Journal of Applied Science and Agriculture, 9(11) Special 2014, Pages: 109-118
AENSI Journals
Journal of Applied Science and Agriculture
ISSN 1816-9112
Journal home page: www.aensiweb.com/JASA
A Review on the Role of Earthworms in Degradation and Decomposition of Organic
and Industrial Waste Materials with the Emphasize on the Significance of Secreted
Enzymes from Their Symbiont Microbes
1
1
2
Fereshteh Azadeh and 2Mehdi Zarabi
Department of Life Sciences Engineering, Faculty of New Sciences and Technologies, University of Tehran, Tehran, Iran
Department of Sciences and Environmental Technologies, Faculty of New Sciences and Technologies, University of Tehran, Tehran, Iran
ARTICLE INFO
Article history:
Received 25 June 2014
Received in revised form
8 July 2014
Accepted 10 August May 2014
Available online 30 August 2014
Keywords:
Earthworms, Enzymes, Degradation,
Remediation,
Decomposition,
Hydrocarbons, organic wastes
ABSTRACT
Regarding to the urbanization and industrialization and population growth in the world,
there isan urgent need to overcome waste materials recycling problems. Different
approaches have been taken for waste evanescence. One of the successful approaches
might be through vermitechnology. Earthworms are key soil invertebrates in organic
matter decomposition and because of their interactions with soil microorganisms. They
accelerate organic waste decomposition rates and removal of hydrocarbons especially
recalcitrant ones and also petroleum derived hydrocarbons and its products. These
animals use various approaches in this route, either by burrowing and feeding (direct
effects) or cast ageing and aeration (indirect effects). Although, they require demanded
conditions, like optimum pH, moisture, temperature, etc. Moreover, for efficient zoo
remediation, a large number of worms are required. Several studies have investigated
the effects of soil amended with different pollutants on earthworms such as
polychlorinated bi-phenols, petroleum hydrocarbons and Polyaromatic hydrocarbons
(PAH). Earthworms have the ability to degrade these materials through not well-known
mechanisms. It is believed that the pollutants are degraded by the earthworms’
cytochrome p450 enzymatic system activity. Hydrolases and dehydrogenase activities
of earthworm enzymes as well as the earthworm microflora are responsible for organic
matter decomposition. Earthworms contain beneficial microorganisms in different parts
of their body such as nephridia, foregut, midgut and hindgut. So far, diverse
microorganism capable of producing enzymes have been isolated from earthworms
which are involved in the decomposition and degradation process including cellulase,
xylanase, laccase, endo-β-1,4-mannanase. In this review, we will concentrate on the
role of symbiont microorganisms besides the earthworm role in enhancing waste
material degradation.
© 2014 AENSI Publisher All rights reserved.
To Cite This Article: Fereshteh Azadeh and Mehdi Zarabi., A Review on the Role of Earthworms in Degradation and Decomposition of
Organic and Industrial Waste Materials with the Emphasize on the Significance of Secreted Enzymes from Their Symbiont Microbes. J.
Appl. Sci. & Agric., 9(11): 109-118, 2014
INTRODUCTION
Industrial activities have caused heavy metal release into the environments (Wu et al., 2010). Activities
such as deforestation, contamination with pollutants lead to the gradual disappearance of forests and other
natural vegetations which has great impacts on soil quality and fauna (Brito-Vega and Espinosa-Victoria, 2009).
A healthy soil encourages plant growth and development and microbial activity in rhizosphere. Industries
produce massive quantities of liquid, gaseous or solid wastes, which cause environmental pollution.
Contamination of ground water, soils, as well as, food resources are due to dumping the waste materials into
water streams and resources (Suther, 2008).
Earthworms are the member of the phylum: Annelida, order: Oligochaeta (Edwards and Lofty, 1977).
Currently more than 7,245 species of Oligochaetes have been classified at globally (Reynolds, 1998).
