Multitrophic Interaction in the Rhizosphere of Maize: Root Feeding of Western Corn Rootworm Larvae Alters the Microbial Community Composition

BACKGROUND: Larvae of the Western Corn Rootworm (WCR) feeding on maize roots cause heavy economical losses in the US and in Europe. New or adapted pest management strategies urgently require a better understanding of the multitrophic interaction in the rhizosphere. This study aimed to investigate the effect of WCR root feeding on the microbial communities colonizing the maize rhizosphere. METHODOLOGY/PRINCIPAL FINDINGS: In a greenhouse experiment, maize lines KWS13, KWS14, KWS15 and MON88017 were grown in three different soil types in presence and in absence of WCR larvae. Bacterial and fungal community structures were analyzed by denaturing gradient gel electrophoresis (DGGE) of the 16S rRNA gene and ITS fragments, PCR amplified from the total rhizosphere community DNA. DGGE bands with increased intensity were excised from the gel, cloned and sequenced in order to identify specific bacteria responding to WCR larval feeding. DGGE fingerprints showed that the soil type and the maize line influenced the fungal and bacterial communities inhabiting the maize rhizosphere. WCR larval feeding affected the rhiyosphere microbial populations in a soil type and maize line dependent manner. DGGE band sequencing revealed an increased abundance of Acinetobacter calcoaceticus in the rhizosphere of several maize lines in all soil types upon WCR larval feeding. CONCLUSION/SIGNIFICANCE: The effects of both rhizosphere and WCR larval feeding seemed to be stronger on bacterial communities than on fungi. Bacterial and fungal community shifts in response to larval feeding were most likely due to changes of root exudation patterns. The increased abundance of A. calcoaceticus suggested that phenolic compounds were released upon WCR wounding

Accumulation of Sulfonamide Resistance Genes in Arable Soils Due to Repeated Application of Manure Containing Sulfadiazine ▿

Two soils were amended three times with pig manure. The abundance of sulfonamide resistance genes was determined by quantitative PCR 2 months after each application. In both soils treated with sulfadiazine-containing manure, the numbers of copies of sul1 and sul2 significantly increased compared to numbers after treatments with antibiotic-free manure or a control and accumulated with repeated applications

DGGE fingerprints of ITS fragments PCR-amplified from TC DNA extracted from soil and rhizosphere samples and corresponding UPGMA dendrogram.

<p>(A) DGGE fingerprints of dominant fungal populations in Haplic Chernozem (HC) soil and in the maize rhizosphere of KWS13, KWS14, KWS15 and MON88017 grown in the same soil type. The independent replicates are labeled 1 to 4. M: fungal marker prepared with the ITS fragments amplified from <i>Verticillium nigrescens</i>, <i>Basidiomycete</i> sp., <i>Trichoderma</i> sp., <i>Doratomyces</i> sp., <i>Verticillium dahliae</i>, <i>Penicillium canescens</i>, <i>Fusarium graminearum</i>, <i>Nectria haematococca</i>, <i>Fusarium solani</i>, <i>Fusarium redolens</i>, and <i>Sclerotinia sclerotiorum</i>. Arrows indicate maize genotype effects. (B) UPGMA dendrogram constructed using the Pearson correlation coefficient. The scale shows similarity values. Rh: rhizosphere samples.</p

Percentage dissimilarity (<i>D</i>) and significant values (<i>P</i>) of rhizosphere fungal or bacterial fingerprints between different maize lines (KWS13, KWS14, KWS15 and MON88017) grown in the soil types Haplic Chernozem, Haplic Luvisol, and Eutric Vertisol.

<p>Values of <i>P</i><0.05 indicate significant differences between rhizosphere samples of different maize lines grown in the same soil type. Permutation testing was done with 10.000 simulations. Bold values indicate significant differences.</p

Percentage dissimilarity (<i>D</i>) and significance values (<i>P</i>) of rhizosphere fungal or bacterial fingerprints between maize lines in presence and in absence of WCR larval feeding (Larvae+/−), in the soil types Haplic Chernozem, Haplic Luvisol, and Eutric Vertisol.

<p><i>P</i> values<0.05 indicate significant differences between rhizosphere samples of the same maize line grown with and without larval feeding in the same soil type. Values obtained by Permutation testing using 10.000 simulations. Values in bold show significant values.</p

UPGMA dendrograms of DGGE fingerprints of 16S rRNA gene and ITS fragments PCR-amplified from TC DNA of three different soil types.

<p>HC: Haplic Chernozem; HL: Haplic Luvisol; EV: Eutric Vertisol. A: UPGMA of fungal fingerprints; B: UPGMA of bacterial fingerprints. Independent replicates are labeled 1 to 4. The dendrograms were constructed using the Pearson correlation coefficient. The scale shows similarity values.</p