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The current work aimed to use agro-industrial wastes as a strategy to obtain biosurfactant from a new Candida tropicalis UCP 1613 isolated from mangrove sediments of Rio Formoso, Pernambuco State, Brazil. The yeast was identified based on 18S rRNA sequencing method and blast homology search. The promising strain showed the ability to use an optimal composition of a cheap medium containing whey (3%), cassava wastewater (7%) and soybean post frying oil (10%) during 96h which reduced significantly the surface tension from 70 to 28.8 mN/m. The yield of the biosurfactant obtained was 4.9 g/L and the minimum value of critical micelle concentration was 1.5%. In addition, this was isolated and characterized as an anionic polymeric molecule, composed of proteins (51%), lipids (37%) and carbohydrates (11%), and confirmed by Fourier transform infrared spectroscopy (FTIR) analysis. Also, biosurfactant was capable in forming stable emulsions at different ranges of temperature, pH and salinity. Alternatively, the biosurfactant displayed no toxicity against the different vegetable evaluated seeds Brassica oleracea, Lactuca sativa L. and Solanum lycopersicum. The antimicrobial activity of this biosurfactant was verified showing the main efficacy against Gram-positive bacteria besides inhibiting the antifungal activity against the yeast tested. The results obtained suggest its potential application to pharmaceutical, as well as environmental area.

This study screened four Rhizopus species as biosurfactant producers using different markers. First of all, Rhizopus spp. UCP 1607 was identified as Rhizopus arrhizus by morphological and molecular methods. The production of biosurfactant/bioemulsifier was investigated by submerged fermentation using soybean post-frying oil (5% v/v) and sodium glutamate (1% w/v) medium. The primary markers' hemolysis and parafilm M tests showed that R. arrhizus UCP1607 strain exhibited higher hemolytic activity (49 mm of clear zone) on sheep blood agar and a larger drop diameter (12 mm) on parafilm hydrophobic surface. The experimental results showed the most promising biosurfactant production by R. arrhizus UCP 1607 strain led to a reduction of surface tension (31.8 mN/m) and the diameter of the oil-spreading covered an area of 66.4 cm 2 . The strains Rhizopus microsporus var. chinensis UCP1296, R. microsporus var. microsporus UCP1304, and R. arrhizus UCP1607 were capable of forming stable emulsions corresponding to 91.7, 94.8, and 82.6%, respectively in crude oil.

Monohexosylceramides (CMHs) are highly conserved fungal glycosphingolipids playing a role in several cellular processes such as growth, differentiation and morphological transition. In this study, we report the isolation, purification and chemical characterization of CMHs from Rhizopus stolonifer and R. microspores. Using positive ion mode ESI-MS, two major ion species were observed at m/z 750 and m/z 766, respectively. Both ion species consisted of a glucose/galactose residue attached to a ceramide moiety containing 9-methyl-4,8-sphingadienine with an amidic linkage to a hydroxylated C16:0 fatty acid. The antimicrobial activity of CMH was evaluated against Gram positive and Gram negative bacteria using the agar diffusion assay. CMH from both Rhizopus species inhibited the growth of Bacillus terrae, Micrococcus luteus (M. luteus) and Pseudomonas stutzeri (P. stutzeri) with a MIC50 of 6.25, 6.25 and 3.13 mg/mL, respectively. The bactericidal effect was detected only for M. luteus and P. stutzeri, with MBC values of 25 and 6.25 mg/mL, respectively. Furthermore, the action of CMH on the biofilm produced by methicillin-resistant Staphylococcus aureus (MRSA) was analyzed using 12.5 and 25 mg/mL of CMH from R. microsporus. Total biofilm biomass, biofilm matrix and viability of the cells that form the biofilm structure were evaluated. CMH from R. microsporus was able to inhibit the MRSA biofilm formation in all parameters tested.