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

Effect of initial material bulk density and easily-degraded organic matter content on temperature changes during composting of cucumber stalk

To inactivate the potentially pathogenic microorganisms and safely utilize vegetable waste compost, ultra-high temperatures (>70°C) should be maintained during the composting without having an inhibitory effect on maturity. This study investigated the influence of bulk density (part 1) and easily-degraded organic matter content (EDOMC, part 2) on temperature evolution during vegetable waste composting: Part 1: corn straw with different particle sizes was used to achieve different bulk densities in the composting material (BD1-BD3); Part 2: partial or total substitution of the corn straw by corn starch was carried out to obtain different EDOMC (ED1-ED4). The composting experiments were conducted in a lab-scale reactor (1.75kg material) and lasted for 30d. Temperature and CO₂ emission were recorded daily, and the organic matter, lignocellulose, microbial activity, germination index (GI) and C/N of the samples were measured at different stages. The highest temperature (65.7°C) in part 1 occurred in the treatment with the bulk density of 0.35g/cm³, which also had the longest thermophilic phase. Bulk density was found to seriously influence the utilization efficiency of O₂ and heat transfer through materials, rather than heat production from organic matter degradation. In experiment part 2, the highest temperature was obtained with EDOMC of 45% (71.4°C). Therefore, adjusting the bulk density to 0.35g/cm³ and the easily-degraded organic matter content of the initial material to 45% was the best combination for reaching temperatures above 70°C during composting, with no inhibitory effect on the maturity of the compost product.

Energetic enhancement of thermal assistance in the cooling stage of biodrying by stimulating microbial degradation

In this study, thermal assistance was employed in the cooling stage of conventional biodrying. The results indicated that thermal assistance greatly enhanced water removal with improved vapor-carrying capacity of air-flow, and rapidly decreased moisture contents (MCs) from 45.15% to 49.42% to 15.20-25.85% in 6 days, which were much lower than those of conventional biodrying (CB, 34.90-40.85%). More importantly, a synergistic enhancement of physical and biological effects was observed in thermally assisted biodrying (TB) in terms of stimulated enzymes activity and microbial metabolism (higher oxygen uptake rate and degradation coefficient k). Among the degraded organics, lignocellulose was noted to be important for bio-heat generation in cooling stages, especially for straw as bulking agent. Heat balance results suggested that small fractions of thermal heat (19.76-24.73%) were required to upgrade CB processes for water evaporation with higher energy efficiency. Based on economic viability analysis and with consideration of the further drying for CB products, thermally assisted biodrying presented more economic benefits with less investment and shorter payback period. This research provided an efficient engineering approach to upgrade the cooling stage of conventional biodrying with low external heat cost.

Improved lignocellulose-degrading performance during straw composting from diverse sources with actinomycetes inoculation by regulating the key enzyme activities

This study was conducted to assess the effect of thermophilic actinomycetes inoculation on the lignocellulose degradation, enzyme activities and microbial community during different types of straw composting from wheat, rice, corn and soybean. The results showed that actinomycetes inoculation not only changed the structure of actinomycetic and bacterial community but also accelerated the degradation of cellulose, hemicellulose and lignin and increased the key enzymes activities including CMCase, Xylanase, manganese peroxidase, lignin peroxidase and laccase during composting particularly from wheat straw and rice straw. The key enzyme and physiochemical parameters which affected organic fractions degradation have been identified by redundancy analysis. The combined application of actinomycete inoculation and urea addition as a source of nitrogen was suggested to regulate the key enzyme activities and lignocellulose degradation, which lays a foundation for effectively managing organic wastes from different types of crop straws by composting.

