Serratia Proteamaculans Strain Research Articles

Identification and Characterization of a New Serratia proteamaculans Strain That Naturally Produces Significant Amount of Extracellular Laccase.

Natural biodegradation processes hold promises for the conversion of agro-industrial lignocellulosic biomaterials into biofuels and fine chemicals through lignin-degrading enzymes. The high cost and low stability of these enzymes remain a significant challenge to economic lignocellulosic biomass conversion. Wood-degrading microorganisms are a great source for novel enzyme discoveries. In this study, the decomposed wood samples were screened, and a promising γ-proteobacterial strain that naturally secreted a significant amount of laccase enzyme was isolated and identified as Serratia proteamaculans AORB19 based on its phenotypic and genotypic characteristics. The laccase activities in culture medium of strain AORB19 were confirmed both qualitatively and quantitatively. Significant cultural parameters for laccase production under submerged conditions were identified following a one-factor-at-a-time (OFAT) methodology: temperature 30°C, pH 9, yeast extract (2 g/l), Li+, Cu2+, Ca2+, and Mn2+ (0.5 mM), and acetone (5%). Under the selected conditions, a 6-fold increase (73.3 U/L) in laccase production was achieved when compared with the initial culturing conditions (12.18 U/L). Furthermore, laccase production was enhanced under alkaline and mesophilic growth conditions in the presence of metal ions and organic solvents. The results of the study suggest the promising potential of the identified strain and its enzymes in the valorization of lignocellulosic wastes. Further optimization of culturing conditions to enhance the AORB19 strain laccase secretion, identification and characterization of the purified enzyme, and heterologous expression of the specific enzyme may lead to practical industrial and environmental applications.

Promotion of saltgrass growth in a saline petroleum hydrocarbons contaminated soil using a plant growth promoting bacterial consortium

The goal of this study was to establish a plant growth promoting bacterial consortium, using strains previously isolated from a solid waste management unit (SWMU), and determine its effectiveness with respect to enhancing saltgrass colonization of contaminated soil from the SWMU. Bacterial strains were identified exhibit certain growth promoting characteristics and were tolerant to site relevant levels of petroleum hydrocarbons, salinity and pH. Five best performing strains including Pseudomonas sp. strain PFS1 and BSS3B2, Serratia proteamaculans strain S1BD1, Alcaligenes sp. strain PKS1 and Bacillus sp. strain PSS2 were selected to establish a plant growth promoting bacterial consortium named PGPBc, which was then tested to determine its effectiveness in facilitating saltgrass seed germination and growth both in vitro and in contaminated soil. The results showed that PGPBc inoculation had no significant effect on the germination of saltgrass seeds, but had significantly positive effect on plant biomass production in contaminated soil covered with a surface layer of potting soil. PGPBc inoculation increased plant biomass in sterilized soil by 4-fold and in unsterilized soil by 6.6-fold. In this study, we reported the phosphate solubilization ability of Serratia proteamaculans, and demonstrated the use of PGPBc for promoting saltgrass growth in hydrocarbon contaminated soil.

Influence of volatile organic compounds emitted by Pseudomonas and Serratia strains on Agrobacterium tumefaciens biofilms

The ability to form biofilms plays an important role in bacteria-host interactions, including plant pathogenicity. In this work, we investigated the action of volatile organic compounds (VOCs) produced by rhizospheric strains of Pseudomonas chlororaphis 449, Pseudomonas fluorescens B-4117, Serratia plymuthica IC1270, as well as Serratia proteamaculans strain 94, isolated from spoiled meat, on biofilms formation by three strains of Agrobacterium tumefaciens which are causative agents of crown-gall disease in a wide range of plants. In dual culture assays, the pool of volatiles emitted by the tested Pseudomonas and Serratia strains suppressed the formation of biofilms of A. tumefaciens strains grown on polycarbonate membrane filters and killed Agrobacterium cells in mature biofilms. The individual VOCs produced by the tested Pseudomonas strains, that is, ketones (2-nonanone, 2-heptanone, 2-undecanone), and dimethyl disulfide (DMDS) produced by Serratia strains, were shown to kill A. tumefaciens cells in mature biofilms and suppress their formation. The data obtained in this study suggest an additional potential of some ketones and DMDS as protectors of plants against A. tumefaciens strains, whose virulence is associated with the formation of biofilms on the infected plants.

