Antagonism and Antimicrobial Capacity of Epiphytic and Endophytic Bacteria against the Phytopathogen Xylella fastidiosa

Abstract

Olive quick decline syndrome (OQDS), which is caused by Xylella fastidiosa, poses a severe threat to the agriculture of Mediterranean countries and causes severe damage to the olive trees in Italy. Since no effective control measures are currently available, the objective of this study was the screening of antagonistic bacteria that are potentially deployable as biocontrol agents against X. fastidiosa. Therefore, two approaches were used, i.e., the evaluation of the antagonistic activity of (i) endophytic bacteria isolated from two different cultivars of olive trees (Leccino and Ogliarola salentina) and (ii) epiphytic bacteria isolated from the phyllospheres of different host plant species of X. fastidiosa. In vitro dual culture tests showed that 12 out of 200 isolates inhibited X. fastidiosa growth, with appearances of clear zones between 4.0 and 38.6 mm. 16S rRNA gene sequencing revealed different species of the genera Paenibacillus, Bacillus, Pantoea, Microbacterium, Stenotrophomonas, Delftia, and Pseudomonas. Furthermore, an investigation for antimicrobial activity identified 5 out of the 12 antagonistic bacteria, Paenibacillus rigui, Bacillus subtilis, Bacillus pumilus, Microbacterium oxydans, and Stenotrophomonas rhizophila, that were able to produce culture filtrates with inhibitory activities. Our results are promising for further investigation to develop an eco-sustainable strategy to control X. fastidiosa using biocontrol agents or their secreted metabolites.

Exploring the phytobeneficial and biocontrol capacities of endophytic bacteria isolated from hybrid vanilla pods

“…Bacteria competing in the environment with other micro-organisms possess direct antagonistic activities against pathogens through hyperparasitism or antibiosis and others through competition for nutrients [23], [24]. On the other hand, direct antagonists, which actively produce a broad spectrum of antimicrobial metabolites, are considered most effective against competitors, allowing advantages for antibiotic-producing microorganisms in resource-limited environments [25]. Several studies have been carried out on the phytobenefic properties of orchid endophytes [26].…”

Antimicrobial profile of the culturable olive sporobiota and its potential as a source of biocontrol agents for major phytopathogens in olive agriculture

“…Reports have in particular alluded towards the potential of Bacillus spp. as antimicrobial agent for the most detrimental plant pests 12–14 …”

“…Our group recently isolated and characterized the spore‐forming community of Spanish olive groves, incorporating both soil and leaf (surface and internal) inhabitants, and termed the culturable olive sporobiota 26 . Due to their extraordinary antimicrobial potential, low‐price/large‐scale production and stability of endospores, Bacillus and related spore forming genera hence present a great potential as biological pest control agent 12,23,26 …”

“…as antimicrobial agent for the most detrimental plant pests. [12][13][14] Members of the Bacillus genus are one of the predominant microbial communities of the soil, playing an important role in maintaining healthy soils conducive for plant growth and nutrition. 15 The gram-positive Bacillus spp.…”

“…26 Due to their extraordinary antimicrobial potential, lowprice/large-scale production and stability of endospores, Bacillus and related spore forming genera hence present a great potential as biological pest control agent. 12,23,26 Given the previous considerations, in this study we first aimed to characterize the antimicrobial profile of the culturable olive sporobiota 26 against a range of human and food pathogens. We then set out to identify novel potential biocontrol agents against X. fastidiosa and V. dahliae.…”