Earthworms were divided into three ecological categories. Epigeic species which live in the litter; feed on
organic matters and produce casts at the soil surface and make structured soil with macropores. Anecic species
live in vertical burrows. Endogeic species make horizontal or randomly oriented burrows in mineral soil.
Earthworms are believed to be the most abundant animal biomass. They are called ecosystem engineers since
Corresponding Author: Mehdi Zarabi, Department of Sciences and Environmental Technologies, Faculty of New Sciences
and Technologies, University of Tehran, Tehran, Iran, Tel: 0098-21-88618094/Fax: 0098-2188617087, Geophysics Building No. 3, Amir Abad/ North Kargar.
E-mail address: [email protected]
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Journal of Applied Science and Agriculture, 9(11) Special 2014, Pages: 109-118
they have a large impact on soil structure. Earthworms show an excellent potential in managing ecosystem
services [(Blouin et al., 2013), (Bouche, 1977), (Lee, 1985)].
In late 19th century, Charles Darwin described the importance of earthworm activity in soil quality
(Darwin, 1881). Nowadays, it is well known, that earthworms and other soil macrofauna modify the soil
physical properties and affect soil organic matter decomposition and regulate carbon fluxes and nitrogen cycling
(Parmelee et al., 1998). There is abundant evidence that this decomposition and degradation of organic materials
and release of mineral nutrients into the soil are resulted from earthworms and microorganisms relationships
(Edwards and Fletcher, 1988).
Earthworms can tolerate many chemical contaminants like heavy metals and organic pollutants in soil and
can accumulate them in their tissues. Earthworm species like Eisenia fetida, Eisenia tetraedra, L. terrestris, L.
rubellus and Allobophora chlorotica remove heavy metals (Cd, Pb, Cu, Hg, etc.) pesticides and lipophilic
organic micropollutants such as Polycyclic aromatic hydrocarbons (PAHs) from soil (Sinha et al., 2008).
Vermiculture which means rearing earthworms, include steps such as: preparation of seed stocks and providing
optimum food, moisture, air and temperature conditions. “Vermicomposting involves bio-oxidation and
stabilization of organic matter through the interactions between earthworms and microorganisms (Aira and
Dominguez, 2011). Microorganisms are the main cause of the biochemical degradation of organic matters but
earthworms also play a critical role in this process through fragmenting the substrates, increasing the surface
area for growth of microorganisms, aeration and changing their activities [(Aira and Dominguez 2011),
(Dominguez 2004), (Dominguez and Edwards 2004)].
Studies show that during the first stage of organic matter decompostition, the interactions between
earthworms and microorganisms are somehow mutualistic (Aira et al., 2007). Earthworms are considered as
natural bioreactors which in their gut, microorganisms proliferate and therefore provide required conditions for
the biodegradation of wastes (Munnoli et al., 2010), i.e. earthworms provide food supplements for
microorganisms causing their proliferation.
The impact of earthworms gut enzyme in biodegradation and biodecomposition of wastes have been
mentioned in several literatures [(Kim et al., 2011), (Blouin et al., 2013), (Sanchez-Hernandez et al., 2009)].
These enzymes are either originated from their intestinal juice or are the result of microbial activity in the
earthworms’ gut. Investigations showed that microorganisms that have high enzymatic activities form symbiotic
and synergistic relationships with earthworms (Hong et al., 2011).
In this review, we will focus on the role of earthworms and their symbiont microorganisms in enhancing
waste material degradation.
1. Different approaches towards remediation of wastes:
Four methods exist for remediation and removing hazardous heavy metals including chemical/ physical
remediation, animal remediation (zoo-remediation), phytoremediation and microremediation (bioremediation
(bacteria) and mycoremediation (fungi)). Plants and microbes are more cost-effectiveness, ecofriendly and have
fewer side effects. Animal remediation mainly refers to earthworm remediation because it is the most important
soil organisms and plays an important role in soil ecosystem by burrowing, feeding, excreting and metabolic
redox material. The effectiveness and efficiency of earthworm remediation depends too much on the
environmental conditions. It might not the optimum method of removing heavy metals, but could be
accompanied with other methods for the best efficiency (Wu et al., 2010).
