New insight into the role of oxygen supply for surfactin production in bench-scale bioreactors using induced surface aeration.

Surfactin biosurfactant produced by Bacillus sp. has been studied, because it has enormous potential in several applications in the oil and cosmetics industry. The cultivation conditions for obtaining this bioproduct, however, still require attention, as, for example, parameters related to oxygen supply and consumption. In this study, different volumetric oxygen transfer coefficient (KLa) levels (0-11.56 h-1) were tested in bench-scale bioreactor for surfactin biosurfactant production by Bacillus velezensis H2O-1, using induced surface aeration. While conditions close to anaerobiosis showed insignificant production of surfactin, an intermediated KLa condition (4.24 h-1) generated the best surfactin concentration (579.6 mg L-1), with a volumetric productivity of 11.9 mg L-1 h-1. These results showed that the oxygen demand to produce surfactin is not high, being possible to use induced surface aeration strategy in bioreactors, minimizing foam formation. In addition, in all KLa conditions tested, surfactin homologues C14 and C15 had higher relative abundance. Nevertheless, the KLa parameter seems to have had minimal influence on affecting the relative abundances of surfactin homologues produced. Particularly noteworthy in this study is the possibility of producing surfactin using a low-cost and scale-up feasible aeration strategy, unlike the foam collection strategies developed in other studies to obtain this bioproduct.

Novel combination of a biosurfactant with entomopathogenic fungi enhances efficacy against Bemisia whitefly.

BACKGROUND: Microbial surfactants are multifunctional surface-active molecules that have been overlooked in formulating microbial biopesticides. We report a novel approach using the biosurfactant rhamnolipid (RML) against the destructive cosmopolitan insect pest Bemisia tabaci, as well as the combined action of RML with aerial conidia of two entomopathogenic fungi, Cordyceps javanica and Beauveria bassiana. RML was also tested as a suspension agent to improve the recovery rate of conidia from solid substrate for fungal preparations. RESULTS: The recovery rate of conidia increased dramatically (two to five times) with RML compared with a standard surfactant (Tween 80). Spraying solutions of 0.075% and 0.1% (w/v) RML on B. tabaci third instar nymphs induced 100% mortality within 4 days. Conidial suspensions at 5 × 106 conidia/mL amended with RML at 0.01% or 0.05% markedly increased nymphal mortalities and considerably reduced LC50 . Conidial suspensions of B. bassiana with 0.05% RML added were more effective against whitefly nymphs (87.3% mortality) than C. javanica + RML (51.4% mortality). CONCLUSION: Our results show that this bacterium-based RML improved the recovery rate of hydrophobic conidia, and that mixtures of RML with fungal spore suspensions increased their insecticidal activity. © 2019 Society of Chemical Industry.