Production Of Extracellular Enzymes Research Articles

Soil enzymes are preferentially associated with larger particles in highly organic Arctic tundra soils

Microbial processes, including extracellular enzyme (exoenzyme) production, are a major driver of decomposition and a current topic of interest in Arctic soils due to the effects of climate warming. While enzyme activity levels are often assessed, we lack information on the specific location of these exoenzymes within the soil matrix. Identifying the locations of different soil enzymes is needed to improve our understanding of microbial and overall ecosystem function. Using soil obtained from Utqiaġvik, Alaska, our objectives in the study are (1) to measure the activity of enzymes in soil pore water, (2) to examine the distribution of activity among soil particle size fractions using filtration, and (3) to cross these particle size fraction analyses with disruption techniques (blending to shred and sonication to further separate clumped/aggregated soil materials) to assess how tightly bound the enzymes are to the particles. The results of the soil pore water assays showed little to no enzyme activity (<0.05 nmol g soil–1 h–1), suggesting that enzymes are not abundant in soil pore water. In the soil cores, we detected activity for most of the hydrolytic enzymes, and there were clear differences among the particle size and disruption treatments. Higher activities in unfiltered and 50-µm filters relative to much finer 2-µm filters suggested that the enzymes were preferentially associated with larger particles in the soil, likely the organic material that makes up the bulk of these Arctic soils. Furthermore, in the sonication + blending treatment with no filter, 5 of 6 hydrolytic enzymes showed higher activity compared to blending only (and much higher than sonication only), further indicating that enzyme–substrate complexes throughout the organic matter component of the soil matrix are the sites of hydrolytic enzyme activity. These results suggest that the enzymes are likely bound to either the producing microbes, which are bound to the substrates, or directly to the larger organic substrates they are decomposing. This close-proximity binding may potentially minimize the transport of decomposition products away from the microbes that produce them.

Trade-off between microbial carbon use efficiency and microbial phosphorus limitation under salinization in a tidal wetland

Sea level rise–induced salinization is projected to influence the decomposition of soil carbon (C) in tidal wetlands. Despite evidence showing that microbial metabolism can determine the fate of soil C decomposition, the response of microbial metabolism to salinization in tidal wetlands remains largely unknown. Microbial metabolism is impacted by the microbial metabolic limitation and carbon use efficiency (CUE), which can provide mechanistic insights into soil C decomposition. Here, we measured microbial metabolic limitation, microbial CUE, and extracellular enzyme activities along an estuarine salinity gradient ranging from freshwater (0.1 ± 0.1 mg g−1) to oligohaline (2.1 ± 0.5 mg g−1) in a tidal wetland. Overall, microorganisms were limited by phosphorus (P) in the tidal wetlands, where salinization increased microbial P limitation by 34%. The enhanced microbial P limitation was attributed to increases in soil C:P and belowground biomass, as well as decreases in root C:P with increasing salinity. Microbial CUE decreased from 0.38 to 0.33 as salinity increased, while microbial P limitation was negatively correlated with microbial CUE, representing the trade-off between the two. Furthermore, microbial P limitation was positively associated with C-, nitrogen (N)-, and P-acquiring extracellular enzyme activities, while all these enzyme activities were negatively correlated with microbial CUE. These results illustrate that to balance microbial P limitation with salinization, microorganisms transfer more energy from the microbial CUE to extracellular enzyme production, and this was the mechanism underlying the trade-off. Microorganisms were also limited by C in the tidal wetlands. However, as the increasing belowground biomass alleviated microbial C limitation with salinization, no relationship was observed between microbial C limitation and CUE. Future C and nutrient models aimed to simulate tidal wetland ecosystem responses to salinization will benefit from the inclusion of trade-off between microbial CUE and microbial P limitation for more accurate prediction.

Quorum sensing disruption regulates hydrolytic enzyme and biofilm production in estuarine bacteria.

