Agricultural systems are highly affected by climatic factors such as temperature, rain, humidity, wind, and solar radiation, so the climate and its changes are major risk factors for agricultural activities. A small portion of the agricultural areas of Brazil is irrigated, while the vast majority directly depends on the natural variations of the rains. The increase in temperatures due to climate change will lead to increased water consumption by farmers and a reduction in water availability, putting production capacity at risk. Drought is a limiting environmental factor for plant growth and one of the natural phenomena that most affects agricultural productivity. The response of plants to water stress is complex and involves coordination between gene expression and its integration with hormones. Studies suggest that bacteria have mechanisms to mitigate the effects of water stress and promote more significant growth in these plant species. The underlined mechanism involves root-to-shoot phenotypic changes in growth rate, architecture, hydraulic conductivity, water conservation, plant cell protection, and damage restoration through integrating phytohormones modulation, stress-induced enzymatic apparatus, and metabolites. Thus, this review aims to demonstrate how plant growth-promoting bacteria could mitigate negative responses in plants exposed to water stress and provide examples of technological conversion applied to agroecosystems.

BACKGROUND: A plethora of bacteria-fungal interactions occurs on the extended fungal hyphae network in soil. The mycosphere of saprophytic fungi can serve as a bacterial niche boosting their survival, dispersion, and activity. Such ecological concepts can be converted to bioproducts for sustainable agriculture. Accordingly, we tested the hypothesis that the well-characterized beneficial bacterium Serratia marcescens UENF-22GI can enhance their plant growth-promoting properties by combination with Trichoderma longibrachiatum UENF-F476. RESULTS: The colony and cell interactions demonstrated S. marcescens and T. longibrachiatum compatibility. Bacteria cells were able to attach, forming aggregates-biofilms and migrates through fungal hyphae network. Bacterial migration through growing hyphae was confirmed using two-compartment Petri dishes assay. Fungal inoculation increased the bacteria survival rates into the vermicompost substrate over the experimental time. Also, in vitro indolic compound, phosphorus, and zinc solubilization bacteria activities increased in the presence of the fungus. In line with the ecophysiological bacteria fitness, tomato and papaya plantlet growth was boosted by bacteria-fungi combination applied under plant nursery conditions. CONCLUSION: Mutualistic interaction between mycosphere-colonizing bacterium S. marcescens UENF-22GI and the saprotrophic fungi T. longibrachiatum UENF-F467 increased the ecological fitness of the bacteria alongside with beneficial potential for plant growth. A proper combination and delivery of compatible beneficial bacteria-fungus represent an open avenue for biological enrichment of plant substrates technologies in agricultural systems.