Enrichment experiment changes microbial interactions in an ultra-oligotrophic environment

Abstract

The increase of nutrients in water bodies, in particular nitrogen (N) and phosphorus (P) due to the recent expansion of agricultural and other human activities is accelerating environmental degradation of these water bodies, elevating the risk of eutrophication and reducing biodiversity. To evaluate the ecological effects of the influx of nutrients in an oligotrophic and stoichiometrically imbalanced environment, we performed a replicated in situ mesocosm experiment. We analyzed the effects of a N- and P-enrichment on the bacterial interspecific interactions in an experiment conducted in the Cuatro Cienegas Basin (CCB) in Mexico. This is a desert ecosystem comprised of several aquatic systems with a large number of microbial endemic species. The abundance of key nutrients in this basin exhibits strong stoichiometric imbalance (high N:P ratios), suggesting that species diversity is maintained mostly by competition for resources. We focused on the biofilm formation and antibiotic resistance of 960 strains of cultivated bacteria in two habitats, water and sediment, before and after 3 weeks of fertilization. The water habitat was dominated by Pseudomonas, while Halomonas dominated the sediment. Strong antibiotic resistance was found among the isolates at time zero in the nutrient-poor bacterial communities, but resistance declined in the bacteria isolated in the nutrient-rich environments, suggesting that in the nutrient-poor original environment, negative inter-specific interactions were important, while in the nutrient-rich environments, competitive interactions are not so important. In water, a significant increase in the percentage of biofilm-forming strains was observed for all treatments involving nutrient addition.

Two Pseudomonas aeruginosa clonal groups belonging to the PA14 clade are indigenous to the Churince system in Cuatro Ciénegas Coahuila, México

“…Therefore, we determined the antibiotic resistant profile of the 15 strains studied in this work against carbenicillin (500 μg/ml), tetracycline (150 μg/ml), kanamycin (200 μg/ml), streptomycin (200 μg/ml), chloramphenicol (200 μg/ml), gentamycin (150 μg/ml), and apramycin (100 μg/ml). In agreement with previous results for Pseudomonas isolated from the intermediate lagoon (Ponce-Soto et al, 2015), we found that the 15 analysed strains are resistant to carbenicillin and kanamycin and sensitive to the rest of the antibiotics tested. This, along with their unique phylogenetic position reinforces the idea of these two clonal groups being native to the Churince system.…”

“…Many strains belonging to species of the fluorescent Pseudomonas isolated from the Churince system are unable to produce fluorescent siderophores even belonging to fluorescent Pseudomonas species (Escalante et al ., ; Toribio et al ., ; Bonilla‐Rosso et al ., ; Rodríguez‐Verdugo et al ., ; Ponce‐Soto et al ., ), and the same is true for P. aeruginosa strains isolated in 2011 (44 strains) and 2015 (5 strains) analysed in this work.…”

“…Antibiotic resistance of P. aeruginosa strains belonging to the 2A and 2B clonal groups It has been reported previously that the production and resistance to antibiotics are ecologically significant traits in the Churince system not only in sediment-associated Bacillus (Pérez-Gutiérrez et al, 2012) but also in the water column Pseudomonads inhabitants (Aguirre-von-Wobeser et al, 2014;Ponce-Soto et al, 2015). Therefore, we determined the antibiotic resistant profile of the 15 strains studied in this work against carbenicillin (500 μg/ml), tetracycline (150 μg/ml), kanamycin (200 μg/ml), streptomycin (200 μg/ml), chloramphenicol (200 μg/ml), gentamycin (150 μg/ml), and apramycin (100 μg/ml).…”

“…Given its cultivable nature, several studies at CCB water bodies have been focused in the genus Pseudomonas and hundreds of novel isolates have been identified (Escalante et al, 2009;Toribio et al, 2011;Bonilla-Rosso et al, 2012;Rodríguez-Verdugo et al, 2012;Ponce-Soto et al, 2015). Twice each year for more than ten years, samples have been obtained from defined points in the Churince system to study the stability of different bacterial communities, and in the case of Pseudomonads it has also been determined the effect in their composition of fluctuations in temperature along the year (Rodríguez-Verdugo et al, 2012), and of nutrient availability, for example (Ponce-Soto et al, 2015). It is interesting that despite extensive sampling effort, only one P. aeruginosa strain (M10) was isolated from the Churince spring in 2008, which was very similar to the PAO1 type strain (Grosso-Becerra et al, 2014).…”

Synergistic effects of dual parasitism in Daphnia magna under nutrient limitation

“…In freshwater aquatic ecosystems, biochemical and elemental composition of natural seston fluctuates considerably and affects food web dynamics (sønDergaarD et al 1999;De senerPont Domis et al 2013), for instance via the microbial community (eLser et al 1995;cotner et al 2010;Ponce-soto et al 2015), but also via zooplankton performance in terms of reproduction, mortality, growth rate and community composition (sterner et al 1993;VerreyDt et al 2012;sarPe et al 2014). For instance, the keystone grazer Daphnia (Crustacea, Branchiopoda) requires a sufficient amount of P to invest in P-rich ribosomal RNA (rRNA), which is needed for protein synthesis and growth (eLser et al 2000(eLser et al , 2003.…”