Degradation of Phthalate Esters by Fusarium sp. DMT-5-3 and Trichosporon sp. DMI-5-1 Isolated from Mangrove Sediments

The importance of conditionally rare taxa for the assembly and interaction of fungal communities in mangrove sediments

The fungal communities provide the nutrients and drive the cycles of elements in nature, and the rare fungal taxa are proved to be crucial for these communities in many environments. However, the ecological functions of rare taxa for the fungal communities in mangrove ecosystems are poorly assessed until now. This work aims to reveal the importance of rare taxa for the assembly of fungal communities in mangrove sediments by using the amplicon sequencing analysis of different spatiotemporal samples collected from Sanya mangroves, China. The results showed that Ascomycota and Basidiomycota were the dominant phyla in the conditionally rare taxa (CRT). The fungal communities possessed outstanding stability against the spatiotemporal variation and most collected environmental factors. The CRT possessed narrower niches and were more affected by the environmental variables than the abundant taxa. The current work demonstrated that the CRT had significantly higher relative abundances, degrees (the number of adjacent edges), clustering coefficients, and closeness centralities in the top 8 modules of the co-occurrence network (p < 0.05), indicating the important role of the CRT for the interaction of fungal communities in mangrove sediments. These findings indicate the importance of the CRT for the fungal community structures in mangrove sediments, and would deepen our understanding of dynamic functions of mangrove fungi, thereby facilitating the management, utilization, and protection of mangrove ecosystems. KEY POINTS: • Fungal communities in mangrove sediments are stable against environment variations. • The conditionally rare taxa (CRT) possessed narrower niches than the abundant fungal taxa. • The CRT are central for the co-occurrence network and interaction of fungal communities.

Enhanced esterase activity during the degradation of dibutyl phthalate by Fusarium species in liquid fermentation

Dibutyl phthalate (DBP) is one of the most abundantly produced and used plasticizers and is incorporated into plastic to make it more flexible and malleable. DBP has been found to be an environmental contaminant and reported as an endocrine disruptor. Therefore, it is crucial to develop ecofriendly alternatives to eliminate phthalate pollution. In the present research, the growth of F. culmorum and F. oxysporum in the presence of DBP was studied in liquid fermentation. The esterase activity, specific growth rate, and growth and enzymatic yield parameters were determined in DBP-supplemented media (1,500 or 2,000 mg/L) and in control medium (lacking DBP). These results show that in general, for both Fusarium species, the highest esterase activities, specific growth rates, and yield parameters were observed in media supplemented with DBP. It was observed that 1,500 and 2,000 mg of DBP/L did not inhibit F. culmorum or F. oxysporum growth and that DBP induced esterase production in both fungi. These organisms have much to offer in the mitigation of environmental pollution caused by the endocrine disruptor DBP. This study reports, for the first time, esterase production during the degradation of high concentrations (i.e., 1,500 and 2,000 mg/L) of DBP by F. culmorum F. oxysporum.

Microbial capability for the degradation of chemical additives present in petroleum-based plastic products: A review on current status and perspectives

Plastic additives are present as pollutants in the environment because they are released from plastics and have been reported to be toxic to mammals. Due to this toxicity, it is crucial to develop ecofriendly tools to decontaminate the environment. Microorganisms are a promising alternative for efficient and effective plastic additive removal. This review describes the current knowledge and significant advances in the microbial degradation of plastic additives (i.e. plasticizers, flame retardants, stabilizers and antioxidants) and biotechnological research strategies that are being used to accelerate the biodegradation process of these additives. It is expected that further research supported by advances in genomics, proteomics, gene expression, enzyme immobilization, protein design, and nanotechnology can substantially increase our knowledge to enhance the enzymatic degradation efficiency, which will accelerate plastic additive degradation and establish successful and cost-effective bioremediation processes. Investigations should also address the identification of the enzymes involved in the degradation process and their catalytic mechanisms to achieve full metabolization of organopollutants (i.e. plastic additives) while avoiding harmful plastic additive biodegradation products. Microorganisms and their enzymes undoubtedly represent a potential resource for developing promising environmental biotechnologies, as they have the best systems for pollutant degradation, and their actions are essential for decontaminating the environment.