Earthworms feed on organic matter and modify the soil chemistry, therefore reduce the amount of
contaminant sorption on soil particles, leading to an increase in the availability of contaminants, so the
contamination will readily be exposed to phytoremediation. In many studies earthworms were applied as bioindicators for detection of the extent of contamination and toxicity of contaminated soil [(Brulle et al., 2010),
(Nahmani et al., 2007), (Rombke et al., 2006)]. A number of laboratory experiments have been performed on
soil amended with organic chemicals and a range of earthworms, for instance, soil amended with
polychlorinated biphenols [(Singer et al., 2001), (Kelsey et al., 2011)], petroleum hydrocarbons [(Schaefer et
al., 2007), (Schaefer et al., 2005), (Oboh et al., 2007)] or polyaromatic hydrocarbons (PAHs) [(Ma et al., 1995),
(Contreras-Ramos et al., 2008, 2009)]. Studies usually use either epigeic or anecic earthworms, with only two
authors using an Endogeic earthworm [(Kelsey et al., 2011), (Schaefer and Filser, 2007)].
Polycyclic aromatic hydrocarbons (PAHs) are derived from oil and oil-derivatives, they refer to a group of
over 100 chemicals of which anthracene, benzo(a)pyrene, naphthalene, pyrene are common. When
microorganisms break the aromatic rings PAHs are degraded and produce aliphatic compounds that readily
enter the tricarboxylic acid cycle, a metabolic activity in living cells (Sinha et al., 2008). Areas contaminated are
often associated with co-contaminants such as benzene, toluene, ethylene and xylene (BTEX) compounds,
heavy metals and aliphatic hydrocarbons, which can be an obstacle in the way of remediation attempts. There
are three fundamentally different mechanisms in the aerobic metabolism of PAHs by microorganisms and
specific details of bacterial and fungal PAH metabolism. The basis of these mechanisms is the oxidation of the
aromatic ring, followed by the systematic breakdown of the compound to PAH metabolites and/or carbon
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Journal of Applied Science and Agriculture, 9(11) Special 2014, Pages: 109-118
dioxide. Anaerobic metabolism of PAHs is thought to occur via the hydrogenation of the aromatic ring
(Bamforth and Singleton, 2005).
2. The role of earthworms in decomposition of organic materials:
Earthworms are key regulators of the dynamics soil organic matter (SOM) in many agroecosystems (Fonte
et al., 2009). The degradation of organic materials by earthworms deals with a large amount of organic matter
wastes derived from urban environments [(Guggenberger et al., 1996), (Blanchart et al., 1997), (Blouin et al.,
2013)]. Earthworms are heterotrophic organisms that are involved in the degradation of organic matter and
molecules, mainly produced by plants [(Ingham et al., 1985), (Seeber et al., 2008)]. Earthworms enhance the
incorporation of organic matter into soil and the formation of macroaggregates through their burrowing,
consumption and egestion activities [(Guggenberger et al., 1996), (Blanchart et al., 1997)].
The interaction between Earthworms and soil arthropods can influence decomposition rates; the
development of large populations of soil arthropods, mainly springtails, in the mesocosms with earthworms is a
characteristic feature of the initial stages of the earthworm-driven decomposition process (Monroy, 2011).
The role of earthworms in humus formation has been investigated; the darkening of soil is a slow process,
which involves primarily chemical reactions and microbial activity. This process could be accelerated by
earthworms that prepare the soil and litter mixtures composed of fragmented and macerated leaves and fine soil
particles for microbial attack (Edwards et al., 2011).
