Sole Carbon Resource Research Articles

Integrated proteome and pangenome analysis revealed the variation of microalga Isochrysis galbana and associated bacterial community to 2,6-Di-tert-butyl-p-cresol (BHT) stress.

The phenolic antioxidant 2,6-Di-tert-butyl-p-cresol (BHT) has been detected in various environments and is considered a potential threat to aquatic organisms. Algal-bacterial interactions are crucial for maintaining ecosystem balance and elemental cycling, but their response to BHT remains to be investigated. This study analyzed the physiological and biochemical responses of the microalga Isochrysis galbana and the changes of associated bacterial communities under different concentrations of BHT stress. Results showed that the biomass of I. galbana exhibited a decreasing trend with increasing BHT concentrations up to 40mg/L. The reduction in chlorophyll, carotenoid, and soluble protein content of microalgal cells was also observed under BHT stress. The production of malondialdehyde and the activities of superoxide dismutase, peroxidase, and catalase were further determined. Scanning electron microscopy analysis revealed that BHT caused surface rupture of the algal cells and loss of intracellular nutrients. Proteomic analysis demonstrated the upregulation of photosynthesis and citric acid cycle pathways as a response to BHT stress. Additionally, BHT significantly increased the relative abundance of specific bacteria in the phycosphere, including Marivita, Halomonas, Marinobacter, and Alteromonas. Further experiments confirmed that these bacteria had the ability to utilize BHT as the sole carbon resource for growth, and genes related to the degradation of phenolic compounds were detected through pangenome analysis.

Engineering synthetic microbial consortium for cadaverine biosynthesis from glycerol.

1,5-pentanediamine (cadaverine) is a C5 platform chemical, also an important raw material for bio-polyamide PA5X. With increasing concerns about the depletion of fossil resources and global environmental protection, cadaverine bio-production has attracted more attentions. Here, a microbial consortium consisting of Corynebacterium glutamicum cgl-FDK and Escherichia coli BL-ABST-Spy was constructed to de novo synthesize cadaverine utilizing glycerol as the sole carbon resource. The glycerol utilization pathway was initially constructed in C. glutamicum cgl-FDK to produce lysine from glycerol. Then, the pyridoxal 5'-phosphate (PLP) biosynthesis pathway and SpyTag/SpyCatcher protein-ligation system for lysine decarboxylase (CadA) and cadaverine-lysine antiporter protein (CadB) were introduced into E. coli BL-ABST-Spy to synthesize cadaverine from lysine. Furthermore, the fermentation conditions of microbial consortium were optimized and the cadaverine production reached 9.3g/L with glycerol as the sole carbon source. This work provides a promising strategy for efficiently producing cadaverine from glycerol with an artificial microbial consortium.

Bioaugmentation of polycyclic aromatic hydrocarbon (PAH)-contaminated soil with the nitrate-reducing bacterium PheN7 under anaerobic condition

The remediation of polycyclic aromatic hydrocarbon (PAH)-contaminated soil under anaerobic condition is still a huge challenge. In this study, an anaerobic Bacillus firmus strain named PheN7 was firstly isolated from mixture of contaminated soil and sludge samples with phenanthrene as the sole carbon resource under nitrate reducing environment. The anaerobic strain was then inoculated combining with nitrate into the phenanthrene-spiked PAH-contaminated soil to investigate the remediation efficiency by anaerobic bioaugmentation (BA). Results showed that the synergy between PheN7 and indigenous degrading bacteria promoted the remediation efficiency of soil. The average removal efficiencies of phenanthrene in 56 days were 1.73 mg/kg soil·d in BA group, much higher than biostimulation group (sole nitrate addition) and natural degradation which achieved 1.48 mg/kg soil·d and 1.24 mg/kg soil·d of degradation rate, respectively. The outstanding adaptability of PheN7 made it become the dominant species in soil in the terminal period, but the invasion of PheN7 also resulted in the decline of diversity of the indigenous microbial community. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States 2 (PICRUSt 2) results showed that a series of functional genes encoding anaerobic phenanthrene degradation and nitrate reductase enzymes in soil were remarkably strengthened with the addition of PheN7. This study confirmed the contribution of PheN7 as the anaerobic inoculum in PAH-contaminated soil remediation, further evaluating the practical applicability of anaerobic bioaugmentation technology in on-site remediation of real PAH-contaminated sites.

