Effects of T4 Lysozyme Release from Transgenic Potato Roots on Bacterial Rhizosphere Communities Are Negligible Relative to Natural Factors

Abstract

Rhizosphere bacterial communities of two transgenic potato lines which produce T4 lysozyme for protection against bacterial infections were analyzed in comparison to communities of wild-type plants and transgenic controls not harboring the lysozyme gene. Rhizosphere samples were taken from young, flowering, and senescent plants at two field sites in three consecutive years. The communities were characterized in a polyphasic approach. Cultivation-dependent methods included heterotrophic plate counts, determination of species composition and diversity based on fatty acid analysis of isolates, and community level catabolic profiling. Cultivation-independent analyses were based on denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments amplified from rhizosphere DNA using primers specific for Bacteria, Actinomycetales, or ␣-or ␤-Proteobacteria. Several bands of the DGGE patterns were further characterized by sequence analysis. All methods revealed that environmental factors related to season, field site, or year but not to the T4 lysozyme expression of the transgenic plants influenced the rhizosphere communities. For one of the T4 lysozymeproducing cultivars, no deviation in the rhizosphere communities compared to the control lines was observed. For the other, differences were detected at some of the samplings between the rhizosphere community structure and those of one or all other cultivars which were not attributable to T4 lysozyme production but most likely to differences observed in the growth characteristics of this cultivar.

Oilseed rape cultivation increases the microbial richness and diversity in soils contaminated with cadmium

“…C0, C1, and C2 experimental treatments cropped with oilseed rape in 0, 1, and 2 mg/kg Cd, respectively CK 1 and CK 2 , and C 1 and C 2 display the maximum overlap in bacteria, which demonstrates that the commonality of bacterial communities was improved with the rise of Cd concentration. The extra OTUs in C group than CK group suggest that oilseed rape can promote or control bacterial or fungal diversity, which have been also reported before (Lottmann et al 1999;Heuer et al 2002;Larkin 2003;Rasche et al 2006). So, this reflects that B. napus is able to alleviate the Cd toxicity to microbes so that the cultivation of B. napus is a valid method to restoring the soil bacterial diversity and enrich bacterial population structure.…”

Comunidade bacteriana como indicadora do efeito de feijoeiro geneticamente modificado sobre organismos não alvo

“…As amostras da comunidade rizosférica na primeira e segunda coletas foram representadas com 90% de participação nos agrupamentos na menor faixa de similaridade avaliada (S = 60) e com 30% na maior (S = 80), enquanto as amostras da comunidade não rizosférica só foram representadas na menor faixa de similaridade (S = 60), com 65% de participação na primeira coleta e 80% na segunda (Tabelas 1 e 2). Essa diferença pode ser causada pelo efeito seletivo da rizosfera, já relatado por outros autores (Costa et al, 2000;Gomes et al, 2001;Milling et al, 2004), sem, com isso, descartar a possibilidade de variação em função do emprego de métodos distintos para Tabela 1. Grupos formados com valores de similaridade (S) igual ou superior a 60 e 80% na primeira coleta (26 dias após o plantio, estádio V4 do feijoeiro), em diferentes fontes de amostras da comunidade bacteriana.…”

“…Segundo Heuer et al (2002), a amplificação de grupos específicos aumenta a sensibilidade da análise por DGGE. Em outro estudo, que avaliou o efeito da solarização sobre a comunidade bacteriana, foi observada distinção mais evidente entre o solo solarizado e não solarizado quando se analisaram os perfis de DGGE do subgrupo alfa (α) do filo Proteobacteria (Gelsomino & Cacco, 2006).…”

“…Em outro estudo, que avaliou o efeito da solarização sobre a comunidade bacteriana, foi observada distinção mais evidente entre o solo solarizado e não solarizado quando se analisaram os perfis de DGGE do subgrupo alfa (α) do filo Proteobacteria (Gelsomino & Cacco, 2006). Porém, outros autores, ao comparar plantas transgênicas, observaram a mesma tendência entre os perfis de comunidade bacteriana total e grupos específicos, como alfa e beta, de Proteobacteria, actinomicetos e Pseudomonas (Heuer et al, 2002;Milling et al, 2004).…”

Impact environnemental des cultures transgéniques

“…Alors que les pratiques culturales et les choix variétaux ont une influence marquée sur la microflore (Buckley et Schmidt 2001; Clegg et al 2003;Siciliano et al 1998), les cultures transgéniques montrent en général des effets négligeables sur l'incidence relative des populations microbiennes et animales du sol, ou encore sur le déroulement de processus comme la respiration microbienne ou la décomposition de la matière organique (Kowalchuk et al 2003). Sur une base comparative, plusieurs études démontraient en outre que des variables comme le climat, le site de culture, le génotype de la plante ou même son stade de développement ont un impact beaucoup plus marqué sur les populations du sol que l'utilisation ou non de variétés transgéniques exprimant des caractères recombinants spécifiques comme la résistance aux insectes, la résistance aux agents phytopathogènes ou la tolérance aux herbicides (Dunfield et Germida 2001; Griffiths et al 2000; Gyamfi et al 2002;Heuer et al 2002;Lottmann et Berg 2001;Lukow et al 2000).Dans les années à venir, le développement de lignées transgéniques produisant des protéines à fonctions biologiques variées souvent moins spéci-fiques rendra néanmoins justifiée la poursuite des études sur les interactions entre les cultures modifiées et les organismes du sol. En pratique, la détec-tion et la caractérisation des diverses interactions possibles seront facilitées par un raffinement parallèle des approches méthodologiques adaptées à l'étude des organismes du sol.…”