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Actinomycetales is an order of actinobacteria that have an important role in the decomposition of organic matter. Their abundance and distribution can reflect a good level of soil fertility as well as biological activity. In this research study, actinomycetal diversity in soil was investigated under various field treatments with biowastes. Initially, unvegetated agricultural soil plots of 4 m2 had been annually amended with increasing rates of municipal solid waste compost (MSWC at 40, 80 and 120 t ha−1 year−1) and farmyard manure (FM at 40 and 120 t ha−1 year−1) for eight consecutive years. Control consisted of unamended soil and all treatments were distributed in four randomized complete blocks. At the end of the experimental period, total DNA was extracted from fresh topsoil samples (0–20 cm) then nested PCR-DGGE sequencing method was applied to assess the long-term effect of treatments on the diversity of actinomycetes. Analytical outcomes revealed the presence of ten actinomycetal families with Streptomycetaceae, Pseudonocardiaceae and Nocardioidaceae being the most dominant regardless to changes in experimental conditions. Besides, the long-term accumulation of both biowastes in soil affected the diversity of actinomycetal communities in different ways including contribution, stimulation or inhibition. Interestingly, soil treated with MSWC at an equivalent rate of 40 t ha−1 year−1 was likely to provide optimal growth conditions for major identified genera because it showed the highest actinomycetal diversity as compared to the rest of the treatments. [ABSTRACT FROM AUTHOR]

Seven bacterial isolates, recovered from native Nicotiana glauca plants of the Tunisian Centre-East, and successfully colonizing the internal stem tissues of tomato cv. Rio Grande were screened for their ability to suppress tomato Fusarium wilt, caused by Fusaium oxysporum f. sp . lycopersici , and to enhance plant growth. S18 and S42 isolates were found to be the most effective in decreasing yellowing and wilt symptoms by 94 and 88% and the vascular browning extent by 95–97.5%, respectively, as compared to FOL-inoculated and untreated control. A significant enhancement in growth parameters of tomato plants inoculated with pathogen and treated with S18 and S42 isolates. These two bioactive isolates were characterized and identified using 16S rDNA sequencing genes as Alcaligenes faecalis S18 and Bacillus cereus S42, respectively. Pathogen mycelial growth was inhibited by 44.1 and 42.1% with S42 and S18 isolates, respectively . Using the disc diffusion method, S42 and S18 formed an inhibition zone against FOL of about 11.87–12.37 mm, respectively. The isolate S42 of B. cereus showed a proteolytic and chitinolytic activity. A. faecalis S18 exhibited only chitinolytic activity in chitin-agar medium. This isolate was also able to produce the volatile metabolite hydrogen cyanide. Indole-3-acetic acid production, phosphate solubilizing, and pectinase activity were assessed for these two bioactive isolates for elucidating their plant growth promoting traits and their endophytic colonization ability. This study clearly demonstrated that N. glauca is a potential source for the isolation of potent endophytic bacteria exhibiting Fusarium wilt-suppressive and plant growth-promoting effects on tomato. [ABSTRACT FROM AUTHOR]

The generation of considerable amounts of sewage sludge during wastewater treatment is inevitable and should be carefully addressed. Among the various options available for urban sewage sludge management, the agricultural re-use as a fertilizer/soil conditioner has seen a wide acceptance because of the high amount of nutrients and organic matter contained in this biowaste. Accordingly, the aim of this field-scale study was to evaluate the changes in agricultural soil parameters following two successive annual amendments with increasing amounts of urban sludge (0, 40, 80 and 120 t ha −1 year −1 ). Sludge addition improved the fertility of the topsoil, showing a significant dose-dependent increase of TOC, N, P, and K contents up to the excessive amount of 120 t ha −1 year −1 (1.6%, 0.09, 233 and 21 mg kg −1 , respectively). Consequently, soil biological parameters such as microbial communities and enzymatic activities (dehydrogenase, phosphatase, protease and cellulase) were all enhanced as well. On the other hand, we noticed also a similar increasing trend of soil salinity (EC and Na + ) and phytotoxic heavy metals namely, Cd and Cr (2.4 and 3.8 mg kg −1 at 120 t ha −1 year −1 ). This variation was nonetheless below thresholds; and metal bioavailability to microorganisms and lettuce seeds was likely to be hindered by the non change in soil pH, which varied within a neutral range for all treatments (7.43–7.87). According to the C/N ratio, which reflects organic matter evolution in soil, plots treated at 80 t ha −1 year −1 resulted in C/N values below 15. Therefore, this excessive sludge dose for agricultural reuse is likely to be the best practice that ensures an adequate organic matter mineralization with less contamination after two successive annual amendments. [ABSTRACT FROM AUTHOR]