Engineering and characterization of dehalogenase enzymes from Delftia acidovorans in bioremediation of perfluorinated compounds

Per- and Polyfluorinated alkyl substances (PFAS) are a broad class of synthetic compounds that have fluorine substituted for hydrogen in several or all locations and are globally categorized as PFCs (perfluorochemicals; commonly called fluorinated chemicals). These compounds have unique chemical and physical properties that enable their use in non-stick surfaces, fire-fighting efforts, and as slick coatings. However, recent concerns over the health effects of such compounds, specifically perfluorooctanoic acid and perfluorooctane sulfonic acid (PFOA, PFOS; PFOA/S), have led to increased attention and research by the global community into degradation methods. In this study, soil samples from PFAS-contamination sites were cultured and screened for microbes with PFOA/S degradation potential, which led to the identification of Delftia acidovorans. It was found that D. acidovorans isolated from PFAS-contaminated soils was capable of growth in minimal media with PFOA as a sole carbon resource, and an observable fluoride concentration increase was observed when cells were exposed to PFOA. This suggests potential activity of a dehalogenase enzyme that may be of use in PFOA or PFAS microbial remediation efforts. Several associated haloacid dehalogenases have been identified in the D. acidovorans genome and have been engineered for expression in Escherichia coli for rapid production and purification. These enzymes have shown potential for enzymatic defluorination, a significant step in biological degradation and removal of PFOA/S from the environment. We hypothesize that bioremediation of PFAS using naturally occurring microbial degradation pathways may represent a novel approach to remove PFAS contamination.

Bioaugmentation treatment of polycyclic aromatic hydrocarbon-polluted soil in a slurry bioreactor with a bacterial consortium and hydroxypropyl-β-cyclodextrin

ABSTRACT The aim of the study was to verify the effect of bioaugmentation by the bacterial consortium YS with hydroxypropyl-β-cyclodextrin (HPCD) in a soil slurry. The bacterial consortium YS was enriched from a petroleum-polluted soil using pyrene as sole carbon resource. After 3 weeks, the degradation rate of phenanthrene in CK increased from 22.58% to 55.23 and 78.21% in bioaugmentation (B) and HPCD + bioaugmentation (MB) respectively. The degradation rate of pyrene in CK increased from 17.33% to 51.10% and 60.32% in B and MB respectively in the slurry. The augmented YS persisted in the slurry as monitored by 16S rRNA gene high-throughput sequencing and outcompeted some indigenous bacteria. Enhanced polycyclic aromatic hydrocarbon (PAH) degradation was observed in the addition of HPCD due to the enhanced bioavailability of phenanthrene and pyrene. Additionally, the amount of PAH-degrading bacteria and enzymatic activity in bioaugmentation with HPCD were higher than that in the CK group. The results indicated that bioaugmentation with a bacterial consortium and HPCD is an environmentally friendly method for the bioremediation of PAH-polluted soil.

Temperature‐induced mutagenesis‐based adaptive evolution of Bacillus amyloliquefaciens for improving the production efficiency of menaquinone‐7 from starch

AbstractBACKGROUNDStarch can be used as a carbon source for producing menaquinone‐7 (MK‐7) by Bacillus sp., but the final titer and productivity are unsatisfactory because starch cannot be effectively hydrolyzed to fermentable sugars. This article focuses on developing thermo‐tolerable MK‐7 high‐producing strains by temperature‐induced mutagenesis‐based adaptive evolution.RESULTSHere, we isolated a thermo‐tolerable MK‐7 high‐producing strain B. amyloliquefaciens MK50‐36 after multi‐rounds of acclimation at high temperature. Strain MK50‐36 showed a large growth with soluble starch as carbon source at 50 °C. Compared with the parental strain B. amyloliquefaciens H.β.D.R.‐5 cultivated at 37 °C, MK‐7 yield of strain MK50‐36 increased about twofold at 50 °C when soluble starch was used as the sole carbon resource (17.5 ± 1.5 mg L–1 versus 37.1 ± 2.1 mg L–1). In addition, strain MK50‐36 showed an improvement in starch utilization rate as compared with strain H.β.D.R.‐5 because α‐amylase activity of strain MK50‐36 was the highest at 50 °C. Moreover, MK‐7 yield of strain MK50‐36 was further increased by feeding fresh broth to control the amount of fermentation liquid in fed‐batch fermentation because fermentation broth will be easy to volatilize and thus affect the production of MK‐7 at high temperature, which reached up to 52.7 ± 4.6 mg L–1.CONCLUSIONThese results indicated that soluble starch can act as an effective carbon source for producing MK‐7, and strain MK50‐36 has a superior capacity to produce MK‐7 from soluble starch. © 2020 Society of Chemical Industry

