1,3]dioxole, and designated herzogole, alongside the minor related compound 1-isopropyl-2,3-dimethoxy-5-methylbenzene. The monoterpene benzodioxole featured a distinctive green-phenolic aroma which could raise interest for fragrance use. Since these compounds were not known naturally, a biosynthetic mechanism of their formation was proposed and put in perspective to illustrate the metabolic originality of P. herzogii.
Subject(s)
Asteraceae/chemistry , Benzodioxoles/isolation & purification , Oils, Volatile/analysis , Bicyclic Monoterpenes/isolation & purification , Gas Chromatography-Mass Spectrometry , Limonene/isolation & purification , Monoterpenes/isolation & purification , Oils, Volatile/chemistry , Plant Components, Aerial/chemistry , Plant Oils/analysis , Plant Oils/chemistry , Sesquiterpenes, Germacrane/isolation & purificationABSTRACT
We report here the complete genome sequences of four subcluster L3 mycobacteriophages newly isolated from soil samples, using Mycobacterium smegmatis mc2155 as the host. Comparative genomic analyses with four previously described subcluster L3 phages reveal strong nucleotide similarity and gene conservation, with several large insertions/deletions near their right genome ends.
ABSTRACT
Dialkyl and diaryl dichalcogenides are highly versatile and modular precursors for the synthesis of colloidal chalcogenide nanocrystals. We have used a series of commercially available dichalcogenide precursors to unveil the molecular basis for the outcome of nanocrystal preparations, more specifically, how precursor molecular structure and reactivity affect the final shape and size of II-VI semiconductor nanocrystals. Dichalcogenide precursors used were diallyl, dibenzyl, di-tert-butyl, diisopropyl, diethyl, dimethyl, and diphenyl disulfides and diethyl, dimethyl, and diphenyl diselenides. We find that the presence of two distinctively reactive C-E and E-E bonds makes the chemistry of these precursors much richer and interesting than that of other conventional precursors such as the more common phosphine chalcogenides. Computational studies (DFT) reveal that the dissociation energy of carbon-chalcogen (C-E) bonds in dichalcogenide precursors (R-E-E-R, E=S or Se) increases in the order (R): diallylSubject(s)
Chalcogens/chemistry
, Crystallization/methods
, Models, Chemical
, Models, Molecular
, Nanostructures/chemistry
, Nanostructures/ultrastructure
, Computer Simulation
, Macromolecular Substances/chemistry
, Materials Testing
, Molecular Conformation
, Particle Size
, Surface Properties
ABSTRACT
Analizar la incidencia, características obstétricas y complicaciones maternas de la placenta previa. Estudio retrospectivo y descriptivo de 150 casos atendidos entre 1988 y 1992 en 19.854 nacimientos vivos. Maternidad del Hospital "Dr. Adolfo Prince Lara", Puerto Cabello, Estado Carabobo. La incidencia fue de 0,76 por ciento (1 caso por cada 132 nacimientos), el grupo de edad predominó entre los 27 a 32 años (40,67 por ciento). El 79,33 por ciento (119 casos) fueron multíparas, 70 por ciento (105 casos) fueron embarazos de término. Complicaciones maternas más frecuentes: hemorragias 31,03 por ciento; rotura prematura de membranas 31,03 por ciento y trabajo de parto pretérmino 24,13 por ciento. El 78,67 por ciento terminó por cesárea. El 78 por ciento (114 neonatos) tuvieron peso > a 2 500 g. El 65,47 por ciento presentaron Apgar mayor igual 7 puntos, hubo 1 muerte materna. El manejo expectante de la plancenta previa, el ultrasonido diagnóstico y el uso de cesárea, han contribuido a disminuir la morbi-mortalidad materno-fetal
Subject(s)
Humans , Female , Pregnancy , Placenta Previa , Pregnancy Complications , Hemorrhage , VenezuelaABSTRACT
