Biosurfactant-enhanced hydrogen production from organic fraction of municipal solid waste using co-culture of E. coli and Enterobacter aerogenes

Application of exogenous electron mediator in fermentation to enhance the production of value-added products

Electron transfer is essential for the production efficiency of value-added products in anaerobic fermentation, such as butanol and ethanol as biofuels, and short-chain fatty acids (SCFAs) including butyric acid and acetic acid as platform chemicals. Electron mediators (EMs), also known as electron shuttles, can facilitate electron transfer to counter irreversible or slow redox reactions that limit fermentation. The addition of EMs has been shown to be an effective strategy to promote fermentation by various bacteria, particularly Clostridium species, for these valuable product syntheses. This paper reviews recent advancements in the application of exogenous electron mediators (EEMs) across various scenarios. Common EEM types, their characteristics, and mechanisms are summarized, and different application scenarios are discussed to elucidate the effect of EEMs. Key technical challenges and future directions for EEM application are also explored.

Latest Trends in Lipase-Catalyzed Synthesis of Ester Carbohydrate Surfactants: From Key Parameters to Opportunities and Future Development

Carbohydrate-based surfactants are amphiphilic compounds containing hydrophilic moieties linked to hydrophobic aglycones. More specifically, carbohydrate esters are biosourced and biocompatible surfactants derived from inexpensive renewable raw materials (sugars and fatty acids). Their unique properties allow them to be used in various areas, such as the cosmetic, food, and medicine industries. These multi-applications have created a worldwide market for biobased surfactants and consequently expectations for their production. Biobased surfactants can be obtained from various processes, such as chemical synthesis or microorganism culture and surfactant purification. In accordance with the need for more sustainable and greener processes, the synthesis of these molecules by enzymatic pathways is an opportunity. This work presents a state-of-the-art lipase action mode, with a focus on the active sites of these proteins, and then on four essential parameters for optimizing the reaction: type of lipase, reaction medium, temperature, and ratio of substrates. Finally, this review discusses the latest trends and recent developments, showing the unlimited potential for optimization of such enzymatic syntheses.

Effects of rhamnolipid pretreatment on DOM dissolution characteristics and anaerobic fermentation acid production of waste activated sludge

In this paper, the change characteristics of DOM (dissolved organic matter) and acid production characteristics of anaerobic fermentation in waste activated sludge(WAS) pretreated with rhamnolipid (RL) were studied. The results showed that RL at the dose of 80 mg/gTS could significantly promote the disintegrating of EPS (extracellular polymers) and cell wall in WAS, and a large number of proteins and carbohydrates were dissolved. Three dimensional fluorescence parallel factor analysis showed that the addition of RL enhanced the dissolution and biodegradability of humus-like substances. LC-OCD (Liquid chromatography - organic carbon detection) analysis showed that RL promotes the dissolution of biodegradable components such as Biopolymer, Building Blocks and LMW Neutrals, and ensures the increase of VFA (volatile fatty acids) production in the process of anaerobic fermentation. Under the RL dose of 80 mg/gTS, the maximum VFA production of WAS was obtained at 108 h of anaerobic fermentation, which was 2699.39 mg/L. Acetic acid and propionic acid were the main components in the WAS fermentation broth pretreated by RL. The concentration of butyric acid increased with the increase of RL dose. The RL dose can significantly affect the composition of VFA in WAS fermentation broth.

A critical review on the environmental application of lipopeptide micelles

The importance of lipopeptide micelles in environmental applications has been highlighted. These vessels exhibit various sizes, shapes, and surface properties under different environmental conditions. An in-depth understanding of the tunable assembling behavior of biosurfactant micelles is of great importance for their applications. However, a systematic review of such behaviors with assorted micro/nano micellar structures under given environmental conditions, particularly under low temperature and high salinity, remains untapped. Such impacts on their environmental applications have yet to be summarized. This review tried to fill the knowledge gaps by providing a comprehensive summary of the recent knowledge advancement in genetically regulated lipopeptides production, micelles associated decontamination mechanisms in low temperature and high salinity environments, and up-to-date environmental applications. This work is expected to deliver valuable insights to guide lipopeptide design and discovery. The mechanisms concluded in this study could inspire the forthcoming research efforts in the advanced environmental application of lipopeptide micelles.

Effects of tolC on tolerance to bile salts and biofilm formation in Cronobacter malonaticus

Bile salts is one of essential components of bile secreted into the intestine to confer antibacterial protection. Cronobacter species are associated with necrotizing enterocolitis in newborns and show a strong tolerance to bile salts. However, little attempt has been made to focus on the molecular basis of the tolerance to bile salts. In this study, we investigated the roles of tolC on growth, cell morphology, motility, and biofilm formation ability in Cronobacter malonaticus under bile salt stress. The results indicated that the absence of tolC significantly affected the colony morphology and outer membrane structure in a normal situation, compared with those of the wild type strain. The deletion of tolC caused the decline in resistance to bile salt stress, inhibition of growth, and observable reduction in relative growth rate and motility. Moreover, the bacterial stress response promoted the biofilm formation ability of the mutant strain. The expression of the AcrAB-TolC system (acrA, acrB, and tolC) was effectively upregulated compared with the control sample when exposed to different bile salt concentrations. The findings provide valuable information for deeply understanding molecular mechanisms about the roles of tolC under bile salt stress and the prevention and control of C. malonaticus.