Biofilms of heterotrophic bacteria cover organic matter aggregates and constitute hotspots of mineralization, primarily acting through extracellular hydrolytic enzyme production. Nevertheless, regulation of both biofilm and hydrolytic enzyme synthesis remains poorly investigated, especially in estuarine ecosystems. In this study, various bioassays, mass spectrometry and genomics approaches were combined to test the possible involvement of quorum sensing (QS) in these mechanisms. QS is a bacterial cell-cell communication system that relies notably on the emission of N-acylhomoserine lactones (AHLs). In our estuarine bacterial collection, we found that 28 strains (9%), mainly Vibrio, Pseudomonas and Acinetobacter isolates, produced at least 14 different types of AHLs encoded by various luxI genes. We then inhibited the AHL QS circuits of those 28 strains using a broad-spectrum lactonase preparation and tested whether biofilm production as well as β-glucosidase and leucine-aminopeptidase activities were impacted. Interestingly, we recorded contrasted responses, as biofilm production, dissolved and cell-bound β-glucosidase and leucine-aminopeptidase activities significantly increased in 4%-68% of strains but decreased in 0%-21% of strains. These findings highlight the key role of AHL-based QS in estuarine bacterial physiology and ultimately on biogeochemical cycles. They also point out the complexity of QS regulations within natural microbial assemblages.

Wheat Growth Dependent Succession of Culturable Endophytic Bacteria and Their Plant Growth Promoting Traits.

Endophytic bacteria present ubiquitously in all plant parts. Their community structure may vary depending on plant tissue and growth condition. This work mainly focused on exploring the diversity of culturable nitrogen-fixing endophytic bacteria in above-ground plant parts of wheat by harvesting it during various growth points (Seed stage, 1st, 2nd, and 3rd month old plants, respectively). Distinct endophytic bacterial colonies were selected on Jensen's agar plate. Based on the 16S rRNA sequencing, 43 putative nitrogen-fixing endophytic bacteria were identified. Most of the isolates were found unique to the plant growth phase except for Pseudomonas sp., Bacillus sp., Paenibacillus sp., Microbacterium sp., Exiguobacterium sp. Further, endophytic bacteria were scrutinized for their plant growth promoting traits. They were found positive for IAA production (100%), P-solubilization (21%), Zn-solubilization (63%), ammonia production (93%), and nifH gene (33%). Extracellular enzyme production was found positive for cellulase (98%), pectinase (98%), and protease (100%). Their endophytic colonization ability was assessed using reactive oxygen species (ROS) induction assay, upon their entry inside the host plant.

Los aislados de hongos del género Trichoderma inducen la resistencia al marchitamiento del guisante causada por Fusarium oxysporum f. sp. pisi a través de la inhibición competitiva

Four different Trichoderma species were isolated from the soil rhizosphere of pea field from selected areas of Punjab, Pakistan. Based on morphological and cultural characteristics species were recognized as T. harzianum, T, viridae, T. hamatum and T. koningii. The isolated species were screened for the production of extracellular hydrolytic enzymes. The strains were found positive for chitinase and glucanase activities.  Fusarium oxysporum f. sp. pisi was isolated from roots of wilted pea plants. In-vitro biocontrol potential of the isolated Trichoderma species was assayed by dual culture technique against Fusarium oxysporum f. sp pisi. The maximum growth inhibition was observed by T. viridae (76.42%) followed by T. harzianum (74.29%), T. koningii (71.43%) and T. hamatum (69.64%), after 7 days of incubation. All four isolated species of Trichoderma were used in confrontational assay against Fusarium oxysporum pisi (FOP). A competition of Trichoderma sp. v/s FOP was evident, all Trichoderma strains showed strong antagonistic activity that was clearly observed on dual culture agar plates and further confirmed under scanning electron microscopy (SEM). Pot experiments also confirmed a very strong competitive inhibition of FOP evidently due to presence of glucanase and chitinases in Trichoderma spp. The primary screening and basic findings of present work will be helpful to obtain an efficient and novel biocontrol agent for further experimental trials on pea plants and may also enhance the chance of using Trichoderma species in integrated disease management (IDM) programs as an effective biological agent against several phyto-pathogens.

