Stress of algicidal substances from a bacterium Exiguobacterium sp. h10 on Microcystis aeruginosa.

Microcystis aeruginosa is a cyanobacterial bloom-causing species and is considered a serious threat to human health and biological safety. In this study, the algicidal bacterium h10 showed high algicidal effects on M. aeruginosa 7820, and strain h10 was confirmed to belong to the genus Exiguobacterium, for which the name Exiguobacterium sp. h10 is proposed. Algicidal activity and mode analysis revealed that the supernatant, rather than the bacterial cells, was responsible for the algicidal activity, indicating that the algicidal mode of strain h10 is by indirect attack through the production of algicidal substances. Analysis of the algicidal substance characteristics showed a molecular weight of <1000 Da and that algicidal substances exhibit high thermal stability and pH instability, and the characteristic functional groups of the algicidal substance mainly included carbonyl, amino and hydroxyl groups. Under the effects of the algicidal substance, the cellular pigment content was significantly decreased, and the algal cell structure and morphology were seriously damaged. The results indicate that the algicidal bacterium Exiguobacterium sp. h10 could be a potential bio-agent for controlling cyanobacterial blooms of M. aeruginosa. SIGNIFICANCE AND IMPACT OF THE STUDY: In this study, the effects of algicidal substances from an algicidal bacterium Exiguobacterium sp. h10 on the toxic cyanobacterium, Microcystis aeruginosa 7820, were first investigated. The algicidal mode of action was confirmed as an indirect attack through the production of algicidal substances. The characteristics of the algicidal substance were determined, especially the functional groups analysis that confirmed the algicidal substances were glycolipid mixtures. With the stress of algicidal substances, the algal chlorophyll a synthesis, cell structure and morphology were seriously damaged. This study proved that algicidal bacteria are promising sources of potential cyanobacterial bloom-control, and provided good procedures for the identification and analysis of an algicidal bacterium and substances.

Purification and characterization of a new neutral metalloprotease from marine Exiguobacterium sp. SWJS2.

Among the protease-producing bacterial strains isolated from deep-sea sediments, SWJS2 was finally selected and identified as genus Exiguobacterium. Plackett-Burman and orthogonal array designs were applied to optimize the fermentation conditions, and the results are as follows: Glucose 5g, yeast extract 15g, glycerin 2g and CaCl2 ⋅2H2 O 0.5 g dissolved in 1 L artificial seawater; temperature 25 °C, original pH 7, inoculum rate 2%, seed age 12 H, loading volume 25 mL (250-mL Erlenmeyer flask), shaking speed 150 rpm, and fermentation time 44 H. The protease activity production was improved from about 80 to 660 U/mL under the optimized parameters. The protease was purified fourfold with specificity activity of 30,654.1 U/mg protein and a total yield of 16.2%. The protease exhibited the maximum activity at 40-45 °C and pH 7. Moreover, the enzyme activity was found to be inhibited by Cu(2+) , Ba(2+) , Cd(2+) , Hg(2+) , and Al(3+) at 5 mM, whereas it can be increased by Mg(2+) , Mn(2+) , and Ca(2+) at 0.5-5 mM. The enzyme was totally inactivated by 1 or 5 mM ethylenediaminetetraacetic acid but not by phenylmethanesulfonyl fluoride, tyrpsin inhibitor from Glycine max (STI), benzamidine, 5,5'-dithio-bis-(2-nitro benzoic acid), or pepstatin A, suggesting that it belonged to metalloprotease.

Homology modeling and comparative profiling of superoxide dismutase among extremophiles: exiguobacterium as a model organism.

Superoxide dismutase (SOD), a well known antioxidant enzyme, is known to exert its presence across bacteria to humans. Apart from their well-known antioxidant defense mechanisms, their association with various extremophiles in response to various stress conditions is poorly understood. Here, we have discussed the conservation and the prevalence of SODs among 21 representative extremophiles. A systematic investigation of aligned amino acid sequences of SOD from all the selected extremophiles revealed a consensus motif D-[VLE]-[FW]-E-H-[AS]-Y-[YM]. To computationally predict the correlation of SOD with the various stress conditions encountered by these extremophiles, Exiguobacterium was selected as a model organism which is known to survive under various adverse extremophilic conditions. Interestingly, our phylogenetic study based on SOD homology revealed that Exiguobacterium sibiricum was one of the closest neighbors of Deinococcus radiodurans and Thermus thermophilus. Next, we sought to predict 3-D model structure of SOD for E. sibiricum (PMDB ID: 0078260), which showed >95 % similarity with D. radiodurans R1 SOD. The reliability of the predicted SOD model was checked by using various validation metrics, including Ramachandran plot, Z-score and normalized qualitative model energy analysis score. Further, various physicochemical properties of E. sibiricum SOD were calculated using different prominent resources.

Cross-Species Induction and Enhancement of Antimicrobial Properties in Response to Gamma Irradiation in Exiguobacterium sp. HKG 126.

