Editorial

2 pages, 174 KiB

Open AccessEditorial

Editorial for Special Issue “Microorganisms and Organic Waste Valorisation”

by Camilla M. Braguglia and Simona Rossetti

Microorganisms 2022, 10(8), 1493; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms10081493 - 25 Jul 2022

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Increasing amounts of organic waste are produced globally from a wide range of industrial activities, wastewater treatment plants, agricultural processing, and human food consumption [...] Full article

(This article belongs to the Special Issue Microorganisms and Organic Waste Valorisation)

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17 pages, 2950 KiB

Open AccessArticle

Dynamics of Microbial Communities in Phototrophic Polyhydroxyalkanoate Accumulating Cultures

by Juliana R. Almeida, Joana C. Fradinho, Gilda Carvalho, Adrian Oehmen and Maria A. M. Reis

Microorganisms 2022, 10(2), 351; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms10020351 - 03 Feb 2022

Cited by 6 | Viewed by 2551

Abstract

Phototrophic mixed cultures (PMC) are versatile systems which can be applied for waste streams, valorisation and production of added-value compounds, such as polyhydroxyalkanoates (PHA). This work evaluates the influence of different operational conditions on the bacterial communities reported in PMC systems with PHA [...] Read more.

Phototrophic mixed cultures (PMC) are versatile systems which can be applied for waste streams, valorisation and production of added-value compounds, such as polyhydroxyalkanoates (PHA). This work evaluates the influence of different operational conditions on the bacterial communities reported in PMC systems with PHA production capabilities. Eleven PMCs, fed either with acetate or fermented wastewater, and selected under either feast and famine (FF) or permanent feast (PF) regimes, were evaluated. Overall, results identified Chromatiaceae members as the main phototrophic PHA producers, along with Rhodopseudomonas, Rhodobacter and Rhizobium. The findings show that Chromatiaceae were favoured under operating conditions with high carbon concentrations, and particularly under the PF regime. In FF systems fed with fermented wastewater, the results indicate that increasing the organic loading rate enriches for Rhodopseudomonas, Rhizobium and Hyphomicrobiaceae, which together with Rhodobacter and Chromatiaceae, were likely responsible for PHA storage. In addition, high-sugar feedstock impairs PHA production under PF conditions (fermentative bacteria dominance), which does not occur under FF. This characterization of the communities responsible for PHA accumulation helps to define improved operational strategies for PHA production with PMC. Full article

(This article belongs to the Special Issue Microorganisms and Organic Waste Valorisation)

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19 pages, 3320 KiB

Open AccessArticle

Screening and Application of Ligninolytic Microbial Consortia to Enhance Aerobic Degradation of Solid Digestate

by Ulysse Brémond, Aude Bertrandias, Jérôme Hamelin, Kim Milferstedt, Valérie Bru-Adan, Jean-Philippe Steyer, Nicolas Bernet and Hélène Carrere

Microorganisms 2022, 10(2), 277; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms10020277 - 25 Jan 2022

Cited by 2 | Viewed by 3044

Abstract

Recirculation of solid digestate through digesters has been demonstrated to be a potential simple strategy to increase continuous stirred-tank reactor biogas plant efficiency. This study extended this earlier work and investigated solid digestate post-treatment using liquid isolated ligninolytic aerobic consortia in order to [...] Read more.

Recirculation of solid digestate through digesters has been demonstrated to be a potential simple strategy to increase continuous stirred-tank reactor biogas plant efficiency. This study extended this earlier work and investigated solid digestate post-treatment using liquid isolated ligninolytic aerobic consortia in order to increase methane recovery during the recirculation. Based on sampling in several natural environments, an enrichment and selection method was implemented using a Lab-scale Automated and Multiplexed (an)Aerobic Chemostat system to generate ligninolytic aerobic consortia. Then, obtained consortia were further cultivated under liquid form in bottles. Chitinophagia bacteria and Sordariomycetes fungi were the two dominant classes of microorganisms enriched through these steps. Finally, these consortia where mixed with the solid digestate before a short-term aerobic post-treatment. However, consortia addition did not increase the efficiency of aerobic post-treatment of solid digestate and lower methane yields were obtained in comparison to the untreated control. The main reason identified is the respiration of easily degradable fractions (e.g., sugars, proteins, amorphous cellulose) by the selected consortia. Thus, this paper highlights the difficulties of constraining microbial consortia to sole ligninolytic activities on complex feedstock, such as solid digestate, that does not only contain lignocellulosic structures. Full article

(This article belongs to the Special Issue Microorganisms and Organic Waste Valorisation)

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12 pages, 2190 KiB

Open AccessArticle

It Works! Organic-Waste-Assisted Trichoderma spp. Solid-State Fermentation on Agricultural Digestate

by Carlotta Alias, Daniela Bulgari and Emanuela Gobbi

Microorganisms 2022, 10(1), 164; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms10010164 - 13 Jan 2022

Cited by 12 | Viewed by 3308

Abstract

This study aimed at valorizing digestate through Trichoderma spp. solid-state fermentation (SSF) to produce a potentially ameliorated fertilizer combined with fungal biomass as a value-added bioproduct. Plant-growth-promoting Trichoderma atroviride Ta13, T. reesei RUT-C30, T. asperellum R, and T. harzianum T-22 were tested on [...] Read more.

