# Lactic Acid Bacteria as Biocontrol Agents against Potato (_Solanum tuberosum_ L.) Pathogens
## 3 Results and Discussion
### Growth Medium Selection for L. plantarum KB2 LAB 03 Cultivation  
The willingness to find sustainable management of acid whey, a waste product of cheese manufacture [50], as well as the search for a more economically profitable medium for LAB growth than laboratory medium (MRS), was the reason to select this component as  
Figure 2: Fermentation by-products of 10 most active lactic acid bacteria strains cultivated on MRS medium. 1—_Lactobacillus acidophilus_LOCK938; 2—_Lactobacillus acidophilus_LOCK927; 3—_Lactobacillus acidophilus_LOCK932; 4—_Lactobacillus acidophilus_LOCK934; 5—_Lactiplantiobacillus plantarum_LOCK861; 6—_Levilactobacillus brevis_0984; 7—_Lactiplantiobacillus plantarum_0991; 8—_Lactiplantiobacillus plantarum_KB2 LAB 03; 9—_Lactiplantiobacillus plantarum_BPC2; 10—_Lactiplantiobacillus pentosus_03(2)118A LAB; a–e—results with different letters within the sample are significantly different ([PERSON]’s test, \(\alpha\) = 0.05). the basis for the development of an optimal medium for \(L\). _plantarum_ KB2 LAB 03 growth. Acid whey was previously described as a medium for LAB culture [51] and also specifically for lactic acid production by LAB [52]. Lactic acid bacteria have complex nutritional requirements; however, some studies suggest that the need for supplementation is strain-dependent [51]. In our research, acid whey was supplemented with nitrogen sources (Yeast Extract and peptone K) and mineral sources (ammonium citrate, dipotassium phosphate, sodium acetate, magnesium sulphate heptabhydrate, magnesium sulphate tetrahydrate) in 16 different variants of concentrations. The acid whey itself was a carbon source in the form of lactose. The results of biomass yield (Y\({}_{\text{x}}\)) and maximum specific growth rate (\(\mu_{\text{max}}\)) are presented in Figure 3.  
Out of all variants of the acid whey-based medium, the highest values of biomass yield were achieved for A100 M100, A100 M50, A100 M25 and A50 M100 acid whey-based medium (in the range of 0.8354-0.8900). A high concentration of nitrogen sources played a more significant role in obtaining satisfactory results of Y\({}_{\text{x}}\) than a group of mineral sources. However, within variants with an equal concentration of nitrogen sources, the higher concentration of supplied minerals, the higher Y\({}_{\text{x}}\) and \(\mu_{\text{max}}\) were obtained (with the exception of A100 variants). The highest level of \(\mu_{\text{max}}\), 41% higher than for the A100 M50 variant, was overall observed for the MRS control medium due to the previous adaptation of \(L\). _plantarum_ KB2 LAB 03 to this medium. Nevertheless, the Y\({}_{\text{x}}\) was only 7% higher than the A100 M50 variant Figure 3.  
Figure 3: Biomass yield (Y\({}_{\text{x}}\)) and maximum specific growth rate (\(\mu_{\text{max}}\)) for \(L\). _plantarum_ KB2 LAB 03 cultivated on different variants of acid whey-based media. *—Optical Density; **—MRS water-based medium without glucose; A—group of nitrogen sources (yeast extract, peptone K); M—group of mineral sources (ammonium citrate, dipotassium phosphate, sodium acetate, magnesium sulphate heptabhydrate, magnesium sulphate tetrahydrate). A100 M100—acid whey medium supplemented with 100% base concentration of group A supplements and 100% base concentration of group M supplements. The following numbers (50, 25, 12.5) indicate supplementation with a certain percentage of the base concentration of group A and M supplements. MRS, MRS no glucose—control, water-based media. The specific concentrations of each component are presented in Section 2.4.1 point of Materials and Methodology section. a–k—results with different letters are significantly different (Tukey’s test, \(\alpha=0.05\)). _L. plantarum_ KB2 LAB 03 cultures on four variants of the acid whey-based medium with the highest Y\({}_{\text{x}}\) were selected for the antimicrobial activity evaluation against potato pathogens. The results are presented in Figures 4 and 5. The growth of both bacterial pathogens was inhibited by _L.