Semi-arid agricultural soils have increasingly been subjected to urban sewage sludge (USS) applications due to accelerated soil depletion and shortages in manure supply. Research studies addressing USS reuse have mostly been conducted in cropping systems and focused on changes in topsoil properties of a given texture. Therefore, sludge-soil interactions could be largely influenced by the presence of plants, soil particle composition and depth. In this field study, two agricultural soils (sandy, S and sandy loam, SL) received simultaneously four annual USS applications of 40, 80, and 120 t ha−1 year−1 in absence of vegetation. Outcomes showed the increase of carbon and macronutrients in both soils proportionally to USS dose especially in the topsoil profile (0–20 cm). Subsoil (20–40 cm) was similarly influenced by sludge rates, showing comparable variations of fertility parameters though at significant lower levels. The depth-dependent improvement of soil fertility in both layers enhanced the microbiological properties accordingly, with significant variations in soil SL characterized by a higher clay content than soil S. Besides, positive correlations between increases in sludge dose, salinity, trace metals, and enzyme activities in both soils indicate that excessive sludge doses did not cause soil degradation or biotoxic effects under the described experimental conditions. In particular and despite high geoaccumulation indices of Ni in both soils and profiles, the global concentrations of Cu, Ni, Pb, and Zn were still below threshold levels for contaminated soils. In addition, the maintenance of pH values within neutral range and the increase of organic matter content with respect to control would have further reduced metal availability in amended soils. Therefore, we could closely investigate the effects of texture and depth on the intrinsic resilience of each soil to cope with repetitive USS applications. • Repetitive sludge applications changed soil properties in a dose-dependent manner. • Little variation in clay content influenced largely light-textured soil properties. • Topsoil samples had higher fertility and biological activities than subsoils. • Excessive sludge doses did not provoke soil contamination or degradation. • Absence of plants highlighted closely soil-sludge interactions on the long-term. [ABSTRACT FROM AUTHOR]

Abstract The agricultural reuse of urban sewage sludge in degraded croplands has seen a wide acceptance for biowaste recycling and for the improvement of soil fertility. However, soil degradation and health issues may arise from the fact that sludge addition causes chemical and biological contamination if mismanaged. To closely monitor the long term soil-sludge interactions, a field study was conducted over a three-year period under a semi-arid climate. More precisely, changes in topsoil properties were assessed in 4-m2 uncropped plots amended with sludge rates equivalent to 0, 40, 80 and 120 t ha−1 year−1 for two soil textures: soil A (sandy loam) and soil S (sandy). Results showed that all studied parameters changed significantly in a dose-dependent manner for both soils as compared to untreated controls. As such, sludge addition improved consistently TOC, N, P and K content up to soils treated with 120 t ha−1 year−1. The enhancement of soil nutrient status impacted positively on biological properties, including microbial biomass and soil enzyme activities (dehydrogenase, protease and phosphatase). However, the variation of soil properties was more important in soil A characterized by a higher fine fraction thus stronger retention capacity. Accordingly, XRD analysis of soil A revealed several identifiable peaks representing kaolinite and illite clays in contrast to soil S. Unexpectedly, high to excessive sludge doses of 80 and 120 t ha−1 year−1 did not provoke soil degradation after three repeated annual amendments. In fact, pH values in both soils remained within neutral to alkaline range (7.76–8.63); total heavy metals (Cu, Zn, Ni and Pb), soil salinity and fecal coliforms were all below threshold values for contaminated soils. Highlights • Tunisian croplands have low organic matter content due to overexploitation. • Three successive annual sewage sludge amendments improved soil fertility. • Soil biological activities were positively correlated with the sludge dose. • Soil degradation was not observed even at excessive sludge doses. • A finer texture had more impact on soil parameters after sludge addition. [ABSTRACT FROM AUTHOR]

