# The Process of Natural and Styrene-Butadiene Rubbers Biodegradation by _Lactobacillus plantarum_
## 1 Introduction  
About 1.3 billion tons of non-agricultural waste are generated in the European Union every year. Out of this, approximately 58 million tons are harmful for the natural environment. This amount means that the yearly average of waste production in highly developed countries is around 570 kg per person [1]. One of the most serious global environmental and economic problems is rubber waste. Rubber is commonly used in many applications. This results in a growing amount of rubber waste, which is very difficult to handle due to its long-term durability, propensity to self-ignition, and resistance to chemical and biological destruction [1, 2]. It is very difficult to store and utilize waste from the car industry--used cars and end-of-life rubber elements. The basic process used for rubber waste utilization is the thermal method, mainly pyrolysis. This process requires the installation of expensive equipment that ensures the complete decomposition of waste and capture of toxic gases released during decomposition [3]. The main source of the waste is the automotive industry (about 80% of used rubber products are end-of-life tires) [4]. According to data gathered by the ETRMA (European Tyre and Rubber Manufacturer Association), 3.29 million metric tons of end-of-life tires were generated in Europe in 2016, up 100,000 tons from 2015, and their number is constantly growing [5, 6, 7, 8].  
The use of biological methods to degrade toxic compounds is the most environmentally friendly; although, this requires a long time. Microorganisms that can use waste as a source of carbon and energy in their metabolic pathways are present in waste disposal sites containing rubber waste [9; 10].  
The genus _Lactobacillus_ is the largest group among lactic acid bacteria; it includes 145 species and 27 subspecies. _Lactobacillus_ are common in the natural environment. They are characterized by a simple metabolism. Most of them are able to convert simple sugars into lactic acid. Most often, they occur in places that are rich in amino acids, carbohydrates, and nucleotide derivatives. On the other hand, these microorganisms can adapt to difficult conditions, which increases their occurrence in the environment. Natural habitats of Lactobacillus bacteria are healthy and rotting plants, milk and its products, as well as the genitourinary system and the gastrointestinal tract of humans and animals [11; 12]. The genus _Lactobacillus_ includes species with various glucose metabolism. The main product of metabolism is lactic acid, but formic acid, acetic acid, ethanol and carbon dioxide may also occur [11; 13]. Microorganisms belonging to the genus _Lactobacillus_ are aerotolerants or anaerobes, as well as acidophiles, but there are also species that tolerate acid environments well. There is no information in the literature about the formation of cellulose on the culture surface by _Lactobacillus_[12; 14].  
Suddenly, it occurred to us that the strain we studied, _Lactobacillus plantarum_, could produce cellulose. Moreover, it was able to degrade different mixtures of butadiene-styrene and natural rubbers, which were used in the culture medium as the main carbon source. That was why the authors decided to analyze this phenomenon in detail.  
The aim of this study was to test the ability of a bacterial strain to degrade different mixtures of butadiene-styrene and natural rubbers, which were used as the only carbon source in the culture medium.