# The Process of Natural and Styrene-Butadiene Rubbers Biodegradation by _Lactobacillus plantarum_
## 3 Results and Discussion
The test results turned out to be statistically significant and the effect size measured with the use of eth-square (\(\eta^{2}\)) was 0.74, which indicates a very strong difference between the measurements. The average carbon content (%) after the experiment was significantly lower than before the experiment. The exact values of the discussed analysis are presented in Tables 2 and 3, as well as Figure 3.  
Moreover, before being used as a carbon source for bacteria, styrene-butadiene rubbers mainly consisted of carbon and zinc, and sometimes oxygen was visible during analysis. After the culturing process, the presence of many more different elements was observed. This fact proved that the bacteria conducted their metabolic processes. Additional elements found in the elemental composition analysis showed that the bacteria not only used carbon for themselves, but also produced metabolites during the culturing process. Figure 2: The mean thickness of bacterial cellulose after 14 days of culturing with an addition of different carbon sources. Moreover, an analysis of natural rubber samples after the end of the culturing process, which was performed under a scanning electron microscope, showed the presence of pores in the rubber structure. Figure 4 presents the surface of sulfuric vulcanize of natural rubber with an addition of carbon black and cross-linking substances (NR + CB + cross-linking substances) after 14 days of cultivation using the _Lactobacillus plantarum_ LOCK 1145. Apart from pores (red arrows) on the sample surface, bacteria were observed (green arrows). They were shaped like short rods (4-5 \(\upmu\)m long and up to 1 \(\upmu\)m wide). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Average Carbon**} & \multicolumn{2}{c}{**M**} & \multicolumn{2}{c}{**Me**} & \multicolumn{2}{c}{**SD**} & \multicolumn{2}{c}{**Sk.**} & \multicolumn{2}{c}{**Kurt.**} & \multicolumn{2}{c}{**Min.**} & \multicolumn{2}{c}{**Max.**} \\ \multicolumn{2}{c}{**Content (\%)**} & \multicolumn{1}{c}{**M**} & \multicolumn{1}{c}{**Me**} & \multicolumn{1}{c}{**SD**} & \multicolumn{1}{c}{**Sk.**} & \multicolumn{1}{c}{**Kurt.**} & \multicolumn{1}{c}{**Min.**} & \multicolumn{1}{c}{**Max.**} \\ \hline Before the experiment & 91.49 & 95.08 & 7.51 & \(-2.55\) & 7.21 & 65.12 & 96.58 \\ After the experiment & 59.71 & 56.88 & 6.68 & 1.20 & 1.32 & 51.17 & 78.03 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: An average carbon content in the rubber material before and after realizing the experiments (30 control samples) with basic descriptive statistics: mean, median, standard deviation, skewness, kurtosis, minimum, and maximum value, respectively. Figure 3: Box plots for the average carbon content (%) broken down into measurements before and after the experiment. *—before the experiment, \({}^{\circ}\)—after the experiment. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multicolumn{2}{c}{} & \multicolumn{2}{c}{**Before the Experiment**} & \multicolumn{2}{c}{**After the Experiment**} & & & \\ \multicolumn{2}{c}{} & \multicolumn{2}{c}{**(\(\mu\) = 21)**} & & & \multicolumn{2}{c}{**(\(\mu\) = 21)**} & & & \\ \hline  & \(\mathbf{M_{rank}}\) & \(\mathbf{Mdn}\) & \(\mathbf{IQR}\) & \(\mathbf{M_{rank}}\) & \(\mathbf{Mdn}\) & \(\mathbf{IQR}\) & \(\mathbf{Z}\) & \(p\) & \(\mathbf{\eta}^{2}\) \\ \hline Average carbon & 31.81 & 95.08 & 5.23 & 11.19 & 56.88 & 8.01 & \(-5.51\) & \(<\)0.001 & 0.74 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The results of the Mann–Whitney U test checking the differences between the measurement before and after the cultivation in the mean carbon content (%). In experiments where bacterial activity was observed, mass balances were carried out. The rubber used as the carbon source was weighed before and after experiments. In each case, a mass loss of about 1-5% in relation to the initial weight was observed. The appearance of the rubber material without using a microscope did not change.