Microbiology

Effect of organic carbon sources and environmental factors on cell growth and lipid content of Pavlova lutheri Abstract The present study aimed to investigate the effects of organic carbon sources, cultivation methods, and environmental factors on growth and lipid content of Pavlova lutheri for biodiesel production. In the 250-mL flask bioreactors, P. lutheri was cultivated in the modified artificial seawater (ASW) medium containing glucose, glycerol, sodium acetate, or sucrose as an organic carbon substrate. The effects of different growth conditions (phototrophic, mixotrophic, and heterotrophic) and environmental factors such as photoperiod, light intensity, and salinity were evaluated. Growth of P. lutheri was inhibited under heterotrophy but was enhanced in mixotrophy as compared to phototrophy. Biomass and lipid content of P. lutheri were significantly (p < 0.05) affected by changing photoperiod, light intensity, and salinity. Higher biomass concentration and lipid content were observed at a light intensity of 100 ± 2 μmol photons m−2 s−1, 18 h photoperiod, and 30% salinity, in a modified ASW medium supplemented with 10 mmol sucrose. An increase in biomass concentration from 320 ± 25.53 to 1106 ± 18.52 mg L−1 and high lipid content of 31.11 ± 1.65% (w/w) were observed with the optimized culture conditions, demonstrating a significant (p < 0.05) enhancement in biomass and lipid content due to the improved culture conditions. The present study emphasizes the possible use of sucrose for biomass and lipid production with P. lutheri under the optimized culture conditions. Using low-cost and relatively easy accessible feedstock such as sucrose would be a valuable alternative for growing microalgae with enhanced lipid content.

Demonstrating the potential of abiotic stress-tolerant Jeotgalicoccus huakuii NBRI 13E for plant growth promotion and salt stress amelioration Abstract The present study aimed to demonstrate the potential of abiotic stress-tolerant Jeotgalicoccus huakuii NBRI 13E for plant growth promotion and salt stress amelioration. NBRI 13E was characterized for abiotic stress tolerance and plant growth-promoting (PGP) attributes under normal and salt stress conditions. Phylogenetic comparison of NBRI 13E was carried out with known species of the same genera based on 16S rRNA gene. Plant growth promotion and rhizosphere colonization studies were determined under greenhouse conditions using maize, tomato, and okra. Field experiment was also performed to assess the ability of NBRI 13E inoculation for improving growth and yield of maize crop in alkaline soil. NBRI 13E demonstrated abiotic stress tolerance and different PGP attributes under in vitro conditions. Phylogenetic and differential physiological analysis revealed considerable differences in NBRI 13E as compared with the reported species for Jeotgalicoccus genus. NBRI 13E colonizes in the rhizosphere of the tested crops, enhances plant growth, and ameliorates salt stress in a greenhouse experiment. Modulation in defense enzymes, chlorophyll, proline, and soluble sugar content in NBRI 13E-inoculated plants leads to mitigate the deleterious effect of salt stress. Furthermore, field evaluation of NBRI 13E inoculation using maize was carried out with recommended 50 and 100% chemical fertilizer controls, which resulted in significant enhancement of all vegetative parameters and total yield as compared to respective controls. Jeotgalicoccus huakuii NBRI 13E is reported for the first time for its ability to develop a bioinoculant formulation for stress amelioration and improved crop productivity.

Characterization and comparisons of microbiota in different intestinal segments between adult Chinese Shanxi Black Pigs and Large White Pigs Abstract The carcass weight of Chinese Shanxi Black Pigs is relatively lower in comparison with that of the counterparts, i.e., Large White Pigs, although the former are resistant to harsh conditions. Since gut microflora has been recognized to play a key role in pork production, it is of interest to explore the microbial communities in different intestinal segments of pigs and its potential relatedness with host features. In this study, 16S rRNA gene amplicon sequencing, accompanied by the inter- and intra-group comparisons, was implemented to investigate the structure composition and potential functions of microbial communities of four distinct intestinal segments [duodenum (D), jejunum (J), ileum (I), and cecum (C)] between adult Chinese Shanxi Black Pigs and Large White Pigs. Comparative survey revealed that the dominant phylum in both breeds was Firmicutes, followed by Proteobacteria, and Bacteroidetes. At the genus level, Lactobacillus was predominant in all samples, and Prevotella was specifically prevalent in the cecum. Further inspection showed the differences of dominant species in the same segments between these two groups. Notably, unique taxa in C and D segments were more than that in I and J segments. Additionally, each segment was characterized by specifically enriched genera, and distinctive pathways were predicted in certain intestinal segments. In short, the findings presented a coherent picture of structure composition and predicted functionalities of gut microbiota in diverse intestinal segments of adult Chinese Shanxi Black Pigs and Large White Pigs, and extend the understanding of potential link between intestinal microbiota and their hosts.