Lignin depolymerization and utilization by bacteria

Lignin compound wastes are generated as a result of agricultural and industrial practices. Microorganism-mediated bio-catalytic processes can depolymerize and utilize lignin eco-friendly. Although fungi have been studied since several decades for their ability to depolymerize lignin, strict growth conditions of fungus limit it's industrial application. Compared with fungi, bacteria can tolerate wider pH, temperature, oxygen ranges and are easy to manipulate. Several studies have focused on bacteria involved in the process of lignin depolymerization and utilization. Pseudomonas have been used for paper mill wastewater treatment while Rhodococcus are widely reported to accumulate lipid. In this review, the recent studies on bacterial utilization in paper wastewater treatment, lignin conversion to biofuels, bioplastic, biofertilizers and other value-added chemicals are summarized. As bacteria possess remarkable advantages in industrial production, they may play a promising role in the future commercial lignin utilization.

Effect of inoculation with a microbial consortium that degrades organic acids on the composting efficiency of food waste

In order to overcome the excessive acidification problem, a microbial consortium for the degradation of organic acids (MCDOA), which acts synergistically in degrading organic acids, was developed and used as an inoculum to improve the efficiency of food waste composting. MCDOA could eliminate the initial lag phase of the pile temperature rise because of excessive acidification and effectively shorten the composting period. Fluorescence regional integration analysis of the excitation-emission matrix spectra of dissolved organic matter showed that compared with raw material, in compost with MCDOA inoculation, the percent fluorescence response (Pi,n ) values of Regions I, II and IV decreased by 95.11%, 94.19% and 87.41%, respectively, and Pi,n of Region V increased by 172.57%. The decreased and increased levels were markedly higher than in the two control groups (MgO and K2 HPO4 treatment, and uninoculated compost). These findings revealed that MCDOA accelerated the degradation of proteinaceous compounds and the formation of complicated humic-like materials. Bacterial profiles implied that MCDOA could improve the indigenous bacterial community structure and diversities of acetic and propionic acid-degrading and lignin-degrading bacteria, which might account for the high composting efficiency and degree of humification of the inoculated compost.

Organophosphorus-degrading bacterial community during composting from different sources and their roles in phosphorus transformation

The goals of this study were to identify the key culturable organophosphorus-degrading bacteria (OPDB) that contributed to regulating different phosphorus (P) fractions and evaluate the roles of OPDB and inorganic phosphate-solubilizing bacteria (IPSB) in P transformation during different composting. The results showed that the amounts, incidence and community composition of OPDB for composts from diverse sources were distinctly different but significantly related to temperature and organic matter content. Fifteen key OPDB correlated closely with different P fractions have been selected by redundancy analysis. Two structural equation models were established to compare the roles of OPDB and IPSB on P availability during composting. Variance partitioning further showed that the interactions between IPSB and OPDB communities had a greater impact on P transformation than each independent factor. Therefore, the combined regulation of IPSB and OPDB were suggested to control the transformation of P fractions during composting.

Defining functional diversity for lignocellulose degradation in a microbial community using multi-omics studies

BACKGROUND

Lignocellulose is one of the most abundant forms of fixed carbon in the biosphere. Current industrial approaches to the degradation of lignocellulose employ enzyme mixtures, usually from a single fungal species, which are only effective in hydrolyzing polysaccharides following biomass pre-treatments. While the enzymatic mechanisms of lignocellulose degradation have been characterized in detail in individual microbial species, the microbial communities that efficiently breakdown plant materials in nature are species rich and secrete a myriad of enzymes to perform "community-level" metabolism of lignocellulose. Single-species approaches are, therefore, likely to miss important aspects of lignocellulose degradation that will be central to optimizing commercial processes.

RESULTS

Here, we investigated the microbial degradation of wheat straw in liquid cultures that had been inoculated with wheat straw compost. Samples taken at selected time points were subjected to multi-omics analysis with the aim of identifying new microbial mechanisms for lignocellulose degradation that could be applied in industrial pre-treatment of feedstocks. Phylogenetic composition of the community, based on sequenced bacterial and eukaryotic ribosomal genes, showed a gradual decrease in complexity and diversity over time due to microbial enrichment. Taxonomic affiliation of bacterial species showed dominance of Bacteroidetes and Proteobacteria and high relative abundance of genera Asticcacaulis, Leadbetterella and Truepera. The eukaryotic members of the community were enriched in peritrich ciliates from genus Telotrochidium that thrived in the liquid cultures compared to fungal species that were present in low abundance. A targeted metasecretome approach combined with metatranscriptomics analysis, identified 1127 proteins and showed the presence of numerous carbohydrate-active enzymes extracted from the biomass-bound fractions and from the culture supernatant. This revealed a wide array of hydrolytic cellulases, hemicellulases and carbohydrate-binding modules involved in lignocellulose degradation. The expression of these activities correlated to the changes in the biomass composition observed by FTIR and ssNMR measurements.