This study aimed at valorizing digestate through Trichoderma spp. solid-state fermentation (SSF) to produce a potentially ameliorated fertilizer combined with fungal biomass as a value-added bioproduct. Plant-growth-promoting Trichoderma atroviride Ta13, T. reesei RUT-C30, T. asperellum R, and T. harzianum T-22 were tested on different SSF substrates: whole digestate (WD), digestate dried up with wood sawdust (SSF1), and digestate enriched with food waste and dried up with wood sawdust (SSF2). The fungal biomass was quantified by using a qPCR assay. The growth of the four Trichoderma spp. was only observed on the SSF2 substrate. The highest quantity of mycelium was produced by T. reesei RUT-30 (689.80 ± 80.53 mg/g substrate), followed by T. atroviride Ta13, and T. asperellum R (584.24 ± 13.36 and 444.79 ± 91.02 mg/g substrate). The germination of Lepidium sativum seeds was evaluated in order to assess the phytoxicity of the Trichoderma-enriched substrate. The treatments with 7.5% SSF2-R, 3.75% SSF2-T-22, and 1.8% SSF2-Ta13 equally enhanced the root elongation in comparison to the non-fermented SSF-2. This study demonstrated that digestate, mixed with agro-food waste, was able to support the cultivation of Trichoderma spp., paving the way to the valorization of fermented digestate as a proper biofertilizer. Full article

(This article belongs to the Special Issue Microorganisms and Organic Waste Valorisation)

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11 pages, 1160 KiB

Open AccessArticle

Insights into the Anaerobic Hydrolysis Process for Extracting Embedded EPS and Metals from Activated Sludge

by Barbara Tonanzi, Agata Gallipoli, Andrea Gianico, Maria Cristina Annesini and Camilla Maria Braguglia

Microorganisms 2021, 9(12), 2523; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms9122523 - 06 Dec 2021

Cited by 5 | Viewed by 2013

Abstract

The amount of sewage sludge generated from wastewater treatment plants globally is unavoidably increasing. In recent years, significant attention has been paid to the biorefinery concept based on the conversion of waste streams to high-value products, material, and energy by microorganisms. However, one [...] Read more.

The amount of sewage sludge generated from wastewater treatment plants globally is unavoidably increasing. In recent years, significant attention has been paid to the biorefinery concept based on the conversion of waste streams to high-value products, material, and energy by microorganisms. However, one of the most significant challenges in the field is the possibility of controlling the microorganisms’ pathways in the anaerobic environment. This study investigated two different anaerobic fermentation tests carried out with real waste activated sludge at high organic loading rate (10 g COD L⁻¹d⁻¹) and short hydraulic retention time (HRT) to comprehensively understand whether this configuration enhances extracellular polymeric substance (EPS) and metal solubilisation. The quantity of EPS recovered increased over time, while the chemical oxygen demand to EPS ratio remained in the range 1.31–1.45. Slightly acidic conditions and sludge floc disintegration promoted EPS matrix disruption and release, combined with the solubilisation of organically bound toxic metals, such as As, Be, Cu, Ni, V, and Zn, thereby increasing the overall metal removal efficiency due to the action of hydrolytic microorganisms. Bacteroidetes, Firmicutes, and Chloroflexi were the most abundant phyla observed, indicating that the short HRT imposed on the systems favoured the hydrolytic and acidogenic activity of these taxa. Full article

(This article belongs to the Special Issue Microorganisms and Organic Waste Valorisation)

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10 pages, 1563 KiB

Open AccessArticle

Food Waste-Assisted Metal Extraction from Printed Circuit Boards: The Aspergillus niger Route

by Carlotta Alias, Daniela Bulgari, Fabjola Bilo, Laura Borgese, Alessandra Gianoncelli, Giovanni Ribaudo, Emanuela Gobbi and Ivano Alessandri

Microorganisms 2021, 9(5), 895; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms9050895 - 22 Apr 2021

Cited by 7 | Viewed by 2544

Abstract

A low-energy paradigm was adopted for sustainable, affordable, and effective urban waste valorization. Here a new, eco-designed, solid-state fermentation process is presented to obtain some useful bio-products by recycling of different wastes. Urban food waste and scraps from trimmings were used as a [...] Read more.