Microbial Production of Hydrogen by Mixed Culture Technologies: A Review

With its high energy content and clean combustion, hydrogen is recognized as a renewable clean energy source with enormous potential. Biological hydrogen production is a promising alternative with significant advantages over conventional petroleum-derived chemical processes. Sustainable hydrogen production from renewable resources such as cassava, wastewater, and other agricultural waste is economically feasible for industrial applications. So far, the major bottlenecks in large-scale biological hydrogen production are the low production rate and yield. This review discusses the various factors that affect the metabolic pathways of dark hydrogen production, and highlights the state-of-the-art development of mixed culture technology. The aim of this review is to provide suggestions for the future directions of mixed culture technology, as well as by-product valorization in dark fermentation.

Marine Biosurfactants: Biosynthesis, Structural Diversity and Biotechnological Applications

Biosurfactants are amphiphilic secondary metabolites produced by microorganisms. Marine bacteria have recently emerged as a rich source for these natural products which exhibit surface-active properties, making them useful for diverse applications such as detergents, wetting and foaming agents, solubilisers, emulsifiers and dispersants. Although precise structural data are often lacking, the already available information deduced from biochemical analyses and genome sequences of marine microbes indicates a high structural diversity including a broad spectrum of fatty acid derivatives, lipoamino acids, lipopeptides and glycolipids. This review aims to summarise biosyntheses and structures with an emphasis on low molecular weight biosurfactants produced by marine microorganisms and describes various biotechnological applications with special emphasis on their role in the bioremediation of oil-contaminated environments. Furthermore, novel exploitation strategies are suggested in an attempt to extend the existing biosurfactant portfolio.

Effects of adding EDTA and Fe2+ on the performance of reactor and microbial community structure in two simulated phases of anaerobic digestion

The uptake of trace elements can be impeded by precipitation in the presence of carbonates and sulfates. The objective of this study was to investigate whether ethylenediaminetetraacetic acid (EDTA) enhances the performance of anaerobic digestion by forming dissolved complexes with Fe²⁺. Batch experiments were performed in this study and acidogenic and methanogenic phases were artificially simulated. EDTA was added to both of phases to examine its effects on Fe bioavailability, metabolic parameters and microbial community structure. The results showed that EDTA significantly accelerated the digestion process in both phases because its addition changed the Fe sorption law and increased Fe-bioavailability. The microbial community structure changed following by the change of Fe-fractions which was determined by EDTA. This study demonstrated that EDTA as ligand could increase the Fe-bioavailability and then reduced or replaced the addition of Fe.

Effect of phenolic compounds on hydrogen production from municipal solid waste

The present study evaluates the effect of phenolic inhibitors viz. m-cresol, pentachlorophenol, bisphenol-A, and catechol on hydrogen production from anaerobic digestion of organic fraction of the municipal solid waste. Various concentration range of phenolic compounds (0.5, 2.5, 5.0, 10 and 25 mg/L) was applied. The results revealed that the inhibition coefficient of pentachlorophenol was highest among all the inhibitors resulting in lowest hydrogen production and yield. In control, the cumulative hydrogen production was 227.9 ± 10.5 mL which declined to a minimum of 93.4 ± 10.1 mL, 36.4 ± 10.1 mL, 58.9 ± 10.4 mL and 85.8 ± 10.3 mL for experimental batches supplemented with m-cresol, pentachlorophenol, bisphenol-A and catechol respectively. The corresponding decline in the hydrogen yield was 28.0%, 43.8%, 37.1% and 31.8% respectively. Further analysis revealed that inhibitors were completely removed up to a concentration not exceeding 0.25 mg/L. However, at higher concentrations, inhibitors removal efficiency was declined. COD removal efficiency was also negatively affected by inhibitors.

Pretreatment of grass waste using combined ionizing radiation-acid treatment for enhancing fermentative hydrogen production

In this study, the combined ionizing radiation-acid pretreatment process was firstly applied to enhance hydrogen fermentation of grass waste. Results showed that the combined pretreatment synergistically enhanced hydrogen fermentation of grass waste. The SCOD and soluble polysaccharide contents of grass waste increased by 1.6 and 2.91 times after the combined pretreatment, respectively. SEM observation and crystallinity test showed the combined pretreatment effectively disrupted the grass structure. Owing to the more favorable substrate conditions, the hydrogen yield achieved 68 mL/g-dry grass_added after the combined pretreatment, which was 161.5%, 112.5% and 28.3% higher than those from raw, ionizing radiation pretreated and acid pretreated grass waste, respectively. The VS removal also increased from 13.9% to 25.6% by the combined pretreatment. Microbial community analysis showed that the abundance of dominant hydrogen producing genus Clostridium sensu stricto 1 increased from 37.9% to 69.4% after the combined pretreatment, which contributed to more efficient hydrogen fermentation.

The Glutaredoxin Gene, grxB, Affects Acid Tolerance, Surface Hydrophobicity, Auto-Aggregation, and Biofilm Formation in Cronobacter sakazakii

Cronobacter species are foodborne pathogens that can cause neonatal meningitis, necrotizing enterocolitis, and sepsis; they have unusual abilities to survive in environmental stresses such as acid stress. However, the factors involved in acid stress responses and biofilm formation in Cronobacter species are poorly understood. In this study, we investigated the role of grxB on cellular morphology, acid tolerance, surface hydrophobicity, auto-aggregation (AAg), motility, and biofilm formation in Cronobacter sakazakii. The deletion of grxB decreased resistance to acid stresses, and notably led to weaker surface hydrophobicity, AAg, and biofilm formation under normal and acid stress conditions, compared with those of the wild type strain; however, motility was unaffected. Therefore, grxB appears to contribute to the survival of C. sakazakii in acid stresses and biofilm formation. This is the first report to provide valuable evidence for the role of grxB in acid stress responses and biofilm formation in C. sakazakii.