12 research outputs found
Electron Acceptor-Dependent Respiratory and Physiological Stratifications in Biofilms
Bacterial respiration is an essential
driving force in biogeochemical
cycling and bioremediation processes. Electron acceptors respired
by bacteria often have solid and soluble forms that typically coexist
in the environment. It is important to understand how sessile bacteria
attached to solid electron acceptors respond to ambient soluble alternative
electron acceptors. Microbial fuel cells (MFCs) provide a useful tool
to investigate this interaction. In MFCs with Shewanella
decolorationis, azo dye was used as an alternative
electron acceptor in the anode chamber. Different respiration patterns
were observed for biofilm and planktonic cells, with planktonic cells
preferred to respire with azo dye while biofilm cells respired with
both the anode and azo dye. The additional azo respiration dissipated
the proton accumulation within the anode biofilm. There was a large
redox potential gap between the biofilms and anode surface. Changing
cathodic conditions caused immediate effects on the anode potential
but not on the biofilm potential. Biofilm viability showed an inverse
and respiration-dependent profile when respiring with only the anode
or azo dye and was enhanced when respiring with both simultaneously.
These results provide new insights into the bacterial respiration
strategies in environments containing multiple electron acceptors
and support an electron-hopping mechanism within Shewanella electrode-respiring biofilms
Evidence of Polyethylene Biodegradation by Bacterial Strains from the Guts of Plastic-Eating Waxworms
Polyethylene (PE) has been considered
nonbiodegradable for decades.
Although the biodegradation of PE by bacterial cultures has been occasionally
described, valid evidence of PE biodegradation has remained limited
in the literature. We found that waxworms, or Indian mealmoths (the
larvae of <i>Plodia interpunctella</i>), were capable of
chewing and eating PE films. Two bacterial strains capable of degrading
PE were isolated from this worm’s gut, <i>Enterobacter
asburiae</i> YT1 and <i>Bacillus sp.</i> YP1. Over
a 28-day incubation period of the two strains on PE films, viable
biofilms formed, and the PE films’ hydrophobicity decreased.
Obvious damage, including pits and cavities (0.3–0.4 μm
in depth), was observed on the surfaces of the PE films using scanning
electron microscopy (SEM) and atomic force microscopy (AFM). The formation
of carbonyl groups was verified using X-ray photoelectron spectroscopy
(XPS) and microattenuated total reflectance/Fourier transform infrared
(micro-ATR/FTIR) imaging microscope. Suspension cultures of YT1 and
YP1 (10<sup>8</sup> cells/mL) were able to degrade approximately 6.1
± 0.3% and 10.7 ± 0.2% of the PE films (100 mg), respectively,
over a 60-day incubation period. The molecular weights of the residual
PE films were lower, and the release of 12 water-soluble daughter
products was also detected. The results demonstrated the presence
of PE-degrading bacteria in the guts of waxworms and provided promising
evidence for the biodegradation of PE in the environment
Ultrasonic Treatment Enhanced Ammonia-Oxidizing Bacterial (AOB) Activity for Nitritation Process
Oxidation of ammonia
to nitrite rather than nitrate is critical
for nitritation process for wastewater treatment. We proposed a promising
approach by using controlled ultrasonic treatment to enhance the activity
of ammonia-oxidizing bacteria (AOB) and suppress that of nitrite-oxidizing
bacteria (NOB). Batch activity assays indicated that when ultrasound
was applied, AOB activity reached a peak level and then declined but
NOB activity deteriorated continuously as the power intensity of ultrasound
increased. Kinetic analysis of relative microbial activity versus
ultrasonic energy density was performed to investigate the effect
of operational factors (power, sludge concentration, and aeration)
on AOB and NOB activities and the test parameters were selected for
reactor tests. Laboratory sequential batch reactor (SBR) was further
used to test the ultrasonic stimulus with 8 h per day operational
cycle and synthetic waste urine as influent. With specific ultrasonic
energy density of 0.09 kJ/mg VSS and continuously fed influent containing
above 200 mg NH<sub>3</sub>–N/L, high AOB reproductive activity
was achieved and nearly complete conversion of ammonia-N to nitrite
was maintained. Microbial structure analysis confirmed that the treatment
changed community of AOB, NOB, and heterotrophs. Known AOB <i>Nitrosomonas</i> genus remained at similar level in the biomass
while typical NOB <i>Nitrospira</i> genus disappeared in
the SBR under ultrasonic treatment and after the treatment was off
for 30 days
U(VI) Bioreduction with Emulsified Vegetable Oil as the Electron Donor – Model Application to a Field Test
We
amended a shallow fast-flowing uranium (U) contaminated aquifer
with emulsified vegetable oil (EVO) and subsequently monitored the
biogeochemical responses for over a year. Using a biogeochemical model
developed in a companion article (Tang et al., <i>Environ. Sci.
