You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: Statistical Design, a Powerful Tool for Optimizing Biosurfactant Production: A Review 
Chapter Title:  The Effect of Trace Elements on Bs Production 
1. Abstract of Cited Paper (BIB001):  The nutritional medium requirement for biosurfactant production by Bacillus licheniformis K51 was optimized. The important medium components, identified by the initial screening method of Plackett-Burman, were H3PO4, CaCl2, H3BO3, and Na-EDTA. Box-Behnken response surface methodology was applied to further optimize biosurfactant production. The optimal concentrations for higher production of biosurfactants were (g/l): glucose, 1.1; NaNO3, 4.4; MgSO4 x 7H2O, 0.8; KCl, 0.4; CaCl2, 0.27; H3PO4, 1.0 ml/l; and trace elements (mg/l): H3BO3, 0.25; CuSO4, 0.6; MnSO4, 2.2; Na2MoO4, 0.5; ZnSO4, 6.0; FeSO4, 8.0; CoCl2, 1.0; and Na-EDTA, 30.0. Using this statistical optimization method, the relative biosurfactant yield as critical micelle dilution (CMD) was increased from 10x to 105x, which is ten times higher than the non-optimized rich medium. 
2. Abstract of Cited Paper (BIB002):  Abstract In this work, optimizing trace element composition was attempted as a primary strategy to improve surfactin production from Bacillus subtilis ATCC 21332. Statistical experimental design (Taguchi method) was applied for the purpose of identifying optimal trace element composition in the medium. Of the five trace elements examined, Mg 2+ , K + , Mn 2+ , and Fe 2+ were found to be more significant factors affecting surfactin production by the B. subtilis strain. In the absence of Mg 2+ or K + , surfactin yield decreased to 0.4 g/l, which was only 25% of the value obtained from the control run. When Mn 2+ and Fe 2+ were both absent, the production yield also dropped to ca. 0.6 g/l, approximately one-third of the control value. However, when only one of the two metal ions (Fe 2+ or Mn 2+ ) was missing, the B. subtilis ATCC 21332 strain was able to remain over 80% of original surfactin productivity, suggesting that some interactive correlations among the selected metal ions may involve. Taguchi method was thus applied to reveal the interactive effects of Mg 2+ , K + , Mn 2+ , Fe 2+ on surfactin production. The results show that interaction of Mg 2+ and K + reached significant level. By further optimizing Mg 2+ and K + concentrations in the medium, the surfactin production was boosted to 3.34 g/l, which nearly doubled the yield obtained from the original control. 
3. Abstract of Cited Paper (BIB003):  Great emphasis has recently been given to the environmental impacts caused by chemical surfactants due to their toxicity and difficulty in being degraded in the environment [1]. Increasing environmental concerns, the advance in biotechnology and the emergence of more stringent laws have led to biosurfactants being a potential alternative to the chemical surfac‐ tants available on the market [2, 3]. Although biosurfactants have promising use in bioreme‐ diation processes, their industrial scale production is currently difficult due to high rawmaterial costs, high processing costs and low manufacturing output [3]. As a result, the current research challenges are to increase the yield and to reduce the cost of raw materials [4]. 
4. Abstract of Cited Paper (BIB004):  A Pseudomonas aeruginosa AK6U strain produced rhamnolipid biosurfactants to variable extents when grown on MgSO4 or organosulfur compounds as sulfur sources and glucose as a carbon source. Organosulfur cultures produced much higher biosurfactants amounts compared to the MgSO4 cultures. The surface tension of the growth medium was reduced from 72 mN/m to 54 and 30 mN/m in cultures containing MgSO4 and 4,6-dimethyldibenzothiophene (4,6-DM-DBT), respectively. AK6U cultures produced different rhamnolipid congener profiles depending on the provided sulfur source. The dibenzothiophene (DBT) culture produced more diverse and a higher number of rhamnolipid congeners as compared to the DBT-sulfone and MgSO4 cultures. The number of mono-rhamnolipid congeners in the DBT culture was also higher than that detected in the DBT-sulfone and MgSO4 cultures. Di-rhamnolipids dominated the congener profiles in all the analyzed cultures. The sulfur source can have a profound impact on the quality and quantity of the produced biosurfactants.

Literature Review:
The effect of trace elements (generally metal ions) on Bs production is reported in various articles BIB002  BIB003 . Phosphates have been shown to affect Bs production. Although little is known about their metabolic interaction, phosphates are important constituents of nucleic acids, phospholipids, and cell walls. Iron has also been shown to affect Bs production since it plays important roles in oxidative phosphorylation BIB001 . Furthermore, monovalent and bivalent ions such as K + , Na + , Mg 2+ , Ca 2+ , and trace element salts increase Bs yield BIB004 BIB005 .