Plastic leachates lead to long-term toxicity in fungi and promote biodegradation of heterocyclic dye

The hazardous effects of plastic and plastic leachates on organisms, even bacteria, have attracted widespread attention, but only a limited effort has been devoted to explore the response of fungi to plastic leachate induced by light irradiation. Here, we performed plastic leaching experiments to obtain leachates from polyethylene (PE), polyethylene terephthalate (PET) and polypropylene (PP), and optical properties of plastic leachates were analysed to determine the influence of light conditions and plastic materials on that. The effects of plastic leachates on the production of fungal enzyme and the biodegradation of heterocyclic dye by fungi were evaluated. Results indicated that the UV light greatly enhanced the release of leachates from the three plastics. Both plastic polymers and light irradiation affected the plastic-derived dissolved organic carbon (DOC) and their aromaticity, but the molecular weight of plastic leachates showed no dependency on light irradiation types, and PE was the easiest to photo age and leached more DOC. Plastic leachates had no dose-effect on the production of extracellular enzymes by fungi. PE leachates showed long-term toxicities to fungi, and no manganese peroxidase activities were detected after a 42-day incubation, while that of controls were up to 73.64 ± 8.81 U/L. However, the PE and PP leachates greatly promoted methylene blue degradation by the fungi, but PET leachates relieved the decolouration of methylene blue, probably because of the benzene ring structure in the PET monomer. Fusarium oxysporum had a stronger degradation ability than Phanerochaete chrysosporium. Our results indicate that plastic leachates can influence the production and secretion of fungi ligninolytic extracellular enzymes, and regulate the fungal degradation of heterocyclic dye.

The Biocontrol and Plant Growth-Promoting Properties of Streptomyces alfalfae XN-04 Revealed by Functional and Genomic Analysis.

Fusarium wilt of cotton, caused by the pathogenic fungal Fusarium oxysporum f. sp. vasinfectum (Fov), is a devastating disease of cotton, dramatically affecting cotton production and quality. With the increase of pathogen resistance, controlling Fusarium wilt disease has become a significant challenge. Biocontrol agents (BCAs) can be used as an additional solution to traditional crop breeding and chemical control. In this study, an actinomycete with high inhibitory activity against Fov was isolated from rhizosphere soil and identified as Streptomyces alfalfae based on phylogenetic analyses. Next, an integrative approach combining genome mining and metabolites detection was applied to decipher the significant biocontrol and plant growth-promoting properties of XN-04. Bioinformatic analysis and bioassays revealed that the antagonistic activity of XN-04 against Fov was associated with the production of various extracellular hydrolytic enzymes and diffusible antifungal metabolites. Genome analysis revealed that XN-04 harbors 34 secondary metabolite biosynthesis gene clusters. The ability of XN-04 to promote plant growth was correlated with an extensive set of genes involved in indoleacetic acid biosynthesis, 1-aminocyclopropane-1-carboxylic acid deaminase activity, phosphate solubilization, and iron metabolism. Colonization experiments indicated that EGFP-labeled XN-04 had accumulated on the maturation zones of cotton roots. These results suggest that S. alfalfae XN-04 could be a multifunctional BCA and biofertilizer used in agriculture.

Stability of Soil Aggregates at Different Altitudes in Qinling Mountains and Its Coupling Relationship with Soil Enzyme Activities

To explore changes in soil aggregate stability along an elevation gradient, and its regulating factors, soil samples were taken from the 0-10 cm surface layer at 3 different elevations on Taibai Mountain. We measured and analyzed the distribution of soil aggregates, physical and chemical properties, microbial biomass, and extracellular enzymes. The results showed that: ① the soil aggregates from the 3 elevations had mean weight diameters (MWD) of 2.17 mm, 1.83 mm, and 1.82 mm (increasing elevation), and geometric mean diameters (GMD) of 1.66 mm, 1.39 mm, and 1.32 mm, respectively. ② The change in soil aggregate stability along an elevation gradient was regulated by extracellular enzymes in the soil, in particular, the LAP in soil meso-aggregate and the BG in soil micro-aggregate. ③ Microorganisms can alleviate the N limitation at high elevations by adjusting the relative production of extracellular enzymes and altering nutrient utilization efficiency, which also changes soil aggregate stability along an elevation gradient. The results of this study have important scientific significance for soil quality evaluation and ecological environment protection in Taibai Mountain.