Increased methane concentration alters soil prokaryotic community structure along an artificial pH gradient Abstract Global climate change may have a large impact on increased emission rates of carbon dioxide and methane to total greenhouse gas emissions from terrestrial wetlands. Methane consumption by soil microbiota in alpine wet meadows serves as a biofilter for the methane produced in the waterlogged soil below. Altered pH regimes change microbial community composition and structure by exerting selection pressure on soil microorganisms with different ecological strategies and thus affect greenhouse gas emissions resulting from the metabolic activity of soil microorganisms. However, responses of prokaryotic communities to artificial pH shift under elevated methane concentration remain unclear. In this study, we assessed diversity and relative abundance of soil prokaryotes in an alpine meadow under elevated methane concentration along an artificial pH gradient using laboratory incubation experiments. We established an incubation experiment treated with artificial pH gradient (pH 4.5–8.5). After 3 months of incubation, 300 ml of methane at a concentration of 20,000 ppm was added to stimulate potential methanothrophs in topsoil. Sequencing of 16S rRNA gene indicated increasing of relative abundances of Crenarchaeota, Chloroflexi, Bacteroidetes, and Planctomycetes in soil after addition of methane, while the relative abundances of Actinobacteria and Gemmatimonadetes did not significant change before and after methane treatment. Results of phylogenetic relatedness of soil prokaryotes showed that microbial community is mostly shaped by deterministic factors. Species indicator analysis revealed distinct OTUs among various pH and methane treatments. Network analysis revealed distinct co-occurrence patterns of soil prokaryotic community before and after methane addition, and different correlation patterns among various prokaryotic taxa. Linear regression model revealed significant decrease of methane oxidation along elevated pH gradient. Soil pH constituted a strong environmental filter in species assembly of soil prokaryotic community. Methane oxidation rates decreased significantly with elevated pH. The interactive effects of elevated methane concentration and pH are therefore promising topic for future research.

Chitinolytic actinobacteria isolated from an Algerian semi-arid soil: development of an antifungal chitinase-dependent assay and GH18 chitinase gene identification Abstract The purpose of this study was to explore the microbial potential of a semi-arid sandy soil from south-central Algeria in order to isolate new chitinolytic actinobacteria. This soil is subjected to high temperatures (up to 43 °C) and has low nutrient content. Strains were isolated by plating soil suspensions on Bennett and Colloidal Chitin (CCM) medium. An initial clustering of isolates was made through BOX-PCR genetic profiling. Next, a 16S rRNA gene sequencing of representative isolates was realized. We also identified optimum physicochemical conditions for chitinolytic activity. A rapid in vitro assay based on glucose catabolic repression was developed to select isolates having a chitinase-dependent antifungal activity against two phytopathogenic fungi. Gene identification of glycosyl hydrolase family 18 (GH18) permitted us to assess the divergence of chitinase genes. Forty isolates were obtained from the semi-arid sandy soil. The molecular identification permitted us to assign them to Streptomyces or Micromonospora genera with seven possibly new bacterial species. For chitinolytic activity, 100% of isolates were able to grow and degrade colloidal chitin at pH 7 and at a temperature ranging from 30 to 40 °C. We also observed that Micromonospora strains had atypical activity patterns, with a strong chitinase activity maintained at high temperature. Finally, three strains presented an interesting chitinolytic potential to reduce fungal growth with new GH18 sequences. This study presents a new rapid method to detect antifungal chitinase-dependent activity that allowed to identify potentially new species of actinobacteria and new GH18 gene sequences.