CONCLUSIONS

A combination of mass spectrometry-based proteomics coupled with metatranscriptomics has enabled the identification of a large number of lignocellulose degrading enzymes that can now be further explored for the development of improved enzyme cocktails for the treatment of plant-based feedstocks. In addition to the expected carbohydrate-active enzymes, our studies reveal a large number of unknown proteins, some of which may play a crucial role in community-based lignocellulose degradation.

Nitrification within composting: A review

Composting could be regarded as a process of processes because it entails a number of complex chemical and microbiological reactions and transformations. Nitrification is one of such processes that normally takes place during the curing phase. This process has been studied in detail for wastewater treatment, and it is becoming an extensively studied topic within composting. In the past, nitrate presence in compost has been clearly perceived as a maturation indicator; however, nowadays, nitrate formation is also conceived as a way of conserving nitrogen in compost. Nitrification is a process closely linked to other processes such as ammonification and the possible loss of ammonia (NH₃). Nitrification is defined as conversion of the most reduced form of nitrogen (NH₃) to its most oxidized form (i.e. nitrate) and it is performed in two steps which are carried out by two different groups of microorganisms: the ammonia-oxidizing bacteria or archaea (AOB/AOA) and the nitrite-oxidizing bacteria (NOB). The objectives of this review are: a) to gather relevant information on nitrification, which can specifically occur during composting, b) to outline ultimate findings described by the literature in order to increase the understanding and the application of nitrification within composting, and c) to outline future research direction.

Critical evaluation of post-consumption food waste composting employing thermophilic bacterial consortium

Effect of single-function (oil degrading) and multi-functional bacterial consortium with zeolite as additive for post-consumption food waste (PCFW) composting was investigated through assessing the oil content reduction in a computer controlled 20-L composter. Three treatments of PCFWs combined with 10% zeolite were developed: Treatment-2 and Treatment-3 were inoculated with multi-functional (BC-1) and oil degrading bacterial consortium (BC-2), respectively, while T-1 was without bacterial inoculation and served as control. Results revealed that BC-2 inoculated treatment (T-3) was superior to control treatment and marginally better than T-2 in terms of oil degradation. The reduction of oil content was >97.8% in T-3 and 92.27% in T-2, while total organic matter degradation was marginally higher in T-2 (42.95%) than T-3 (41.67%). Other parameters of compost maturity including germination test indicated that T-2 was marginally better than T-3 and significantly enhanced the oily PCFW decomposition and shortened the composting period by 20days.

Revealing the insoluble metasecretome of lignocellulose-degrading microbial communities

Microbial communities metabolize plant biomass using secreted enzymes; however, identifying extracellular proteins tightly bound to insoluble lignocellulose in these microbiomes presents a challenge, as the rigorous extraction required to elute these proteins also lyses the microbes associated with the plant biomass releasing intracellular proteins that contaminate the metasecretome. Here we describe a technique for targeting the extracellular proteome, which was used to compare the metasecretome and meta-surface-proteome of two lignocellulose-degrading communities grown on wheat straw and rice straw. A combination of mass spectrometry-based proteomics coupled with metatranscriptomics enabled the identification of a unique secretome pool from these lignocellulose-degrading communities. This method enabled us to efficiently discriminate the extracellular proteins from the intracellular proteins by improving detection of actively secreted and transmembrane proteins. In addition to the expected carbohydrate active enzymes, our new method reveals a large number of unknown proteins, supporting the notion that there are major gaps in our understanding of how microbial communities degrade lignocellulosic substrates.