Determinar la incidencia del síndrome HELLP, complicaciones y características del neonato. Estudio retrospectivo y descriptivo de 19 pacientes con diagnóstico de síndrome HELLP desde enero 1998 hasta septiembre 1999. Hospital "Dr. Adolfo Prince Lara", Puerto Cabello, Estado Carabobo. La incidencia fue de 0,27 por ciento sobre el total de nacidos vivos en el período de estudio. El grupo de edad predominante fue de 20 a 29 años, (42,11 por ciento). El 57,90 por ciento fueron embarazos a término y 42,10 por ciento pretérminos. El diagnóstico se hizo en el 68,42 por ciento durante el embarazo y 31,58 por ciento en el puerperio. Las complicaciones úteroplacentarias representaron el 31,56 por ciento las renales 26,31 por ciento hematológicas 5,26 por ciento. El 47,36 por ciento presentó HELLP clase I; 26,32 por ciento clase II y III, respectivamente. Hubo 3 mortinatos. La tasa de mortalidad fetal fue de 0,43X1000. No se reportaron muertes neonatales ni maternas. Es muy importante hacer un buen control prenatal, para prevenir y diagnosticar precozmente la hipertensión inducida por el embarazo y evitar las complicaciones de esta enfermedad como es el HELLP
Subject(s)
Humans , Female , Pregnancy , Pre-Eclampsia , Pregnancy , Fetus , Hypertension , VenezuelaABSTRACT
Se reporta un caso de gemelos unidos, teratódimo, opódimo, tetraoftalmos, rinodimo; en una paciente de 19 años, II gesta, I para con antecedentes de un recien nacido mortinato por eclampsia. Período intergenésico 2 años. El parto termina por cesárea obteniéndose un recién nacido de sexo masculino a término, 3.200 g de peso. Talla 50 cm, circunferencia cefálica 40,5 cm, torácica 36 cm, abdominal 34 cm. Macroscópicamente se observa malformación a nivel del polo cefálico: duplicación de los rasgos faciales. El recién nacido permanece vivo durante 10 horas. El estudio anatomopatológico revela malformación con las características señaladas según la clasificación de León (1959)
Subject(s)
Humans , Female , Pregnancy , Infant, Newborn , Adult , Congenital Abnormalities , Twins, Conjoined/embryology , Eclampsia/mortality , Fetus/abnormalitiesABSTRACT
Determinar la incidencia de embarazo gemelar, antecedentes obstétricos, complicaciones del embarazo, parto, presentación y características del neonato. Hospital "Dr.Adolfo Prince Lara", Puerto Cabello, Edo. Carabobo, Venezuela. Estudio retrospectivo y descriptivo de 311 embarazos gemelares atendidos desde 1987 a 1996 en 41 004 nacimientos vivos. La incidencia fue de 0,77 por ciento o 1 embarazo gemelar por cada 132 nacimientos. El mayor porcentaje 51,13 por ciento ocurrió en el grupo etáreo de 20-29 años. El 73,63 por ciento fueron multíparas; 52,78 por ciento con embarazos menores de 37 semanas. El 55,52 por ciento no tuvo control prenatal. Las patologías asociadas fueron: amenaza de parto prematuro 38,13 por ciento; hipertensión asociada al embarazo 31,25 por ciento y ruptura prematura de membranas 19,34 por ciento. La presencia cefálica fue la más frecuente para el primer feto 74,49 por ciento; la podálica para el segundo 49,79 por ciento. El 56,06 por ciento tuvo parto normal y 43,62 por ciento cesárea. Más de la mitad de los neonatos (59,56 por ciento) presentaron peso menor o igual a 2 500 g. El segundo neonato presentó Apgar al minuto menor que el primero. La mortalidad fetal fue de 0,8 x 1000 nacidos vivos. El 71,50 por ciento de las placentas fueron bicordiales biamnióticas; 24,35 por ciento monocoriales biamnióticas y 4,15 por ciento monocoriales monoamnióticas. El embarazo gemelar se acompaña de una mayor morbimortalidad materno fetal, y amerita diagnóstico precoz, control prenatal adecuado y un programa preventivo docente asistencial, interdisciplinario y con participación de la embarazada