Induction of esterase activity during the degradation of high concentrations of the contaminant di(2-ethylhexyl) phthalate by Fusarium culmorum under liquid fermentation conditions

In this study, the induction of esterase activity during the degradation of a high concentration of di(2-ethylhexyl) phthalate (DEHP) (1500 mg l^-1) by Fusarium culmorum was investigated using Ca(NO₃)₂ as nitrogen source under liquid fermentation conditions. Assessments of esterase activities through biochemical tests and zymographic assays, as well as fungal growth were studied. A high concentration of DEHP increased esterase activity in F. culmorum, which produces five esterase isoforms (26.4, 31.7, 43, 73.6 and 125 kDa), which were different in abundance and molecular weight to those produced constitutively in glucose-containing medium (control medium). F. culmorum showed higher µ and Y _X/S values in DEHP-containing medium than those observed in the control medium. F. culmorum has great potential for use in the restoration of sites contaminated with high concentrations of DEHP and even of other phthalates with less complex structures.

Biotransformation of Phthalate Plasticizers and Bisphenol A by Marine-Derived, Freshwater, and Terrestrial Fungi

Phthalate esters (PEs, Phthalates) are environmentally ubiquitous as a result of their extensive use as plasticizers and additives in diverse consumer products. Considerable concern relates to their reported xenoestrogenicity and consequently, microbial-based attenuation of environmental PE concentrations is of interest to combat harmful downstream effects. Fungal PE catabolism has received less attention than that by bacteria, and particularly fungi dwelling within aquatic environments remain largely overlooked in this respect. We have compared the biocatalytic and biosorptive removal rates of di-n-butyl phthalate (DBP) and diethyl phthalate (DEP), chosen to represent two environmentally prominent PEs of differing structure and hydrophobicity, by marine-, freshwater-, and terrestrial-derived fungal strains. Bisphenol A, both an extensively used plastic additive and prominent environmental xenoestrogen, was included as a reference compound due to its well-documented fungal degradation. Partial pathways of DBP metabolization by the ecophysiologically diverse asco- and basidiomycete strains tested were proposed with the help of UPLC-QTOF-MS analysis. Species specific biochemical reaction steps contributing to DBP metabolism were also observed. The involved reactions include initial cytochrome P450-dependent monohydroxylations of DBP with subsequent further oxidation of related metabolites, de-esterification via either hydrolytic cleavage or cytochrome P450-dependent oxidative O-dealkylation, transesterification, and demethylation steps - finally yielding phthalic acid as a central intermediate in all pathways. Due to the involvement of ecophysiologically and phylogenetically diverse filamentous and yeast-like fungi native to marine, freshwater, and terrestrial habitats the results of this study outline an environmentally ubiquitous pathway for the biocatalytic breakdown of plastic additives. Beyond previous research into fungal PE metabolism which emphasizes hydrolytic de-esterification as the primary catabolic step, a prominent role of cytochrome P450 monooxygenase-catalyzed reactions is established.

Biodegradation patterns of the endocrine disrupting pollutant di(2-ethyl hexyl) phthalate by Fusarium culmorum

Di(2-ethylhexyl) phthalate (DEHP) is a widely used plasticizer, which is considered an endocrine disrupting pollutant. Growth kinetics and esterases activity by biochemical tests and polyacrylamide gel electrophoresis were characterized for Fusarium culmorum grown in DEHP-supplemented (1000 mg/L) medium as the only carbon source and in control medium with glucose. Intermediate compounds of biodegraded DEHP were identified by GC-MS. F. culmorum degraded 92% of DEHP within 36 h. DEHP was degraded to butanol, hexanal, catechol and acetic acid. It is suggested that the first two compounds would transform into butanediol and the last two would enter into the Krebs cycle and would be mineralized to CO₂ and H₂O. DEHP induced eight esterase isoforms, which were different to those constitutive isoforms produced in the control medium. It is suggested that five enzymes (25.7, 29.5, 31.8, 97.6 and 144.5 kDa) detected during the first 36 h be involved in the primary biodegradation of DEHP. The rest of the enzymes (45.9, 66.6 and 202.9 kDa) might be involved in the final steps for DEHP metabolism. F. culmorum has a promising practical application in the treatment of DEHP-contaminated environments because it can secrete specific esterase to breakdown high concentrations of DEHP in a short period of time. This research represents the first approach for the study of esterase involved in the DEHP degradation by fungi using this phthalate as the sole source of carbon and energy.