Reducing nitrogen loss and phytotoxicity during beer vinasse composting with biochar addition

The aim of this study was to investigate the feasibility of composting of beer vinasse generated from brewing industry, the effect of biochar amendment on beer vinasse composting was also evaluated based on the changes of different physicochemical parameters, phytotoxicity and final compost quality. Four different treatments were performed of beer vinasse with biochar addition at 0, 5%, 10%, 15% (w/w dry basis). The final product obtained from beer vinasse composting was phytotoxicity-free (GI: 120.8%), mature (C/N: 19.88, NH₄⁺-N: 295.0mg/kg, DOC: 9.76g/kg) and nutrient-rich (especially for P: 1.92%) compost except high N loss (60.76%), which had the potential to be as soil amendment or fertilizer. Biochar addition contributed to decomposition of DOC indicating higher microbial activity and attain phytotoxicity-free standard rapidly. N loss significantly reduced by 27% with biochar at 15% addition. And 15% biochar addition ensured all parameters, which was involved in composts quality, to attain the mature standard. Therefore, it was suggested that biochar addition at 15% was optimal.

Properties and evolution of dissolved organic matter during co-composting of dairy manure and Chinese herbal residues

Composting is an effective method in treating solid organic wastes, in which dissolved organic matter (DOM) plays an important role in transformation of organic matter and microbial activity. Therefore, an understanding of the properties and evolution of DOM during composting is crucial. In this study, DOM was studied using elemental analysis, spectroscopic analysis (UV-vis, FTIR, and pyrolysis-GC/MS), and colloidal analysis during a 120-day composting. Results showed that the content of N and O in DOM increased while C and H content declined progressively over the composting time. Aliphatic C-H stretching, aromatic C=C or C=O stretching of amide groups, and C-O stretch (carbohydrates) showed an obvious decrease, while COO- and C-N groups had a significant increase. The evolution of DOM indicated a gradual decrease of the lipid and polysaccharide fractions, whereas an increase of aromatic and nitrogenous compounds was observed. The DOM also showed a more stable status, and an accumulation of small molecular compounds occurred with composting proceeded. Taken together, these results shed a good insight into the properties and evolution of DOM during a composting process.

In-Vessel Co-Composting of Food Waste Employing Enriched Bacterial Consortium

The aim of the present study is to develop a good initial composting mix using a bacterial consortium and 2% lime for effective co-composting of food waste in a 60-litre in-vessel composter. In the experiment that lasted for 42 days, the food waste was first mixed with sawdust and 2% lime (by dry mass), then one of the reactors was inoculated with an enriched bacterial consortium, while the other served as control. The results show that inoculation of the enriched natural bacterial consortium effectively overcame the oil-laden co-composting mass in the composter and increased the rate of mineralization. In addition, CO₂ evolution rate of (0.81±0.2) g/(kg·day), seed germination index of (105±3) %, extractable ammonium mass fraction of 305.78 mg/kg, C/N ratio of 16.18, pH=7.6 and electrical conductivity of 3.12 mS/cm clearly indicate that the compost was well matured and met the composting standard requirements. In contrast, control treatment exhibited a delayed thermophilic phase and did not mature after 42 days, as evidenced by the maturity parameters. Therefore, a good composting mix and potential bacterial inoculum to degrade the oil are essential for food waste co-composting systems.

Microbial community structure and dynamics in thermophilic composting viewed through metagenomics and metatranscriptomics

Composting is a promising source of new organisms and thermostable enzymes that may be helpful in environmental management and industrial processes. Here we present results of metagenomic- and metatranscriptomic-based analyses of a large composting operation in the São Paulo Zoo Park. This composting exhibits a sustained thermophilic profile (50 °C to 75 °C), which seems to preclude fungal activity. The main novelty of our study is the combination of time-series sampling with shotgun DNA, 16S rRNA gene amplicon, and metatranscriptome high-throughput sequencing, enabling an unprecedented detailed view of microbial community structure, dynamics, and function in this ecosystem. The time-series data showed that the turning procedure has a strong impact on the compost microbiota, restoring to a certain extent the population profile seen at the beginning of the process; and that lignocellulosic biomass deconstruction occurs synergistically and sequentially, with hemicellulose being degraded preferentially to cellulose and lignin. Moreover, our sequencing data allowed near-complete genome reconstruction of five bacterial species previously found in biomass-degrading environments and of a novel biodegrading bacterial species, likely a new genus in the order Bacillales. The data and analyses provided are a rich source for additional investigations of thermophilic composting microbiology.