In vermicomposting process microbes are responsible for biochemical degradation of organic matter and
earthworm acts as a bioreactor, by comminuting the organic matter; they modify its biological, physical and
chemical state, gradually reducing its C: N ratio (Yadav and Garg, 2011) and increasing the surface area
exposed to microorganisms [(Ingham et al., 1985), (Seeber et al., 2008), (Yadav and Garg, 2011)].
After digestion, some organic compounds are released into the environment as small organic compounds or
mineral nutrients, which are re-used by plants. Therefore, nitrogen mineralization with the presence of
earthworms increases, by the release of N by their metabolic products (casts, urine and mucus, which contains
NH4+, urea, allantoin and uric acid) and dead tissues (directly), or through altering soil physical properties and
fragmentation of organic material, and interactions with other soil organisms (indirectly) [(Lee, 1985),
(Bityutskii et al., 2002)].
Earthworms have impacts on soil microbial communities and microbial processes related to soil organic
matter (SOM) status and nutrient dynamics. They also affect the activities of soil inhabiting invertebrates, either
by modifying their environment or through competition for feeding resources. The effects of earthworms on soil
function thus depend on their interactions with a wide range of identified abiotic and biotic factors that operate
at rather different scales of time and space. There is evidence that some Endogeic species of earthworms ingest
only aggregates that do not exceed the diameter of their mouths, whereas other species may feed on larger
aggregates and split them into smaller aggregates (Lavelle et al., 2004). Endogeic earthworms ingest large
amounts of soil. “During gut transit, microorganisms are transported to new substrates and their activity is
stimulated by (i) the production of readily assimilable organic matter (mucus) and (ii) the possible presence of
fresh organic residues in the ingested soil “(Bernard et al., 2012). The feeding behavior that allows such a
selection has never been described in detail. The long-term effects of earthworms on SOM dynamics vary
depending on the scale of time considered. When earthworms are introduced artificially into an ecosystem, they
use part of the C resources for their activities (Lavelle et al., 2004).
The waste decomposition and earthworm production was associated strongly with the quality of the
substrate, especially with their chemical as well as biological composition (Suthar, 2007).
Three microbial strains were inoculated in two different organic wastes to study their effect on the humic
acid content, acid phosphate activity and microbial properties of the final stabilized products (Pramanik et al.,
2009).
Vegetable-market solid waste is produced in millions of tones in urban areas and creates a problem of safe
disposal Vermitechnology can be used as a potential tool to convert vegetable-market solid waste into some
value-added products, which is earthworms’ nutrient-rich vermicompost (Suthar, 2009).
3. The role of Earthworms in pollutant degradation:
The use of earthworms for the restoration or remediation of contaminated soil can be based on several
different strategies depending on the nature of the contamination. Earthworms could be introduced into soil to
stimulate the microbial population and enhance the biodegradation of organic pollutants. Metabolism of
ingested soil may also lead to direct mineralization of organic contaminants [(Brulle et al., 2010), (Nahmani et
al., 2007), (Rombke et al., 2013)].
Vermicomposting of non-recyclable postconsumer paper waste amended with cow dung with Eisenia fetida
earthworm to convert it into a value-added product (vermicompost) has been studied (Gupta and Garg, 2009).
Vermitechnology in organic waste management would lead to zero waste techno farms without the organic
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waste being wastes and burned (Ansari, 2011). The efficiency of vermicomposting in stabilizing municipal
wastewater was studied as a replacement for the digestion process (Parvaresh et al., 2004).
Metal pollution may disturb soil ecosystems by affecting the structure of soil invertebrate populations
(Spurgeon et al., 1994). Earthworms could be possibly cultured in metal solutions to determine the effects of
metals on accumulation and mortality of them. The toxicity of Cu to the earthworm Aporrectodea caliginosa
was investigated and showed that Na+ and H+ mitigated Cu toxicity but that Mg2+ and Ca2+ had inconsistent
effects (Arnold et al., 2007).