Technol.</i> <b>2013</b>, doi: 10.1021/es304641b) based
on microcosm tests, we simulated geochemical and microbial dynamics
in the field test during and after the 2-h EVO injection. When the
lab-determined parameters were applied in the field-scale simulation,
the estimated rate coefficient for EVO hydrolysis in the field was
about 1 order of magnitude greater than that in the microcosms. Model
results suggested that precipitation of long-chain fatty acids, produced
from EVO hydrolysis, with Ca in the aquifer created a secondary long-term
electron donor source. The model predicted substantial accumulation
of denitrifying and sulfate-reducing bacteria, and UÂ(IV) precipitates.
The accumulation was greatest near the injection wells and along the
lateral boundaries of the treatment zone where electron donors mixed
with electron acceptors in the groundwater. While electron acceptors
such as sulfate were generally considered to compete with UÂ(VI) for
electrons, this work highlighted their role in providing electron
acceptors for microorganisms to degrade complex substrates thereby
enhancing UÂ(VI) reduction and immobilization
Unveiling Fragmentation of Plastic Particles during Biodegradation of Polystyrene and Polyethylene Foams in Mealworms: Highly Sensitive Detection and Digestive Modeling Prediction
It remains unknown whether plastic-biodegrading macroinvertebrates
generate microplastics (MPs) and nanoplastics (NPs) during the biodegradation
of plastics. In this study, we utilized highly sensitive particle
analyzers and pyrolyzer-gas chromatography mass spectrometry (Py-GCMS)
to investigate the possibility of generating MPs and NPs in frass
during the biodegradation of polystyrene (PS) and low-density polyethylene
(LDPE) foams by mealworms (Tenebrio molitor larvae).
We also developed a digestive biofragmentation model to predict and
unveil the fragmentation process of ingested plastics. The mealworms
removed 77.3% of ingested PS and 71.1% of ingested PE over a 6-week
test period. Biodegradation of both polymers was verified by the increase
in the δ13C signature of residual plastics, changes
in molecular weights, and the formation of new oxidative functional
groups. MPs accumulated in the frass due to biofragmentation, with
residual PS and PE exhibiting the maximum percentage by number at
2.75 and 7.27 μm, respectively. Nevertheless, NPs were not
detected using a laser light scattering sizer with a detection limit
of 10 nm and Py-GCMS analysis. The digestive biofragmentation model
predicted that the ingested PS and PE were progressively size-reduced
and rapidly biodegraded, indicating the shorter half-life the smaller
plastic particles have. This study allayed concerns regarding the
accumulation of NPs by plastic-degrading mealworms and provided critical
insights into the factors controlling MP and NP generation during
macroinvertebrate-mediated plastic biodegradation
Biodegradation and Mineralization of Polystyrene by Plastic-Eating Mealworms: Part 1. Chemical and Physical Characterization and Isotopic Tests
Polystyrene
(PS) is generally considered to be durable and resistant
to biodegradation. Mealworms (the larvae of Tenebrio
molitor Linnaeus) from different sources chew and
eat Styrofoam, a common PS product. The Styrofoam was efficiently
degraded in the larval gut within a retention time of less than 24
h. Fed with Styrofoam as the sole diet, the larvae lived as well as
those fed with a normal diet (bran) over a period of 1 month. The
analysis of fecula egested from Styrofoam-feeding larvae, using gel
permeation chromatography (GPC), solid-state <sup>13</sup>C cross-polarization/magic
angle spinning nuclear magnetic resonance (CP/MAS NMR) spectroscopy,
and thermogravimetric Fourier transform infrared (TG–FTIR)
spectroscopy, substantiated that cleavage/depolymerization of long-chain
PS molecules and the formation of depolymerized metabolites occurred
in the larval gut. Within a 16 day test period, 47.7% of the ingested
Styrofoam carbon was converted into CO<sub>2</sub> and the residue
(ca. 49.2%) was egested as fecula with a limited fraction incorporated
into biomass (ca. 0.5%). Tests with α <sup>13</sup>C- or β <sup>13</sup>C-labeled PS confirmed that the <sup>13</sup>C-labeled PS
was mineralized to <sup>13</sup>CO<sub>2</sub> and incorporated into
lipids. The discovery of the rapid biodegradation of PS in the larval
gut reveals a new fate for plastic waste in the environment
Biodegradation and Mineralization of Polystyrene by Plastic-Eating Mealworms: Part 2. Role of Gut Microorganisms
The
role of gut bacteria of mealworms (the larvae of Tenebrio
molitor Linnaeus) in polystyrene (PS) degradation
was investigated. Gentamicin was the most effective inhibitor of gut
bacteria among six antibiotics tested. Gut bacterial activities were
essentially suppressed by feeding gentamicin food (30 mg/g) for 10
days. Gentamicin-feeding mealworms lost the ability to depolymerize
PS and mineralize PS into CO<sub>2</sub>, as determined by characterizing
worm fecula and feeding with <sup>13</sup>C-labeled PS. A PS-degrading
bacterial strain was isolated from the guts of the mealworms, Exiguobacterium sp. strain YT2, which could form
biofilm on PS film over a 28 day incubation period and made obvious
pits and cavities (0.2–0.3 mm in width) on PS film surfaces
associated with decreases in hydrophobicity and the formation of C–O
polar groups. A suspension culture of strain YT2 (10<sup>8</sup> cells/mL)
was able to degrade 7.4 ± 0.4% of the PS pieces (2500 mg/L) over
a 60 day incubation period. The molecular weight of the residual PS
pieces was lower, and the release of water-soluble daughter products
was detected. The results indicated the essential role of gut bacteria
in PS biodegradation and mineralization, confirmed the presence of
PS-degrading gut bacteria, and demonstrated the biodegradation of
PS by mealworms
U(VI) Bioreduction with Emulsified Vegetable Oil as the Electron Donor – Microcosm Tests and Model Development
We
conducted microcosm tests and biogeochemical modeling to study
UÂ(VI) reduction in contaminated sediments amended with emulsified
vegetable oil (EVO). Indigenous microorganisms in the sediments degraded
EVO and stimulated FeÂ(III), UÂ(VI), and sulfate reduction, and methanogenesis.