Composting-Like Conditions Are More Efficient for Enrichment and Diversity of Organisms Containing Cellulase-Encoding Genes than Submerged Cultures

Cost-effective biofuel production from lignocellulosic biomass depends on efficient degradation of the plant cell wall. One of the major obstacles for the development of a cost-efficient process is the lack of resistance of currently used fungal enzymes to harsh conditions such as high temperature. Adapted, thermophilic microbial communities provide a huge reservoir of potentially interesting lignocellulose-degrading enzymes for improvement of the cellulose hydrolysis step. In order to identify such enzymes, a leaf and wood chip compost was enriched on a mixture of thermo-chemically pretreated wheat straw, poplar and Miscanthus under thermophile conditions, but in two different set-ups. Unexpectedly, metagenome sequencing revealed that incubation of the lignocellulosic substrate with compost as inoculum in a suspension culture resulted in an impoverishment of putative cellulase- and hemicellulase-encoding genes. However, mimicking composting conditions without liquid phase yielded a high number and diversity of glycoside hydrolase genes and an enrichment of genes encoding cellulose binding domains. These identified genes were most closely related to species from Actinobacteria, which seem to constitute important players of lignocellulose degradation under the applied conditions. The study highlights that subtle changes in an enrichment set-up can have an important impact on composition and functions of the microcosm. Composting-like conditions were found to be the most successful method for enrichment in species with high biomass degrading capacity.

An optimized regulating method for composting phosphorus fractions transformation based on biochar addition and phosphate-solubilizing bacteria inoculation

The study was conducted to investigate the influence of biochar and/or phosphate-solubilizing bacteria (PSB) inoculants on microbial biomass, bacterial community composition and phosphorus (P) fractions during kitchen waste composting amended with rock phosphate (RP). There were distinct differences in the physic-chemical parameters, the proportion of P fractions and bacterial diversity in different treatments. The contribution of available P fractions increased during composting especially in the treatment with the addition of PSB and biochar. Redundancy analysis showed that bacterial compositions were significantly influenced by P content, inoculation and biochar. Variance partitioning further showed that synergy of inoculated PSB and indigenous bacterial communities and the joint effect between biochar and bacteria explained the largest two proportion of the variation in P fractions. Therefore, the combined application of PSB and biochar to improve the inoculation effect and an optimized regulating method were suggested based on the distribution of P fractions.

Nitrification during extended co-composting of extreme mixtures of green waste and solid fraction of cattle slurry to obtain growing media

Next generation of waste management systems should apply product-oriented bioconversion processes that produce composts or biofertilisers of desired quality that can be sold in high priced markets such as horticulture. Natural acidification linked to nitrification can be promoted during composting. If nitrification is enhanced, suitable compost in terms of pH can be obtained for use in horticultural substrates. Green waste compost (GW) represents a potential suitable product for use in growing medium mixtures. However its low N provides very limited slow-release nitrogen fertilization for suitable plant growth; and GW should be composted with a complementary N-rich raw material such as the solid fraction of cattle slurry (SFCS). Therefore, it is important to determine how very different or extreme proportions of the two materials in the mixture can limit or otherwise affect the nitrification process. The objectives of this work were two-fold: (a) To assess the changes in chemical and physicochemical parameters during the prolonged composting of extreme mixtures of green waste (GW) and separated cattle slurry (SFCS) and the feasibility of using the composts as growing media. (b) To check for nitrification during composting in two different extreme mixtures of GW and SFCS and to describe the conditions under which this process can be maintained and its consequences. The physical and physicochemical properties of both composts obtained indicated that they were appropriate for use as ingredients in horticultural substrates. The nitrification process occurred in both mixtures in the medium-late thermophilic stage of the composting process. In particular, its feasibility has been demonstrated in the mixtures with a low N content. Nitrification led to the inversion of each mixture's initial pH.

