New Malolactic Bacteria Strains Isolated from Wine Microbiota. Characterization and Technological Properties

Malolactic fermentation (MLF) or biological decrease of wine acidity is defined as the enzymatic bioconversion of malic acid in lactic acid, a process performed by lactic acid bacteria (LAB). The procedures for the isolation of new indigenous LAB strains from the red wines produced in Copou Iasi wine center (NE of Romania) undergoing spontaneous malolactic fermentation, resulted in the obtaining of 67 catalase-negative and Gram-positive LAB strains. After testing in the malolactic fermentative process, application of specific screening procedures and identification (API 50 CH), two bacterial strains belonging to the species Oenococcus oeni (strain 13-7) and Lactobacillus plantarum (strain R1-1) with high yield of malolactic bioconversion, non-producing biogenic amines, and with active extracellular enzymes related to wine aroma, were retained and characterized. Tested in synthetic medium (MRS-TJ) for 10 days, the new isolated LAB strains metabolized over 98% of the malic acid at ethanol concentrations between 10 and 14 % (v/v), low pH (>3.0), total SO2 doses up to 70 mg/L and temperatures between 15 and 35 °C, showing high potential for future use in the winemaking process as bacterial starter cultures, in order to obtain high quality wines with increased typicity.

Culturable Bacterial Isolates from Arctic Soil shows High Biotechnological Potential

Polar microbiology remains as the most fascinating area of research which mainly focuses on exploration of psychrophilic organisms for having their cold-active enzymes of biotechnological potential. In this study, we have explored a culturable bacterial community and isolated 27 bacterial isolates with a different morphology from an unexplored site of Arctic region, for the possibility of identifying various active biomolecules. Screening of various isolates in a culture dependent manner helped us to identify strains capable of producing extracellular enzymes. The optimal growth parameters of most of the isolates are ranges between 18-22°C temperature, 3-5 days of incubation, 6-9 pH, and 3-5% (w/v) NaCl in LB media. It has also been found that among these isolates, 63% are able to produce lipase, 17% amylase, 7% xylanase and 7% isolates have responded for phosphatase activity but there are no isolates found for gelatinase and cellulase production ability. In addition, few isolates can also produce secretory protease, urease, β-galactosidase, etc. 16SrRNA gene sequence-based phylogeny revealed that the isolates belong to the genera of Psychrobacter, Planococcus, Halomonas, Arthrobacter, Oceanisphaera, Marinbacter, Pseudomonas, Algoriphagus. Strikingly, none of the Arctic isolates showed resistance towards commonly used antibiotics which indicates that the unexplored habitat is devoid of antibiotic exposure and so does the rise of antimicrobial resistance. The structure-function relationship of the isolated bioactive compounds from these isolates are the major focus of future research.

The lolB gene in Xanthomonas campestris pv. campestris is required for bacterial attachment, stress tolerance, and virulence

Background Xanthomonas campestris pv. campestris (Xcc) is a Gram-negative bacterium that can cause black rot disease in crucifers. The lipoprotein outer membrane localization (Lol) system is involved in the lipoprotein sorting to the outer membrane. Although Xcc has a set of annotated lol genes, there is still little known about the physiological role in this phytopathogen. In this study, we aimed to characterize the role of LolB of Xcc in bacterial attachment, stress tolerance, and virulence. Results To characterize the role of LolB, lolB mutant was constructed and phenotypic evaluation was performed. The lolB mutant revealed reductions in bacterial attachment, extracellular enzyme production, and virulence. Mutation of lolB also resulted in reduced tolerance to a myriad of stresses, including heat and a range of membrane-perturbing agents. Trans-complementation of lolB mutant with intact lolB gene reverted these altered phenotypes to the wild-type levels. From subsequent reporter assay and reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) analysis, the expression of genes that encode the major extracellular enzymes and the stress-related proteins was reduced after lolB mutation. Conclusions The results in this work contribute to the functional understanding of lolB in Xanthomonas for the first time, and provide new insights into the function of lolB in bacteria.

