Agriculture Reference
In-Depth Information
plant growth-promoting rhizospheric bacteria such as
Pseudomonas, Rhizo-
bium, Bacillus, Azosprillium, Azotobacter,
etc. along with rhizospheric soil,
and they might get activated or increased due to the ideal micro-environ-
ment of the gut. Therefore earthworm activity increases the population of
plant growth-promoting rhizobacteria (PGPR) (Sinha et al. 2010). This spe-
cific group of bacteria stimulates plant growth directly by solubilization of
nutrients (Ayyadurai et al. 2007; Ravindra et al. 2008), production of growth
hormone, 1-aminocyclopropane-1-carboxylate (ACC) deaminase (Correa et
al. 2004), nitrogen fixation (Han et al. 2005), and indirectly by suppressing
fungal pathogens. Antibiotics, fluorescent pigments, siderophores and fun-
gal cell-wall degrading enzymes namely chitinases and glucanases (Han et
al. 2005; Sunish et al. 2005; Ravindra et al. 2008; Jha et al. 2009; Pathma
et al. 2010; Pathma et al. 2011a, b) produced by bacteria mediate the fungal
growth-suppression. Earthworms are reported to have association with such
free living soil bacteria and constitute the drilosphere (Ismail 1995). Earth-
worm microbes mineralize the organic matter and also facilitate the chela-
tion of metal ions (Pizl and Novokova 1993; Canellas et al. 2002). Gut of
earthworms
L. terrestris, Allolobophora caliginosa
and
Allolobophora ter-
restris
were reported to contain higher number of aerobes compared to soil
(Parle 1963). Earthworms increased the number of microorganisms in soi1
as much as five times (Edwards and Lofty 1977) and the number of bacteria
and 'actinomycetes' contained in the ingested material increased upto 1,000
fold while passing through their gut (Edwards and Fletcher 1988). Similar
increase was observed in plate counts of total bacteria, proteolytic bacteria
and actinomycetes by passage through earthworms gut (Parle 1963; Daniel
and Anderson 1992; Pedersen and Hendriksen 1993; Devliegher and Vers-
traete 1995). Similarly microbial biomass either decreased (Bohlen and Ed-
wards 1995; Devliegher and Verstraete 1995), or increased (Scheu 1992) or
remained unchanged (Daniel and Anderson 1992) after passage through the
earthworm gut. An oxalate-degrading bacterium
Pseudomonas oxalaticus
was isolated from intestine of
Pheretima
species (Khambata and Bhat 1953)
and an actinomycete
Streptomyces lipmanii
was identified in the gut of
Eise-
nia lucens
(Contreras 1980). Scanning electron micrographs provided evi-
dence for endogenous microflora in guts of earthworms,
L. terrestris
and
Octolasion cyaneum
(Jolly et al. 1993). Gut of
E. foetida
contained various
anaerobic N
2
-fixing bacteria such as
Clostridium butyricum, C. beijerinckii
