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The geochemical analysis of Gafsa rock phosphate (GRP) revealed relatively high concentrations of essential plant minerals and trace heavy metals (HMs). Environmental contamination factors indicated moderate to very strong HM contamination due to GRP soil amendment. The potential use of the Serratia plymuthica BMA1 strain, which is known for its ability to solubilize GRP, to enhance mineral nutrition in Vicia faba L. and its role in HM rhizoaccumulation from GRP were explored. Pot experiments revealed that bacterization with S. plymuthica BMA1 in V. faba grown in sand supplemented with GRP as the sole source of phosphorus significantly increased the potassium concentration by 64% in roots and 40% in shoots, iron by 20% in roots and 10% in shoots, and manganese by 27% in roots and 20% in shoots compared to that in V. faba not inoculated with S. plymuthica BMA1. The total dry biomass of V. faba increased by approximately 85%, while the accumulation of cadmium (Cd), copper (Cu), zinc (Zn), and lead (Pb) in the roots increased by 114%, 30%, 37%, and 44%, respectively. However, in the shoots, they increased by 35%, 10%, 85%, and 25%, respectively, for Cd, Cu, Zn, and Pb compared to those in the non-inoculated V. faba. The evaluation of the HM translocation factor, bioaccumulation factor, and bioconcentration factor with GRP highlighted the key role of S. plymuthica BMA1 in preventing the mobility of toxic HMs from reaching the aerial parts of plants. These findings suggest that S. plymuthica BMA1 has the potential to enhance mineral nutrition in V. faba and facilitate the rhizoaccumulation of toxic HMs, which has implications for plant cultivation and human consumption.

The antibiotic pyrrolnitrin (PRN) is a tryptophan-derived secondary metabolite that plays an important role in the biocontrol of plant diseases due to its broad-spectrum of antimicrobial activities. The PRN biosynthetic gene cluster remains to be characterised in Serratia plymuthica, though it is highly conserved in PRN-producing bacteria. To better understand PRN biosynthesis and its regulation in Serratia, the prnABCD operon from S. plymuthica G3 was cloned, sequenced and expressed in Escherichia coli DH5α. Furthermore, an engineered strain prnind which is a conditional mutant of G3 prnABCD under the control of the Ptac promoter was constructed. This mutant was able to overproduce PRN with isopropylthiogalactoside (IPTG) induction by overexpressing prnABCD, whilst behaving as a conditional mutant of G3 prnABCD in the absence of IPTG. These results confirmed that prnABCD is responsible for PRN biosynthesis in strain G3. Further experiments involving lux-/dsRed-based promoter fusions, combined with site-directed mutagenesis of the putative σS extended -10 region in the prnA promoter, and liquid chromatography-mass spectrometry (LC-MS) analysis extended our previous knowledge about G3, revealing that quorum sensing (QS) regulates PRN biosynthesis through cross talk with RpoS, which may directly activated prnABCD transcription. These findings suggest that PRN in S. plymuthica G3 is produced in a tightly controlled manner, and has diverse functions, such as modulation of cell motility, in addition to antimicrobial activities. Meanwhile, the construction of inducible mutants could be a powerful tool to improve PRN production, beyond its potential use for the investigation of the biological function of PRN.

Serratia plymuthica strain UBCF_13 is a potential biocontrol agent to inhibit pathogen causing anthracnose disease in plants, Colletotrichum gloesporioedes . The production of bacterial antifungal compounds is affected by nutrition and the growth phase of bacteria. This study is aimed to determine the optimal medium and duration of culture for the production of antifungal compounds. This study used three types of liquid media culture for UBCF_13 [ King’s B, Potato Dextrose , and tryptic Soy ] and six variations in duration culture [8, 16, 24, 32, 40, and 48 hours]. Extracellular that has been produced was used for antifungal activity assay against C. gloeosporioides . The results showed that the extracellular produced in the PDB with 48 hours culture duration could inhibit 18%. C. gloeosporioides growth. Different nutritional compositions for UBCF_13 cultures show affect the metabolism and compound produced as well. This was indicated by differences in protein profiles of the intracellular and extracellular. Further studies are necessary to be carried out, particularly to see the mechanism of the nutrient medium that could affect the metabolism of UBCF_13 in the synthesis of antifungal compounds.