In silico genome analysis reveals the metabolic versatility and biotechnology potential of a halotorelant phthalic acid esters degrading Gordonia alkanivorans strain YC-RL2

Members of genus Gordonia are known to degrade various xenobitics and produce secondary metabolites. The genome of a halotorelant phthalic acid ester (PAEs) degrading actinobacterium Gordonia alkanivorans strain YC-RL2 was sequenced using Biosciences RS II platform and Single Molecular Real-Time (SMRT) technology. The reads were assembled de novo by hierarchical genome assembly process (HGAP) algorithm version 2. Genes were annotated by NCBI Prokaryotic Genome Annotation Pipeline. The generated genome sequence was 4,979,656 bp with an average G+C content of 67.45%. Calculation of ANI confirmed previous classification that strain YC-RL2 is G. alkanivorans. The sequences were searched against KEGG and COG databases; 3132 CDSs were assigned to COG families and 1808 CDSs were predicted to be involved in 111 pathways. 95 of the KEGG annotated genes were predicted to be involved in the degradation of xenobiotics. A phthalate degradation operon could not be identified in the genome indicating that strain YC-RL2 possesses a novel way of phthalate degradation. A total of 203 and 22 CDSs were annotated as esterase/hydrolase and dioxygenase genes respectively. A total of 53 biosynthetic gene clusters (BGCs) were predicted by antiSMASH (antibiotics & Secondary Metabolite Analysis Shell) bacterial version 4.0. The genome also contained putative genes for heavy metal metabolism. The strain could tolerate 1 mM of Cd2+, Co2+, Cu2+, Ni2+, Zn2+, Mn2+ and Pb2+ ions. These results show that strain YC-RL2 has a great potential to degrade various xenobiotics in different environments and will provide a rich genetic resource for further biotechnological and remediation studies.

Kinetics and pathway of biodegradation of dibutyl phthalate by Pleurotus ostreatus

Dibutyl phthalate (DBP) is a plasticizer, whose presence in the environment as a pollutant has attained a great deal of attention due to its reported association with endocrine system disturbances on animals. Growth parameters, glucose uptake, percentage of removal efficiency (%E) of DBP, biodegradation constant of DBP (k) and half-life of DBP biodegradation (t_1/2) were evaluated for Pleurotus ostreatus grown on media containing glucose and different concentrations of DBP (0, 500 and 1000 mg l^-1). P. ostreatus degraded 99.6 % and 94 % of 500 and 1000 mg of DBP l^-1 after 312 h and 504 h, respectively. The k was 0.0155 h^-1 and 0.0043 h^-1 for 500 and 1000 mg of DBP l^-1, respectively. t_1/2 was 44.7 h and 161 h for 500 and 1000 mg of DBP l^-1, respectively. Intermediate compounds of biodegraded DBP were identified by GC-MS and a DBP biodegradation pathway was proposed using quantum chemical calculation. DBP might be metabolized to benzene and acetyl acetate, the first would be oxidated to muconic acid and the latter would enter into the Krebs cycle. P. ostreatus has the ability to degrade DBP and utilizes it as source of carbon and energy.

A novel biodegradation pathway of the endocrine-disruptor di(2-ethyl hexyl) phthalate by Pleurotus ostreatus based on quantum chemical investigation

Di(2-ethyl hexyl) phthalate (DEHP) is a plasticizer that interfere with endocrine systems in mammals. Growth parameters for Pleurotus ostreatus grown on media containing glucose and different concentrations of DEHP (0, 500 and 1000mg/L) were evaluated. The highest biomass production was observed in medium supplemented with 1000mg of DEHP/L. Half-life of DEHP biodegradation, biodegradation constant of DEHP, and percentage of removal efficiency (%E) were also determined. P. ostreatus degraded 100% of DEHP after 504h. %E was 99.3% and 98.4% for 500 and 1000mg of DEHP/L, respectively. Intermediate compounds of biodegraded DEHP were identified by GC-MS and a DEHP biodegradation pathway was proposed using quantum chemical investigation. DEHP might be metabolized through three pathways; a de-esterification pathway, an oxidation pathway and an oxidation-hydrolysis pathway, forming phthalic acid, acetic acid and butanediol, respectively. P. ostreatus degrades and uses (as carbon and energy source) high concentrations of DEHP.