Decarboxylase gene expression and cadaverine and putrescine production by Serratia proteamaculans in vitro and in beef

Studies of the molecular basis of microbial metabolic activities that are important for the changes in food quality are valuable in order to help in understanding the behavior of spoiling bacteria in food.The growth of a psychrotrophic Serratia proteamaculans strain was monitored in vitro and in artificially inoculated raw beef. Two growth temperatures (25°C and 4°C) were tested in vitro, while growth at 15°C and 4°C was monitored in beef. During growth, the expression of inducible lysine and ornithine-decarboxylase genes was evaluated by quantitative reverse transcription-PCR (qRT-PCR), while the presence of cadaverine and putrescine was quantified by LC-ESI–MS/MS. The expression of the decarboxylase genes, and the consequent production of cadaverine and putrescine were shown to be influenced by the temperature, as well as by the complexity of the growth medium. Generally, the maximum gene expression and amine production took place during the exponential and early stationary phase, respectively. In addition, lower temperatures caused slower growth and gene downregulation. Higher amounts of cadaverine compared to putrescine were found during growth in beef with the highest concentrations corresponding to microbial loads of ca. 9CFU/g. The differences found in gene expression evaluated in vitro and in beef suggested that such activities are more reliably investigated in situ in specific food matrices.

Andrimid production at low temperature by a psychrotolerant Serratia proteamaculans strain

Andrimid, a known non-ribosomal pseudo-peptide antibiotic, was isolated from a psychrotolerant Serratia proteamaculans strain. The antibiotic peptide was produced at low temperature (8 °C) in a 7.5 l BIOFLO 101 bioreactor under batch culture mode. Andrimid activity from S. proteamaculans culture was only detected at 25 °C and below and potent antibacterial activity was revealed against both, pathogenic and non-pathogenic bacteria. Minimal inhibitory concentration values determined by microdilution experiments varied in the range between 0.01 and 0.78 μg/ml. Antimicrobial purification and structure elucidation were carried out by LC-MS/MS and ¹H/¹³C NMR approaches. The effects on the ultrastructure of sensitive Escherichia coli 35,218 cells were observed by transmission electron microscopy at different inhibition stages. This work demonstrated the significance of bioprospection from cold environments through the screening of microorganisms with ability to produce cold-active biomolecules of biotechnological interest. S. proteamaculans 136 was revealed as a novel microbial source for andrimid production at low temperatures, showing biotechnological potential to be applied in cryopreservation, food or cosmetic industries against pathogenic bacteria.

Improving nodulation, growth and yield of Cicer arietinum L. through bacterial ACC-deaminase induced changes in root architecture

Bacteria containing ACC-deaminase in the vicinity of roots may influence plant growth by modifying root architecture through their potential to regulate ethylene synthesis in plant roots. Approximately 138 isolates capable of utilizing ACC as the sole source of N were isolated from the rhizosphere soil of chickpea ( Cicer arietinum L.) plants. Under axenic conditions, some rhizobacterial isolates were highly effective in increasing root length (up to 2.08 fold), number (up to 3.7 fold) and length (up to 3.9 fold) of lateral roots, and root biomass (up to 83%) of chickpea as compared to uninoculated control. Serratia proteamaculans strain J119 was found to be the most effective plant growth promoting rhizobacterium (PGPR) in improving root and shoot growth, nodulation and grain yield of chickpea as compared to respective controls in growth pouches, pot and field trials. A highly significant direct correlation ( r = 0.99) was observed between number of lateral roots under axenic conditions (jar trial) and number of nodules per plant in pot and field trials. Interestingly, S. proteamaculans J119 also exhibited highest ACC-deaminase activity in addition to root colonization compared to other tested strains. The results of this study demonstrated that changes in root growth and architecture (particularly lateral roots) as a result of inoculation with PGPR containing ACC-deaminase are crucial for improving growth, yield and nodulation of chickpea under field conditions.