Bacteria as biocontrol agents can produce hydrolytic enzymes, one of them is a protease which plays an important role to degrade cell membranes or plasmalemma in fungi composed of protein. Metalloproteases are proteases that contain one or two metal ions on their active sites. The role of metal ions in metalloproteases is to activate water molecules, which act as nucleophiles in the catalysis process. The metalloprotease function of Serratia plymuthica UBCF_13 is unknown, therefore this study aimed to determine the effective metal ion to induce the expression of the UBCF_13 metalloprotease gene. The metalloprotease gene from Serratia plymuthica UBCF_13 was ligated into a pGEM T-easy plasmid. The recombinant plasmid was transformed into Escherichia coli BL21 by the heat shock method. The metalloprotease gene expression was induced by IPTG and a combination of several metal ions namely Zn 2+ , Mn 2+ , Fe 2+ , and Ca 2+ . The highest gene expression was characterized by the thickest protein band based on the result of SDS-PAGE visualization with a molecular weight of 27 kDa after being induced by Fe 2+ metal ions. Proteolytic activity of metalloprotease UBCF_13 was tested using solid LB media containing 2% skim milk. The longest clear zone diameter was obtained up to 0,83 cm after being induced by IPTG combined with Ca 2+ metal ion. These results can be used as a reference for the expression of the UBCF_13 metalloprotease gene. However, further enzyme purification is to be able the enzyme as an antifungal compound.

Background and aims Plant growth-promoting rhizobacteria (PGPR) have important roles in improving plant growth and alleviating stress induced damage under drought stress conditions. The aims of this study are: 1) to isolate and identify drought-tolerant PGPR from rhizosphere soil of jujube, a drought-tolerant plant grown in semi-arid and arid regions; and 2) to evaluate the effects of inoculation with the isolated strains on the growth and physiological responses of jujube seedlings under drought stress conditions. Methods Rhizosphere bacteria with 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity were isolated from the rhizosphere of jujube and were identified by 16S rDNA sequencing analysis. Then, the isolates were screened for drought tolerance and plant growth promoting activities. The growth and physiological changes of jujube under drought stress, including the plant height, shoot and root dry matter, malondialdehyde (MDA), indoleacetic acid (IAA), abscisic acid (ABA) content, superoxide dismutase (SOD), and peroxidase (POD) activity, were also detected. Results Eight ACC deaminase-producing bacterial strains were isolated and identified as Pseudomonas , Bacillus , and Serratia . Under drought stress conditions, Pseudomonas lini and Serratia plymuthica significantly increased plant height, shoot and root dry matter, and relative water content. Moreover, malondialdehyde and ABA levels were decreased, and antioxidant enzyme activities were increased. In addition, they also enhanced soil aggregate stability. The best effect was observed with mixed inoculation. Conclusions Strains of Pseudomonas lini and Serratia plymuthica played an important role in enhancing tolerance of jujube seedling and can be considered as promising bioinoculants of jujube.

