Search Results (8)

Enzymatic modification of Kraft lignin under alkaline conditions was investigated using bilirubin oxidase (BOD) in borate buffer (pH 10). Control solubilization without enzyme addition revealed a notable increase in molar mass (up to 1.7-fold) and potential borate complexation with lignin hydroxyl groups, as evidenced by thermogravimetric and ¹¹B NMR analyses. BOD treatments induced substantial polymerization, with molar mass increases of up to 4-fold for insoluble fractions after 24 h, while soluble fractions exhibited progressive increases over 5 days. Quantitative ³¹P NMR showed reductions in aliphatic and phenolic hydroxyl groups by 20%, suggesting oxidative coupling reactions, particularly through 4-O-5′ and 5-5′ linkages. Solid-state ¹³C NMR confirmed structural changes associated with polymerization. Dynamic light scattering (DLS) indicated the presence of colloidal aggregates, potentially explaining challenges in HSQC NMR signal acquisition. These findings highlight the efficacy of bilirubin oxidase in catalyzing lignin polymerization and underscore the structural impact of borate–lignin interactions in alkaline media, paving the way for advanced lignin valorization strategies. Full article

Rebuilding using outdated methods and tearing down the buildings would have a negative impact on the environment without lowering carbon dioxide emissions or increasing sustainability. This study presents a novel approach to repair that considers environmental and sustainable factors. In contrast to conventional repair methods, the use of Bacillus subtilis as an external biological repair technique could offer a novel and sustainable solution, especially when used on alkali-activated slag (AAS) concrete. By breaking down urea into carbonate and ammonium, alkaliphile bacteria can precipitate calcium carbonate. In an environment rich in calcium, the bacteria’s opposing cell wall (${\mathrm{C}\mathrm{O}}_3^{2-}$) draws in positive calcium anions, which result in the formation of calcite crystals. The pores and crevices in the concrete are filled with these crystals. Incorporating bacteria into the fresh mixing of AAS ingredients is contrasted with using Bacillus subtilis culture in the water curing medium for pure AAS specimens. The effectiveness of both approaches was evaluated. Direct administration of Bacillus subtilis during mixing has a superior outcome regarding mechanical qualities rather than biological therapy, although their effective healing capability in closure of the crack width is similar. The enhancement in compressive and flexural strengths reached 51% and 128% over the control specimens. On the other hand, the healing rate reached nearly 100% for crack widths ranging from 400 to 950 µm. Furthermore, additional studies in this field led to some inferred correlations between the mechanical and durability aspects following healing. Full article

Although biogas is a renewable energy source alternative to natural gas, it contains approximately 40 vol% CO₂ and, hence, a low calorific value. The sequestration of CO₂ from biogas is, therefore, essential before its widespread use. As CO₂ can be easily solubilized as carbonate and bicarbonate in alkaline water, in this study, we isolated and characterized alkaliphilic wild microalgae that grow under high-level CO₂ conditions and evaluated their application potential in CO₂-removal from biogas. For this purpose, freshwater samples were enriched with 10 vol% CO₂ and an alkaline culture medium (pH 9.0), wherein almost free CO₂ was converted to carbonate and bicarbonate to yield alkaliphilic and high-level CO₂-tolerant microalgae. Ten microalgal strains of Micractinium, Chlorella, Scenedesmus/Tetradesmus, or Desmodesmus spp. were isolated, some of which demonstrated good growth even under conditions of >pH 10 and >30 vol% CO₂. All algal strains grew well through fixing biogas-derived CO₂ in a vial-scale biogas upgrading experiment, which reduced the CO₂ level in biogas to an undetectable level. These strains yielded antioxidant carotenoids, including lutein, astaxanthin, zeaxanthin, and β-carotene, particularly rich in lutein (up to 7.3 mg/g dry cells). In addition, these strains contained essential amino acids, accounting for 42.9 mol% of the total amino acids on average, and they were rich in unsaturated fatty acids (comprising 62.2 wt% of total fatty acids). The present study identified strains that can contribute to biogas upgrading technology, and the present findings suggest that their biomass can serve as useful raw material across the food, nutraceutical, and feed industries. Full article

Microbial treatment of free-cyanide-polluted wastewater is a cost-effective, efficient, and eco-friendly method. Free-cyanide-degrading microbial cultures were isolated from different sources using batch-enrichment culture techniques, with acetate as the carbon source. Five microbial cultures were able to tolerate and grow at 1500 mg/L free cyanide, which was used as the only nitrogen source under strongly alkaline conditions (pH = 11). Among them, one bacterial strain (B11) was selected for further study because of its high free-cyanide-biodegradation efficiency. Bacterial strain B11 was molecularly identified as Bacillus licheniformis CDBB B11. Free cyanide inhibited the growth rate of B. licheniformis CDBB B11 at initial cyanide concentrations >75 mg/L. Despite this, the bacterial strain demonstrated 100% cyanide-biodegradation efficiency at initial cyanide concentrations ranging from 25 to 75 mg/L, which decreased to 32% as the initial cyanide concentration increased from 75 to 1500 mg/L. Free-cyanide biodegradation corresponds to bacterial growth and ammonia accumulation in the culture medium. The alkaliphilic B. licheniformis CDBB B11 strain is a robust candidate for the detoxification of free-cyanide-laden wastewater because it tolerates and efficiently degrades free cyanide at concentrations of up to 1500 mg/L. Full article

