## 1 Introduction  
Plants are important source of bioactive substances with medicinal significance. These substances are the secondary metabolites of medicinal plants, which are some of the main sources of drugs for the pharmaceutical industry and traditional medicine [1, 2]. Such bioactive compounds could also serve as lead molecules for the development of many synthetic drugs [3]. Currently, plants are viewed as the main source for the discovery of new therapeutic compounds [4]. Among the most important medicinal properties of plants is their antimicrobial activity, which serves to protect the plant from existing pathogenic microorganisms. This important property, which is used in medicine, agriculture and the food industry, is due to various substances produced and exuded by the plants--essential oils, alkaloids, phenols, tannins, flavonoids, terpenes, glycosides, saponins, etc. [5; 6]. A number of studies have shown that the synergistic effect of phytochemicals plays an important role in the use of plant extracts as antimicrobial agents [7]. Phytochemical agents can act alone or in combination with antibiotics to enhance the antimicrobial activity against a wide range of microorganisms [6]. The concentration of bioactive compounds in each plant species largely depends on the environmental conditions and the pathosystem. The presence of various pathogens induces the production and exudation of the relevant antimicrobial substances [5]. Because of the ongoing development of resistance to existing antibiotics, there is a continuous need for new antimicrobial agents [8]. Moreover, the products of beneficial medicinal plants could be a more natural and safer alternative to synthesized antibiotics and other chemotherapeutics [4; 9]. Another important property of medicinal plants is their antioxidant activity, which is due to the high content of natural antioxidants in a plant. Antioxidants are used to preserve food quality, mainly through the prevention of the oxidative deterioration of lipid constituents. Nowadays, the most commonly used antioxidants are butylated hydroxyanisol (BHA), butylated hydroxytoluene (BHT), propyl gallate (PG) and tetra-butylhydroquinone (TBHQ) [2; 10]. However, there is a tendency to restrict the use of butylated derivates because of the potentially resultant liver damage and carcinogenesis [11]. Therefore, the search for effective antioxidants of natural origin is a priority nowadays. These antioxidants could protect the human and animal body by scavenging free radicals and preventing the subsequent oxidative damage that induces degenerative and pathological processes, including aging and cancer [12]. Phenols and flavonoids are among the main antioxidant compounds of the plants that are useful not only as pharmaceutical ingredients but also as food preservatives [10]. _Acorus calamus_ L. (Family Acoraceae), commonly known as \"sweet flag\", is a renowned semiaquatic medicinal plant native to temperate to subtemperate regions of Europe, India, The Himalayas and Southern Asia. The plant rhizomes of _A. calamus_ are considered to possess a great deal of beneficial properties--they are known to be spasmolytic, criminality, antimicrobial, antichemitmic, insecticidal, vascular modulators, anticancer, antioxidant, memory enhancing, etc. [13; 14]. Green microalgae (such as _Chlorella vulgaris_ Beijerinck (family Chlorellaceae) and _Sceendesmus dimorphitus_ ([PERSON]) [PERSON] (family Scenedesmaaceae)) are a diverse group of photosynthetic microorganisms found in soil and fresh water environments. They have the ability to produce a wide range of active substances with antimicrobial, immunostimulant, cytotoxic, antioxidant, anticoagulant, anti-inflammatory, antiallergenic and enzyme-inhibiting activities [15; 16; 17]. _Lemma minuta_ Kunth (family Araceae) is an aquatic plant with a small size commonly known as \"duck-weed\". It is native to parts of the Americas, and because of its ever-expanding distribution, it is found on other continents, including Europe. Although the plants of _Lemma_ spp.