Aquaponics are efficient systems that associate aquatic organisms’ production and plants by recirculating water and nutrients between aquaculture and hydroponic tanks. In this study, we characterised the bacterial communities in the freshwater aquaponics system that can mineralise polysaccharides and phytate by producing carbohydrate-degrading enzymes and phytases, by 16S rRNA gene sequencing and in vitro culture techniques. Around 20% of the operational taxonomic units (zOTUs) identified were previously reported to carry fibre-degrading enzyme putative genes, namely β-glucanase (1%), xylanase (5%), or cellulases (17%). Ten % of the zOTUs were previously reported to carry putative genes of phytases with different catalytic mechanisms, namely β-propeller (6%), histidine acid phytases (3%), and protein tyrosine phytase (<1%). Thirty-eight morphologically different bacteria were isolated from biofilms accumulated in fish and plant compartments, and identified to belong to the Bacilli class. Among these, 7 could produce xylanase, 8 produced β-glucanase, 14 produced cellulase, and 11 isolates could secrete amylases. In addition, Staphylococcus sp. and Rossellomorea sp. could produce consistent extracellular phytate-degrading activity. The PCR amplification of β-propeller genes both in environmental samples and in the isolates obtained showed that this is the most ecologically relevant phytase type in the aquaponics systems used. In summary, the aquaponics system is abundant with bacteria carrying enzymes responsible for plant-nutrient mineralisation.

Smart Capillary Barrier (SCB) has been recently promoted to decrease soil salinity and improve water use efficiency and the sustainability of arid land agriculture. In this study, we investigated the effect of SCB on soil microbial diversity, enumeration, and respiration in a tomato field trial. SCB soil and control (unstructured homogenous soils, H) plots were irrigated with four levels of salinity (EC w = 0.8, 3, 6, and 9 dS m −1). Microbial diversity was assessed by ITS and 16S rRNA gene sequencing, enumeration of culturable heterotrophs by agar plates, and microbial respiration by MicroResp™ assays. Salinity was the main driver of the soil microbial diversity, showing a substantial reduction in the number of operational taxonomic units (− 8% for both bacteria and fungi), enumeration of culturable heterotrophs (− 51% for bacteria and − 53% for fungi), and respiration (− 18%) at 9 dS m −1 water salinity. Microbial community composition was significantly different between the SCB and H soils, as evidenced by multivariate analyses and by the appearance of 3352 unique operational taxonomic units at SCB samples that were absent in H plots. The SCB soil showed a steeper metabolic quotient increase in response to soil salinity than the H soils. The abundance of functional microbes such as nitrogen-fixing and nitrifying prokaryotes, as well as mycorrhiza, was also significantly increased in the SCB soils in comparison with the H soils. Our findings suggest that adopting SCB design leads to higher overall soil microbial biodiversity, including those communities unable to withstand extreme soil salinity conditions.

Aquaponics are efficient systems that associate aquatic organisms&rsquo; production and plants by recirculating water and nutrients between aquaculture and hydroponic tanks. In this study, we have characterised the bacterial communities in the fresh water aquaponics system that can mineralise polysaccharides and phytate by producing carbohydrate degrading enzymes and phytases, by 16S rRNA gene sequencing and in vitro culture techniques. Around 20% of the operational taxonomic units (OTUs) identified were previously reported to carry fibre-degrading enzymes putative genes, namely &beta;-glucanase (1%), xylanase (5%) or cellulases (17%). Ten % of the OTUs were previously reported to carry putative genes of phytases with different catalytic mechanisms, namely &beta;-propeller (6%), histidine acid phytases (3%) and protein tyrosine phytase (&amp;lt;1%). Thirty-eight morphologically different bacteria were isolated from biofilms accumulated in fish and plant compartments, and identified to belong to the Bacilli class. Among these, seven could produce xylanase, 8 produced &beta;-glucanase, 14 produced cellulase, and 11 isolates could secrete amylases. In addition, Staphylococcus sp. and Rossellomorea sp. could produce consistent extracellular phytate-degrading activity. The PCR amplification of &beta;-propeller genes both in environmental samples and in the isolates obtained showed that this is the most ecologically relevant phytase type in the aquaponics systems used. In summary, the aquaponics system is abundant with bacteria carrying enzymes responsible for plant-nutrient mineralisation.