Symbiotic bacteria can produce secondary metabolites and volatile compounds that contribute to amphibian skin defense. Some of these symbionts have been used as probiotics to treat or prevent the emerging disease chytridiomycosis. We examined 20 amphibian cutaneous bacteria for the production of prodigiosin or violacein, brightly colored defense compounds that pigment the bacteria and have characteristic spectroscopic properties making them readily detectable, and evaluated the antifungal activity of these compounds. We detected violacein from all six isolates of Janthinobacterium lividum on frogs from the USA, Switzerland, and on captive frogs originally from Panama. We detected prodigiosin from five isolates of Serratia plymuthica or S. marcescens, but not from four isolates of S. fonticola or S. liquefaciens. All J. lividum isolates produced violacein when visibly purple, while prodigiosin was only detected on visibly red Serratia isolates. When applied to cultures of chytrid fungi Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal), prodigiosin caused significant growth inhibition, with minimal inhibitory concentrations (MIC) of 10 and 50 µM, respectively. Violacein showed a MIC of 15 µM against both fungi and was slightly more active against Bsal than Bd at lower concentrations. Although neither violacein nor prodigiosin showed aerosol activity and is not considered a volatile organic compound (VOC), J. lividum and several Serratia isolates did produce antifungal VOCs. White Serratia isolates with undetectable prodigiosin levels could still inhibit Bd growth indicating additional antifungal compounds in their chemical arsenals. Similarly, J. lividum can produce antifungal compounds such as indole-3-carboxaldehyde in addition to violacein, and isolates are not always purple, or turn purple under certain growth conditions. When Serratia isolates were grown in the presence of cell-free supernatant (CFS) from the fungi, CFS from Bd inhibited growth of the prodigiosin-producing isolates, perhaps indicative of an evolutionary arms race; Bsal CFS did not inhibit bacterial growth. In contrast, growth of one J. lividum isolate was facilitated by CFS from both fungi. Isolates that grow and continue to produce antifungal compounds in the presence of pathogens may represent promising probiotics for amphibians infected or at risk of chytridiomycosis. In a global analysis, 89% of tested Serratia isolates and 82% of J. lividum isolates were capable of inhibiting Bd and these have been reported from anurans and caudates from five continents, indicating their widespread distribution and potential for host benefit.

Indole‐3‐acetic acid (IAA) is emerging as a key intra‐ and inter‐kingdom signal molecule that modulates a wide range of processes of importance during plant–microorganism interaction. However, the mechanisms by which IAA carries out its functions in bacteria as well as the regulatory processes by which bacteria modulate auxin production are largely unknown. Here, we found that IAA synthesis deficiency results in important global transcriptional changes in the broad‐range antibiotic‐producing rhizobacterium Serratia plymuthica A153. Most pronounced transcriptional changes were observed in various gene clusters for aromatic acid metabolism, including auxin catabolism. To delve into the corresponding molecular mechanisms, different regulatory proteins were biochemically characterized. Among them, a TyrR orthologue was essential for IAA production through the activation of the ipdc gene encoding a key enzyme for IAA biosynthesis. We showed that TyrR specifically recognizes different aromatic amino acids which, in turn, alters the interactions of TyrR with the ipdc promoter. Screening of mutants defective in various transcriptional and post‐transcriptional regulators allowed the identification of additional regulators of IAA production, including PigP and quorum sensing‐related genes. Advancing our knowledge on the mechanisms that control the IAA biosynthesis in beneficial phytobacteria is of biotechnological interest for improving agricultural productivity and sustainable agricultural development.

This study develops an optimized hybrid system to treat sodium dodecyl sulfate (SDS)-contaminated wastewater that synergistically integrates microbial biodegradation with physical adsorption within a Response Surface Methodology (RSM) framework. A highly effective SDS-degrading bacterium, Serratia plymuthica strain BSU-AH-03, was isolated from hydrocarbon-contaminated soil. Using a Box-Behnken Design (BBD), the optimal biodegradation conditions (pH 7.9, 20 °C, 300 mg L⁻¹ SDS) yielded a degradation efficiency of 90.46% (predicted 91.27%, R² = 0.981). Subsequently, natural anthracite coal was employed as an adsorbent to polish the effluent. The anthracite exhibited a high surface area (890.9 m² g⁻¹) and a heterogeneous micro-mesoporous structure. Batch adsorption experiments achieved a maximum SDS uptake capacity of 158.7 mg g⁻¹ and a near-complete removal efficiency of 99.58% at 318 K and pH 7. The adsorption process was endothermic (ΔH° = 58.4 kJ mol⁻¹), spontaneous (ΔG° from – 5.15 to -10.65 kJ mol⁻¹), and followed pseudo-second-order kinetics and the Langmuir isotherm, indicating chemisorption as the dominant mechanism. Mechanistic analysis revealed that SDS adsorption involves intra-particle pore diffusion, hydrophobic interactions, electrostatic forces, and hydrogen bonding, culminating in interfacial hemi-micellar aggregation. The synergistic combination of tailored biodegradation and advanced adsorption provides a highly efficient, statistically optimized strategy for the complete remediation of surfactant-laden industrial effluents.