Endo-1,4-β-xylanase catalyzes the random hydrolysis of β-1,4-D-xylosidic bonds in xylan, resulting in the formation of oligomers of xylose. This study aims to demonstrate the promise of endoxylanases from alkaliphilic Bacillus halodurans for the production of xylooligosaccharides (XOS) from oil palm empty fruit bunch (EFB) at high pH. Two enzyme preparations were employed: recombinant endoxylanase Xyn45 (GH10 xylanase) and nonrecombinant endoxylanases, a mixture of two extracellular endo-1,4-β-xylanases Xyn45 and Xyn23 (GH11 xylanase) produced by B. halodurans. EFB was first treated with an alkaline solution. Then, the dissolved xylan-containing fraction was retained, and a prepared enzyme was added to react at pH 8 to convert xylan into XOS. Compared with the use of only Xyn45, the combined use of Xyn45 and Xyn23 resulted in a higher yield of XOS, suggesting the synergistic effect of the two endoxylanases. The yield of XOS obtained from EFB was as high as 46.77% ± 1.64% (w/w), with the xylobiose-to-xylotriose ratio being 6:5. However, when the enzyme activity dose was low, the product contained more xylotriose than xylobiose. Four probiotic lactobacilli and bifidobacteria grew well on a medium containing XOS from EFB. The presence of XOS increased cell mass and reduced pH, suggesting that XOS promoted the growth of probiotics. Full article

Lake Chitu is a highly productive soda lake found in the East African Rift Valley, where Arthrospira fusiformis (Spirulina platensis) is the main primary producer. High biomass accumulation requires an adequate supply of nitrogen. However, Lake Chitu is a closed system without any external nutrient input. A recent study has also demonstrated the presence of a diverse group of denitrifying bacteria, indicating a possible loss of nitrate released from the oxidation of organic matter. The aim of this study was to isolate culturable nitrogen-fixing alkaliphiles and evaluate their potential contribution in the nitrogen economy of the soda lake. A total of 118 alkaliphiles belonging to nine different operational taxonomic units (OTUs) were isolated using a nitrogen-free medium. Nineteen isolates were tested for the presence of the nifH gene, and 11 were positive. The ability to fix nitrogen was tested by co-culturing with a non-nitrogen-fixing alkaliphile, Alkalibacterium sp. 3.5*R1. When inoculated alone, Alkalibacterium sp. 3.5*R1 failed to grow on a nitrogen-free medium, but grew very well when co-cultured with the nitrogen-fixing alkaliphile NF10m6 isolated in this study, indicating the availability of nitrogen. These results show that nitrogen fixation by alkaliphiles may have an important contribution as a source of nitrogen in soda lakes. Full article

The novel extreme obligate alkaliphilic Bacillus marmarensis DSM 21297 is known to produce polyhydroxybutyrate (PHB). However, the detailed mechanism of PHB synthesis in B. marmarensis is still unknown. Here, we investigated which metabolic pathways and metabolic enzymes are responsible for PHB synthesis in order to understand the regulatory pathway and optimize PHB synthesis in B. marmarensis. In accordance with the fact that beta-galactosidase, 3-hydroxyacyl-CoA dehydrogenase, and Enoyl-CoA hydratase together with acyl-CoA dehydrogenase and lipase were annotated in B. marmarensis according to the RAST server, we used glucose, lactose, and olive oil to understand the preferred metabolic pathway for the PHB synthesis. It was found that B. marmarensis produces PHB from glucose, lactose, and olive oil. However, the highest PHB titer and the highest amount of PHB synthesized per dry cell mass (Y_P/X) were achieved in the presence of lactose, as compared to glucose and olive oil. Additionally, in the absence of peptone, the amount of PHB synthesized is reduced for each carbon source. Interestingly, none of the carbon sources studied yielded an efficient PHB synthesis, and supplementation of the medium with potassium ions did not enhance PHB synthesis. According to these experimental results and the presence of annotated metabolic enzymes based on the RAST server, PHB accumulation in the cells of B. marmarensis could be improved by the level of the expression of 3-hydroxybutyryl-CoA dehydrogenase (1.1.1.157), which increases the production of NADPH. Additionally, the accumulation of 3-hydroxyacyl-CoA could enhance the production of PHB in B. marmarensis in the presence of fatty acids. To our knowledge, this is the first report investigating the regulatory system involved in the control of PHB metabolism of B. marmarensis. Full article

Bacterial respiration of nitrate is a natural process of nitrate reduction, which has been industrialized to treat anthropic nitrate pollution. This process, also known as “microbial denitrification”, is widely documented from the fundamental and engineering points of view for the enhancement of the removal of nitrate in wastewater. For this purpose, experiments are generally conducted with heterotrophic microbial metabolism, neutral pH and moderate nitrate concentrations (<50 mM). The present review focuses on a different approach as it aims to understand the effects of hydrogenotrophy, alkaline pH and high nitrate concentration on microbial denitrification. Hydrogen has a high energy content but its low solubility, 0.74 mM (1 atm, 30 °C), in aqueous medium limits its bioavailability, putting it at a kinetic disadvantage compared to more soluble organic compounds. For most bacteria, the optimal pH varies between 7.5 and 9.5. Outside this range, denitrification is slowed down and nitrite (NO₂⁻) accumulates. Some alkaliphilic bacteria are able to express denitrifying activity at pH levels close to 12 thanks to specific adaptation and resistance mechanisms detailed in this manuscript, and some bacterial populations support nitrate concentrations in the range of several hundred mM to 1 M. A high concentration of nitrate generally leads to an accumulation of nitrite. Nitrite accumulation can inhibit bacterial activity and may be a cause of cell death. Full article