Abstract Microbial and enzymatic kinetics are important factors during the aerobic degradation of the organic fraction of municipal solid waste, these depend mainly on the incubation temperature and aeration rates. The objective of this research was to evaluate the process of aerobic degradation, by multiple variables and their combination to understand the interactions between aeration rates in aerobic degradation and their responses. Aeration rates were set at 0.032, 0.064, 0.125, 0.251 and 0.392 L of moist air kg-1 min-1 at 35 °C with inoculum. Microbial activity was evaluated indirectly by means of respirometry, that is, CO2 production and O2 consumption. Extracellular enzymatic activities (ie., pectinases, cellulases, xylanases and proteases) were quantified by releasing the reducing sugars. The different tests were carried out at the Metropolitan Autonomous University, Iztapalapa Unit in September 2019. Finding a strong positive relationship between xylanase and pectinase enzymatic activity and dry weight loss, along with increased cellulase and xylanase activities at higher aeration rates.

Resumen La cinética microbiana y enzimática son factores importantes durante la degradación aerobia de la fracción orgánica de los residuos sólidos urbanos, estas dependen principalmente de la temperatura de incubación y las tasas de aireación. El objetivo de esta investigación fue evaluar el proceso de degradación aerobia, por múltiples variables y su combinación para comprender las interacciones entre las tasas de aireación en la degradación aerobia y sus respuestas. Las tasas de aireación se fijaron en 0.032, 0.064, 0.125, 0.251 y 0.392 L de aire húmedo kg-1 min-1 a 35 °C con inóculo. La actividad microbiana se evaluó de forma indirecta por medio de la respirometria; es decir, la generación de CO2 y el consumo de O2. Las actividades enzimáticas extracelulares (es decir, pectinasas, celulasas, xilanasas y proteasas) se cuantificaron mediante la liberación de los azúcares reductores. Los diferentes ensayos se realizaron en la Universidad Autónoma Metropolitana Unidad Iztapalapa en septiembre de 2019. Encontrando una fuerte relación positiva entre la actividad enzimática xilanasa y pectinasa con la pérdida de peso en seco, junto con el aumento de las actividades celulasas y xilanasas a mayores tasas de aireación.

In this work, fifty yeast strains, isolated from the spontaneous alcoholic fermentation of Agave duranguensis to produce mezcal, were tested using the double coupling system. These yeasts were from the genera Pichia, Torulaspora, Saccharomyces, Kluyveromyces, Deckera, Hanseniaspora, and Candida. P. fermentans ITD00165 was the best isoamyl acetate producer, yielding 0.38 g/L of ester after incubation for 24 h, while K. marxianus ITD00211 produced 0.32 g/L of ester. Thus P. fermentans TD00165 could be considered as an excellent choice for use in optimization studies of the culture medium and bioreactor operating conditions to develop a process for biotechnological production of isoamyl acetate.

Conidia production of entomopathogenic fungi Beauveria bassiana (Bals.-Criv.) Vuill. is performed in a solid state culture (SSC) using agricultural products and their residues, such as rice (Oryza sativa) and sugarcane (Saccharum ojjicinarum) bagasse, where CO2 can be accumulated as a product of metabolism. In this study rice (Oryza sativa var. japonica) was used as substrate using two atmospheric compositions: normal air and other enriched with CO2 (5 %), through exchanges every 12 or 24 h. The effect of these treatments was determined on the conidial production and amylase enzymes by B. bassiana, using a completely randomized design and analysis of variance using Tukey-Kramer test (p< 0.05). Maximum conidia production per g of initial dry substrate (gssi) was obtained with the normal atmosphere (1.14×10(9) conidia gssi-1), while with 5 % of CO2 the conidia production decreased up to 85 % (1.8×10(8) conidia gssi-1). However, in this latter treatment amylase activity increased three times (16.58 UI gssi-1) with respect to the normal atmosphere (5.41 UI gssi-1). These results are important for the conidia and enzymes production by fungi in SSC, with the recommendation to modify the concentration of CO2, as it is required to favor the type of product.

