Biosurfactants from marine thermophilic bacilli for mitigating soil dehydration and preventing plant diseases

To explore novel wetting and humectant agents, the hydration performances of biosurfactants (BSs) from three thermophilic bacilli, Bacillus licheniformis B3-15, B. horneckiae SBP3, and B. licheniformis s7s-1, of shallow hydrothermal vents of the Aeolian Islands (Italy) origin were investigated. Specifically, the following characteristics were evaluated in commercial soil: (i) wetting properties, measuring the reduction in water contact angle (theta) and the water-drop penetration time; (ii) moisture uptake capacity; (iii) water retention rate under high solar irradiance, and (iv) molecular-level structural dynamics hydration (water content from 0 to 160% w/w). Although all BSs were attributed to surfactin-like lipopeptides, each differed in chemical structure and consequently, in hydrating performances, with BS s7s-1 being the best wetting agent and BS SBP3 the best humectant. The molecular structural dynamics of BS s7s-1 and BS SBP3 confirmed their greater ability to capture liquid water than BS B3-15 and elucidated the molecular interaction mechanisms. Under high solar irradiance, BS s7s-1 and BS SBP3 retained water in soil (51.1 and 43.2%, respectively) more efficiently than BS B3-15 (33.5%). As assessed by the inhibition of bacterial bioluminescence and Steinernema feltiae viability, BS SBP3 and BS s7s-1 were fourfold less toxic than the lichenysin-like BS B3-15. Moreover, BS s7s-1 (500 & micro;g mL-1) efficiently reduced biofilm formation by two phytopathogens, Pseudomonas mediterranea (33.7%) and P. corrugata (49.4%), without affecting Bacillus subtilis. As low-toxic, wetting and humectant agents, BS s7s-1 and BS SBP3 could represent potential alternatives to industrial additives for mitigating soil dehydration and preventing plant diseases.