Evidence has been presented showing that arsenic induces expression of metallothionein in earthworms,
which sequesters arsenic in certain cells and tissues [(Button et al., 2011), (Sinha et al., 2008)]. Earthworm
mucus may increase the concentration of dissolved organic carbon in the soil solution resulting in greater
competition between Arsenic and organic carbon for binding surfaces on positively charged soil constituents
such as iron and manganese oxides leading to an increase in Arsenic mobility (Sizmur et al., 2011). Metals can
be accumulated in various worm tissues to reduce of metal level in during the vermicomposting process and soil
(Suthar, 2008).
Earthworms apparently possess a number of mechanisms for uptake, immobilization and excretion of heavy
metals and other chemicals (Sinha et al., 2008). One of the major routes in this process is diffusion of metal ions
through the body wall of earthworms either dermal uptake or gut uptake (Oste et al., 2001). They either ‘biotransform’ or ‘biodegrade’ the chemical contaminants rendering them harmless in their bodies. Most biotransformations and biodegradation are done in the gut before the contaminants enter the worm tissues. Soil
physicochemical characteristics and contamination levels alter the bioavailability of metals to terrestrial
invertebrates. The simulated earthworm gut (SEG) was developed to measure the bio-accessibility of metals in
soil to earthworms by mimicking the gastrointestinal fluid composition of earthworms (Ma et al., 2009).
The earthworm treatment can reduce the concentrations of Cd in soil, and Cd cause a shift in the bacterial
communities in the guts of M. posthuma [(Liang et al., 2009), (Sturzenbaum et al., 2001)].
The potential of earthworms to methylate inorganic-Hg because of the anaerobic and nutrient-rich
conditions in their digestive tracts and the action of bacteria was also investigated (Rieder et al., 2013).
Partial bioremediation of polychlorinated biphenyl (PCB)-contaminated soils was obtained using bioaugmentation with PCB degrading bacteria and earthworms. Earthworms facilitate PCB bioremediation by
providing environmental conditions that favor the growth and activity of indigenous PCB-degrading bacteria
and accelerating the dispersal of PCB-degrading bacteria in bio-augmented columns (Luepromchai et al., 2002).
In recent years, the impact of earthworm on Atrazine (2-chloro-ethylamino-6-isopropylamino-s-triazine)
herbicide mineralization has been assessed in representative soil microsites of earthworm activities (gut
contents, casts, and burrow linings) (Kersante et al., 2006). Generally earthworms enhance the degradation of
organic compounds to about 30%, which their mechanism is not entirely clear (Blouin et al., 2013).
The organic matter plays an important role in PAH biodegradation through contribution of soil nutrients as
a result of their mineralization and by stimulating microbial activity. Therefore, the co-application of organic
wastes and E. fetida for the bioremediation of benzo(a)pyrene polluted soil is desired (Tejada and Masciandaro,
2011). Lumbricus terrestris and E. fetida can easily survive 0.5% of crude oil in soil for 15 days (Safawat and
Weaver, 2002).
Recent studies by Markman et al. (2007) have shown that the earthworms can bio-accumulate significantly
high concentrations of endocrine disrupting chemical (EDCs) (dibutylphthalate, dioctylphthalate, bisphenol-A
and 17 b-estradiol) in their tissues (Markman et al., 2007). Earthworms can also either accumulate or degrade
‘organochlorine pesticide’ and ‘polycyclic aromatic hydrocarbons’ (PAHs) residues in the medium in which it
feeds. Ma et al. (1995) found that earthworms in soil enhance the degradation of organic contaminants like
phthalate, phenanthrene and fluoranthene. Studies of the bacterial flora associated with the intestine and
vermicasts of the earthworms and found species like Pseudomonas, Paenibacillus, Azoarcus, Burkholderia,
Spiroplasm, Acaligenes and Acidobacterium. Some of them, such as Pseudomonas, Acaligenes and
Acidobacterium, are known to degrade hydrocarbons. Some fungi such as Pencillium, Mucor and Aspergillus
have also been found in the intestine of earthworms and they degrade hydrocarbons. Acaligenes can even
degrade PCBs and Mucor dieldrin. Dieldein is one of the most poisonous toxicants (Sinha et al., 2008).
