RESUMO
In this study, a microbial consortium from an acid-treated rumen fluid was used to improve the yields of H2 production from paper residues in batch reactors. The anaerobic batch reactors, which contained paper and cellulose, were operated under three conditions: (1) 0.5 g paper/L, (2) 2 g paper/L, and (3) 4 g paper/L. Cellulase was added to promote the hydrolysis of paper to soluble sugars. The H2 yields were 5.51, 4.65, and 3.96 mmol H2/g COD, respectively, with substrate degradation ranging from 56 to 65.4 %. Butyric acid was the primary soluble metabolite in the three reactors, but pronounced solventogenesis was detected in the reactors incubated with increased paper concentrations (2.0 and 4.0 g/L). A substantial prevalence of Clostridium acetobutylicum (99 % similarity) was observed in the acid-treated rumen fluid, which has been recognized as an efficient H2-producing strain in addition to ethanol and n-butanol which were also detected in the reactors.
Assuntos
Celulose/metabolismo , Clostridium acetobutylicum/metabolismo , Hidrogênio/metabolismo , Papel , Resíduos Sólidos , Celulose/química , HidróliseRESUMO
La solventogénesis y la esporulación son mecanismos de las células de Clostridium para resistir ambientes hostiles. Este segundo proceso ha sido estudiado utilizando como modelo lo que sucede con Bacillus, aunque se reconocen diferencias marcadas entre los dos géneros especialmente en el inicio, específicamente en los eventos por medio de los que se da la fosforilación del regulador maestro Spo0A. En la actualidad se ha avalado la teoría que afirma que tres histidin quinasas huérfanas, diferentes a las proteínas Spo0B (histidin quinasa) y Spo0F(fosfotransferasa) en Bacillus, son las encargadas de fosforilar en Clostridium de forma directa a Spo0A, que posteriormente activa la transcripción de diferentes factores sigma relacionados, de forma similar en los dos géneros bacterianos. La proteína Spo0A, perteneciente a la familia de reguladores de respuesta, se comporta como una entidad regulatoria global que tiene injerencia sobre los procesos de formación de esporas y solventes, modulando genes necesarios para que se produzcan acetona y butanol, además de genes de esporulación. El entendimiento de este proceso ha llevado a los investigadores a emplear diferentes técnicas moleculares que permitan incrementar la producción de solventes, así como eliminar la propiedad de las células de producir endosporas. Por tal razón, este escrito presenta un resumen de estas dos redes de expresión de genes, conectadas por el regulador maestro Spo0A.
Solventogenesis and sporulation are mechanisms used by Clostridium cells to resist hostile environments. Sporulation has been studied using as a model what happens with Bacillus, but marked differences were recognized, particularly in the events that led the phosphorylation of the master controller Spo0A. Currently, a theory that claims that three orphan histidine kinases, different from Spo0B (histidin kinase) and spo0F (phosphotransferase) proteins in Bacillus, phosphorilate directly Spo0A in Clostridium activating transcription of different sigma factors which are similar in the two bacterial genera, has been supported. Spo0A protein, which belongs to the family of response regulators, behaves as an entity that has global regulatory interference on the processes of spore formation and solvents, modulating genes necessary to produce acetone and butanol. The understanding of this process has led researchers to employ different molecular techniques that increase the production of solvents, and remove the property of the cells to produce endospores. Reason why, this paper presents an updated summary of these two gene expression networks, connected by the master regulator spo0A.