Life in the Wheat Litter: Effects of Future Climate on Microbiome and Function During the Early Phase of Decomposition

Even though it is widely acknowledged that litter decomposition can be impacted by climate change, the functional roles of microbes involved in the decomposition and their answer to climate change are less understood. This study used a field experimental facility settled in Central Germany to analyze the effects of ambient vs. future climate that is expected in 50–80 years on mass loss and physicochemical parameters of wheat litter in agricultural cropland at the early phase of litter decomposition process. Additionally, the effects of climate change were assessed on microbial richness, community compositions, interactions, and their functions (production of extracellular enzymes), as well as litter physicochemical factors shaping their colonization. The initial physicochemical properties of wheat litter did not change between both climate conditions; however, future climate significantly accelerated litter mass loss as compared with ambient one. Using MiSeq Illumina sequencing, we found that future climate significantly increased fungal richness and altered fungal communities over time, while bacterial communities were more resistant in wheat residues. Changes on fungal richness and/or community composition corresponded to different physicochemical factors of litter under ambient (Ca2+, and pH) and future (C/N, N, P, K+, Ca2+, pH, and moisture) climate conditions. Moreover, highly correlative interactions between richness of bacteria and fungi were detected under future climate. Furthermore, the co-occurrence networks patterns among dominant microorganisms inhabiting wheat residues were strongly distinct between future and ambient climates. Activities of microbial β-glucosidase and N-acetylglucosaminidase in wheat litter were increased over time. Such increased enzymatic activities were coupled with a significant positive correlation between microbial (both bacteria and fungi) richness and community compositions with these two enzymatic activities only under future climate. Overall, we provide evidence that future climate significantly impacted the early phase of wheat litter decomposition through direct effects on fungal communities and through indirect effects on microbial interactions as well as corresponding enzyme production.

Chaetomium and Chaetomium-like Species from European Indoor Environments Include Dichotomopilus finlandicus sp. nov.

The genus Chaetomium is a frequently occurring fungal taxon world-wide. Chaetomium and Chaetomium-like species occur in indoor environments, where they can degrade cellulose-based building materials, thereby causing structural damage. Furthermore, several species of this genus may also cause adverse effects on human health. The aims of this research were to identify Chaetomium and Chaetomium-like strains isolated from indoor environments in Hungary and Finland, two geographically distant regions of Europe with drier and wetter continental climates, respectively, and to study their morphological and physiological properties, as well as their extracellular enzyme activities, thereby comparing the Chaetomium and Chaetomium-like species isolated from these two different regions of Europe and their properties. Chaetomium and Chaetomium-like strains were isolated from flats and offices in Hungary, as well as from schools, flats, and offices in Finland. Fragments of the translation elongation factor 1α (tef1α), the second largest subunit of RNA polymerase II (rpb2) and β-tubulin (tub2) genes, as well as the internal transcribed spacer (ITS) region of the ribosomal RNA gene cluster were sequenced, and phylogenetic analysis of the sequences performed. Morphological examinations were performed by stereomicroscopy and scanning electron microscopy. Thirty-one Chaetomium sp. strains (15 from Hungary and 16 from Finland) were examined during the study. The most abundant species was Ch. globosum in both countries. In Hungary, 13 strains were identified as Ch. globosum, 1 as Ch. cochliodes, and 1 as Ch. interruptum. In Finland, 10 strains were Ch. globosum, 2 strains were Ch. cochliodes, 2 were Ch. rectangulare, and 2 isolates (SZMC 26527, SZMC 26529) proved to be representatives of a yet undescribed phylogenetic species from the closely related genus Dichotomopilus, which we formally describe here as the new species Dichotomopilus finlandicus. Growth of the isolates was examined at different temperatures (4, 15, 20, 25, 30, 37, 35, 40, and 45 °C), while their extracellular enzyme production was determined spectrophotometrically.

A HU-like protein is required for full virulence in Xanthomonas campestris pv. campestris.