Effect of actinobacteria agent inoculation methods on cellulose degradation during composting based on redundancy analysis

In this study, actinobacteria agent including Streptomyces sp. and Micromonospora sp. were inoculated during chicken manure composting by different inoculation methods. The effect of different treatments on cellulose degradation and the relationship between inoculants and indigenous actinobacteria were investigated during composting. The results showed that inoculation in different stages of composting all improved the actinobacteria community diversity particularly in the cooling stage of composting (M3). Moreover, inoculation could distinctly accelerate the degradation of organic matters (OM) especially celluloses. Redundancy analysis indicated that the correlation between indigenous actinobacteria and degradation of OM and cellulose were regulated by inoculants and there were significant differences between different inoculation methods. Furthermore, synergy between indigenous actinobacteria and inoculants for degradation of OM and cellulose in M3 was better than other treatments. Conclusively, we suggested an inoculation method to regulate the indigenous actinobacteria based on the relationship between inoculants and indigenous actinobacteria and degradation content.

Phosphorus availability from rock phosphate: Combined effect of green waste composting and sulfur addition

Rock phosphate constitutes a natural phosphorus (P) source for organic farming systems, but with a limiting direct agricultural use due to its poor inherent reactivity. Thus, this work studies the effect of the co-composting of rock phosphate with green wastes and elemental sulfur on phosphorus availability. Six composts were prepared combining different green wastes and rock phosphate in three different proportions (0%, 0.27% and 0.54% P fresh mass basis) and elemental sulfur in two proportions (0% and 0.5% S fresh mass basis). During composting, the temperature of the mixtures was monitored, as were physico-chemical and chemical parameters, especially those related to phosphorus. The co-composting of green wastes with rock phosphate improved phosphorus mobilization and also constituted a viable method to manage green wastes, obtaining P-enriched compost for organic farming systems. Sulfur addition favored the composting process and also phosphorus solubilization, especially in the mixture with the lowest proportion of rock phosphate.

Wheat straw: An inefficient substrate for rapid natural lignocellulosic composting

Composting is a promising method for the management of agricultural wastes. However, results for wheat straw composts with different carbon-to-nitrogen ratios revealed that wheat straw was only partly degraded after composting for 25days, with hemicellulose and cellulose content decreasing by 14% and 33%, respectively. No significant changes in community structure were found after composting according to 454-pyrosequencing. Bacterial communities were represented by Proteobacteria and Bacteroidetes throughout the composting process, including relatively high abundances of pathogenic microbes such as Pseudomonas and Flexibacter, suggesting that innocent treatment of the composts had not been achieved. Besides, the significant lignocellulose degrader Thermomyces was not the exclusively dominant fungus with relative abundance only accounting for 19% of fungal communities. These results indicated that comparing with maize straw, wheat straw was an inefficient substrate for rapid natural lignocellulose-based composting, which might be due to the recalcitrance of wheat straw.

Dynamic changes of the dominant functioning microbial community in the compost of a 90-m(3) aerobic solid state fermentor revealed by integrated meta-omics

The dynamic changes in the composition and function of both bacterial and fungal communities over time and at various depths in the compost of a 90-m(3) industrial-scale fermentor were explored using integrated meta-omics. The microbial communities in the middle layer (1.2m) of the compost developed a stable and simple structure over time, which was mainly composed of Thermobifida, Bacillus, Thermomyces and Aspergillus. According to the metaproteomic results, the bacterial community was more focused on cellulose degradation, characterized by 44% of the cellulases that were secreted by Thermobifida, while the fungal community was more likely to degrade hemicellulose, mainly via Thermomyces and Aspergillus. The results revealed that, under artificial control of the temperature and oxygen concentration, the efficiency of organic waste degradation was greatly increased and the fermentation cycle was shortened to 11 days.