Endophytic bacterium Serratia plymuthica A30 was identified as a superior biocontrol agent due to its effective colonization of potato tuber, tolerance to cold conditions, and strong inhibitory action against various soft rot pathogens, including Dickeya solani . We characterized transcriptome changes in potato tubers inoculated with S . plymuthica A30, D . solani , or both at the early and the late phases of interaction. At the early phase and in the absence of the pathogen, A30 influenced the microbial recognition system to initiate plant priming. In the presence of the pathogen alongside biocontrol strain, defense signaling was highly stimulated, characterized by the induction of genes involved in the detoxification system, reinforcement of cell wall structure, and production of antimicrobial metabolites, highlighting A30’s role in enhancing the host resistance against pathogen attack. This A30-induced resistance relied on the early activation of jasmonic acid signaling and its production in tubers, while defense signaling mediated by salicylic acid was suppressed. In the late phase, A30 actively interferes with plant immunity by inhibiting stress- and defense-related genes expression. Simultaneously, the genes involved in cell wall remodeling and indole-3-acetic acid signaling were activated, thereby enhancing cell wall remodeling to establish symbiotic relationship with the host. The endophytic colonization of A30 coincided with the induction of genes involved in the biosynthesis and signaling of ethylene and abscisic acid, while downregulating those related to gibberellic acid and cytokinin. This combination suggested fitness benefits for potato tubers by preserving dormancy, and delaying sprouting, which affects durability of tubers during storage. This study contributes valuable insights into the tripartite interaction among S . plymuthica A30, D . solani , and potato tubers, facilitating the development of biocontrol system for soft rot pathogens under storage conditions.

The qualified presumption of safety (QPS) process was developed to provide a safety assessment approach for microorganisms intended for use in food or feed chains. In the period covered by this Statement, no new information was found that would change the status of previously recommended QPS taxonomic units (TUs). The TUs in the QPS list were updated based on a verification, against their respective authoritative databases, of the correctness of the names and completeness of synonyms. Of 54 microorganisms notified to EFSA between April and September 2024 (33 as feed additives, 17 as food enzymes or additives, 4 as novel foods), 50 were not evaluated because: 12 were filamentous fungi, 1 was Enterococcus faecium and 8 were Escherichia coli (all excluded from the QPS evaluation), and 29 were TUs that already have a QPS status. One notification (Ensifer adhaerens) was already evaluated in a previous Panel Statement. Another notification (Enterococcus lactis) was already evaluated in the previous 3‐year QPS cycle and was reassessed within this document. Two TUs were notified for the first time and were assessed for a possible QPS status: Serratia plymuthica and Lacticaseibacillus huelsenbergensis. Bacillus thuringiensis and Bacillus nakamurai have been assessed for a possible QPS status in response to internal requests. The following was concluded on the five assessed TUs. L. huelsenbergensis can be granted the QPS status based on its close relatedness to several other QPS Lacticaseibacillus species. E. lactis is not recommended for the QPS status due to insufficient information on safety. S. plymuthica and B. thuringiensis are not recommended for the QPS status due to safety concerns. B. nakamurai cannot be recommended for the QPS list due to a lack of body of knowledge for its use in the food and feed chain.