Two‐stage fermentation optimization for poly‐3‐hydroxybutyrate production from methanol by a new Methylobacterium isolate from oil fields

We aimed to explore a new Methylobacterium isolate to produce polyhydroxybutyrate (PHB) by using methanol as a sole carbon resource and improve PHB production. A new PHB-producing isolate (Methylobacterium sp. 1805) was obtained from oil fields by using methanol as a sole carbon source. The fermentation situation of PHB production was further optimized by using Box-Behnken response surface methodology (RSM). Before optimization, the cell biomass was 0·6gl-1 after 3-day culture and 0·3gl-1 PHB was produced after 5-day methanol-inducing stage. The RSM growth medium was optimized as 15gl-1 glycerol, 10gl-1 beef extract and 0·65gl-1 MgSO4 ·7H2 O. The RSM methanol-inducing medium was optimized as 0·65gl-1 MgSO4 (metal ions), 20mmoll-1 PBS pH 6·5 and final 2% methanol (v/v). The biomass and PHB production reached 1·0 and 0·55gl-1 after 3-day culture, respectively. The PHB yield increased by about 80% when compared with before optimization. The optimization of a two-stage fermentation process improved PHB production from methanol by using Methylobacterium sp. 1805. A new Methylobacterium isolate was isolated and produced high-level PHB by using methanol as a sole carbon resource. The bacteria will provide a potential tool for C1 resource in producing PHB.

Improving co-fermentation of glucose and xylose by adaptive evolution of engineering xylose-fermenting Saccharomyces cerevisiae and different fermentation strategies

Xylose utilization of engineered yeast is vulnerable to inhibitors generated during pretreatment of lignocellulose. In this study, adaptive evolution was applied to enhance the tolerance of xylose-fermenting strain. Compared to the parental strain, the ethanol yield was increased by 60% and 80% for the adapted strain (E7-403) when xylose was used as the sole carbon resource with 20% and 50% inhibitor cocktails, respectively. E7-403 removed furfural more effectively than parental strain (E7) in the fermentation with 100% inhibitor cocktails. In the fermentation with mixed sugar and high inhibitor concentration, glucose was depleted within 36 h for E7-403 while 6.1 g/L glucose was still left after 120 h for E7. Consequently, ethanol yield of E7-403 was 22.9% higher than that of E7. It was demonstrated that E7-403 strain exhibited an enhanced ability for regulating cellular reactive oxygen species, which alleviated the harmful effects of inhibitors. Meanwhile, E7-403 strain was further applied in co-culture and pre-fermentation process to improve xylose utilization.

Comparative Study of Carbon Materials Synthesized "Greenly" for 2-CP Removal.

Carbon nanotubes (CNTs), graphene (GA) and carbon nanospheres (CNSs) were prepared respectively using grass (Festucaarundinace) as the sole carbon resource by solvothermal method and characterized as adsorbent and photocatalyst for 2-chlorophenol (2-CP) removal in water. With H2O2/HNO3/H2SO4, the CNTs were firstly produced from grass (Festucaarundinace) at 300 °C by hydrolysis and oxidization, the CNTs were secondly opened to form the GA by oxidization at 400 °C, and the GA was lastly rolled-up to form the CNSs by oxidization at 500 °C. All adsorption equilibration of the CNTs, GA, and CNSs for 2-CP were achieved within 120 min, and 60.35%, 20.12%, and 76.22% of 2-CP (5 mg L−1, pH = 6.3) were adsorbed, respectively. Furthermore, the high removal rates of 2-CP were about 88.23%, 92.90%, and 79.64% by the CNTs, GA, and CNSs, after 120 min adsorption and 160 min irradiation. On the basis of these results, the CNSs were suitable for removal 2-CP as adsorbent, and the GA was suitable as photocatalyst. The photooxidation of 2-CP was mainly initiated by O2·− or ·OH which was generated from the combine with simulated sunlight and the CNTs or GA, respectively. However, the CNTs was not suitable for removal 2-CP owing to the increasing toxicity.

Promotion of Ni2+ removal by masking toxicity to sulfate-reducing bacteria: addition of citrate.