Quorum-sensing-directed protein expression in Serratia proteamaculans B5a.

N-Acyl-L-homoserine-lactone-producing Serratia species are frequently encountered in spoiling foods of vegetable and protein origin. The role of quorum sensing in the food spoiling properties of these bacteria is currently being investigated. A set of luxR luxI homologous genes encoding a putative quorum sensor was identified in the N-(3-oxo-hexanoyl)-L-homoserine lactone (3-oxo-C6-HSL)-producing Serratia proteamaculans strain B5a. The 3-oxo-C6-HSL synthase SprI showed 79 % similarity with EsaI from Pantoea stewartii and the putative regulatory protein SprR was 86 % similar to the SpnR of Serratia marcescens. Proteome analysis suggested that the presence of at least 39 intracellular proteins was affected by the 3-oxo-C6-HSL-based quorum sensing system. The lipB-encoded secretion system was identified as one target gene of the quorum sensing system. LipB was required for the production of extracellular lipolytic and proteolytic activities, thus rendering the production of food-deterioration-relevant exoenzymes indirectly under the control of quorum sensing. Strain B5a caused quorum-sensing-controlled spoilage of milk. Furthermore, chitinolytic activity was controlled by quorum sensing. This control appeared to be direct and not mediated via LipB. The data presented here demonstrate that quorum-sensing-controlled exoenzymic activities affect food quality.

Influence of food preservation parameters and associated microbiota on production rate, profile and stability of acylated homoserine lactones from food-derived Enterobacteriaceae

Quorum-dependent regulation is mediated by N-acyl- l-homoserine lactones (AHLs) in several Gram-negative bacteria. The production of AHLs has typically been studied using pure bacteria cultures grown in nutrient-rich media at optimal temperature. AHLs are produced in several chill-stored foods by Gram-negative bacteria participating in spoilage. As part of our investigation of the role of AHLs in food quality, we studied the AHL production in two Enterobacteriaceae isolated from cold-smoked salmon under growth conditions typical of those found in cold-smoked salmon. We tested the influence of carbon source (glucose, sucrose, xylose, arabinose, mannose, mannitol and sorbitol), temperature (5 and 25 °C), salt concentration (0–7%), pH (6, 7 and 8) and co-existing lactic acid bacteria microflora on the AHL profile and production rate from Serratia proteamaculans strain B5a and Enterobacter agglomerans strain B6a. The two strains produced the same types of AHLs under all conditions tested. The specific AHL concentrations (moles/liter/OD 450) changed slightly for both strains at the various conditions. S. proteamaculans strain B5a produced approximately 150 nM/OD 450 N-3-oxo-hexanoyl homoserine lactone (OHHL) and E. agglomerans strain B6a produced two major signals, OHHL and N-3-oxo-octanoyl homoserine lactone (OOHL) in a 1:9 ratio with a total concentration of approximately 3000 nM/OD 450. The AHL signal molecules became unstable with increasing pH (>7.5). In cold-smoked salmon, pH is approximately 6 and therefore only a low degree of pH-induced turnover is expected to occur in this product. Overall, our study demonstrates that food-derived Enterobacteriaceae produce AHLs of the same type and in the same magnitude when grown under food-relevant conditions as when grown in laboratory media at high temperature. Also, the AHLs produced in foods will be relatively stable and their regulatory impact lasting during storage.

An inducible activator produced by a Serratia proteamaculans strain and its soybean growth-promoting activity under greenhouse conditions