Effects of Different Soils on the Biomass and Photosynthesis of Rumex nepalensis in Subalpine Region of Southwestern China

The performance of Rumex nepalensis, an important medicinal herb, varies significantly among subalpine grasslands, shrublands and forest ecosystems in southwestern China. Plant–soil feedback is receiving increasing interest as an important driver influencing plant growth and population dynamics. However, the feedback effects of soils from different ecosystems on R. nepalensis remain poorly understood. A greenhouse experiment was carried out to identify the effects of different soil sources on the photosynthesis and biomass of R. nepalensis. R. nepalensis was grown in soils collected from the rooting zones of R. nepalensis (a grassland soil, RS treatment), Hippophae rhamnoides (a shrub soil, HS treatment), and Picea asperata (a forest soil, PS treatment). The chlorophyll contents, net photosynthetic rates, and biomasses of R. nepalensis differed significantly among the three soils and followed the order of RS > HS > PS. After soil sterilization, these plant parameters followed the order of RS > PS > HS. The total biomass was 16.5 times higher in sterilized PS than in unsterilized PS, indicating that the existence of soil microbes in P. asperata forest ecosystems could strongly inhibit R. nepalensis growth. The root to shoot biomass ratio of R. nepalensis was the highest in the sterilized PS but the lowest in the unsterilized PS, which showed that soil microbes in PS could change the biomass allocation. Constrained redundancy analysis and path analysis suggested that soil microbes could impact the growth of R. nepalensis via the activities of soil extracellular enzymes (e.g., β-1,4-N-acetylglucosaminidase (NAG)) in live soils. The soil total soluble nitrogen concentration might be the main soil factor regulating R. nepalensis performance in sterilized soils. Our findings underline the importance of the soil microbes and nitrogen to R. nepalensis performance in natural ecosystems and will help to better predict plant population dynamics.

Salicylic acid effect on the mechanism of Lelliottia amnigena causing potato soft rot

Salicylic acid (SA) plays an important role in protecting plants from biotic stresses. Lelliottia amnigena is a newly identified potato soft rot pathogen and there are no adequate studies on this soft rot pathogen. Therefore, this paper focussed on the effect of SA on the mechanism under which L. amnigena causes potato soft rot. L. amnigena was examined and detected to secrete pectinase, proteases, pectin lyase and cellulase, which are the most important pathogenic enzymes involved in the production of plant diseases. Sterilised healthy potato tubers were inoculated with 0.2 mL of L. amnigena suspension (3.69 CFU · mL−1 × 107 CFU · mL−1). After 24 h, 200 μL of four different SA concentrations (0.5 mM, 1.0 mM, 1.5 mM and 2.0 mM) were used to treat the tubers. Co-culture of L. amnigena and SA significantly reduced the activity of pectinase, protease, pectin lyase and cellulase by an average of 33.8%, 43.4%, 67.7% and 46.9%, across the four concentrations (0.5 mM, 1.0 mM, 1.5 mM and 2.0 mM), respectively, compared to the control. The average disease index was reduced by 54.7% across the four SA concentrations. Treatment with SA induced transcriptional levels of the superoxide dismutase, peroxide, catalase and glutathione S-transferase across the four levels by an average of 3.87, 3.25, 3.97 and 3.94-fold, respectively, compared to control. Based on our results, we could state that SA could reduce the activities of these extracellular enzymes produced by L. amnigena by modulating both enzymatic and non-enzymatic antioxidant activities and gene expression that induce natural resistance in plants against bacterial infections.

Misconception of consumers and retailers regarding fungal spoilage of onion and prevalence of fungi in rotten onion

Onion is an inevitable part of our food habits. Fungal infection is one of the major reasons of onion spoilage which not only cause economic losses but also may cause public health threat through mycoses and mycotoxicoses. A total 15 onion samples from different places in Chattagram, Bangladesh were collected to assess the fungal contaminants.Onion consumers along with retailers were interviewed to evaluate their awareness about fungal food spoilage and associated health risk. Three different fungal species were identified and isolated by analysing their macroscopic and microscopic features. These isolates were Aspergillus niger, Aspergillus flavus, and Penicillium spp. A. niger was the most prevalent and found in 14 samples out of 15. Biochemical characterization of the isolated fungi was also done to assess their ability to produce extracellular enzymes and amylase, protease, and cellulase activities were observed. Survey data showed that only around 20% of the interviewees had some idea about fungal contamination, while nearly about 80% of them believed that washing, sunburn and cooking can make the food safe. Bioresearch Commu. 8(1): 1068-1076, 2022 (January)

Role of Growth-Promoting Bacteria as Biocontrol Agent Against Root Knot Nematode of Tomato

