Light and storage time influence the microbial quality of minimally processed rocket

Ready-to-eat minimally processed fruits and vegetables are an ideal substrate for the growth of microorganisms, including human pathogens and mycotoxin-producing species, which question their quality and safety for customers. While we are aware of the importance of production workflows in structuring the products' microbial communities, we still know little about the factors that shape microbiomes during the timeframe products are available to customers, and beyond this timeframe. Here, we study the influence of storage light condition (light or dark) on microbiological and physico-chemical parameters of minimally processed rocket leaves at different shelf life timepoints (the day the product becomes available to consumers, expiration date, 3 days after the expiration date). Our results suggest that the total microbial load increases from the day the product becomes available to consumers, to the expiry date and after the product's expiration. However, when studying the composition of the fungal microbiome, we did not observe significant changes in its structure as the effect of product shelf life or storage light condition. We also found that products stored under light condition had a higher total bacterial load compared to those stored in darkness. Our results might be helpful in crafting improved workflows for product's storage during its shelf life, which might ultimately lead to a re-evaluation of storage times resulting in reduced food waste due to product spoilage or expiration.     

Heterologous expression and periplasmic secretion of an antifungal Bacillus amyloliquefaciensBLB369 endo‐β‐1,3‐1,4‐glucanase in Escherichia coli

The endo‐β‐1,3‐1,4‐glucanases are glycoside hydrolases involved in the enzymatic depolymerization of 1,3‐1,4 β‐glucans and showed an antifungal activity against some fungi. Bacillus amyloliquefaciensBLB369 has a high antagonistic activity against phytopathogenic fungi. Its glu369 full‐coding sequence of the endo‐β‐1,3‐1,4‐glucanase gene (732 bp) was sequenced, cloned and successfully expressed in Escherichia coli Top10. The encoded protein (243 amino acids) has a calculated molecular mass of 27.3 kDa. To simplify the purification procedure, the glu369 coding sequence was cloned into the vector pKJD4. The produced OmpA‐His‐Glu369 harboured OmpA signal sequence for E. coli periplasmic localization and followed by a 6His residues for its purification. The purified His‐tagged proteins revealed two bands on SDS‐PAGE analysis with molecular masses of about 30.5 (His‐Glu369) and 32.5 kDa (OmpA‐His‐Glu369). They had the ability to inhibit the growth of phytopathogenic fungus Alternaria alternata. These favourable properties make the endo‐β‐1,3‐1,4‐glucanase a good candidate for biotechnological applications.     

Triangular gold nanoparticles modify shell characteristics and increase antioxidant enzyme activities in the clam Ruditapes decussatus

Context: Nanoparticles may cause adverse environmental effects but there is limited information on their interactions with marine organisms.

Objective: Our aim was to examine the effects of triangular gold nanoparticles (Tr-Au NPs) on the clam, Ruditapes decussatus.

Materials and methods: Clams were exposed to Tr-Au1?=?5?µg/L and Tr-Au2?=?10?µg/L for 2 and 7?days. Effects on shell structure were investigated. Superoxide dismutase (SOD), catalase (CAT), glutathione transferase (GST) activities, protein carbonyl levels and malondialdehyde content were used to assess biochemical status.

Results: Transmission electron microscopy (TEM) and electron dispersive X-ray microanalysis (EDX) showed that Tr-Au NPs modified shell structure and morphology. Tr-Au NPs size increased forming aggregate particles. Tr-Au NPs increased SOD, CAT and GST activities in gill and digestive gland in a concentration- and time-dependent manner indicating defence against oxidative stress. Enhanced lipid peroxidation and protein carbonyl levels confirmed oxidative stress.

Conclusion: Tr-Au NPs cause oxidative stress and affect shell structure of clams. These findings may have relevance to other marine species.     

Physiological responses and antioxidant enzyme changes in <Emphasis Type="Italic">Sulla coronaria</Emphasis> inoculated by cadmium resistant bacteria

Plant growth promoting bacteria (PGPB) may help to reduce the toxicity of heavy metals on plants growing in polluted soils. In this work, Sulla coronaria inoculated with four Cd resistant bacteria (two Pseudomonas spp. and two Rhizobium sullae) were cultivated in hydroponic conditions treated by Cd; long time treatment 50 µM CdCl₂ for 30 days and short time treatment; 100 µM CdCl₂ for 7 days. Results showed that inoculation with Cd resistant PGPB enhanced plant biomass, thus shoot and root dry weights of control plants were enhanced by 148 and 35% respectively after 7 days. Co-inoculation of plants treated with 50 and 100 µM Cd increased plant biomasses as compared to Cd-treated and uninoculated plants. Cadmium treatment induced lipid peroxidation in plant tissues measured through MDA content in short 7 days 100 µM treatment. Antioxidant enzyme studies showed that inoculation of control plants enhanced APX, SOD and CAT activities after 30 days in shoots and SOD, APX, SOD, GPOX in roots. Application of 50 µM CdCl₂ stimulated all enzymes in shoots and decreased SOD and CAT activities in roots. Moreover, 100 µM of CdCl₂ increased SOD, APX, CAT and GPOX activities in shoots and increased significantly CAT activity in roots. Metal accumulation depended on Cd concentration, plant organ and time of treatment. Furthermore, the inoculation enhanced Cd uptake in roots by 20% in all treatments. The cultivation of this symbiosis in Cd contaminated soil or in heavy metal hydroponically treated medium, showed that inoculation improved plant biomass and increased Cd uptake especially in roots. Therefore, the present study established that co-inoculation of S. coronaria by a specific consortium of heavy metal resistant PGPB formed a symbiotic system useful for soil phytostabilization.     