La producción de conidios del hongo entomopatógeno Beauveria bassiana (Bals.-Criv.) Vuill. se realiza en cultivo en medio sólido (CMS) utilizando productos agrícolas y sus residuos, como arroz (Oryza sativa) y bagazo de caña (Saccharum ojjicinarum), donde el CO2 puede acumularse como producto del metabolismo. En este estudio se usó arroz (Oryza sativa var. japonica) como sustrato usando dos composiciones atmosféricas: aire normal y otra enriquecida con CO2 (5 %), a través de recambios cada 12 o 24 h. Se determinó el efecto de estos tratamientos en la producción de conidios y de enzimas amilasas por B. bassiana, mediante un diseño completamente al azar y análisis de varianza usando la prueba de Tukey-Kramer (p<0.05). La producción máxima de conidios por g de sustrato seco inicial (gssi) se obtuvo con la atmósfera normal (1.14×10(9) conidios gssi-1), mientras que con 5 % de CO2 la producción de conidios disminuyó hasta 85 % (1.8×10(8) conidios gssi-1). Sin embargo, en este último tratamiento la actividad de amilasas se incrementó tres veces (16.58 UI gssi-1) respecto a la atmósfera normal (5.41 UI gssi-1). Estos resultados son importantes para la producción de conidios y de enzimas por hongos en CMS, con la recomendación de modificar la concentración de CO2, según se requiera favorecer el tipo de producto.

The aim of the present work was to study the effect of moisture content and inoculum on the growth and conidia production by Beauveria bassiana on wheat bran (WB).The highest growth rate of B. bassiana 885.2 on WB media was obtained at a w=1.0, with no detected growth at a w < 0.97. Solid-state fermentation (SSF) using WB (66% moisture; a w=1.0) achieved a maximal yield of 1.18x10 10 conidia per gram of dry substrate (gds). This yield decreased one order of magnitude with higher moisture contents or the addition of sugarcane bagasse (SCB) as a texturiser. In SSF using WB (66% humidity),the time to obtain a yield of 1x10(10) conidia/gds, referred to as t10, could be predicted using a model considering common inoculum levels and maximal yields. For instance, t10 was 285 h with an inoculum of 1x10(6) conidia/gds; however, t10 was reduced to 232 h and 148 for inocula of 7x10(6) and 5x10(7) conidia/gds, respectively. The estimation of t10 values allowed both comparison between the cultures and prediction of harvesting times in production processes. Values for hydrophobicity were within 90 and 92%, whereas viability averages were around 70% for all the cultures

Estudo em cultura contínua da bactéria ruminal Megasphaera elsdenii que utiliza lactato como fonte de carbono foi realizada. Butirato, foi o produto produzido em menor concentração na cultura em batelada, porém em cultura contínua foi o produto de maior concentração. Sob condições definidas a concentração de biomassa aumentou de 0.46 a 0.72 g l-1. A adição do aditivo Yea Sacc não resultou num aumento da disponibilidade do carbono. As quantidades produzidas de valerato e CO2 foram calculadas pelo uso combinado do balanço e grau de redução do carbono. De acordo com esses resultados, o catabolismo de lactato de M. elsdenii foi mudado pela adição de aditivo a base de levedura. Maior rendimento em butirato e redução na produção de valerato foi observada, por outro lado a produção deacetato e propionato não foi afetada. Os resultados desse trabalho sugerem que os componentes solúveis presentes no aditivo a base de levedura aumentam o anabolismo de M. elsdenii modificando o fluxo de carbono através de suas vias de metabólicas, pelo aumento do butirato e redução do valerato. Em cultura contínua.

Continuous culture study of the ruminal bacterium Megasphaera elsdenii using lactate as carbon source is reported. Butyrate, the minor product in batch culture, was the main product in continuous culture. Under steady state conditions the biomass concentration was increased from 0.46 to 0.72 g l-1. Addition of Yea Sacc did not result an increased availability of carbon. The produced amounts of valerate and CO2 were calculated by using a combined carbon and degree of reduction balances. According to these results, the lactate catabolism of M. elsdenii was changed by the presence of yeast additive, yielding more butyrate and diminishing the production of valerate, while acetate and propionate production was not affected. Results reported in this work suggested that soluble compounds present in the yeast additive filtrate enhanced the anabolism of M. elsdenii and modified the carbon fluxes through its pathways by increasing butyrate and decreasing valerate production in continuous culture.