The Astrakhan region is the main vegetable-growing and melon-growing center of Russia, characterized by favorable agro–climatic conditions for growing vegetable and gourd crops. The agro-climatic conditions of the region make it possible to obtain the earliest, highest and most stable yields. Currently, in the southern regions, the problem of reducing the use of mineral fertilizers and pesticides in agriculture with their replacement by biological methods of plant protection is quite acute. Biological methods, in comparison with chemical means of protection, are distinguished by the selectivity of impact and by the environmental safety. Preliminary studies have shown that the studied laboratory sample of the agent based on Bacillus atrophaeus B‐11474 has pronounced fungistatic and growth-stimulating activities, which were confirmed by the field research results. The studied laboratory sample of the agent had a positive effect on the germination, development and biometric parameters of watermelon. The sample helped to increase productivity, reduce anthracnose, improve the qualitative and quantitative indicators of the cultivated crop. The prospects for using the triple treatment (spraying the bottom of the furrow and double spillage under the root of the plant with a laboratory sample of the agent have been established. In general, the use of a biological agent in the cultivation of watermelon in the fields of the Astrakhan region will make it possible to obtain environmentally friendly and safe products.

Microbiological monitoring of the Northern Caspian proved that for the research period in 2013-2018 the average annual value of the total number of bacteria (TBN) was 1.35 million cells/ml. The TBN maximum value (1.46 million cells/ml) was recorded in 2013, the minimum (1.19 million cells/ml) - in 2014. Concentration of saprotrophic bacteria in the waters of the Northern Caspian during the research period varied from 50.94 thousand CFU/ml in 2013 to 1.66 thousand CFU/ml in 2014. The concentration of saprotrophic bacteria remained practically unchanged within 2014-2018. The values of the ratio of the total abundance of microorganisms and saprotrophic bacteria show the eutrophication of the waters of the North Caspian in 2013 and in 2016, in other periods the water quality corresponded to the readings of an oligotrophic reservoir. The maximum number of oil-oxidizing bacteria (OOB) (8.28 thousand CFU/ml) in the waters of the Northern Caspian was recorded in 2013, the minimum (0.21 thousand CFU/ml) - in 2014. Starting from 2015 there was recorded an increasing number of OOBs and its stabilization until the end of the research period. The ratio of NOB and saprotrophs in water varied from 16.47 to 52.47%. Analysis of microbiological and hydrological-hydrochemical indicators revealed positive correlations of TBN and annual runoff (r = + 0.77), TBN and the content of mineral forms of nitrogen (r = + 0.60), the number of saprotrophic bacteria and nitrogen (r = + 0.83), the amount of NOB and mineral nitrogen and silicon (r = + 0.81). In the long-term aspect, an improvement in the microbiological situation was recorded against the background of a growing total number of bacterioplankton under a simultaneous decrease in the number of saprotrophic and oil-oxidizing bacteria.

In the spring of 2020, in most of the water area of the northern Caspian, the prevalence of saprotrophic floras did not exceed 50000 cells/ml, which microbiota level in summer. The number of oligotrophs in most of the water area was inferior to saprotrophs, which indicated an mbalance in the heterotrophic microbial community. In summer, in the northern part of the Caspian Sea, a decrease in the average heterotrophic group of bacterioplankton and bacteriobenthos was recorded, which indicated the process of self-purification of the marine environment from allochthonous elements. Viewing in the summer period in the waters of the Northern Caspian Sea, the zone of the zone with water saprobicity corresponding to the “polluted” category, the process of self-cleaning of the reservoir after the spring flood was not completed. In the autumn of 2020, the distribution of heterotrophic bacterioplankton and bacteriobenthos reached its lowest levels for all periods of research. In water, the number of saprotrophs was inferior to oligotrophs, which indicated the presence of a heterotrophic microbiota in the water, but they remained in the zone of increased saprobicity. An analysis of the taxonomic structure microbiota showed that heterotrophic communities of bacterioplankton and bacteriobenthos form representatives of the 6th family of gram-negative bacteria (Alsaligenaceae,Enterobacteriaceae, Flavobacteriaceae, Moraxellaceae, Pseudomonadaceae and Vibrionaceae), as well as gram-positive microorganisms. Gram-positive bacteria are most often found in enrichment cultures, mainly of the listed families. Some of the isolated bacteria belong to the group of opportunistic pathogens, which led to the identification of a potential danger to aquatic organisms. However, most of the identified representatives are true saprophytes, covering the inhabitants of water and bottom sediments. The predominance of indigenous microbiocenosis tends to reduce the bacterial pressure of the ecosystem in the water area and improve the state of the habitat of aquatic biological resources in terms of biological micro-characteristics.

Both the habitat of aquatic biological resources and almost all ecological and trophic groups of biocenoses are subject to the negative impact of anthropogenic activities in the coastal zone and in the Caspian Sea. Anthropogenic eutrophication caused by domestic and industrial wastewater, fertilizers, disrupts the balance in the structure of biocenoses. Toxic technogenic emissions lead to changes in the state of natural aquatic ecosystems. In order to maintain balance in the face of anthropogenic changes, it is necessary to assess the state of these ecosystems. Оne of the indicators in assessing the quality of the habitat of aquatic biological resources is the sanitary condition of the reservoirs of the Volga-Caspian region. The sanitary and bacteriological state of the northern part of the Caspian Sea was studied as a fishery reservoir and habitat for aquatic biological resources. Based on the results obtained, the degree of pollution of the reservoir and the anthropogenic impact on the studied reservoir. In 2021 seasonal changes in the number of saprotrophic and oligotrophic bacteria in sea water and soil were noted in the waters of the Northern Caspian. In summer, water quality was classified as “clean” water (category 1), while in autumn it deteriorated and was assessed as “polluted” water (category 2). High values of the coli index and the presence of lactose-positive E. coli testified to the presence of household, including fecal, pollution in the coastal zone of the Northern Caspian Sea. At the same time, conditionally pathogenic bacteria (aeromonads, pseudomonads) were not isolated in the studied water samples. The obtained microbiological data indicate a slight anthropogenic impact on the study area.