Evaluation of microbially enhanced composting of sophora flavescens residues

The effects of inoculants on the composting of Sophora flavescens residues were evaluated based on several physical, chemical and biological parameters, as well as the infrared spectra. Compared to the control compost without inoculants, the treatment compost with inoculants (Bacillus subtilis strain G-13 and Chaetomium thermophilum strain GF-1) had a significantly longer thermophilic duration, higher cellulase activity and a higher degradation rate of cellulose, hemicellulose and lignin (P < 0.05). Thus, a higher maturity degree of compost with apparently lower C:N ratio (15.88 vs. 17.77) and NH₄-N:NO₃-N ratio (0.16 vs. 0.20) was obtained with the inoculation comparing with the control (P < 0.05). Besides, the inoculants could markedly accelerate the composting process and increase the maturity degree of compost as indicated by the germination index (GI) in which the treatment reached the highest GI of 133.2% at day 15 while the control achieved the highest GI of 125.7% at day 30 of the composting. Inoculation with B. subtilis and C. thermophilum is a useful method to enhance the S. flavescens residues composting according to this study.

Thermomyces lanuginosus is the dominant fungus in maize straw composts

The microbial community composition and function of three self-heating maize straw composts were compared by integrated meta-omics. The results revealed that the fungal communities were primarily dominated by the phylum Ascomycota (>90%) regardless of different nitrogen sources, which were exclusively composed of the Thermomyces, a genus of hemicellulose degraders. The bacterial community composition was affected by the addition of nitrogen sources, as the abundance of the Actinobacteria increased, while the Proteobacteria and Bacteroidetes decreased. Various hemicellulases and cellulases were detected in the composts, and the major xylanase secreted by Thermomyces lanuginosus was always present, revealing that it was the dominant fungus in hemicellulose hydrolysis and that bacteria and fungi might synergistically degrade lignocellulose. Thus, microbial communities in composts may develop a simple and stable structure of a dominant fungal species and limited numbers of bacterial species under the selective pressure of high temperature and maize straw as starting materials.

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.

Numerical simulation of organic waste aerobic biodegradation: a new way to correlate respiration kinetics and organic matter fractionation

Composting wastes permits the reuse of organic matter (OM) as agricultural amendments. The fate of OM during composting and the subsequent degradation of composts in soils largely depend on waste OM quality. The proposed study aimed at developing a model to predict the evolution in organic matter quality during the aerobic degradation of organic waste, based on the quantification of the various OM fractions contained in the wastes. The model was calibrated from data gathered during the monitoring of four organic wastes (two non-treated wastes and their digestates) exposed to respirometric tests. The model was successfully fitted for all four wastes and permitted to predict respiration kinetics, expressed as CO2 production rates, and the evolution of OM fractions. The calibrated model demonstrated that hydrolysis rates of OM fractions were similar for all four wastes whereas the parameters related to microbial activity (eg. growth and death rates) were specific to each substrate. These later parameters have been estimated by calibration on respirometric data, thus demonstrating that coupling analyses of OM fractions in initial wastes and respirometric tests permit the simulation of the biodegradation of various type of waste. The biodegradation model presented in this paper could thereafter be integrated in a composting model by implementing mass and heat balance equations.

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.

Diversity and dynamics of the microbial community on decomposing wheat straw during mushroom compost production

The development of communities of three important composting players including actinobacteria, fungi and clostridia was explored during the composting of wheat straw for mushroom production. The results revealed the presence of highly diversified actinobacteria and fungal communities during the composting process. The diversity of the fungal community, however, sharply decreased in the mature compost. Furthermore, an apparent succession of both actinobacteria and fungi with intensive changes in the composition of communities was demonstrated during composting. Notably, cellulolytic actinomycetal and fungal genera represented by Thermopolyspora, Microbispora and Humicola were highly enriched in the mature compost. Analysis of the key cellulolytic genes revealed their prevalence at different composting stages including several novel glycoside hydrolase family 48 exocellulase lineages. The community of cellulolytic microbiota also changed substantially over time. The prevalence of the diversified cellulolytic microorganisms holds the great potential of mining novel lignocellulose decomposing enzymes from this specific ecosystem.

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.