A gram positive, extreme haloalkaliphilic, radioresistant bacterium was isolated from mangrove region of Kerala (India) which was characterized as Exiguobacterium sp. HKG-126 using morphological, physiological, biochemical and molecular characterization. Present investigation was undertaken to examine Exiguobacterium sp. as a potential source of broad-spectrum antimicrobial activity and enhancement in this activity was observed due to cross-species/cross-genera induction and also in response to high dose of gamma (γ) irradiation. Individual studies on the antimicrobial activity of all the co-cultivated bacterial strains before and after mixed culture fermentation, showed excellent enhancement in antimicrobial activity of Exiguobacterium sp. against a variety of clinical pathogens. To the best of our knowledge, this is the first report showing existence of an extremely high radioresistant strain of (up to 15 kGy) Exiguobacterium sp.

Dynamic metabolomic crosstalk between Chlorella saccharophila and its new symbiotic bacteria enhances lutein production in microalga without compromising its biomass.

The microalgae Chlorella saccharophila UTEX247 was co-cultured with its symbiotic indigenous isolated bacterial strain, Exiguobacterium sp., to determine the possible effects of bacteria on microalgae growth and lutein productivity. Under optimal conditions, the lutein productivity of co-culture was 298.97 µg L-1 d-1, which was nearly 1.45-fold higher compared to monocultures i.e., 103.3 µg L-1 d-1. The highest lutein productivities were obtained in co-cultures, accompanied by a significant increase in cell biomass up to 0.84-fold. These conditions were analyzed using an untargeted metabolomics approach to identify metabolites enhancing valuable renewables, i.e., lutein, without compromising growth. Our qualitative metabolomic analysis identified nearly 30 (microalgae alone), 41 (bacteria alone), and 75 (co-cultures) metabolites, respectively. Among these, 46 metabolites were unique in the co-culture alone. The co-culture interactions significantly altered the role of metabolites such as thiamine precursors, reactive sugar anomers like furanose and branched-chain amino acids (BCAA). Nevertheless, the central metabolism cycle upregulation depicted increased availability of carbon skeletons, leading to increased cell biomass and pigments. In conclusion, the co-cultures induce the production of relevant metabolites which regulate growth and lutein simultaneously in C. saccharophila UTEX247, which paves the way for a new perspective in microalgal biorefineries.

Pan-genomic comparison of a potential solvent-tolerant alkaline protease-producing Exiguobacterium sp. TBG-PICH-001 isolated from a marine habitat.

The identification and applicability of bacteria are inconclusive until comprehended with genomic repositories. Our isolate, Exiguobacterium sp. TBG-PICH-001 exhibited excellent halo- and organic solvent tolerance with simultaneous production of alkaline protease/s (0.512 IU/mL). The crude protease (1 IU) showed a 43.57% degradation of whey protein. The bulk proteins in the whey were hydrolyzed to smaller peptides which were evident in the SDS-PAGE profile. With such characteristics, the isolate became interesting for its genomic studies. The TBG-PICH-001 genome was found to be 3.14 Mb in size with 17 contigs and 47.33% GC content. The genome showed 3176 coding genes, and 2699 genes were characterized for their functionality. The Next-Generation-Sequencing of the genome identified only the isolate's genus; hence we attempted to delineate its species position. The genomes of the isolate and other representative Exiguobacterium spp. were compared based on orthologous genes (Orthovenn2 server). A pan-genomic analysis revealed the match of TBG-PICH-001 with 15 uncharacterized Exiguobacterium genomes at the species level. All these collectively matched with Exiguobacterium indicum, and the results were reconfirmed through phylogenetic studies. Further, the Exiguobacterium indicum genomes were engaged for homology studies rendering 11 classes of protease genes. Two putative proteases (Zinc metalloprotease and Serine protease) obtained from homology were checked for PCR amplification using genomic DNA of TBG-PICH-001 and other Exiguobacterium genomes. The results showed amplification only in the Exiguobacterium indicum genome. These protease genes, after sequencing, were matched with the TBG-PICH-001 genome. Their presence in its whole genome experimentally validated the study. Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-023-03796-5.

Identification and molecular characterization of a psychrophilic GH1 ß-glucosidase from the subtropical soil microorganism Exiguobacterium sp. GXG2.

The products of bacterial ß-glucosidases with favorable cold-adapted properties have industrial applications. A psychrophilic ß-glucosidase gene named bglG from subtropical soil microorganism Exiguobacterium sp. GXG2 was isolated and characterized by function-based screening strategy. Results of multiple alignments showed that the derived protein BglG shared 45.7% identities with reviewed ß-glucosidases in the UniProtKB/Swiss-Prot database. Functional characterization of the ß-glucosidase BglG indicated that BglG was a 468 aa protein with a molecular weight of 53.2 kDa. The BglG showed the highest activity in pH 7.0 at 35 °C and exhibited consistently high levels of activity within low temperatures ranging from 5 to 35 °C. The BglG appeared to be a psychrophilic enzyme. The values of Km, Vmax, kcat, and kcat/Km of recombinant BglG toward ρNPG were 1.1 mM, 1.4 µg/mL/min, 12.7 s-1, and 11.5 mM/s, respectively. The specific enzyme activity of BglG was 12.14 U/mg. The metal ion of Ca2+ and Fe3+ could stimulate the activity of BglG, whereas Mn2+ inhibited the activity. The cold-adapted ß-glucosidase BglG displayed remarkable biochemical properties, making it a potential candidate for future industrial applications.

