Influence of Organic Matter on the Transport of Mineral Colloids in the River-Sea Transition Zone

The River-Sea Transition Zone has a significant impact on marine ecosystems, especially at present, due to increased anthropogenic pressure on rivers. The colloidal form of river runoff has not been practically studied, unlike the dissolved and suspended one, but this form is particularly important for the transport of river substances. The mechanisms of substance transfer were studied using model systems (colloidal clay, Fe(OH)3 sol), particle aggregation was estimated by changes in optical density, turbidity and particle size. The influence of the nature of dissolved organic matter (DOM) and salinity on colloid transport was studied. It was found that humic substances (HS) (recalcitrant DOM) stabilize mineral colloids with increasing salinity, while their interaction with chitosan (labile DOM) promotes flocculation and further precipitation in the mixing zone. In natural conditions, labile DOM can be released during viral lysis of bacteria or salt stress of biota. It was shown that clay particles modified with HS are flocculated more effectively than pure clays. HS can facilitate the transport of Fe(OH)3 into the outer part of the mixing zone even in the presence of flocculants. The flocculation mechanism and modern views on this process are considered

The Variability of the Order Burkholderiales Representatives in the Healthcare Units

Background and Aim. The order Burkholderiales became more abundant in the healthcare units since the late 1970s; it is especially dangerous for intensive care unit patients and patients with chronic lung diseases. The goal of this investigation was to reveal the real variability of the order Burkholderiales representatives and to estimate their phylogenetic relationships. Methods. 16S rDNA and genes of the Burkholderia cenocepacia complex (Bcc) Multi Locus Sequence Typing (MLST) scheme were used for the bacteria detection. Results. A huge diversity of genome size and organization was revealed in the order Burkholderiales that may prove the adaptability of this taxon’s representatives. The following variability of the Burkholderiales in Russian healthcare units has been revealed: Burkholderiaceae (Burkholderia, Pandoraea, and Lautropia), Alcaligenaceae (Achromobacter), and Comamonadaceae (Variovorax). The Burkholderia genus was the most diverse and was represented by 5 species and 16 sequence types (ST). ST709 and 728 were transmissible and often encountered in cystic fibrosis patients and in hospitals. A. xylosoxidans was estimated by 15 genotypes. The strains of first and second ones were the most numerous. Conclusions. Phylogenetic position of the genus Lautropia with smaller genome is ambiguous. The Bcc MLST scheme is applicable for all Burkholderiales representatives for resolving the epidemiological problems