Bacteria harbour several abundant small DNA‐binding proteins known as nucleoid‐associated proteins (NAPs) that contribute to the structure of the bacterial nucleoid as well as to gene regulation. Although the function of NAPs as global transcriptional regulators has been comprehensively studied in the model organism Escherichia coli, their regulatory functions in other bacteria remain relatively poorly understood. Xanthomonas campestris pv. campestris (Xcc) is a gram‐negative bacterium that causes black rot disease in almost all members of the crucifer family. In previous work, we demonstrated that a Fis homologue protein, which we named Fis‐like protein (Flp), contributes to the regulation of virulence, type III secretion, and a series of other phenotypes in Xcc. Here we have examined the role of XC_1355, which is predicted to encode a DNA‐binding protein belonging to the HU family herein named HU‐like protein (Hlp). We show that mutation of XC_1355 in Xcc reduces the virulence, extracellular polysaccharide production, and cell motility, but has no effect on the production of extracellular enzymes and induction of the hypersensitive response. These data together with transcriptome analysis indicate that hlp is a previously uncharacterized gene involved in virulence that has partially overlapping and complementary functions with flp in Xcc, although the two regulators have opposite effects on the expression of genes involved in type III secretion. The findings add to our understanding of the complex regulatory pathways that act to regulate virulence in Xcc.

Effect of Pretreated Colza Straw on the Growth and Extracellular Ligninolytic Enzymes Production by Lentinula edodes and Ganoderma lucidum

Lentinula edodes 3565 and Ganoderma lucidum 9621 were compared for their ability to produce lignocellulolytic enzymes in submerged (SM) and surface liquid (SL) fermentation of hydrolysed colza straw lignin waste that remained after the production of furfural and bioethanol (CS lignin). Application of cultivated mushrooms to dispose of pretreated colza straw agricultural waste is an approach to decrease the quantity of residual lignin while simultaneously obtaining active substances, e.g., the ligninolytic enzyme complex from mycelium. The effect of adding CS lignin to culture media on the yield of L. edodes and G. lucidum mycelium and extracellular laccase activity was studied. It was revealed that the mycelial growth of G. lucidum on solid media was significantly improved by adding CS lignin. Laccase activity during SL cultivation of L. edodes on medium with CS lignin gradually increased over the experiment starting on day 21 and peaked at 520 U/mL on day 28. G. lucidum expressed the maximum laccase activity, 540 U/mL, during the first 14 days of mycelium SM cultivation. Extracellular laccase activity was enhanced about 35- to 40-fold at cultivation of L. edodes and about 10- to 15-fold in the case of G. lucidum by supplementing liquid culture media with CS lignin.

Multifarious functional traits of free-living rhizospheric fungi, with special reference to Aspergillus spp. isolated from North Indian soil, and their inoculation effect on plant growth

PurposeRhizospheric soil fungi are critical for plant and soil health. However, their multiple functional traits and impact on plant growth have not been systematically explored.MethodsDuring this study, biochemical traits of 73 indigenous soil fungal isolates and 15 unidentified isolates related to plant growth promotion and production of extracellular enzymes were studied.ResultsForty four (65.67%) of the total isolates produced indole acetic acid (IAA) followed by siderophore (52.23%), phosphate solubilization (37.31%), and antibiotic (11.93%). 91.04% of the studied isolates produced ammonia whereas 28.35% produced organic acid. Extracellular enzyme activities of lipase, amylase, chitinase, and cellulase were detected among 95.52%, 61.11%, 35.82%, and 41.79% isolates, respectively. Based on these activities, 73 fungal isolates were categorized into different biotypes. Quantitative analysis of IAA production and phosphate solubilization was carried out for Aspergillus, Penicillium, and Rhizopus isolates. Aspergillus isolates exhibited varying activities of IAA production and phosphate solubilization. Most of the Aspergillus isolates and some other fungi demonstrated multiple activities. Based on the multiple traits of selected fungal isolates, Aspergillus sp-07, Penicillium sp-03, and Rhizopus sp-02 were further evaluated in different combinations for their inoculation effect on the growth and yield of wheat under field conditions.ConclusionsThe results indicated that these isolates could be developed into bio-inoculants to enhance plant growth. The consortium of these three isolates was also found to be compatible and beneficial for plant growth.