Acetate concentration peaked in 100–120 days in the EVO microcosms
versus 10–20 days in the oleate microcosms, suggesting that
triglyceride hydrolysis was a rate-limiting step in EVO degradation
and subsequent reactions. Acetate persisted 50 days longer in oleate-
and EVO- than in ethanol-amended microcosms, indicating that acetate-utilizing
methanogenesis was slower in the oleate and EVO than ethanol microcosms.
We developed a comprehensive biogeochemical model to couple EVO hydrolysis,
production, and oxidation of long-chain fatty acids (LCFA), glycerol,
acetate, and hydrogen, reduction of FeÂ(III), UÂ(VI) and sulfate, and
methanogenesis with growth and decay of multiple functional microbial
groups. By estimating EVO, LCFA, and glycerol degradation rate coefficients,
and introducing a 100 day lag time for acetoclastic methanogenesis
for oleate and EVO microcosms, the model approximately matched observed
sulfate, UÂ(VI), and acetate concentrations. Our results confirmed
that EVO could stimulate UÂ(VI) bioreduction in sediments and the slow
EVO hydrolysis and acetate-utilizing methanogens growth could contribute
to longer term bioreduction than simple substrates (e.g., ethanol,
acetate, etc.) in the subsurface
Biodegradation of Polyethylene and Plastic Mixtures in Mealworms (Larvae of <i>Tenebrio molitor</i>) and Effects on the Gut Microbiome
Recent
studies have demonstrated the ability for polystyrene (PS)
degradation within the gut of mealworms (<i>Tenebrio molitor</i>). To determine whether plastics may be broadly susceptible to biodegradation
within mealworms, we evaluated the fate of polyethylene (PE) and mixtures
(PE + PS). We find that PE biodegrades at comparable rates to PS.
Mass balances indicate conversion of up 49.0 ± 1.4% of the ingested
PE into a putative gas fraction (CO<sub>2</sub>). The molecular weights
(<i>M</i><sub>n</sub>) of egested polymer residues decreased
by 40.1 ± 8.5% in PE-fed mealworms and by 12.8 ± 3.1% in
PS-fed mealworms. NMR and FTIR analyses revealed chemical modifications
consistent with degradation and partial oxidation of the polymer.
Mixtures likewise degraded. Our results are consistent with a nonspecific
degradation mechanism. Analysis of the gut microbiome by next-generation
sequencing revealed two OTUs (<i>Citrobacter</i> sp. and <i>Kosakonia</i> sp.) strongly associated with both PE and PS as
well as OTUs unique to each plastic. Our results suggest that adaptability
of the mealworm gut microbiome enables degradation of chemically dissimilar
plastics
Methanogenesis Facilitated by Geobiochemical Iron Cycle in a Novel Syntrophic Methanogenic Microbial Community
Production
and emission of methane have been increasing concerns
due to its significant effect on global climate change and the carbon
cycle. Here we report facilitated methane production from acetate
by a novel community of methanogens and acetate oxidizing bacteria
in the presence of poorly crystalline akaganeite slurry. Comparative
analyses showed that methanogenesis was significantly enhanced by
added akaganeite and acetate was mostly stoichiometrically converted
to methane. Electrons produced from anaerobic acetate oxidation are
transferred to akaganeite nanorods that likely prompt the transformation
into goethite nanofibers through a series of biogeochemical processes
of soluble FeÂ(II) readsorption and FeÂ(III) reprecipitation. The methanogenic
archaea likely harness the biotransformation of akaganeite to goethite
by the FeÂ(III)–FeÂ(II) cycle to facilitate production of methane.
These results provide new insights into biogeochemistry of iron minerals
and methanogenesis in the environment, as well as the development
of sustainable methods for microbial methane production