This study investigated the development of fungal community composition in arable soil during the degradation of straw residue. We explored the short-term responses of the fungal community over 28 days of decomposition in soil using culture-independent polymerase chain reaction in combination with a clone library and denaturing gradient gel electrophoresis (DGGE). Fungal cellobiohydrolase I (cbhI) genes in the soil were also characterized, and their diversity suggested the existence of a different cellulose decomposer. The DGGE profiles based on fungal internal transcribed spacer analysis showed different successions of fungal populations during residue decomposition. Members of Lecythophora and Sordariales were dominant in the early succession, while Hypocrea and Engyodontium were better adapted in the late succession. The succession of fungal communities might be related to changes of residue quality during decomposition. Collectively, sequences assigned to Ascomycota members were dominant at different stages of the fungal succession during decomposition, revealing that they were key drivers responsible for residue degradation in the arable soil tested.

Many Gram-negative plant pathogenic bacteria employ a N-acylhomoserine lactone (AHL)-based quorum sensing (QS) system to regulate their virulence traits. A sustainable biocontrol strategy has been developed using quorum quenching (QQ) bacteria to interfere with QS and protect plants from pathogens. Here, the prevalence and the diversity of QQ strains inhabiting tobacco leaf surfaces were explored. A total of 1177 leaf-associated isolates were screened for their ability to disrupt AHL-mediated QS, using the biosensor Chromobacterium violaceum CV026. One hundred and sixty-eight strains (14%) are capable of interfering with AHL activity. Among these, 106 strains (63%) of the culturable quenchers can enzymatically degrade AHL molecules, while the remaining strains might use other QS inhibitors to interrupt the chemical communication. Moreover, almost 79% of the QQ strains capable of inactivating AHLs enzymatically have lactonase activity. Further phylogenetic analysis based on 16S rDNA revealed that the leaf-associated QQ bacteria can be classified as Bacillus sp., Acinetobacter sp., Lysinibacillus sp., Serratia sp., Pseudomonas sp., and Myroides sp. The naturally occurring diversity of bacterial quenchers might provide opportunities to use them as effective biocontrol reagents for suppressing plant pathogen in situ.

No abstract

The phyllosphere is inhabited by large populations of epiphytic bacteria that are able to modulate their phenotypes and behavior by quorum sensing (QS). However, the impact of acyl-homoserine lactones (AHLs) involved in QS on the ecology of bacteria in their natural habitat remains unclear. Therefore, we used a bioassay and liquid chromatographyemass spectrometry to detect AHLs in the tobacco phyllosphere. Our results identified several AHLs in the tobacco phyllosphere, the majority of which were short-chain AHLs. Furthermore, the addition of an exogenous N-(3-oxohexanoyl) homoserine lactone (3OC6HSL), which is seen in the naturally occurring tobacco phyllosphere, generated variability in the composition of the bacterial community as determined by denaturing gradient gel electrophoresis (DGGE) analysis and phospholipid fatty acid (PLFA) analysis. Notably, the ratio of Gram-positive (GP) bacteria increased in response to treatment with 1 mM AHL, but decreased incipiently when treated with 10 mM AHL. These observations provide insight into the composition of the leaf-colonizing epiphyte community responsible for AHLs, particularly GP bacteria as they do not use AHLs as signaling molecules for QS.