Lose-lose consequences of bacterial community-driven invasions in soil.

BACKGROUND: Community-driven invasion, also known as community coalescence, occurs widely in natural ecosystems. Despite that, our knowledge about the process and mechanisms controlling community-driven invasion in soil ecosystems is lacking. Here, we performed a set of coalescence experiments in soil microcosms and assessed impacts up to 60 days after coalescence by quantifying multiple traits (compositional, functional, and metabolic) of the invasive and coalescent communities. RESULTS: Our results showed that coalescences significantly triggered changes in the resident community's succession trajectory and functionality (carbohydrate metabolism), even when the size of the invasive community is small (~ 5% of the resident density) and 99% of the invaders failed to survive. The invasion impact was mainly due to the high suppression of constant residents (65% on average), leading to a lose-lose situation where both invaders and residents suffered with coalescence. Our results showed that surviving residents could benefit from the coalescence, which supports the theory of "competition-driven niche segregation" at the microbial community level. Furthermore, the result showed that both short- and long-term coalescence effects were predicted by similarity and unevenness indexes of compositional, functional, and metabolic traits of invasive communities. This indicates the power of multi-level traits in monitoring microbial community succession. In contrast, the varied importance of different levels of traits suggests that competitive processes depend on the composition of the invasive community. CONCLUSIONS: Our results shed light on the process and consequence of community coalescences and highlight that resource competition between invaders and residents plays a critical role in soil microbial community coalescences. These findings provide valuable insights for understanding and predicting soil microbial community succession in frequently disturbed natural and agroecosystems. Video Abstract.

Bridging ecological assembly process and community stability upon bacterial invasions.

Understanding the link between microbial community stability and assembly processes is crucial in microbial ecology. Here, we investigated whether the impact of biotic disturbances would depend on the processes controlling community assembly. For that, we performed an experiment using soil microcosms in which microbial communities assembled through different processes were invaded by Escherichia coli. We show that the ecological assembly process of the resident community plays a significant role in invader-resident competition, invader survival, and compositional stability of the resident community. Specifically, the resident communities primarily assembled through stochastic processes were more susceptible to invader survival. Besides, E. coli invasion acts as a biotic selection pressure, leading to competition between the invader and resident taxa, suppressing the stochasticity in the resident community. Taken together, this study provides empirical evidence for the interpretation of microbial community assemblage on their (potential) ecosystem functions and services, such as the prevention of pathogen establishment and the pathogenic states of soil microbiomes.

Use of endophytic diazotrophic bacteria as a vector to express the cry3A gene from "Bacillus thuringiensis"

The goal of this study was to evaluate the potential of endophytic diazotrophic bacteria as a vector to express a 'cry' gene from "Bacillus thuringiensis", envisaging the control of pests that attack sugarcane plants. The endophytic nitrogen-fixing bacteria "Gluconacetobacter diazothophicus" strain BR11281 and "Herbaspirillum seropedicae" strain BR11335 were used as models. The 'cry3A' gene was transferred by conjugation using a suicide plasmid and recombinant strains were selected by their ability to fix nitrogen in semi-solid N-free medium. The presence of the 'cry' gene was detected by Southern-blot using an internal fragment of 1.0 kb as a probe. The production of (delta)-endotoxin by recombinant "H. seropedicae" strain was detected by dot blot while for "G. diazotrophicus" the Western-blot technique was used. In both cases, a specific antibody raised against the "B. thuringiensis" toxin was applied. The (delta)-endotoxin production showed by the "G. diazotrophicus" recombinant strain was dependent on the nitrogen fixing conditions since the 'cry3A' gene was fused to a 'nif' promoter. In the case of "H. seropedicae" the (delta)-endotoxin expression was not affected by the promoter ('rhi') used. These results suggest that endophytic diazotrophic bacteria can be used as vectors to express entomopathogenic genes envisaging control of sugarcane pests