Effects of the Secondary Metabolite Producing Pseudomonas fluorescens CHA0 on Soil Protozoa and Bacteria

Bacteria producing secondary metabolites with antagonistic effects on fungal pathogens have received attention during the last decades as an alternative to chemical pesticides. They, however, might also have effects on indigenous soil organisms like bacteria and protozoa, the latter ones being among the most important grazers of bacteria in soil. The present study reports on the effect of the potential biocontrol agent Pseudomonas fluorescens CHA0 and its genetically modified derivative CHA0/pME3424 on indigenous soil bacteria and protozoa in a soil system. CHA0/pME3424 overproduces two of the secondary metabolites produced by CHA0: the polyketide antibiotics pyoluteorin (Plt) and 2,4-diacetylphloroglucinol (DAPG). P. fluorescens CHA0/gfp1 and CHA0/pME3424 both negatively affected the abundance of soil bacteria and protozoa and the genetic community structure of Kinetoplastida studied by PCR-DGGE. The negative effects were detectable after 14 days but were decreasing and are expected to be temporary. The overproducer of secondary metabolites did not differ in effect from the wild type. The soil respiration and bacterial genetic community structure were not significantly affected. The study shows the soil bacteria and protozoa to be temporary affected by bacteria producing secondary metabolites, which can have implications for nutrient-cycling in soil and environmental risks of biocontrol agents

Factors Affecting Vegetable Growers’ Exposure to Fungal Bioaerosols and Airborne Dust

We have quantified vegetable growers’ exposure to fungal bioaerosol components including (1→3)-β-d-glucan (β-glucan), total fungal spores, and culturable fungal units. Furthermore, we have evaluated factors that might affect vegetable growers’ exposure to fungal bioaerosols and airborne dust. Investigated environments included greenhouses producing cucumbers and tomatoes, open fields producing cabbage, broccoli, and celery, and packing facilities. Measurements were performed at different times during the growth season and during execution of different work tasks. Bioaerosols were collected with personal and stationary filter samplers. Selected fungal species (Beauveria spp., Trichoderma spp., Penicillium olsonii, and Penicillium brevicompactum) were identified using different polymerase chain reaction-based methods and sequencing. We found that the factors (i) work task, (ii) crop, including growth stage of handled plant material, and (iii) open field versus greenhouse significantly affected the workers’ exposure to bioaerosols. Packing of vegetables and working in open fields caused significantly lower exposure to bioaerosols, e.g. mesophilic fungi and dust, than harvesting in greenhouses and clearing of senescent greenhouse plants. Also removing strings in cucumber greenhouses caused a lower exposure to bioaerosols than harvest of cucumbers while removal of old plants caused the highest exposure. In general, the exposure was higher in greenhouses than in open fields. The exposures to β-glucan during harvest and clearing of senescent greenhouse plants were very high (median values ranging between 50 and 1500 ng m−3) compared to exposures reported from other occupational environments. In conclusion, vegetable growers’ exposure to bioaerosols was related to the environment, in which they worked, the investigated work tasks, and the vegetable crop

State of Knowledge of Soil Biodiversity: Status, Challenges, and Potentialities

This report presents the threats to soil biodiversity and the solutions that soil biodiversity can provide to problems in different fields, including agriculture, environmental conservation, climate change adaptation and mitigation, nutrition, medicine and pharmaceuticals, remediation of polluted sites, and many others. There is increasing attention on the importance of biodiversity for food security and nutrition, especially above-ground biodiversity such as plants and animals. Less attention is being paid to the biodiversity beneath our feet: soil biodiversity. Yet the rich diversity of soil organisms drives many processes that produce food, regenerate soil or purify water. This report is the result of an inclusive process involving more than 300 scientists from around the world under the auspices of FAO's Global Soil Partnership and its Intergovernmental Technical Panel on Soils, the Convention on Biological Diversity, the Global Soil Biodiversity Initiative, and the European Commission

Soil networks become more connected and take up more carbon as nature restoration progresses

Soil organisms have an important role in aboveground community dynamics and ecosystem functioning in terrestrial ecosystems. However, most studies have considered soil biota as a black box or focussed on specific groups, whereas little is known about entire soil networks. Here we show that during the course of nature restoration on abandoned arable land a compositional shift in soil biota, preceded by tightening of the belowground networks, corresponds with enhanced efficiency of carbon uptake. In mid- and long-term abandoned field soil, carbon uptake by fungi increases without an increase in fungal biomass or shift in bacterial-to-fungal ratio. The implication of our findings is that during nature restoration the efficiency of nutrient cycling and carbon uptake can increase by a shift in fungal composition and/or fungal activity. Therefore, we propose that relationships between soil food web structure and carbon cycling in soils need to be reconsidered