Importance of biofilm formation for promoting plant growth under salt stress in Pseudomonas putida KT2440.

An underutilized experimental design was employed to isolate adapted mutants of the model bacterium Pseudomonas putida KT2440. The design involved subjecting a random pool of mini-Tn5 mutants of P. putida KT2440 to multiple rounds of selection in the rhizosphere of soybean plants irrigated with a NaCl solution. The isolated adapted mutants, referred to as MutAd, exhibited a mutation in the gene responsible for encoding the membrane-binding protein LapA, which plays a role in the initial stages of biofilm formation on abiotic surfaces. Two MutAd bacteria, MutAd160 and MutAd185, along with a lapA deletion mutant, were selected for further investigation to examine the impact of this gene on salt tolerance, rhizosphere fitness, production of extracellular polymeric substances (EPS), and promotion of plant growth. Despite the mutants' inability to form biofilms, they were able to attach to soybean seeds and roots. The MutAd bacteria demonstrated an elevated production of EPS when cultivated under saline conditions, which likely compensated for the absence of biofilm formation. MutAd185 bacteria exhibited enhanced root attachment and promoted the growth of soybean plants in slightly saline soils. The proposed experimental design holds promise for expediting bacterial adaptation to the rhizosphere of plants under specific environmental conditions, identifying genetic mutations that enhance bacterial fitness in those conditions, and thereby increasing their capacity to promote plant growth.

Vinasse as a substrate for inoculant culture and soil fertigation: Advancing the circular and green economy.

Vinasse is a by-product with a key role in circular economy. In this work, we analyze sugarcane vinasse as culture medium for obtaining single and mixed inoculants. Trichoderma harzianum MT2 was cultured in single and sequential co-culture with Pseudomonas capeferrum WCS358 or Rhizobium sp. N21.2. Fungal biomass in single culture was more than three folds higher in vinasse than in a standard medium, and was higher in co-culture with Rhizobium sp. N21.2 than with P. capeferrum WCS358. Bacterial growths in vinasse, in particular P. capeferrum WCS358, were improved in co-culture with T. harzianum MT2. Residual vinasses, obtained after microbial growth, presented almost neutral pH and lower conductivities and toxicity than raw vinasse. Fertigation with residual vinasses modifies characteristics of soil evidenced in the total N, cation exchange capacity, urease and acid phosphatase, and microbial metabolic diversity, in comparison to raw vinasse. In general, soil fertigation with residual vinasse from co-culture with P. capeferrum WCS358 is more similar to irrigation with water. Treatment evaluation indicates that vinasse is suitable for the production of mixed inoculants containing T. harzianum. The co-culture with P. capeferrum WCS358 improves the characteristics of the residual vinasse allowing a fertigation with less detrimental effect in soil in comparison to Rhizobium sp. N21.2. Obtaining valuable biomass of single or mixed inoculants in vinasse with lower ecological impact is relevant for the circular and green economy.

Actinobacteria consortium as an efficient biotechnological tool for mixed polluted soil reclamation: Experimental factorial design for bioremediation process optimization.

The objective of the present work was to establish optimal biological and physicochemical parameters in order to remove simultaneously lindane and Cr(VI) at high and/or low pollutants concentrations from the soil by an actinobacteria consortium formed by Streptomyces sp. M7, MC1, A5, and Amycolatopsis tucumanensis AB0. Also, the final aim was to treat real soils contaminated with Cr(VI) and/or lindane from the Northwest of Argentina employing the optimal biological and physicochemical conditions. In this sense, after determining the optimal inoculum concentration (2gkg-1), an experimental design model with four factors (temperature, moisture, initial concentration of Cr(VI) and lindane) was employed for predicting the system behavior during bioremediation process. According to response optimizer, the optimal moisture level was 30% for all bioremediation processes. However, the optimal temperature was different for each situation: for low initial concentrations of both pollutants, the optimal temperature was 25°C; for low initial concentrations of Cr(VI) and high initial concentrations of lindane, the optimal temperature was 30°C; and for high initial concentrations of Cr(VI), the optimal temperature was 35°C. In order to confirm the model adequacy and the validity of the optimization procedure, experiments were performed in six real contaminated soils samples. The defined actinobacteria consortium reduced the contaminants concentrations in five of the six samples, by working at laboratory scale and employing the optimal conditions obtained through the factorial design.