Macarena del Mar Jurado

Dynamics of bacterial microbiota during lignocellulosic waste composting: Studies upon its structure, functionality and biodiversity

An intensive isolation program carried out in three replicated composting piles allowed the identification of the resident and transient components of the composting microbiome. More than 4000 bacterial strains were isolated, enzymatically characterized and identified by partial sequencing of their 16S rRNA gene. While microorganisms isolated under mesophilic conditions were prominent throughout the process, thermophilic stages gathered the highest total counts and spore-forming bacteria prevailed at the bio-oxidative phase of composting. Enzymatic capabilities related to the degradation of polymeric materials were exhibited by most of the isolates and as a result of these activities, more soluble compounds could be made available to the entire composting microbiota. A high proportion of isolates showed to be thermotolerant as they were detected at mesophilic and thermophilic phases. Isolated strains belonged to 187 bacterial species. Biodiversity was greater at the central stages of composting and mesophilic, thermophilic and cooling phases shared 50% of species.

Exploiting composting biodiversity: Study of the persistent and biotechnologically relevant microorganisms from lignocellulose-based composting

The composting ecosystem is a suitable source for the discovery of novel microorganisms and secondary metabolites. This work analyzes the identity of microbial community that persists throughout lignocellulose-based composting, evaluates their metabolic activities and studies the capability of selected isolates for composting bioaugmentation. Bacterial species of the phyla Firmicutes, Actinobacteria and Proteobacteria and fungi of the phylum Ascomycota were ubiquitous throughout the composting. The species Arthrobacter russicus, Microbacterium gubbeenense, Ochrocladosporium frigidarii and Cladosporium lignicola are detected for the first time in this ecosystem. In addition, several bacterial and fungal isolates exhibited a wide range of metabolic capabilities such as polymers (lignocellulose, protein, lipids, pectin and starch) breakdown and phosphate-solubilization that may find many biotechnological applications. In particular, Streptomyces albus BM292, Gibellulopsis nigrescens FM1397 and FM1411, Bacillus licheniformis BT575, Bacillus smithii AT907 and Alternaria tenuissima FM1385 exhibited a great potential as inoculants for composting bioaugmentation.

Tracking organic matter and microbiota dynamics during the stages of lignocellulosic waste composting.

The dynamics of biologically meaningful soluble and polymeric carbon fractions and the combined relationships between physical, chemical and biological parameters during composting of lignocellulosic waste were evaluated. The first thermophilic stage is crucial in determining the further evolution of soluble and polymeric carbon fractions but the dynamics of carbon is still important at the maturation stage. Multivariate data analysis showed that not only are all parameters interrelated but also influence one anothers variability. To discern completion of bio-oxidative stage other parameters in addition to temperature should be measured. Evaluation of soluble organic carbon, microbial biomass carbon, pH and inorganic nitrogen can be of great use in detecting the composting stage. This study offers new insights into the mechanisms involved in the biodegradation of organic matter and help to prioritize the parameters that contribute at critical stages of the process.

Evolution of enzymatic activities and carbon fractions throughout composting of plant waste.

Many alternatives for the proper disposal of horticultural plant wastes have been studied, and composting is one of the most attractive due to its insignificant environmental impact and low cost. The quality of compost for agronomical use is related to the degree of organic matter maturation and stabilization. Traditional parameters as well as temperature, ratio C/N, cationic exchange capacity, extractable carbon, or evolution of humificated substances have been successfully used to assess compost maturity and stability. However, microorganisms frequently isolated during composting release a wide range of hydrolytic enzymes, whose activity could apparently give interesting information on the rate of decomposition of organic matter and, therefore, on the product stability. The aim of this work was to study the evolution of some important enzymatic activities during composting of agricultural wastes and their comparison with other chemical parameters commonly employed as quality and maturity indexes, to establish a relationship between the degradation intensity of specific organic carbon fractions throughout the process. In this work, the chemical and biochemical parameters of plant wastes were studied along a composting process of 189 days to evaluate their importance as tools for compost characterization. Results showed an intense enzymatic activity during the first 2-3 weeks of composting (bio-oxidative phase), because of the availability of easily decomposable organic compounds. From a biological point of view, a less intense phase was observed between second and third month of composting (mesophilic or cooling phase). Finally, chemical humification parameters were more closely associated with the period between 119 and 189 days (maturation phase). Significant correlations between the enzymatic activities as well as between enzyme activities and other more traditional parameters were also highlighted, indicating that both kind of indexes can be a reliable tool to determine the degree of stability and maturation of horticultural plant wastes based-compost.

Enhanced turnover of organic matter fractions by microbial stimulation during lignocellulosic waste composting.

Enhanced organic matter turnover was detected in lignocellulosic composting piles inoculated with microorganisms specifically capable of decomposing polymeric compounds. In comparison to uninoculated piles, the following results were obtained in the inoculated piles: degradation of hemicellulose, cellulose and lignin were 28%, 21% and 25% respectively higher. Total organic matter, total sugars and phenolic compounds also decreased more intensely. Greater amounts of soluble organic carbon, reducing sugars and soluble proteins were available to the composting microbiota. Recycling of organic to inorganic nitrogen was improved and humification was more intense and earlier attained. Microbial community structure was also affected by inoculation. It was initially thought that these effects were due to enzymatic capabilities of inoculants, however, microbial counts, especially those corresponding to functional groups, revealed that inoculation induced a true stimulation of microbial growth and activity in the entire composting microbiota which was actually responsible for all the beneficial effects reported here.

Enzymatic characterization of microbial isolates from lignocellulose waste composting: Chronological evolution

Successful composting is dependent upon microbial performance. An interdependent relationship is established between environmental and nutritional properties that rule the process and characteristics of the dominant microbial communities. To reach a better understanding of this relationship, the dynamics of major metabolic activities associated with cultivable isolates according to composting phases were evaluated. Ammonification (72.04%), amylolysis (35.65%), hemicellulolyis (30.75%), and proteolysis (33.61%) were the more frequent activities among isolates, with mesophilic bacteria and fungi as the prevalent microbial communities. Bacteria were mainly responsible for starch hydrolysis, while a higher percentage of hemicellulolytic and proteolytic isolates were ascribable to fungi. Composting seems to exert a functional selective effect on microbial communities by promoting the presence of specific metabolically dominant groups at each stage of the process. Moreover, the application of conglomerate analysis led to the statement of a clear correlation between the chronology of the process and characteristics of the associated microbiota. According to metabolic capabilities of the isolates and their density, three clear clusters were obtained corresponding to the start of the process, including the first thermophilic peak, the rest of the bio-oxidative stage, and the maturation phase.

Biodiversity and succession of mycobiota associated to agricultural lignocellulosic waste-based composting.

A comprehensive characterization of the culturable mycobiota associated to all stages of lignocellulose-based composting was achieved. A total of 77 different isolates were detected, 69 of which were identified on the basis of the 5.8-ITS region sequencing. All the isolates were assigned to the phyla Ascomycota and Basidiomycota, with prevalence of the Sordariomycetes (19) and Eurotiomycetes (17) classes. Penicillium was the most represented genus (11 species), while the species Gibellulopsis nigrescens and Microascus brevicaulis were detected at all the composting stages and showed the highest relative abundances. Fungal diversity decreased as the process proceed, while similarity between fungal communities associated to different samples were maximal for those phases closely connected chronologically and showing similar biological activity degree. Thus, the structure of the lignocellulose-based composting mycobiota can be divided into two major stages corresponding to bio-oxidative phase and maturation phase together with the final product, with a transitional cooling stage joining both of them.