A low-energy paradigm was adopted for sustainable, affordable, and effective urban waste valorization. Here a new, eco-designed, solid-state fermentation process is presented to obtain some useful bio-products by recycling of different wastes. Urban food waste and scraps from trimmings were used as a substrate for the production of citric acid (CA) by solid state fermentation of Aspergillus niger NRRL 334, with a yield of 20.50 mg of CA per gram of substrate. The acid solution was used to extract metals from waste printed circuit boards (WPCBs), one of the most common electronic waste. The leaching activity of the biological solution is comparable to a commercial CA one. Sn and Fe were the most leached metals (404.09 and 67.99 mg/L, respectively), followed by Ni and Zn (4.55 and 1.92 mg/L) without any pre-treatments as usually performed. Commercial CA extracted Fe more efficiently than the organic one (123.46 vs. 67.99 mg/L); vice versa, biological organic CA recovered Ni better than commercial CA (4.55 vs. 1.54 mg/L). This is the first approach that allows the extraction of metals from WPCBs through CA produced by A. niger directly grown on waste material without any sugar supplement. This “green” process could be an alternative for the recovery of valuable metals such as Fe, Pb, and Ni from electronic waste. Full article

(This article belongs to the Special Issue Microorganisms and Organic Waste Valorisation)

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20 pages, 2184 KiB

Open AccessArticle

Direct Conversion of Food Waste Extract into Caproate: Metagenomics Assessment of Chain Elongation Process

by Simona Crognale, Camilla M. Braguglia, Agata Gallipoli, Andrea Gianico, Simona Rossetti and Daniele Montecchio

Microorganisms 2021, 9(2), 327; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms9020327 - 05 Feb 2021

Cited by 39 | Viewed by 3206

Abstract

In a circular economy strategy, waste resources can be used for the biological production of high added-value substances, such as medium chain fatty acids (MCFAs), thus minimising waste and favouring a sustainable process. This study investigates single-stage fermentation processes for the production of [...] Read more.

In a circular economy strategy, waste resources can be used for the biological production of high added-value substances, such as medium chain fatty acids (MCFAs), thus minimising waste and favouring a sustainable process. This study investigates single-stage fermentation processes for the production of MCFAs in a semi-continuous reactor treating the extract of real food waste (FW), without the addition of external electron donors. Two sequential acidogenic fermentation tests were carried out at an organic loading rate (OLR) of 5 and 15 gCOD L⁻¹d⁻¹ with a hydraulic retention time of 4 days and pH controlled at 6 ± 0.2. The highest level of caproate (4.8 g L⁻¹) was observed at OLR of 15 gCOD L⁻¹d⁻¹ with a microbiome mainly composed by lactate-producing Actinomyces, Atopobium, and Olsenella species and caproate-producing Pseudoramibacter. Metagenomic analysis revealed the presence of key enzymes for the production of lactate, such as lactate dehydrogenase and pyruvate ferredoxin oxidoreductase, as well as several enzymes involved in the reverse β-oxidation pathway, thus suggesting the occurrence of a lactate-based chain elongation process. Full article

(This article belongs to the Special Issue Microorganisms and Organic Waste Valorisation)

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23 pages, 4417 KiB

Open AccessArticle

Three Novel Clostridia Isolates Produce n-Caproate and iso-Butyrate from Lactate: Comparative Genomics of Chain-Elongating Bacteria

by Bin Liu, Denny Popp, Nicolai Müller, Heike Sträuber, Hauke Harms and Sabine Kleinsteuber

Microorganisms 2020, 8(12), 1970; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms8121970 - 11 Dec 2020

Cited by 30 | Viewed by 3907

Abstract

The platform chemicals n-caproate and iso-butyrate can be produced by anaerobic fermentation from agro-industrial residues in a process known as microbial chain elongation. Few lactate-consuming chain-elongating species have been isolated and knowledge on their shared genetic features is still limited. Recently [...] Read more.

The platform chemicals n-caproate and iso-butyrate can be produced by anaerobic fermentation from agro-industrial residues in a process known as microbial chain elongation. Few lactate-consuming chain-elongating species have been isolated and knowledge on their shared genetic features is still limited. Recently we isolated three novel clostridial strains (BL-3, BL-4, and BL-6) that convert lactate to n-caproate and iso-butyrate. Here, we analyzed the genetic background of lactate-based chain elongation in these isolates and other chain-elongating species by comparative genomics. The three strains produced n-caproate, n-butyrate, iso-butyrate, and acetate from lactate, with the highest proportions of n-caproate (18%) for BL-6 and of iso-butyrate (23%) for BL-4 in batch cultivation at pH 5.5. They show high genomic heterogeneity and a relatively small core-genome size. The genomes contain highly conserved genes involved in lactate oxidation, reverse β-oxidation, hydrogen formation and either of two types of energy conservation systems (Rnf and Ech). Including genomes of another eleven experimentally validated chain-elongating strains, we found that the chain elongation-specific core-genome encodes the pathways for reverse β-oxidation, hydrogen formation and energy conservation, while displaying substantial genome heterogeneity. Metabolic features of these isolates are important for biotechnological applications in n-caproate and iso-butyrate production. Full article

(This article belongs to the Special Issue Microorganisms and Organic Waste Valorisation)

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