Exopolysaccharides produced by Lactobacillus plantarum : technological properties, biological activity, and potential application in the food industry Abstract Some lactic acid bacteria are capable of producing capsular or extracellular polysaccharides, with desirable technological properties and biological activities. Such polysaccharides produced by lactic acid bacteria are called exopolysaccharides and can be used to alter rheological properties, acting in processes involving viscosity, emulsification, and flocculation, among others. They may also be involved in prebiotic, probiotic, and biological activities, as well as having potential application in the food industry. In this mini-review, the objectives were to present some beneficial properties of exopolysaccharides (EPS) produced by Lactobacillus plantarum that have not been commercially explored. For that, the article focused to summarize revision of current publications within the following topics: (1) rheological properties, (2) prebiotic properties, (3) biological activities, and (4) potential application in the food industry. EPS produced by Lb. plantarum can be used as gelling agent, emulsifier, or stabilizer for food products. The glucan nature of the produced EPS enhances probiotic properties of this LAB species. Lactobacillus plantarum EPS has antioxidant, antibiofilm, and antitumor activities. Finally, there is an improvement in texture of fermented food products where Lb. plantarum is used as starter culture which is related to EPS production in situ. Therefore, EPS produced by Lb. plantarum have important and desirable properties to be explored for several applications, including health and food areas.

Probiotic properties of Lactobacillus strains with high cinnamoyl esterase activity isolated from jeot-gal, a high-salt fermented seafood Abstract Cinnamoyl esterases (CEs) improve the bioavailability of caffeic acid, a potent antioxidant with beneficial health effects. This study aimed to characterize the probiotic properties of 14 strains of CE-producing lactic acid bacteria (LAB) isolated from jeot-gal, a high-salt fermented seafood. We evaluated properties of the probiotic LAB with high CE activity, including tolerance to low pH and bile salts, antimicrobial activity, surface hydrophobicity, adhesion, and immunomodulatory effects, in vitro. All LAB tested tolerated pH 2.0 and 3% Oxgall, i.e., conditions comparable with those in the gastrointestinal environment. Three isolates, Lactobacillus paracasei JBCC10650, Lactobacillus pentosus JBCC10659, and Lactobacillus plantarum JBCC10543, showed stronger adherence to epithelial cells (12.3, 9.6, and 9.4%) than a commercial probiotic Lactobacillus rhamnosus GG (9.1%; p < 0.05), and exhibited broad antibacterial activity against putative pathogens. Most of the 14 LAB strains were able to regulate mRNA expression of pro- and anti-inflammatory cytokines in macrophages, indicating their potential immunomodulatory effects. Our findings suggest that the newly isolated CE-producing probiotics may show beneficial health effects by supporting the host immune system.

Inhibition of TOR signalling in lea1 mutant induces apoptosis in Saccharomyces cerevisiae Abstract The target of rapamycin, TOR, maintains cell growth and proliferation under vivid environmental conditions by orchestrating wide array of growth-related process. In addition to environmental conditions, e.g., nutrient and stress, TOR also governs cellular response to varied intracellular cues including perturbed intracellular mRNA levels which may arise due to altered regulation of mRNA processing at splicing or turnover levels. The purpose of this study is to explore the role of TOR signalling in growth of cells with accumulated unprocessed RNA. Growth analysis of lea1∆ (splicing deficient) was carried out under varied conditions leading to nitrogen starvation. The expression of TORC1 and TORC2 marker genes was examined in this delete strain. Sensitivity of the lea1∆ towards oxidative agents was observed. Apoptosis was analyzed in caffeine-treated lea1∆ cells. The hypersensitivity of lea1∆ cells towards caffeine is outcome of highly perturbed TOR signalling. The growth defect is independent of PKC pathway. Cells with accumulated unprocessed RNA experience high oxidative stress that induces apoptosis. An inadequate TOR signalling in lea1∆ cells substantiates the effect of oxidative stress induced by accumulated RNA to the extent of inducing cell death via apoptosis.

