Production of novel polyhydroxyalkanoates (PHAs), biodegradable polymers for
biomedical applications, and biomaterials based on them is a promising trend in
modern bioengineering. We studied the ability of an effective strain-producer
Azotobacter chroococcum 7B to synthesize not only
poly(3-hydroxybutyrate) homopolymer (PHB) and its main copolymer
poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), but also a novel
copolymer, poly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate) (PHB4MV). For
the biosynthesis of PHB copolymers, we used carboxylic acids as additional
carbon sources and monomer precursors in the chain of synthesized copolymers.
The main parameters of these polymers’ biosynthesis were determined:
strain-producer biomass yield, polymer yield, molecular weight and monomer
composition of the synthesized polymers, as well as the morphology of
A. chroococcum 7B bacterial cells. The physico-chemical
properties of the polymers were studied using nuclear magnetic resonance
spectroscopy (NMR), differential scanning calorimetry (DSC), contact angle
test, and other methods. In vitro biocompatibility of the
obtained polymers was investigated using stromal cells isolated from the bone
marrow of rats with the XTT cell viability test. The synthesis of the novel
copolymer PHB4MV and its chemical composition were demonstrated by NMR
spectroscopy: the addition of 4-methylvaleric acid to the culture medium
resulted in incorporation of 3-hydroxy-4-methylvalerate (3H4MV) monomers into
the PHB polymer chain (0.6 mol%). Despite the low molar content of 3H4MV in the
obtained copolymer, its physico-chemical properties were significantly
different from those of the PHB homopolymer: it has lower crystallinity and a
higher contact angle, i.e. the physico-chemical properties of the PHB4MV
copolymer containing only 0.6 mol% of 3H4MV corresponded to a PHBV copolymer
with a molar content ranging from 2.5% to 7.8%. In vitro
biocompatibility of the obtained PHB4MV copolymer, measured in the XTT
test, was not statistically different from the cell growth of PHB and PHBV
polymers, which make its use possible in biomedical research and development.
Soil surface wettability is the main physical property that defines organization of elementary soil particles into soil structure. Human impact affects the changing in properties of soils under arable land use. The objective of this research is to study this impact by the example of two profiles of Chernozems (Kursk region), located under the forest and at the arable field. For both profiles some soil solid phase properties (contact angle, aggregate composition, aggregate waterstability) were measured. There was a positive correlation between the content of organic matter and soil’s wettability in studied soils – a growth of contact angle with the increasing the content of organic matter. Under the forest the content of soil organic matter was changed from 6.41% on the surface to 1.9% at the depth of 100 cm. In the Chernozem under the arable land use the organic carbon content in arable horizon is almost two times less. The maximum of hydrophobicity (78.1°) was observed at the depth of 5 cm under the forest. In the profile at the arable field the contact angle value at the same depth was 50°. The results of the structure analysis showed a decrease in the content of agronomically valuable and water stable aggregates in the profile under arable land.
Kaolinite suspensions were inoculated by microorganisms (Bacillus velezensis) for 2 months. During the period of inoculation the formation of microaggregates of a certain shape and size was traced by electron microscopy. During the experiment the initially predominant planar structure was partially transformed. The newly-formed large (up to 250 µm in diameter) organo-mineral aggregate-like particles were registered. We suppose that during the 2-month period of incubation B. velezensis microorganisms partially destroyed the crystal structure of minerals to obtain the vitally necessary potassium. The protein compounds produced by bacteria hydrophobized the surface of the minerals which resulted in the formation of organo-mineral aggregates by bonds of hydrophobic-hydrophilic interaction.
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