Serratia proteamaculans 1-102 (1-102) promotes soybean-bradyrhizobia nodulation and growth, but the mechanism is unknown. After adding isoflavonoid inducers to 1-102 culture, an active peak with a retention time of about 105 min in the HPLC fractionation was isolated using a bioassay based on the stimulation of soybean seed germination. The plant growth-promoting activity of this material was compared with 1-102 culture (cells) and supernatant under greenhouse conditions. The activator was applied to roots in 83, 830 and 8300 HPLC microvolts (microV) per seedling when plants were inoculated with bradyrhizobia or sprayed onto the leaves in same concentrations at 20 d after inoculation. The root-applied activator, especially at 1 ml of 830 microV per seedling, enhanced soybean nodulation and growth at the same level as 1-102 culture under both optimal and sub-optimal root zone temperatures. Thus, this activator stimulating soybean seed germination is also responsible for the plant growth-promoting activity of 1-102 culture. However, when sprayed onto the leaves, the activator did not increase growth and in higher concentrations decreased average single leaf area. The results suggest that this inducible activator might be a lipo-chitooligosaccharide (LCO) analogue. LCOs act as rhizobia-to-legume signals stimulating root nodule formation. The activator could provide additional 'signal', increasing in the signal quality (the signal-to-noise ratio, SNR) of the plant-rhizobia signal exchange process.

An inducible activator produced by a Serratia proteamaculans strain and its soybean growth‐promoting activity under greenhouse conditions

Serratia proteamaculans 1‐102 (1‐102) promotes soybean–bradyrhizobia nodulation and growth, but the mechanism is unknown. After adding isoflavonoid inducers to 1‐102 culture, an active peak with a retention time of about 105 min in the HPLC fractionation was isolated using a bioassay based on the stimulation of soybean seed germination. The plant growth‐promoting activity of this material was compared with 1‐102 culture (cells) and supernatant under greenhouse conditions. The activator was applied to roots in 83, 830 and 8300 HPLC microvolts (μV) per seedling when plants were inoculated with bradyrhizobia or sprayed onto the leaves in same concentrations at 20 d after inoculation. The root‐applied activator, especially at 1 ml of 830 μV per seedling, enhanced soybean nodulation and growth at the same level as 1‐102 culture under both optimal and sub‐optimal root zone temperatures. Thus, this activator stimulating soybean seed germination is also responsible for the plant growth‐promoting activity of 1‐102 culture. However, when sprayed onto the leaves, the activator did not increase growth and in higher concentrations decreased average single leaf area. The results suggest that this inducible activator might be a lipo‐chitooligosaccharide (LCO) analogue. LCOs act as rhizobia‐to‐legume signals stimulating root nodule formation. The activator could provide additional ‘signal’, increasing in the signal quality (the signal‐to‐noise ratio, SNR) of the plant–rhizobia signal exchange process.

Methods for detecting acylated homoserine lactones produced by Gram-negative bacteria and their application in studies of AHL-production kinetics

In the process of evaluating the role of acylated homoserine lactones (AHLs) in food-spoiling Gram-negative bacteria, we have combined a range of bacterial AHL monitor systems to determine the AHL-profile and the kinetics of AHL-production. AHL production from 148 strains of Enterobacteriaceae isolated from foods was tested using Escherichia coli pSB403 (LuxR), Agrobacterium tumefaciens A136 (TraR) and both induction and inhibition of Chromobacterium violaceum CV026 (CviR). All strains except one was found to produce AHL(s). In no case could a single monitor system identify more than 64% of the Enterobacteriaceae as AHL-producers, showing that the simultaneous use of monitor strains is required in the process of screening bacterial populations for AHL-production. AHLs from 20 selected strains were profiled by thin layer chromatography. Most strains produced more than one AHL with 3- N-oxo-hexanoyl homoserine lactone being the most prominent. It was found that the simultaneous use of monitor strains in the top-layer was necessary for the detection of (presumably) all the AHLs. An agar well-diffusion assay based on A. tumefaciens pDZLR4 was used for quantifying AHLs from bacterial supernatants and enabled an assessment of the kinetics of AHL-production of 3 strains ( Serratia proteamaculans strain B5a, Erwinia carotovora ATCC 39048 and V. fischeri strain MJ-1). As expected, the production of AHL (OHHL) and luminescence in Vibrio fischeri strain MJ-1 increased faster than growth indicating up-regulation of the AHL regulated phenotype and auto-induction of AHL production. In contrast, production kinetics of AHL (OHHL) in the two Enterobacteriaceae indicated lack of auto-induction.