Hypocholesterolaemic action of Lactobacillus plantarum VJC38 in rats fed a cholesterol-enriched diet Abstract This study was conducted to evaluate hypocholesterolaemic activity of probiotic strains Lactobacillus plantarum VJC38 and VJI21 in Wistar albino rats fed a cholesterol-enriched diet. The experimental animals were divided into five groups (n = 6) viz., normal diet control group (NDC), hypercholesterolaemic diet (HD) control group (HDC), HD supplemented with 3 × 108 CFU/ml of L. plantarum VJC38 group (HD-C38), HD supplemented with 3 × 108 CFU/ml of L. plantarum VJI21 group (HD-I21), and HD supplemented with 3 × 108 CFU/ml of L. rhamnosus GG group (HD-GG) as positive control. Animals were administered bacterial culture by oral gavage once daily for 45 days. After trial, animals were sacrificed and blood samples were collected. Serum total cholesterol (T-CHO), triglyceride (TG), high-density lipoprotein (HDL) cholesterol, glucose, glutamyl pyruvate transaminase (GPT), and glutamyl oxaloacetate transaminase (GOT) levels were determined. Serum low-density lipoprotein (LDL) cholesterol levels were estimated using the Friedewald's equation. Liver and fecal lipid contents and fecal cholic acids were measured. Serum T-CHO levels were significantly decreased by 15.6 and 17.4% in the HD-GG and HD-C38 groups, respectively, but not in the HD-I21 group compared with HDC group (P < 0.05). HD-GG and HD-C38 groups showed 26.3 and 27.2% reduction in serum LDL cholesterol, respectively when compared with HDC group (P < 0.05). Serum LDL cholesterol levels in HD-I21 group were not significantly different from HDC group. Serum TG levels in the HD-GG and HD-C38 were decreased by 14.2 and 22.8%, respectively compared with HDC group (P < 0.05). Liver T-CHO and TG levels in the HD-GG, HD-C38, and HD-I21 were reduced significantly compared with the HDC group (P < 0.05). Atherogenic coefficient values of HD-GG, HD-C38, and HD-21 were significantly decreased compared with HDC group (P < 0.05). Serum GPT levels in the HD-GG, HD-C38, and HD-I21 were decreased by 20.6, 10.9, and 20.6%, respectively, vs. the HDC group. Serum GOT levels were not significantly different among the groups. Serum glucose levels were significantly low in HD-GG, HD-C38, and HD-I21 compared with HDC group (P < 0.05). Fecal cholesterol and cholic acid levels were significantly higher in the HD-C38 and HD-GG groups than other groups (P < 0.05). This study suggests that L. plantarum VJC38 exhibits hypocholesterolaemic effect through hydrolysis of conjugated bile acids in the small intestine and excretion of cholesterol in feces. Lactobacillus plantarum VJC38 could be used as a potential cholesterol-lowering probiotic after validation of the hypocholesterolaemic activity in placebo-controlled human clinical trials.

Macrophomina phaseolina : microbased biorefinery for gold nanoparticle production Abstract Biofabrication of nanoparticles via the principles of green nanotechnology is a key issue addressed in nanobiotechnology research. There is a growing need for development of a synthesis method for producing biocompatible stable nanoparticles in order to avoid adverse effects in medical applications. We report the use of simple and rapid biosynthesis method for the preparation of gold nanoparticles using Macrophomina phaseolina (Tassi) Goid, a soil-borne pathogen. The effect of pH and temperature on the synthesis of gold nanoparticles by M. phaseolina was also assessed. Different techniques like UV-Visible Spectroscopy, Transmission Electron Microscopy (TEM), Dynamic light scattering (DLS) measurements, Fourier transform infrared (FTIR), and EDX were used to characterize the gold nanoparticles. The movement of these gold nanoparticles inside Escherichia coli (ATCC11103) along with effect on growth and viability was evaluated. The biogenic gold nanoparticle was synthesized at 37 °C temperature and neutral pH. UV-Visible Spectroscopy, TEM, EDX, and DLS measurements confirm the formation of 14 to 16 nm biogenic gold nanoparticles. FTIR substantiates the presence of protein capping on Macrophomina phaseolina-mediated gold nanoparticles. The non-toxicity of gold nanoparticles was confirmed by the growth and viability assay while the TEM images validated the entry of gold nanoparticles without disrupting the structural integrity of E. coli. Biogenic method for the synthesis of nanoparticles using fungi is novel, efficient, without toxic chemicals. These biogenic gold nanoparticles themselves are nontoxic to the microbial cells and offer a better substitute for drug delivery system.