The effect of increase in earthworm (Eudrilus eugeniae) concentration on the acceleration of
bioremediation of used engine oil contaminated soil, amended with poultry manure, was investigated (Opuada
Ameh et al., 2012).
The performance of a conventional biofilter (BF) and a vermifilter containing the earthworm, Eisenia
foetida, (VF) for the treatment of domestic wastewater sludge were compared with the earthworm–
microorganism interaction mechanisms involved in sludge stabilization. This study resulted a significant
stabilization of the sludge by enhancing the reduction in volatile suspended solids in presence of earthworms
(Zhao et al., 2010).
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Hospital wastes are hazardous and need to be disinfected before disposal. Composting of bio-degradable
part of infected hospital waste using earthworms (Eisenia fetida and Eudrilus eugeniae) was carried out without
causing any adverse impact on the environment and human health (Mathur et al., 2006).
The metabolizing potential of a bacterial strain isolate Rhodococcus MTCC 6716 from the gut of an Indian
earthworm (Metaphire posthuma) was studied for endosulfan bioremediation (Verma et al., 2011).
4. Earthworms interactions with microorganisms:
Earthworms contain a large quantity of microorganisms in their body parts, including the gut and nephridia.
Nephridia are paired osmoregulatory-excretory organs present in each segment of the earthworm body. One
of the apparent species-specific microbial symbionts in the ampullas of the nephridia was confirmed as a
member of the genus Acidovorax (Schramm et al., 2003). Since the discovery of symbionts in E. fetida
nephridia, several studies regarding bacterial colonization of earthworm nephridia have been reported
[(Davidson and Stahl, 2008), (Pinel et al., 2008)].
Some active phyla in gut contents of earthworms were detected as Acidobacteria (Acidobacteriales,
Acidobacteriaceae), Actinobacteria [(Byzov et al., 2009), (Wust, 2011), (Zhang et al., 2013)] (Acidimicrobiales,
Acidimicrobiaceae, Iamiaceae, Actinomycetales, Actinosynnemataceae, Beutenbergiaceae, Cellulomonadaceae,
Cryptosporangiaceae,
Frankiaceae,
Intrasporangiaceae,
Microbacteriaceae,
Micrococcaceae,
Micromonosporaceae,
Mycobacteriacae,
Nakamurellaceae,
Nocardiaceae,
Nocardioidaceae,
Propionibacteriaceae, Pseudonocardiaceae, Sporichthyaceae, Streptomycetaceae, Rubrobacterales,
Rubrobacteraceae,
Solirubrobacterales,
Patulibacteraceae),
Bacteroidetes
(Flavobacteriales,
Flavobacteriaceae, Sphingobacteriales [(Byzov et al., 2009), (Wust, 2011), (Sumathi and Thaddeus, 2013)],
Chitinophagaceae, Flexibacteraceae), Chloroflexi, Cyanobacteria, Firmicutes (Bacillales, Bacillaceae [(Byzov
et al., 2009), (Wust, 2011), (Picon and Teisaire 2012), (Sumathi and Thaddeus, 2013), (Zhang et al., 2013)],
‘Paenibacillaceae’ (Byzov et al., 2007), ‘Lachnospiraceae’, ‘Peptostreptococcaceae’, Veillonellaceae),
Gemmatimonadetes (Gemmatimonadales, Gemmatimonadaceae), Nitrospirae (Nitrospirales, Nitrospiraceae),
Planctomycetes (Planctomycetales, Planctomycetaceae), Proteobacteria-α-Proteobacteria (Caulobacterales,
Caulobacteraceae,
Rhizobiales,
Beijerinkiaceae,
Bradyrhizobiaceae,
Hyphomicrobiaceae,
Methylobacteriaceae, Methylocystaceae, Phylobacteriaceae, Xanthobacteraceae, Rhodobacteriales,
Rhodobacteriaceae,
Rhodospirillales,
Acetobacteraceae,
Rhodospirillaceae)-β-Proteobacteria
