Olive Grove Bacteria May Hold Key to Combating Xylella

A research team from the University of Jaén has iden­ti­fied a group of dor­mant bac­te­ria in the leaves and soil of olive trees that pro­tect them from envi­ron­men­tal chal­lenges.

Genetic analy­sis has demon­strated that sev­eral microor­gan­isms pro­vide bio­log­i­cal advan­tages akin to a sec­ondary immune sys­tem. The researchers hope their find­ings may allow for devel­op­ing a nat­ural biopes­ti­cide to com­bat the deadly pathogen Xylella fas­tidiosa.

Xylella fas­tidiosa is believed to have arrived in Italy in 2008 by intro­duc­ing a sin­gle cof­fee plant from Costa Rica.

Xylella fas­tidiosa, which causes the deadly olive quick decline syn­drome, has caused wide­spread out­breaks in Europe over the past 15 years and is esti­mated to have an annual eco­nomic impact of over €5.5 bil­lion.

The bac­terium has proven to be a sig­nif­i­cant chal­lenge to man­age, as there is cur­rently no effec­tive field con­trol method to erad­i­cate it.

In the research arti­cle pub­lished in Microbiology Spectrum, how­ever, the researchers iden­ti­fied a group of bac­te­ria, Bacillus spp., that they believe could hold the key to com­bat­ing the pathogen.

Bacillus species have dis­tinct char­ac­ter­is­tics that make them valu­able for med­ical, biotech­no­log­i­cal and agri­cul­tural appli­ca­tions.

They can be used in bio­fuel, biopoly­mer and bioac­tive mol­e­cule pro­duc­tion. In agri­cul­ture, they can enhance plant growth, serve as biofer­til­iz­ers, stim­u­late growth and con­trol pathogens, mak­ing them promis­ing for sus­tain­able agri­cul­ture.

Bacillus-based biofer­til­iz­ers enhance plant growth and yield by improv­ing nutri­ent avail­abil­ity, nitro­gen fix­a­tion, phos­pho­rus sol­u­bi­liza­tion and the pro­duc­tion of plant growth reg­u­la­tors.

These bac­te­ria can also pro­duce antimi­cro­bial com­pounds, are cost-effec­tive and form spores for sta­bil­ity, offer­ing a nat­ural alter­na­tive to chem­i­cal pes­ti­cides.

Bacillus thuringien­sis is well-known for its insec­ti­ci­dal prop­er­ties, while other species like B. sub­tilis and Bacillus amy­loliq­ue­fa­ciens have been suc­cess­fully used as bio­con­trol agents in var­i­ous com­mer­cial crops.

Moreover, the abil­ity of some Bacillus species to pro­duce bac­te­ri­ocins, antimi­cro­bial pep­tides, shows promise for plant treat­ment.

While these ben­e­fits have already been demon­strated in crops includ­ing wheat, sun­flow­ers and pota­toes, the research con­ducted by the University of Jaén team focused on ana­lyz­ing their pres­ence in Spanish olive groves and their resis­tance to a series of envi­ron­men­tal chal­lenges.

Under the super­vi­sion of Hikmate Abriouel, the team embarked on the SMART-AGRI-SPORE project, a European Marie Curie ini­tia­tive aimed at devel­op­ing a biopes­ti­cide to com­bat Xylella fas­tidiosa. The project involved the analy­sis of 417 bac­te­ria of the genus Bacillus spp. col­lected from olive groves in Jaén and Málaga.

The researchers sought to iden­tify those bac­te­ria capa­ble of form­ing spores and hiber­nat­ing to over­come adverse exter­nal con­di­tions and revive when con­di­tions become favor­able.

These spores act as a pro­tec­tive shield, mak­ing the bac­te­ria resis­tant to extreme tem­per­a­tures, radi­a­tion and harm­ful chem­i­cals. To iso­late those strains with this capa­bil­ity, the team sub­jected their sam­ples to tem­per­a­tures reach­ing 80 ºC, thus erad­i­cat­ing all those not meet­ing the cri­te­rion.

“Faced with an adverse event, such as a lack of nutri­ents in the envi­ron­ment, these bac­te­ria enter a state of rest, like a kind of hiber­na­tion, until the dan­ger dis­ap­pears and they can resume their nor­mal vital func­tions,” explained Julia Manetsberger, one of the paper’s authors.

To fur­ther under­stand the resis­tance of Bacillus spp. to envi­ron­men­tal chal­lenges, the researchers exposed the bac­te­ria to vary­ing quan­ti­ties of antibi­otics and inor­ganic fer­til­iz­ers.

Their resis­tance was nor­mal, sim­i­lar to that of other bac­te­r­ial species. This resilience sug­gests that Bacillus spp. would sur­vive in nature when exposed to such com­monly used agri­cul­tural com­pounds, con­tin­u­ing to impart the desired ben­e­fits to the olive grove.

The dis­cov­ery of these unique bac­te­ria in Spanish olive groves opens up pos­si­bil­i­ties for future agri­cul­tural appli­ca­tions.

Given that Bacillus spp. already play a cen­tral role as one of the most widely used biopes­ti­cides, their poten­tial for novel biotech­no­log­i­cal appli­ca­tions in agri­cul­ture is promis­ing. The researchers pro­pose the devel­op­ment of a nat­ural biopes­ti­cide uti­liz­ing this group of microor­gan­isms to com­bat Xylella fas­tidiosa out­breaks.

In addi­tion, the bac­te­ria have pre­vi­ously been shown to with­stand metal expo­sure and remove heavy met­als from soil, effec­tively detox­i­fy­ing the envi­ron­ment.

Heavy metal con­t­a­m­i­na­tion poses a sig­nif­i­cant prob­lem for com­mer­cial agri­cul­ture and food pro­duc­tion since plants can absorb these met­als, which make their way into the food chain.

The team, there­fore, exam­ined the tol­er­ance of their sam­ples to a range of heavy met­als. They found that the tested iso­lates had good tol­er­ance, with iron being the most tol­er­ated, fol­lowed by cop­per, nickel, man­ganese, zinc and cad­mium.

This sug­gests that mem­bers of the olive sporo­biota could poten­tially thrive in soils with ele­vated metal lev­els due to envi­ron­men­tal fac­tors or human activ­i­ties.