Biology subjects

Piccardi, P.

Publications and source records attributed to Piccardi, P..

4 recordsLinked to original sources

bioRxiv2024

The evolution of reduced facilitation in a four-species bacterial community

Microbial evolution is typically studied in mono-cultures or in communities of competing species. But microbes do not always compete and how positive inter-species interactions drive evolution is less clear: Initially facilitative communities may either evolve increased mutualism, increased reliance on certain species according to the Black Queen Hypothesis (BQH), or weaker interactions and resource specialization. To distinguish between these outcomes, we evolved four species for 44 weeks either alone or together in a toxic pollutant. These species initially facilitated each other, promoting each others survival and pollutant degradation. After evolution, two species (Microbacterium liquefaciens and Ochrobactrum anthropi) that initially relied fully on others to survive continued to do so, with no evidence for increased mutualism. Instead, Agrobacterium tumefaciens and Comamonas testosteroni (Ct) whose ancestors interacted positively, evolved in community to interact more neutrally and grew less well than when they had evolved alone, suggesting that the community limited their adaptation. We detected several gene loss events in Ct when evolving with others, but these events did not increase its reliance on other species, contrary to expectations under the BQH. We hypothesize instead that these gene loss events are a consequence of resource specialization. Finally, co-evolved communities degraded the pollutant worse than their ancestors. Together, our results support the evolution of weakened interactions and resource specialization, similar to what has been observed in competitive communities.

evolutionary biology↗

bioRxiv2022

Microbial invasion of a toxic medium is facilitated by a resident community but inhibited as the community co-evolves

Predicting whether microbial invaders will colonize an environment is critical for managing natural and engineered ecosystems, and controlling infectious disease. Invaders often face competition by resident microbes. But how invasions play out in communities dominated by facilitative interactions is less clear. We previously showed that growth medium toxicity can promote facilitation between four bacterial species, as species that cannot grow alone rely on others to survive. Following the same logic, here we allowed other bacterial species to invade the four-species community, and found that invaders could more easily colonize a toxic medium when the community was present. In a more benign environment instead, invasive species that could survive alone colonized more successfully when the residents were absent. Next, we asked whether early colonists could exclude future ones through a priority effect, by inoculating the invaders into the resident community only after its members had co-evolved for 44 weeks. Compared to the ancestral community, the co-evolved resident community was more competitive toward invaders, and less affected by them. Our experiments show how communities may assemble by facilitating one another in harsh, sterile environments, but that arriving after community members have co-evolved can limit invasion success.

microbiology↗

bioRxiv2019

Toxicity drives facilitation between four bacterial species

Competition between microbes is extremely common, with many investing in a wide range of mechanisms to harm other strains and species. Yet positive interactions between species have also been documented. What makes species help or harm each other is currently unclear. Here, we studied the interactions between four bacterial species capable of degrading Metal-Working Fluids (MWF), an industrial coolant and lubricant, which contains growth substrates as well as toxic biocides. We were surprised to find only positive or neutral interactions between the four species. Using mathematical modeling and further experiments, we show that positive interactions in this community are likely due to the toxicity of MWF, whereby each species detoxification benefited the others by facilitating their survival, such that they could grow and degrade MWF better when together. The addition of nutrients, the reduction of toxicity or the addition of more species instead resulted in competitive behavior. Our work provides support to the stress gradient hypothesis by showing how harsh, toxic environments can strongly favor facilitation between microbial species and mask underlying competitive interactions.

ecology↗

bioRxiv2019

Phage efficacy in infecting dual-strain biofilms of Pseudomonas aeruginosa

Bacterial viruses, or phage, play a key role in shaping natural microbial communities. Yet much research on bacterial-phage interactions has been conducted in liquid cultures involving single bacterial strains. Critically, phage often have a very narrow host range meaning they can only ever target a subset of strains in a community. Here we explore how strain diversity affects the success of lytic phage in structured communities. In particular, we infect a susceptible Pseudomonas aeruginosa strain PAO1 with lytic phage Pseudomonas 352 in the presence versus absence of an insensitive P. aeruginosa strain PA14, in liquid culture versus colonies growing on agar. We find that competition between the two bacterial strains reduces the likelihood of the susceptible strain evolving resistance to the phage. This result holds in liquid culture and in colonies. However, while in liquid the phage eliminate the whole sensitive population, colonies contain refuges wherein bacteria can remain sensitive yet escape phage infection. These refuges form mainly due to reduced growth in colony centers. We find little evidence that the presence of the insensitive strain provides any additional protection against phage. Our study reveals that living in a spatially structured population can protect bacteria against phage infection, while the presence of competing strains may instead reduce the likelihood of evolving resistance to phage, if encountered.

microbiology↗