There are significant losses which have occurred in crops due to the infestation of plant parasitic nematode which are known as hidden enemy due to their presence in rhizosphere and their infection site on the roots. Synthetic nematicidal control is an effective strategy to combat this biotic stress but an inappropriate and deficient application of chemical pesticides have an adverse effect on soil micro-flora and fauna. Due to the environmental and regulatory pressure, use of potential biocontrol agents is the new approach for nematode management by the farming community. For this study, four potential rhizobacteria from different habitats BHU1, BHU2, BHU3 and BHU4 were assessed for their antagonistic activities against Meloidogyne incognita infecting tomato plant. These were characterized on the basis of their morphological and biochemical activities. In vitro screening of bacterial isolates was conducted in a 25-microwell plate by addition of second stage juvenile (J2) of M. incognita with nematode application. Among four bacteria,, three potential antagonistic bacteria were able to kill nematode within 24 hours. Mortality percentage of J2 M. incognita observed in sterile distilled water selected bacterial isolates ranged from 23.33 to 100% in 3h to 24h periods. Moreover, all bacterial isolates except BHU2 isolate were found positive for production of extracellular enzymes like catalase, oxidase, chitinase, amylase and gelatinase which favour effective biopesticide activity of bacteria. Further selected isolates of bacteria associated with tomato have shown a great potential as biocontrol agents against root-knot nematode in tomato during pot experiment. Based on the fact stated above, the current research focused on plant growth promoting rhizobacteria based nematodes biocontrol strategies with direct and indirect mechanism of PGPR for nematode management.

Extracellular Enzyme Activities and Carbon/Nitrogen Utilization in Mycorrhizal Fungi Isolated From Epiphytic and Terrestrial Orchids

Fungi employ extracellular enzymes to initiate the degradation of organic macromolecules into smaller units and to acquire the nutrients for their growth. As such, these enzymes represent important functional components in terrestrial ecosystems. While it is well-known that the regulation and efficiency of extracellular enzymes to degrade organic macromolecules and nutrient-acquisition patterns strongly differ between major fungal groups, less is known about variation in enzymatic activity and carbon/nitrogen preference in mycorrhizal fungi. In this research, we investigated variation in extracellular enzyme activities and carbon/nitrogen preferences in orchid mycorrhizal fungi (OMF). Previous research has shown that the mycorrhizal fungi associating with terrestrial orchids often differ from those associating with epiphytic orchids, but whether extracellular enzyme activities and carbon/nitrogen preference differ between growth forms remains largely unknown. To fill this gap, we compared the activities of five extracellular enzymes [cellulase, xylanase, lignin peroxidase, laccase, and superoxide dismutase (SOD)] between fungi isolated from epiphytic and terrestrial orchids. In total, 24 fungal strains belonging to Tulasnellaceae were investigated. Cellulase and xylanase activities were significantly higher in fungi isolated from terrestrial orchids (0.050 ± 0.006 U/ml and 0.531 ± 0.071 U/ml, respectively) than those from epiphytic orchids (0.043 ± 0.003 U/ml and 0.295 ± 0.067 U/ml, respectively), while SOD activity was significantly higher in OMF from epiphytic orchids (5.663 ± 0.164 U/ml) than those from terrestrial orchids (3.780 ± 0.180 U/ml). Carboxymethyl cellulose was more efficiently used by fungi from terrestrial orchids, while starch and arginine were more suitable for fungi from epiphytic orchids. Overall, the results of this study show that extracellular enzyme activities and to a lesser extent carbon/nitrogen preferences differ between fungi isolated from terrestrial and epiphytic orchids and may indicate functional differentiation and ecological adaptation of OMF to local growth conditions.

Potential Antagonistic Bacteria against Verticillium dahliae Isolated from Artificially Infested Nursery

As an ecofriendly biocontrol agent, antagonistic bacteria are a crucial class of highly efficient fungicides in the field against Verticillium dahliae, the most virulent pathogen for cotton and other crops. Toward identifying urgently needed bacterial candidates, we screened bacteria isolated from the cotton rhizosphere soil for antagonisitic activity against V. dahliae in an artificially infested nursery. In preliminary tests of antagonistic candidates to characterize the mechanism of action of on culture medium, 88 strains that mainly belonged to Bacillus strongly inhibited the colony diameter of V. dahliae, with inhibiting efficacy up to 50% in 9 strains. Among the most-effective bacterial strains, Bacillus sp. ABLF-18, and ABLF-50 and Paenibacillus sp. ABLF-90 significantly reduced the disease index and fungal biomass of cotton to 40–70% that of the control. In further tests to elucidate the biocontrol mechanism (s), the strains secreted extracellular enzymes cellulase, glucanase, and protease, which can degrade the mycelium, and antimicrobial lipopeptides such as surfactin and iturin homologues. The expression of PAL, MAPK and PR10, genes related to disease resistance, was also elicited in cotton plants. Our results clearly show that three candidate bacterial strains can enhance cotton defense responses against V. dahliae; the secretion of fungal cell-wall-degrading enzymes, synthesis of nonribosomal antimicrobial peptides and induction of systemic resistance shows that the strains have great potential as biocontrol fungicides.