(Burkholderiales, Alcaligenaceae, Oxalobacteraceae)-ϒ-Proteobacteria (Aeromonadales, Aeromonadaceae,
Alteromonadales, Shewanellaceae, Legionellales, Legionellaceae, Pseudomonadales, Pseudomonadaceae
[(Byzov et al., 2009), (Wust, 2011), (Picon 2012), (Ihssen et al., 2003)], Xanthomonadales, Sinobacteriaceae,
Xanthomonadaceae)-Δ-Proteobacteria (Myxococcales, Cystobacteraceae, Polyangiaceae) [(Byzov et al.,
2009), (Wust, 2011), (Zhang et al., 2013)], Tenericutes, Verrucomicrobia (Opitutales, Opitutaceae,
Verrucomicrobiales) (Wust, 2011).
Edward and Fletcher (1988) showed that the number of bacteria and ‘actinomycetes’ contained in the
ingested material by earthworms increased up to 1000-fold by transit through the gut (Sinha et al.,2008).
Earthworms are considered as natural bioreactors in which microorganisms proliferate and provide
favorable conditions for the biodegradation of wastes (Munnoli et al., 2010). Stimulation of microbial activity
by earthworms for biodegradation of chemical contaminants in soil has been reported by several authors (Aira
and Dominguez, 2011). In the first stages of organic matter decomposition, the relationships established
between earthworms and microorganisms are close to some kind of mutualism, however this kind of
relationship could occur outside of the earthworms’ body and in their castings (Aira et al., 2007).
The presence of worm-worked material in the fresh organic matter will result in an inoculum of different
microorganisms and nutrients which interacts with microbial communities in fresh organic matter. Inoculation
of worm-worked substrates caused significant increases in microbial biomass and enzyme activities (βglucosidase, cellulase, phosphatase and protease) (Aira and Dominguez, 2011).
Although, not all the species develop mutualistic relationships with the ingested microorganisms.
Cellobiase and cellulase found in intestinal contents of Pontoscolex corethi-urus Müll. from Palma Sola,
Veracruz (Mexico) were produced by ingested soil microflora since they were not found in gut tissue culture.
Polyplieretinza eloiagata Pen. From Sainte Anne (Martinique), Hyperiodrilus africurzus Bedd. and
Diclzognster terrae nigrae Omo. et Vld. from Lamto (Côte d’Ivoire) possess a complete enzymatic system for
hydrolyzing cellulose (Lattaud et al., 1999).
5. The significance of gut produced enzymes in degradation processes:
The guts of herbivorous animals, invertebrates, and insects have attracted a great deal of interests as sources
of various aerobic and anaerobic microorganisms that produce novel fibrolytic enzymes with unique
characteristics with respect to their molecular structure, catalytic activity, and/or substrate specificity (Kim et
al., 2011).
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Whether it is the earthworms, microorganisms stimulated in their gut or a collective action of both
organisms that are responsible for the mineralization is still controversial (Blouin et al., 2013). Enzyme
activities and contents of nutrients and organic matter of surrounding soil were compared with the
corresponding properties of earthworm casts (Kizilkiya and Hepsen, 2004).
Enzymes screened in the gut were amylases, endoglucanase, cellulase, sucrase and protease. Lactobacillus
viridescense, L. minor and Bacillus pumilus, B. licheniformis and Flavobacterium were also identified (Sumathi
and Thaddeus, 2013).