Extracellular Enzymes Production and Non-phytopathogenic Potential Fungi Isolation for the Purpose of Solid Waste Management of Safe Food Production

Extracellular Enzymes Production and Non-phytopathogenic Potential Fungi Isolation for the Purpose of Solid Waste Management of Safe Food Production

Comparison of two commercial recirculated aquacultural systems and their microbial potential in plant disease suppression

BackgroundAquaponics are food production systems advocated for food security and health. Their sustainability from a nutritional and plant health perspective is, however, a significant challenge. Recirculated aquaculture systems (RAS) form a major part of aquaponic systems, but knowledge about their microbial potential to benefit plant growth and plant health is limited. The current study tested if the diversity and function of microbial communities in two commercial RAS were specific to the fish species used (Tilapia or Clarias) and sampling site (fish tanks and wastewaters), and whether they confer benefits to plants and have in vitro antagonistic potential towards plant pathogens.ResultsMicrobial diversity and composition was found to be dependent on fish species and sample site. The Tilapia RAS hosted higher bacterial diversity than the Clarias RAS; but the later hosted higher fungal diversity. Both Tilapia and Clarias RAS hosted bacterial and fungal communities that promoted plant growth, inhibited plant pathogens and encouraged biodegradation. The production of extracellular enzymes, related to nutrient availability and pathogen control, by bacterial strains isolated from the Tilapia and Clarias systems, makes them a promising tool in aquaponics and in their system design.ConclusionsThis study explored the microbial diversity and potential of the commercial RAS with either Tilapia or Clarias as a tool to benefit the aquaponic system with respect to plant growth promotion and control of plant diseases.

Isolation of Halophilic Bacteria and Their Screening for Extracellular Enzyme Production

Halophiles are those microorganisms which are found at high salt concentration. These microorganisms have the capability to form a wide array of bioactive substances that have different applications in various industries. This work focussed at the isolation and screening of various halophilic bacterial strains from different places in Rajasthan and Tamil Nadu. Using a complete medium with different salt concentrations, 70 halophilic bacteria were isolated from 4 different sites. These isolated bacteria were then examined and screened out for the synthesis of different extracellular enzymes, such as cellulase, lipase and amylase. Out of the total, 24 isolates were found positive for amylase, 9 for lipase and 16 for cellulase. These enzymes can perform the hydrolytic activity at high salt concentrations. The various halophilic bacterial strains isolated from various places show a prospective for use in a range of biotechnological and molecular biology experiments and the extremozymes obtained from these bacteria have great industrial importance.

RNA Chaperones Hfq and ProQ Play a Key Role in the Virulence of the Plant Pathogenic Bacterium Dickeya dadantii

Dickeya dadantii is an important pathogenic bacterium that infects a number of crops including potato and chicory. While extensive works have been carried out on the control of the transcription of its genes encoding the main virulence functions, little information is available on the post-transcriptional regulation of these functions. We investigated the involvement of the RNA chaperones Hfq and ProQ in the production of the main D. dadantii virulence functions. Phenotypic assays on the hfq and proQ mutants showed that inactivation of hfq resulted in a growth defect, a modified capacity for biofilm formation and strongly reduced motility, and in the production of degradative extracellular enzymes (proteases, cellulase, and pectate lyases). Accordingly, the hfq mutant failed to cause soft rot on chicory leaves. The proQ mutant had reduced resistance to osmotic stress, reduced extracellular pectate lyase activity compared to the wild-type strain, and reduced virulence on chicory leaves. Most of the phenotypes of the hfq and proQ mutants were related to the low amounts of mRNA of the corresponding virulence factors. Complementation of the double mutant hfq-proQ by each individual protein and cross-complementation of each chaperone suggested that they might exert their effects via partially overlapping but different sets of targets. Overall, it clearly appeared that the two Hfq and ProQ RNA chaperones are important regulators of pathogenicity in D. dadantii. This underscores that virulence genes are regulated post-transcriptionally by non-coding RNAs.

A New Extracellular β-Galactosidase Producing Kluyveromyces sp. PCH397 from Yak Milk and Its Applications for Lactose Hydrolysis and Prebiotics Synthesis.

The online version contains supplementary material available at 10.1007/s12088-021-00955-1.