Physiological and biochemical parameters: new tools to screen barley root exudate allelopathic potential (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L. subsp. <Emphasis Type="Italic">vulgare</Emphasis>)

Morphological markers/traits are often used in the detection of allelopathic stress, but optical signals including chlorophyll a fluorescence emission could be useful in developing new screening techniques. In this context, the allelopathic effect of barley (Hordeum vulgare subsp. vulgare) root exudates (three modern varieties and three landraces) were assessed on the morphological (root and shoot length, biomass accumulation), physiological (F_v/F_m and F₀), and biochemical (chlorophyll and protein contents) variables of great brome (Bromus diandrus Roth., syn. Bromus rigidus Roth. subsp. gussonii Parl.). All the measured traits were affected when great brome was grown in a soil substrate in which barley plants had previously developed for 30 days before being removed. The response of receiver plants was affected by treatment with activated charcoal, dependent on barley genotype and on the nature of the growing substrate. The inhibitory effect was lower with the addition of the activated charcoal suggesting the release of putative allelochemicals from barley roots into the soil. The barley landraces were more toxic than modern varieties and their effect was more pronounced in sandy substrate than in silty clay sand substrate. In our investigation, the chlorophyll content and F_v/F_m were the most correlated variables with barley allelopathic potential. These two parameters might be considered as effective tools to quantify susceptibility to allelochemical inhibitors in higher plants.     

New horizons in culture and valorization of red microalgae

Research on marine microalgae has been abundantly published and patented these last years leading to the production and/or the characterization of some biomolecules such as pigments, proteins, enzymes, biofuels, polyunsaturated fatty acids, enzymes and hydrocolloids. This literature focusing on metabolic pathways, structural characterization of biomolecules, taxonomy, optimization of culture conditions, biorefinery and downstream process is often optimistic considering the valorization of these biocompounds. However, the accumulation of knowledge associated with the development of processes and technologies for biomass production and its treatment has sometimes led to success in the commercial arena. In the history of the microalgae market, red marine microalgae are well positioned particularly for applications in the field of high value pigment and hydrocolloid productions. This review aims to establish the state of the art of the diversity of red marine microalgae, the advances in characterization of their metabolites and the developments of bioprocesses to produce this biomass.     

Amycolatopsis camponoti sp. nov., new tetracenomycin-producing actinomycete isolated from carpenter ant Camponotus vagus

An actinobacterial strain A23^T, isolated from adult ant Camponotus vagus collected in Ryazan region (Russia) and established as tetracenomycin X producer, was subjected to a polyphasic taxonomic study. Morphological characteristics of this strain included well-branched substrate mycelium and aerial hyphae fragmented into rod-shaped elements. Phylogenetic analyses based on 16S rRNA gene and genome sequences showed that strain A23^T was most closely related to Amycolatopsis pretoriensis DSM 44654^T. Average nucleotide identity and digital DNA–DNA hybridization values between the genome sequences of isolate A23^T and its closest relative, Amycolatopsis pretoriensis DSM 44654^T, were 39.5% and 88.6%, which were below the 70% and 95–96% cut-off point recommended for bacterial species demarcation, respectively. The genome size of the isolate A23^T was 10,560,374 bp with a DNA G?+?C content of 71.2%. The whole-cell hydrolysate contained meso-diaminopimelic acid and arabinose and galactose as main diagnostic sugars as well as ribose and rhamnose. It contained MK-9(H4) as the predominant menaquinone and iso-C_16:0, iso-C_15:0, anteiso-C_17:0 and C_16:0 as the major cellular fatty acids. Diphosphatidylglycerol and phosphatidylethanolamine prevailed among phospholipids. Mycolic acids were not detected. Based on the phenotypic, genomic and phylogenetic data, isolate A23^T represents a novel species of the genus Amycolatopsis, for which the name Amycolatopsis camponoti sp. nov. is proposed, and the type strain is A23^T (=?DSM 111725^T?=?VKM Ac-2882^T).

     

Overexpression of wheat dehydrin DHN-5 enhances tolerance to salt and osmotic stress in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Late Embryogenesis Abundant (LEA) proteins are associated with tolerance to water-related stress. A wheat (Triticum durum) group 2 LEA proteins, known also as dehydrin (DHN-5), has been previously shown to be induced by salt and abscisic acid (ABA). In this report, we analyze the effect of ectopic expression of Dhn-5 cDNA in Arabidopsis thaliana plants and their response to salt and osmotic stress. When compared to wild type plants, the Dhn-5 transgenic plants exhibited stronger growth under high concentrations of NaCl or under water deprivation, and showed a faster recovery from mannitol treatment. Leaf area and seed germination rate decreased much more in wild type than in transgenic plants subjected to salt stress. Moreover, the water potential was more negative in transgenic than in wild type plants. In addition, the transgenic plants have higher proline contents and lower water loss rate under water stress. Also, Na⁺ and K⁺ accumulate to higher contents in the leaves of the transgenic plants. Our data strongly support the hypothesis that Dhn-5, by its protective role, contributes to an improved tolerance to salt and drought stress through osmotic adjustment.