Contaminants could be degraded by enzymatic activity called ‘Cytochrome P 450’ system in earthworms
(Sinha et al., 2008). Carboxylesterases (CbEs) are key enzymes in pesticide detoxification which are involved in
the biochemical mechanism for pesticide resistance in some pest species. The natural tolerance of earthworms
against pesticide toxicity was examined. The earthworms are capable to secrete pesticide-detoxifying enzymes
for a set of (eco)toxicological implications and environmental applications (Sanchez-Hernandez et al., 2009).
The tissue-specific response of ChE and carboxylesterase (CE) activities in Lumbricus terrestris experimentally
exposed to chlorpyrifos-spiked field soils was tested in another study (Vejares et al., 2010).
A study was carried out to evaluate the biochemical activity in different regions of earthworm gut and
vermireactors through the assay of hydrolase (cellulase, phosphatase) and dehydrogenase activities. It is
believed that the dehydrogenase, hydrolytic activities and microflora provide a clear indication of the dynamics
of organic matter degradation (Kumar et al., 2010).
Cellulolysis occurs as the result of the combined action of fungi and bacteria with different requirements.
Earthworms influence decomposition because the guts of some species possess cellulolytic activity. As fungi
may be part of the diet of earthworms, the activity of E. fetida lead to fungal growth during vermicomposting.
The activation of microorganisms in the intestine of earthworms leads to a more intense and efficient
cellulolysis during vermicomposting of organic wastes [(Aira et al., 2006), (Nazaki et al., 2009)]. It is not well
known whether the origin of those cellulases are the earthworm themselves or their symbionts. In a case study,
zymogram analysis suggested that one cellulase (endo-β-1, 4-glucanase, EC3.2.1.4) mainly digested cellulose in
Pheretima hilgendorfi. These results strongly suggested that the earthworm has the ability to produce the
endogenous and functional mid-foregut cellulase and use this cellulase with the support of intestinal caecum
(Nazaki et al., 2009).
Endosymbiotic microbes produce extracellular enzymes that degrade cellulose and phenolic compounds,
enhancing the degradation of ingested material. Decomposition is also enhanced through the action of
endosymbiotic microbes that reside in the gut of earthworms.
ManK with high catalytic activity is a novel endo-β-1,4-mannanase with unique substrate specificity for
degrading mannose-based substrates has been isolated from the digestive tract of E. fetida from
Cellulosimicrobium sp. strain HY-13 (Kim et al., 2011).
The activity of amylase, cellulase, xylanase, cellobiase, endoglucanase, acid phosphatase, alkaline
phosphatase and nitrate reductase were assayed in the gut E. eugeniae and E. fetida. Enzyme activity in
earthworms is regionally specialized and influenced by physiological state, age and microorganisms. Digestive
enzymes like cellulase, xylanase, acid phosphatase and alkaline phosphatase were found to be more in the gut of
E. fetida as compared to E. eugeniae. While the activity of amylase, cellobiase, endoglucanase and nitrate
reductase was higher in the gut of E. eugeniae as compared to E. fetida. Amylase, cellulase, acid phosphatase,
alkaline phosphatase and nitrate reductase were secreted in the gut of the earthworms due to increased presence
of microorganisms in it. Enzymes produced jointly by earthworms and gut microflora are supposed to play a
central role in the process of digestion and humification of soil organic matter (Prabha et al., 2007).
6. Conclusion:
Regarding to different methodologies and approaches for removing wastes from environment, the
environmental problems should be easily solved. Although, most of these approaches are not solely efficient.
They could be used consecutively and one by one or even simultaneously. For example, co-application of
vermitechnology and phytoremediation.
Vermiremediation and applying earthworms in this track, is convenient and eco-friendly. The microbial
load in the earthworms’ body and cast could be stimulated and their enzymes could be engineered in order to
achieve higher yields in biodegradation and biodecomposition of wastes.
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