Effects of the cultivation of genetically modified Bt crops on nontarget soil organisms - Microbial Ecology in Sustainable Agroecosystems - page 172

Blackwood and Buyer, 2004; Brusetti et al., 2004; Devare et al., 2004; Wu et al., 2004a, 2004b;
Baumgarte and Tebbe, 2005; Fang et al., 2005; Flores et al., 2005; Griffiths et al., 2005, 2006;
Rui et al., 2005; Shen et al., 2006; Devare et al., 2007; Griffiths, Heckmann, et al., 2007;
Lamarche and Hamelin, 2007; Icoz and Stotzky, 2008a; Liu et al., 2008; Oliveira et al., 2008;
Hu et al., 2009; Lu et al., 2010a, 2010b; Miethling-Graff et al., 2010; Tan et al., 2010; Li et al.,
2011; Xue et al., 2011). When purified Bt proteins were added to soil, there was no effect
of Cry1Ab on culturable bacteria (Donegan et al., 1995), on the population size of cultur-
able heterotrophic bacteria (Ferreira et al., 2003), or on microbial community structure as
determined by phospholipid fatty acid (PLFA) analysis (Griffiths, Heckmann, et al., 2007).
There was also no effect of the addition of purified Cry1Ac protein on culturable inorganic
phosphate-dissolving or potassium-dissolving bacteria (Rui et al., 2005). Similarly, there
was no effect of purified Cry1Ab, Cry3A, or Cry4 protein on growth of selected bacteria
(eight gram-negative five gram-positive bacteria, and a cyanobacterium) in vitro, in pure
and mixed cultures, using dilution, disk diffusion, and sporulation assays (Koskella and
Stotzky, 2002).
In studies in which biomass of Bt plants was added to soil, there were generally no
negative effects on the numbers of culturable bacteria (Saxena and Stotzky, 2001a; Flores
et al., 2005) or on soil microbial community structure as determined by DGGE (Tan et al.,
2010). In decomposition studies, there was no difference in bacterial growth on Bt maize
versus non- Bt maize leaves; however, bacterial growth was lower on the feces of wood lice
( Porcellio scaber ) that were fed Bt maize leaves (Escher et al., 2000). There were no negative
effects on bacterial decomposer communities of litterbags containing Bt maize biomass
(cobs, roots, or stems plus leaves) (Xue et al., 2011) or Bt rice biomass (straw or roots) (Lu et al.,
2010a; Lu et al., 2010b) as demonstrated through terminal restriction fragment length poly-
morphism (T-RFLP) analysis or a direct toxic effect on culturable bacteria in soil amended
with Bt rice straw (Wu et al., 2004b). When ground, dried roots and shoots of Bt cotton or
non- Bt cotton were mixed with field-collected soil and incubated for 2 months, there was
no significant difference in urease, phosphatase, dehydrogenase, phenol oxidase, or pro-
tease activities between the Bt and non- Bt biomass treatments; however, enzyme activity
was stimulated by the addition of both Bt and non- Bt cotton biomass (Shen et al., 2006).
In soil cultivated with Bt or non- Bt maize in the laboratory, Saxena and Stotzky (2001a)
detected no significant difference in the CFUs of culturable bacteria (including actino-
mycetes) between rhizosphere soil of Bt and non- Bt maize after 45 days or between soil
amended with Bt and non- Bt maize biomass (Saxena and Stotzky, 2001a). When Bt maize
and non- Bt maize were cultivated in a growth chamber, there was no difference in bacte-
rial community structure detected between bulk soil of Bt and non- Bt maize using PLFA
analysis (Blackwood and Buyer, 2004). Although a small difference in rhizosphere bacte-
rial community structure was detected in the Bt versus non- Bt maize cultivated soil (as
determined by community-level physiological profiles [CLPPs]), the differences in the rhi-
zosphere microbial community between the Bt and non- Bt maize cultivated soil were most
influenced by soil type and texture (Blackwood and Buyer, 2004).
In greenhouse studies, there was also no difference in rhizosphere bacterial commu-
nity structure in soil cultivated with Bt maize and non- Bt maize as determined by commu-
nity-level catabolic profiling (CLCP) (Brusetti et al., 2004). However, when soil was treated
with a root exudate solution collected from Bt or non- Bt maize plants grown hydroponi-
cally, differences in bacterial community structure were detected by automated ribosomal
intergenic spacer analysis (ARISA), suggesting that changes in root exudates may influ-
ence the rhizosphere bacterial community more than the expression of Bt protein (Brusetti
et al., 2004). Using DGGE analysis and 16S rRNA gene sequences, Tan et al. (2010) detected