Because of significant yield losses caused by fungal pathogens, new efficient and environmentally safe methods of pest control are needed, and amphiphilic compounds (biosurfactants) produced by many microbes are considered a good alternative. In the present study, biosurfactants produced by the rhizosphere isolate Bacillus mojavensis P1709 were assessed for their ability to protect postharvest cherry tomatoes from decay and mycotoxin contamination caused by Fusarium oxysporum f. sp. lycopersici. It was demonstrated that the genome of B. mojavensis P1709 contained the fenD and srfAA genes, which are responsible for the synthesis of compounds of the fengycin and surfactin families. APF (acid-precipitated fraction) of B. mojavensis P1709 culture medium at a concentration of 20 g L−1 inhibited pathogen radial growth on agar plates by 93%, and T-2 and HT-2 mycotoxin production by 98%, after 5 days of cultivation. APF also suppressed fungal growth in the in vivo test on cherry tomato fruits by 93% and 25% on the 2nd and 7th days of incubation, respectively. The results obtained demonstrate that biosurfactants produced by B. mojavensis P1709 are an efficient tool for protecting postharvest cherry tomatoes from fungal mold decay and mycotoxin contamination.
Around the globe, only 30–50% of the amount of oil estimated to be in reservoirs (“original oil in place”) can be obtained using primary and secondary oil recovery methods. Enhanced oil recovery methods are required in the oil processing industry, and the use of microbially produced amphiphilic molecules (biosurfactants) is considered a promising efficient and environmentally friendly method. In the present study, biosurfactants produced by the Pseudomonas putida PP021 isolate were extracted and characterized, and their potential to enhance oil recovery was demonstrated. It was found that the cell-free biosurfactant-containing supernatant decreased the air–water interface tension from 74 to 28 mN m−1. Using TLC and FTIR methods, the biosurfactants produced by the isolate were classified as mono- and di-rhamnolipid mixtures. In the isolates’ genome, the genes rhlB and rhlC, encoding enzymes involved in the synthesis of mono- and di-rhamnolipids, respectively, were revealed. Both genes were expressed when the strain was cultivated on glycerol nitrate medium. As follows from the sand-packed column and core flooding simulations, biosurfactants produced by P. putida PP021 significantly enhance the degree of recovery, resulting in additional 27% and 21%, respectively.
Rhamnolipids as biosurfactants have a potentially wide range of applications, for example, as “green” surfactants or components of drug delivery systems, which is associated with the features of their interaction with cell membranes. However, as noted in the literature, those kind of features have not been sufficiently studied now. This paper presents a study of the interaction of a natural mixture of rhamnolipids produced by bacteria of the rhizosphere zone of plants Pseudomonas aeruginosa with model membranes—liposomes based on dioleoylphosphatidylcholine (DOPC), depending on the method of their preparation and the content of sterols—ergosterol, cholesterol, lanosterol. Liposomes with rhamnolipids were prepared by two protocols: with film method from a mixture of DOPC and rhamnolipids; with film method from DOPC and injection of water solution of rhamnolipids. Joint analysis of the data of 31P NMR spectroscopy and ATR-FTIR spectroscopy showed that in the presence of rhamnolipids, the mobility of the head group of the DOPC phospholipid increases, the conformational disorder of the hydrophobic tail increases, and the degree of hydration of the C=O and P=O groups of the phospholipid decreases. It can be assumed that, when prepared from a mixture, rhamnolipids are incorporated into the membrane in the form of clusters and are located closer to the middle of the bilayer; while when prepared by injection, rhamnolipid molecules migrate into the membrane in the form of individual molecules and are located closer to the head part of phospholipids. The sterol composition of the model membrane also affects the interaction of rhamnolipids with the membrane. Here it is worth noting the possible presence of type of interaction between rhamnolipids and ergosterol differ from other investigated sterols, due to which rhamnolipid molecules are embedded in the area where ergosterol is located.
Biosurfactants produced by soil microorganisms are now widely used in various industries and are able to compete with synthetic detergents. However, in contrast with chemical surfactants, biological ones have disadvantage: it is difficult to obtain the product of high purity since the microbes usually produce a complex mixture of compounds, besides the cultural medium itself contains a lot of various components. Thus, the conventional scheme of lipopeptide isolation involves acid precipitation, extraction with the solvent, filtration and drying. However, it is reported that often the biosurfactants obtained still contain a lot of impurities, and new methods are required to obtain the compounds of higher quality. This work presents the application of a new method for purifying of lipopeptides produced by Bacillus subtilis strain HZMJW 1-10 to obtain highly pure product. It was compared with the conventional method, which yielded up to 100 mg l-1, while the yield of the new product was only 9 mg l-1. However, the product was completely colorless, did not contain foreign impurity phases, that can influence biological and physical properties. Emulsifying activity (E24) with crude oil at 100 ppm was estimated to be 60% and 85% for the conventional and new products, respectively. FTIR spectrum of the new product contained less peaks in the non-specific regions as compared with that of the conventional one.
Public gardens and park zones are an important and widely visited component of urban spaces worldwide, however they can be polluted and even dangerous for humans and animals visiting them. The simplest way to screen the level of pollution of those green zones is to assess their ecological toxicity. In the present study, to assess the ecotoxicity of soil and ground samples obtained in 15 parks and public gardens in the city of Kazan (Russia) with 1 Mio citizens were investigated. Two elutriate assays with Ceriodaphnia affinis and Chlorella vulgaris and one contact assay with Bacillus pumilus were used in order to estimate the ecotoxicity of the samples. It was revealed that B. pumilus was less sensitive to the components present in ground samples from the green zones. Thus, the lowest toxicity of the undiluted sample was estimated to be 3.33% (sample Gorkiy Central Park of Culture and Leisure) and the highest � 27% (�Dubovyj kordon� public garden). For C. affinis, we managed to assess the toxicity without dilution step for 7 samples out of 15. For the other 8 samples, the additional dilution series was prepared, and the LID10 index was calculated. Thus, the LID10 index these samples for C.affinis ranged from 34 to 40, for Chl. vulgaris varied from 13 to 50. It should be noted that samples with the highest toxicity (revealed for at least one test object) were obtained from the parks that visually looked less clean and organized.
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