Seven culturable bacterial isolates, obtained from the internal stem tissues of Solanum elaeagnifolium and successfully colonizing the internal stem tissues of tomato cv. Rio Grande, were screened for their in vivo antifungal activity against Fusarium oxysporum f.sp. lycopersici ( FOL) and their growth-promoting potential on tomato plants. SV101 and SV104 isolates, assessed on pathogen-challenged tomato plants led to a significant decrease (77-83%) in Fusarium wilt severity and vascular browning extent (76%), as compared to the inoculated and untreated control. Isolates enhanced growth parameters on pathogen-challenged and unchallenged tomato plants. SV104 and SV101 isolates were most effective in suppressing disease and enhancing plant growth. These two isolates were identified as Bacillus sp. str. SV101 () and B. tequilensis str. SV104 (). They displayed antifungal activity against FOL; pathogen growth was inhibited by 64% and an inhibition zone (11.50 and 19.75 mm) against FOL could be formed using whole cell suspensions. SV101 and SV104 extracellular metabolites also inhibited FOL growth by 20 and 55%, respectively, as compared to control. B. tequilensis str. SV104 was shown to produce protease, chitinase, pectinase, IAA and siderophores. Bacillus sp. str. SV101 displayed pectinase activity and was found to be an IAA-producing and phosphate-solubilizing agent. To our knowledge, this is the first study reporting on S. elaeagnifolium use as a potential source of potent biocontrol and plant growth-promoting agents. [ABSTRACT FROM AUTHOR]

A putative endophyticBacillus cereusstr. S42 (KP993206), recovered from surface-sterilised stems ofNicotiana glaucawas assessedin vitroandin vivofor its antifungal potential towardsFusarium oxysporumf. sp.lycopersici(FOL). Pathogen sporulation was significantly inhibited byB. cereusstr. S42. FOL mycelial growth was reduced using its whole-cell suspensions, cell-free culture supernatant and chloroform extract. Its extracellular metabolites remained effective after heating at 50–100 °C with a decline in their activity was observed beyond 100 °C, when added with proteinase K and/or after pH adjustment to 2 and 12. Chitinase gene was detected using PCR amplification. Gas chromatography–mass spectrometry analysis of its chloroform extract matched phthalic acid, dibutyl ester with high level of similarity.B. cereusstr. S42 cell-free culture supernatant and whole-cell suspensions had significantly suppressed Fusarium wilt severity by 87–96% and enhanced tomato growth by 39–79% compared to FOL-inoculated and untreated control. [ABSTRACT FROM AUTHOR]

Nine non-pathogenic bacterial isolates, recovered fromDatura metelorgans and able to colonise the internal stem tissues of tomato cultivar Rio Grande, were screened for their ability to suppress tomato Fusarium wilt disease caused byFusarium oxysporumf. sp. lycopersici(FOL), and to enhance plant growth. S33 and S85 isolates tested were found to be the most effective in decreasing Fusarium wilt severity by 94–95% compared to FOL-inoculated and untreated control. A significant enhancement of growth parameters was recorded on tomato plants inoculated or not with FOL. Both isolates were characterised and identified using 16S rDNA sequencing genes asStenotrophomonassp. str. S33 (KR818084) andPseudomonassp. str. S85 (KR818087). Screenedin vitrofor their antifungal activity towards FOL, these isolates led to 38.7% and 22.5% decrease in pathogen radial growth and to the formation of an inhibition zone of 12.75 and 8.37 mm respectively.Stenotrophomonassp. str. S33 andPseudomonassp. str. S85 were found to be chitinase-, protease- and pectinase-producing strains but unable to produce hydrogen cyanide. Production of indole-3-acetic acid-like compounds, phosphate solubilising ability and pectinase activity were investigated for elucidating their plant growth-promoting traits and their endophytic colonisation ability. [ABSTRACT FROM PUBLISHER]