Reduction of hexavalent chromium by Exiguobacterium mexicanum isolated from chromite mines soil

Hexavalent chromium is a highly toxic element generated due to indiscriminate chromite mining in Sukinda, Odisha. In the present research investigation a relatively higher Cr(VI) resistant (900 mg L−1) bacterium CWB-54 was isolated from the chromite mine water. Based on the biochemical and molecular analysis the strain (CWB-54) was identified as Exiguobacterium mexicanum. When this bacterium was grown at 35 °C, 100 rpm, pH~8.0, and fructose as an electron donor, it could reduce the total hexavalent chromium (100 mg L−1) supplemented in the medium within 33 h of incubation period. Though experiment was carried out to study the effect of Mn, Ni, Cd, Hg and Zn on Cr(VI) reduction by the strain E. mexicanum it has been observed that in the presence of Cd and Hg, Cr(VI) reduction drastically decreased. Characterization of Cr(VI) reduced product by SEM-EDX and TEM analysis revealed intracellular and extracellular Cr(III) deposition in the bacterium, which is assumed to be Cr(OH)3 precipitate in nanometric size. But the extracellular chromate reductase enzyme production is found to be negligible as compared to the intracellular enzyme production. The increased concentration of Cr(VI) above (1000 mg L−1) also showed the genotoxic effect on the DNA. Several reports have been published on Exiguobacterium sp. on different scientific aspect but the current report on the reduction of toxic Cr(VI) by a new species E. mexicanum is a novel one which established the potentiality of this microorganism for a broad area of application.

Biological potential and chemical composition of bioactive compounds from endophytic fungi associated with thai mangrove plants

Plant endophytic microorganisms, which live symbiotically within their plant host, are a novel resource of active secondary metabolites. The current study was carried out to isolate fungal endophytes from 11 mangrove plants, to investigate their antifungal activity against phytopathogenic fungi and to assess their enzyme production. The ethyl acetate crude extracts of selected endophytic fungi were determined for their antioxidant and anti-mutagenic activities and the active compounds present in the extracts were identified. Of the 37 isolates of endophytic fungi, 30 were isolated from leaves and 7 from stems. For anti-pathogenic activity, all endophytes were tested against 5 plant pathogens. The results revealed that AmL-02 and CtL-06 had the highest growth inhibition of Curvularia sp. and Fusarium sp. respectively and they were chosen for phytochemical analysis and to explore further their anti-mutagenic activities. A preliminary qualitative phytochemical analysis of the fungal crude extracts revealed the presence of constituents such as alkaloids, tannins and coumarins. Gas chromatography-mass spectrometry analysis of the ethyl acetate extract of AmL-02 revealed the presence of various chemical compounds with the highest amount present being 1,3-butanediol (11.37%), while the highest amount of compound present in CtL-06 was kojic acid (95.6%). The antimutagenic activities were determined of AmL-02 and CtL-06 against the mutagenic substances 3-amino-1-methyl-gamma-carboline (Trp-P-2) and 7,12-dimethylbenzo[a]anthracene (DMBA) based on an Ames test using the Salmonella Typhimurium strains TA98 and TA100 which revealed that the extracts of AmL-02 and CtL-06 had strong antimutagenic activity against both mutagens. All the endophytic isolates were assessed for their potential role in producing extracellular enzymes on solid media. The results showed that the endophytic isolates had the capability of producing lipase (78%) cellulase (30%) protease (22%) and pectinase (19%), but none could produce amylase. One of the endophytic isolates (XmL-02) isolated from leaves had significant maximum lipase enzyme activity based on extracellular enzyme production ratio values (3.56 mm). Isolate XmL-02 had the highest lipase activity (82.22 U/ml) in the culture media for 72 hours at 30°C and pH 3. Hence, the three isolates, AmL-02, CtL-06 and XmL-02, were identified based on a combination of their morphological characteristics and internal transcribed spacer (ITS) sequences. The results revealed that CtL-06, AmL-02 and XmL-02 were as Aspergillus luchuensis, Xylaria feejeensis and Colletotrichum gloeosporioides, respectively. These results indicated that the mangrove plants at this location harbored rich sources of fungal endophytes with different types of bioactivity.