Degradation of Di(2-Ethylhexyl) Phthalate by a Novel Gordonia alkanivorans Strain YC-RL2

One bacterial strain, YC-RL2, isolated from petroleum-contaminated soil, could utilize environmental hormone Di(2-Ethylhexyl) phthalate (DEHP) as a sole carbon source for growth. Strain YC-RL2 was identified as Gordonia alkanivorans by 16S rRNA gene analysis and Biolog tests. The effects of environmental factors which might affect the degrading process were optimized at 30 °C and pH 8.0. Strain YC-RL2 showed superior halotolerance and could tolerate up to 0-5% NaCl in trace element medium supplemented with DEHP, although the DEHP degradation rates slowed as NaCl concentration increased. It also showed an outstanding performance in a wide range of pH (6.0-11.0). Meanwhile, strain YC-RL2 was able to withstand high concentrations of DEHP (from 100 to 800 mg/L), and the degradation rates were all above 94%. The DEHP intermediates were detected by HPLC-MS, and the degradation pathway was deduced tentatively. DEHP was transformed into phthalic acid (PA) via mono (2-ethylhexyl) phthalate (MEHP), and PA was further utilized for growth via benzoic acid (BA). The enzyme expected to catalyze the hydrolysis of MEHP to PA was identified from strain YC-RL2. Further investigation found that the enzyme could catalyze the transformation of a wide range of monoalkyl phthalates to PA. This study is the first report about species G. alkanivorans which could degrade several kinds of phthalic acid esters (PAEs), and indicates its application potential for bioremediation of PAE-polluted sites.

Degradation of di(2-ethyl hexyl) phthalate by Fusarium culmorum: Kinetics, enzymatic activities and biodegradation pathway based on quantum chemical modelingpathway based on quantum chemical modeling

Di(2-ethylhexyl) phthalate (DEHP) is a plasticizer widely used in the manufacture of plastics, and it is an environmental contaminant. The specific growth rate (μ), maximum biomass (Xmax), biodegradation constant of DEHP (k), half-life (t1/2) of DEHP biodegradation and removal efficiency of DEHP, esterase and laccase specific activities, and enzymatic yield parameters were evaluated for Fusarium culmorum grown on media containing glucose and different concentrations of DEHP (0, 500 and 1000mg/L). The greatest μ and the largest Xmax occurred in media supplemented with 1000mg of DEHP/L. F. culmorum degraded 95% of the highest amount of DEHP tested (1000mg/L) within 60h of growth. The k and t1/2 were 0.024h(-1) and 28h, respectively, for both DEHP concentrations. The removal efficiency of DEHP was 99.8% and 99.9% for 1000 and 500mg/L, respectively. Much higher specific esterase activity than specific laccase activity was observed in all media tested. The compounds of biodegradation of DEHP were identified by GC-MS. A DEHP biodegradation pathway by F. culmorum was proposed on the basis of the intermolecular flow of electrons of the identified intermediate compounds using quantum chemical modeling. DEHP was fully metabolized by F. culmorum with butanediol as the final product. This fungus offers great potential in bioremediation of environments polluted with DEHP.

Fungal Community Successions in Rhizosphere Sediment of Seagrasses Enhalus acoroides under PAHs Stress

Seagrass meadows represent one of the highest productive marine ecosystems and are of great ecological and economic values. Recently, they have been confronted with worldwide decline. Fungi play important roles in sustaining the ecosystem health as degraders of polycyclic aromatic hydrocarbons (PAHs), but fewer studies have been conducted in seagrass ecosystems. Hence, we investigated the dynamic variations of the fungal community succession under PAH stress in rhizosphere sediment of seagrasses Enhalus acoroides in this study. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), quantitative PCR (qPCR) and a clone library have been employed to analyze the fungal community’s shifts. Sequencing results of DGGE and the clone library showed that the predominant species belong to phyla Ascomycota and Basidiomycota. The abundance of three groups decreased sharply over the incubation period, whereas they demonstrated different fungal diversity patterns. Both the exposure time and the PAH concentrations affected the microbial diversity as assessed by PCR-DGGE analysis. Redundancy analysis (RDA) indicated that significant factors driving community shifts were ammonium and pH (p < 0.05). Significant amounts of the variations (31.1%) were explained by pH and ammonium, illustrating that those two parameters were the most likely ones to influence or be influenced by the fungal communities’ changes. Investigation results also indicated that fungal communities in seagrass meadow were very sensitive to PAH-induced stress and may be used as potential indicators for the PAH contamination.