The sulfate-reducing bioprocess is a promising technology for the treatment of heavy metal-containing wastewater. This work was conducted to investigate the possibility of promoting heavy metal removal by the addition of citrate to mask Ni2+ toxicity to sulfate-reducing bacteria (SRB) in batch reactors. SRB growth was completely inhibited in Ni2+-containing medium (1 mM) when lactate served as the sole carbon resource, leading to no sulfate reduction and Ni2+ removal. However, after the addition of citrate, SRB grew well, and sulfate was quickly reduced to sulfide. Simultaneously, the Ni-citrate complex was biodegraded to Ni2+ and acetate. The NiS precipitate was then formed, and Ni2+ was completely removed from the solution. It was suggested that the addition of citrate greatly alleviates Ni2+ toxicity to SRB and improves the removal of Ni2+, which was confirmed by quantitative real-time PCR targeting dissimilatory sulfite reductase (dsrAB) genes. Analysis of the carbon metabolism indicated that lactate instead of acetate served as the electron donor for sulfate reduction. This study offers a potential approach to increase the removal of heavy metals from wastewater in the single stage SRB-based bioprocess.

Simultaneous denitrifying phosphorus accumulation in a sequencing batch reactor

In order to achieve simultaneous nitrogen and phosphorus removal in the biological treatment process, denitrifying phosphorus accumulation (DNPA) and its affecting factors were studied in a sequencing batch reactor (SBR) with synthetic wastewater. The results showed that when acetate was used as the sole carbon resource in the influent, the sludge acclimatized under anaerobic/aerobic operation had good phosphorus removal ability. Denitrifying phosphorus accumulation was observed soon when fed with nitrate instead of aeration following the anaerobic stage, which is a vital premise to DNPA. If DNPA sludge is fed with nitrate prior to the anaerobic stage, the DNPA would weaken or even disappear. At the high concentration of nitrate fed in the anoxic stage, the longer anoxic time needed, the better the DNPA was. Induced DNPA did not disappear even though an aerobic stage followed the anoxic stage, but the shorter the aerobic stage lasted, the higher the proportions of phosphorus removal via DNPA to total removal.

Screening and characterization of yeasts for xylitol production

To discover novel naturally occurring xylitol producing yeast species with potential for industrial applications. Exactly 274 strains were cultivated on both solid and liquid screening medium with xylose as the sole carbon resource. Five strains were selected on the basis of significant growth and high degree of xylose assimilation. Their phylogenetic position was confirmed by the PCR-RFLP and sequence analysis of the D1/D2 domain of the 5' end of the large subunit rDNA gene (5'-LSU rDNA). Enzymatic analysis was conducted to compare xylose metabolism in each strain. Candida guilliermondii Xu280 and Candida maltosa Xu316 were found to have high xylose consumption rates and xylitol yields in the batch fermentation under micro-aerobic condition. The effect of the different media with high initial xylose concentration on biosynthesis of xylitol by both strains was investigated. We have identified Candida spp. strains, which exhibit high levels of xylitol production from xylose suggesting that these may have potential for industrial applications. Microbial species are of importance for xylitol production. Xylitol production involves complicated metabolic regulation including xylose transport, production of key enzymes and cofactor regeneration. Thus, screening of naturally occurring xylose-utilizing micro-organisms is a viable and effective mean to obtain xylitol producing organisms with industrial application. Moreover, the research on selected strains will contribute to a better understanding of regulatory properties of xylose metabolism in different yeasts.

Purification and characterization of chitin deacetylase from Scopulariopsis brevicaulis

An extracellular chitin deacetylase from Scopulariopsis brevicaulis has been produced using chitin as sole carbon resource of culture medium. The enzyme activity was 10–11 units ml −1 culture supernatant after the strain was shaken at 200 rpm and 29 °C for 96 h. The enzyme was purified 74-fold at 38% yield through ammonium sulfate precipitation, and Sephadex G-25, and G-100 column chromatography. The apparent molecular weight of 55 kDa, as determined by SDS-PAGE and gel filtration chromatography, suggested that the enzyme exists as a single component. The enzyme was active on chitooligosaccharides with at least two N-acetyl-glucosamine residues, but the activity increased with the number of N-acetyl-glucosamine residues. When hexa- N-acetylchitohexaose was used as substrate, the optimum pH for enzyme activity was determined to be 7.5, and the optimum temperature was 55 °C. Under these conditions, the activity of enzyme was studied on water-soluble chitosan, chitin from Aspergillus niger and shrimp crystalline chitin. The structures of products were characterized by FT-IR, XRD and potentiometric titration. The results indicated that degree of substrate crystallinity had an important effect on enzyme activity. The enzyme had high deacetylating activity on amorphous chitin from A. niger mycelium (37% deacylation) and water-soluble chitosan (33%) but low. activity on shrimp crystalline chitin (3.7%).