Dr. Joe E Lepo

Biologically produced “surface-active agents" – commonly termed “biosurfactants” – have applications in environmental bioremediation of oil spills and numerous industrial applications, e.g., microbially enhanced oil recovery [MEOR], paints, cosmetics, and birth control. Microbial biosurfactants are amphipathic molecules biosynthesized by microbes such as yeasts or bacteria. One poorly investigated category of microorganisms for biosurfactant activities is lipid-dependent yeasts that are symbiotic on human skin. Because lipids in skin oil are hydrophobic, their efficient use as a C-source likely requires a surfactant. Therefore, lipid-dependent yeasts are promising candidates for surfactant-producing microbes.

The goal of this project was to determine if skin characteristics, such as skin type and history of skin ailments, were correlated with the presence of lipid-dependent yeast. We focused on areas of human skin that have high-lipid concentrations, such as the forehead/hairline and nasal fold regions, to maximize the potential of growth.
Though this project drew from several published papers, the specific combination of sampling and isolation methods were unique. The research performed will provide an updated source for those seeking more information on human-associated lipophilic yeasts.

Sanguinarine has strong inhibitory effects against the cyanobacterium Microcystis aeruginosa. However, previous studies were mainly limited to laboratory tests. The efficacy of sanguinarine for mitigation of cyanobacterial blooms under field conditions, and its effects on aquatic microbial community structure remain unknown. To elucidate these issues, we carried out in situ cyanobacterial bloom mitigation tests. Our results showed that sanguinarine decreased population densities of the harmful cyanobacteria Microcystis and Anabaena. The inhibitory effects of sanguinarine on these cyanobacteria lasted 17 days, after which the harmful cyanobacteria recovered and again became the dominant species. Concentrations of microcystins in the sanguinarine treatments were lower than those of the untreated control except during the early stage of the field test. The results of community DNA pyrosequencing showed that sanguinarine decreased the relative abundance of the prokaryotic microorganisms Cyanobacteria, Actinobacteria, Planctomycetes and eukaryotic microorganisms of Cryptophyta, but increased the abundance of the prokaryotic phylum Proteobacteria and eukaryotic microorganisms within Ciliophora and Choanozoa. The shifting of prokaryotic microbial community in water column was directly related to the toxicity of sanguinarine, whereas eukaryotic microbial community structure was influenced by factors other than direct toxicity. Harmful cyanobacteria mitigation efficacy and microbial ecological effects of sanguinarine presented in this study will inform the broad application of sanguinarine in cyanobacteria mitigation.
[Display omitted]
•Sanguinarine effectively decreases the cell density of harmful cyanobacteria.•Sanguinarine treatment decreases microcystins concentration in water column.•Sanguinarine treatment improves water quality.•Prokaryotic community shifting is different from that of eukaryotic microbes.

•Reduced V-ATPase and V-PPase activity improved nitrogen use efficiency.
•Reduced V-ATPase and V-PPase activity decreased Cd2+ tolerance.•Decreased NO3− vacuolar sequestration capacity (VSC) enhanced Atclca-2 Cd2+ VSC.
•Enhanced Cd2+ VSC decreased NO3− VSC in AtCAX4-OE.•Regulating Cd2+ and NO3− vacuolar accumulation enhances NUE and Cd2+ tolerance.

The transmembrane transport of NO3− and Cd2+ into plant cell vacuoles relies on the energy from their tonoplast proton pumps, V-ATPase and V-PPase. If the activity of these pumps is reduced, it results in less NO3− and Cd2+ being transported into the vacuoles, which contributes to better nitrogen use efficiency (NUE) and lower Cd2+ tolerance in plants. The physiological mechanisms that regulate the balance between NUE and Cd2+ tolerance remain unknown. In our study, two Brassica napus genotypes with differential NUEs, xiangyou 15 and 814, and Atclca-2 mutant and AtCAX4 over-expression line (AtCAX4-OE) of Arabidopsis thaliana, were used to investigate Cd2+ stress responses. We found that the Brassica napus genotype, with higher NUE, was more sensitive to Cd2+ stress. The AtCAX4-OE mutant, with higher Cd2+ vacuolar sequestration capacity (VSC), limited NO3− sequestration into root vacuoles and promoted NUE. Atclca-2 mutants, with decreased NO3− VSC, enhanced Cd2+ sequestration into root vacuoles and conferred greater Cd2+ tolerance than the WT. This may be due to the competition between Cd2+ andNO3− in the vacuoles for the energy provided by V-ATPase and V-PPase. Regulating the balance between Cd2+ and NO3− vacuolar accumulation by inhibiting the activity of CLCa transporter and increasing the activity of CAX4 transporter will simultaneously enhance both the NUE and Cd2+ tolerance of Brassica napus, essential for improving its Cd2+ phytoremediation potential.

A high concentration of ammonium (NH4+) as the sole source of nitrogen in the growth medium often is toxic to plants. The nitrate transporter NRT1.1 is involved in mediating the effects of NH4+ toxicity; however, the mechanism remains undefined. In this study, wild-type Arabidopsis (Arabidopsis thaliana Columbia-0 [Col-0]) and NRT1.1 mutants (chl1-1 and chl1-5) were grown hydroponically in NH4NO3 and (NH4)(2)SO4 media to assess the function of NRT1.1 in NH4+ stress responses. All the plants grew normally in medium containing mixed nitrogen sources, but Col-0 displayed more chlorosis and lower biomass and photosynthesis than the NRT1.1 mutants in (NH4)(2)SO4 medium. Grafting experiments between Col-0 and chli-5 further confirmed that NH4+ toxicity is influenced by NRT1.1. In (NHASO, medium, NRT1.1 induced the expression of NH4+ transporters, increasing NH4+ uptake. Additionally, the activities of glutamine synthetase and glutamate synthetase in roots of Col-0 plants decreased and soluble sugar accumulated significantly, whereas pyruvate kinase-mediated glycolysis was not affected, all of which contributed to NH4+ accumulation. By contrast, the NRT1.1 mutants showed reduced NH4+ accumulation and enhanced NH4+ assimilation through glutamine synthetase, glutamate synthetase, and glutamate dehydrogenase. Moreover, the up-regulation of genes involved in ethylene synthesis and senescence in Col-0 plants treated with (NH4)(2)SO4 suggests that ethylene is involved in NH4+ toxicity responses. This study showed that NH4+ toxicity is related to a nitrate-independent signaling function of NRT1.1 in Arabidopsis, characterized by enhanced NH4+ accumulation and altered NH4+ metabolism, which stimulates ethylene synthesis, leading to plant senescence.