# Microbial Life on the Surface of Microlgistics in Natural Waters
## 2 Bacterial Neuston as a Source of Microorganisms for Interaction with Microplastics  
The term neuston was proposed by Swedish hydrobiologist [PERSON] [33] for determination of the inhabitants of the surface film of a body of small reservoirs with fresh water. Life of the near-surface layer of the sea remained unexplored for a long time. It is believed that a number of factors, namely, solar radiation, shortwave ultraviolet light penetrating the depths of water just a few centimeters, heaving of the sea, unsteady-state temperature, especially seasonal temperature changes, create impossible living conditions for marine inhabitants. However, [PERSON] in 1959 discovered this when studying the distribution of mullet roe in marine neustons in the Black Sea [34; 35; 36]: a significant concentration of bacteria in the surface film of different natural bodies of water made it possible to assert the existence of bacterioneuston [37; 38]. So, bacterioneuston is the community of _Bacteria_ present within the neuston in the thin surface microlayer between the atmosphere and deeper layers of water in natural water bodies. This surface microlayer is thick and is considered to be the top 1 mm or less of natural water bodies [35; 39], but usually the thickness of biofilm is from 10 to 100 \(\upmu\)m [40]. The concentration of hydrophobic and surface-active substance and bacterial cells in the bacterial neuston may be some thousand times higher than in the bulk water. This may be due to the increased concentration of organic substances because of their poor water solubility, surface activity and hydrophobic properties in the surface film [41]. It was shown that the sea surface microlayer contains carbohydrates, proteins, lipids, and humic substances in relatively high concentrations [42; 43]. The minimum concentration of organic components at which reproduction of saprophyytes occurs is in the range from 0.001 to 0.01%. In lake water, their content varies from 1 to 50 mg/L; in the sea from 1 to 5 and can reach 40 mg/L, but in the surface film increases significantly. The study of the distribution of \({}^{14}\)C-glucose, \({}^{14}\)C-carbonate and \({}^{32}\)P-phosphate introduced into water showed that after 24 h they concentrated in the surface layer. The thickness of the biofilm formed depends on the content of organic matter in the water. In addition, the conditions in the biofilm promote the existence of aerobic or microaerobic organisms. For example, the concentration of bacteria in the surface film in the Volga estuary was up to 300 million per ml, which was 100-1000 times higher than in the water  
Figure 1: Concept of interaction between microplastic particles, bacterioneuston, considering its location in water column and natural organic matter. column. Most often under natural conditions, cells are in a state of starvation, which is accompanied by an increase of the concentration of bacteria in the film. A correlative relationship between the degree of oligotrophy of lakes and the number of bacteria in the surface layer was shown [44]. The main physico-chemical parameter of the cell surface which determines the interaction of the cell with air-water interface is the hydrophobicity of the cell surface [45,46]. Bacteria concentration can be increased by the addition of a source of nutrients with hydrophobic properties in water. There are a lot of studies on bacterioneuston composition. Surprisingly, it was found that bacterioneuston in the sea water was characterized with a significantly lower bacterial diversity than the pelagic seawater, and just two groups of organisms were determined, _Vibrio_ spp., 68%, and _Pseudoalteromonas_ spp., 21% of clones [47]. Another study showed the similarity between bacterial compositions of sea bacterioneuston and bacterioplankton communities with a predominance of representatives of two families _Flavobacterium_ and _Cryomorplucae_[48].