A study on prevalence of microbial contamination on the surface of raw salad vegetables.

The present work evaluates the microbiological quality of raw salad vegetables (RSV) consumed in Dhanbad city, India. A total of 480 samples of 8 different raw salad vegetables from local market were examined for overall microbial quality in terms of aerobic mesophilic, psychrotrophic counts, yeast, mould and total coliform levels. E. coli O157:H7, Listeria monocytogenes and Salmonella sp. were detected by real-time polymerase chain reaction (qPCR) subsequent to isolation. Results showed that all the samples were found positive for total coliform; however, E. coli was detected in 16.7% of the total samples. Pathogenic microorganisms such as E. coli O157:H7, L. monocytogenes and Salmonella spp. were detected in 1.3, 3.5 and 4.0%, respectively, of the total samples. However, pathogens were not detected in any of the cabbage samples. The Exiguobacterium sp. (Strain ISM SP 2014) was detected in the spinach sample while studying the bacterial contamination, reported for the first time on the surface of RSV. The 16S rRNA gene sequencing showed less than 92% similarity with sequences available in the public domain.

Characterization of cadmium biosorption by Exiguobacterium sp. isolated from farmland soil near Cu-Pb-Zn mine.

Bacteria have the ability to bind heavy metals on their cell wall. Biosorption is a passive and energy-independent mechanism to adsorb heavy metals. The efficiency of heavy metal biosorption can vary depending on several factors such as the growth phase of bacteria, solution pH, and existence of competitive heavy metals. In this study, Exiguobacterium sp. isolated from farmland soil near a mine site were used, and optimal conditions for Cd biosorption in solution were investigated. As bacterial growth progressed, Cd biosorption increased, which is attributed to changes in the structure and composition of the cell wall during bacterial growth. The biosorption process was rapid and was completed within 30 min. Cadmium biosorption was highest at pH 7 due to the dissociation of hydrogen ions and the increase of negative charges with increasing pH. In the mixed metal solution of Cd, Pb, and Zn, the amount of biosorption was in the order of Pb>Cd>Zn while in a single metal solution, the order was Cd≥Pb>Zn. The maximum adsorption capacity for Cd by the isolated bacteria was 15.6 mg/g biomass, which was calculated from the Langmuir isotherm model. Different adsorption efficiencies under various environmental conditions indicate that, to control metal mobility, the conditions for biosorption should be optimized before applying bacteria. The results showed that the isolated bacteria can be used to immobilize metals in metal-contaminated wastewater.

Efficient production of polymer-grade L-lactate by an alkaliphilic Exiguobacterium sp. strain under nonsterile open fermentation conditions.

In this study, a newly isolated alkaliphile Exiguobacterium sp. strain 8-11-1 was used to produce optically pure L-lactate. With an initial glucose concentration of 80 g/L, a high overall L-lactic acid productivity of 8.15 g/L/h was achieved using NaOH as a neutralizing agent. The fed-batch fermentations were carried out under both sterile and nonsterile conditions. Under the nonsterile condition, 125 g/L L-lactic acid was obtained with a high percent yield and average productivity of 98.33% and 3.79 g/L/h, respectively. These values were consistent with the results from sterile condition. No d-isomers of lactic acid were detected, resulting in an optical purity of 100% in both conditions. The high levels of optically pure L-lactic acid produced by Exiguobacterium sp. 8-11-1, combined with the ease of handling and low costs associated with the open fermentation strategy, provide a novel and potentially important approach for L-lactic acid production in the future.

Mechanistic antimicrobial approach of extracellularly synthesized silver nanoparticles against gram positive and gram negative bacteria.

The development of eco-friendly and reliable processes for the synthesis of nanoparticles has attracted considerable interest in nanotechnology. In this study, an extracellular enzyme system of a newly isolated microorganism, Exiguobacterium sp. KNU1, was used for the reduction of AgNO3 solutions to silver nanoparticles (AgNPs). The extracellularly biosynthesized AgNPs were characterized by UV-vis spectroscopy, Fourier transform infra-red spectroscopy and transmission electron microscopy. The AgNPs were approximately 30 nm (range 5-50 nm) in size, well-dispersed and spherical. The AgNPs were evaluated for their antimicrobial effects on different gram negative and gram positive bacteria using the minimum inhibitory concentration method. Reasonable antimicrobial activity against Salmonella typhimurium, Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus was observed. The morphological changes occurred in all the microorganisms tested. In particular, E. coli exhibited DNA fragmentation after being treated with the AgNPs. Finally, the mechanism for their bactericidal activity was proposed according to the results of scanning electron microscopy and single cell gel electrophoresis.