Yeast biofilms are complex multicellular structures, in which the cells are well protected against drugs and other treatments and thus highly resistant to antifungal therapies. Colony biofilms represent an ideal system for studying molecular mechanisms and regulations involved in development and internal organization of biofilm structure as well as those that are involved in fungal domestication. We have identified here antagonistic functional interactions between transcriptional regulators Cyc8p and Tup1p that modulate the life-style of natural S. cerevisiae strains between biofilm and domesticated mode. Herein, strains with different levels of Cyc8p and Tup1p regulators were constructed, analyzed for processes involved in colony biofilm development and used in the identification of modes of regulation of Flo11p, a key adhesin in biofilm formation. Our data show that Tup1p and Cyc8p regulate biofilm formation in the opposite manner, being positive and negative regulators of colony complexity, cell-cell interaction and adhesion to surfaces. Notably, in-depth analysis of regulation of expression of Flo11p adhesin revealed that Cyc8p itself is the key repressor of FLO11 expression, whereas Tup1p counteracts Cyc8p’s repressive function and, in addition, counters Flo11p degradation by an extracellular protease. Interestingly, the opposing actions of Tup1p and Cyc8p concern processes crucial to the biofilm mode of yeast multicellularity, whereas other multicellular processes such as cell flocculation are co-repressed by both regulators. This study provides insight into the mechanisms regulating complexity of the biofilm lifestyle of yeast grown on semisolid surfaces. Yeast biofilms have become an increasingly important clinical problem over the years. Biofilms are often associated with infections resistant to antifungals, which are particularly prevalent in immunosuppressed patients. High resistance is mediated by cell reprogramming leading to the specific organization of internal biofilm structure and development of numerous protective mechanisms including extracellular matrix formation. Colony biofilms, with architecture and protective mechanisms similar to natural biofilms, represent an ideal model for studying molecular mechanisms and regulations behind biofilm development and organization. Here, we describe a new mechanism of antagonistic regulation of biofilm-specific processes and formation of complex colony biofilm structure by Cyc8p and Tup1p transcriptional regulators. Both these regulators are widespread and conserved among yeasts forming clinically important biofilms, including pathogenic yeasts of Candida spp. The identification of Tup1p as a positive regulator of biofilm formation makes Tup1p-orthologs in yeast pathogens potential targets for the design of new strategies of treatment of biofilm infections.

Objectives: Vibrio parahaemolyticus is a major foodborne pathogen in aquatic animals and a threat to human health worldwide. This study investigated the prevalence, antimicrobial resistance, antimicrobial resistance genes (ARGs), and biofilm formation of V. parahaemolyticus strains isolated from fish mariculture environments in Cat Ba Island, Vietnam.Methods: In total, 150 rearing water samples were collected from 10 fish mariculture farms in winter and summer. A polymerase chain reaction assay was used to identify V. parahaemolyticus, its virulence factors, and ARGs. The antimicrobial resistance patterns and biofilm formation ability of V. parahaemolyticus strains were investigated using the disk diffusion test and a microtiter plate-based crystal violet method, respectively.Results: Thirty-seven V. parahaemolyticus isolates were recovered from 150 samples. The frequencies of the tdh and trh genes among V. parahaemolyticus isolates were 8.1% and 21.6%, respectively. More than 90% of isolates were susceptible to ceftazidime, cefotaxime, and chloramphenicol, but over 72% were resistant to ampicillin, tetracycline, and erythromycin. Furthermore, 67.57% of isolates exhibited multidrug resistance. The presence of ARGs related to gentamicin (aac(3)-IV), tetracycline (tetA) and ciprofloxacin (qnrA) in V. parahaemolyticus isolates was identified. Conversely, no ARGs related to ampicillin or erythromycin resistance were detected. Biofilm formation capacity was detected in significantly more multidrug-resistant isolates (64.9%) than non-multidrug-resistant isolates (18.9%).Conclusion: Mariculture environments are a potential source of antibiotic-resistant V. parahaemolyticus and a hotspot for virulence genes and ARGs diffusing to aquatic environments. Thus, the prevention of antibiotic-resistant foodborne vibriosis in aquatic animals and humans requires continuous monitoring.

Saccharomyces cerevisiae is a mainly beneficial yeast, widely used in the food industry. However, there is growing evidence of its potential pathogenicity, leading to fungemia and invasive infections. The medical impact of yeast pathogens depends on formation of biofilms: multicellular structures, protected from the environment. Cell adhesion is a prerequisite of biofilm formation. We investigated the adherence of wild and genetically modified S. cerevisiae strains, formation of solid–liquid interface biofilms and associated regulation. Planktonic and static cells of wild strain BRF adhered and formed biofilms in glucose-free medium. Tup1p and Cyc8p were key positive and negative regulators, respectively. Glucose caused increased Cyc8p levels and blocked cell adhesion. Even low glucose levels, comparable with levels in the blood, allowed biofilm dispersal and release of planktonic cells. Cyc8p could thus modulate cell adhesion in different niches, dependently on environmental glucose level, e.g., high-glucose blood versus low-glucose tissues in host organisms.

Papiliotrema huenov was previously reported to be highly tolerant of a range of extremely toxic heavy metals. This study aimed to identify the potential of P. huenov to remove manganese and copper from aqueous solution. Physical conditions which affect removal of Mn(II) and Cu(II) were determined. Optimal temperature for adsorption of both metal ions was 30 °C, and optimal pH for maximum uptake of Mn(II) and Cu(II) were 5 and 6, respectively. Under these conditions, living cells of P. huenov accumulated up to 75.58% of 110 mg/L Mn(II) and 70.5% of 128 mg/L Cu(II) over 120 h, whereas, the removal efficiency of metal ions by dead cells over 1 h was 60.3% and 56.5%, respectively. These results indicate that living cells are more effective than dead biomass for bioremediation, but that greater time is required. The experimental data extends the potential use of P. huenov in biosorption and bioaccumulation of toxic heavy metals to copper and manganese, two of the most common industrial contaminants.

Thermotolerant yeasts are widely considered to be alternative strains to traditional yeasts for bioethanol production at high temperatures. In this study, thirty-two yeasts isolated from lychees were screened for thermotolerance, and seven selected isolates were identified as Candida tropicalis (isolates H8, H19, and H23), Meyerozyma guilliermondii (isolates H1 and H12) and Saccharomyces cerevisiae (isolates H10 and H18). They tolerated up to 45 °C, 12% (v/v) ethanol concentration, 10 g/L acetic acid, and 5 g/L furfural, respectively, and produced 47.96 to 70.18 g/L of ethanol from 160 g/L glucose at 40 °C during 48 h of fermentation. Among the evaluated yeasts, M. guilliermondii H1 showed great potential for second-generation bioethanol fermentation with its ability to ferment xylose and arabinose. Under the optimal conditions resulting from a Plackett Burman design and a Box Behnken design, the highest ethanol concentration of 11.12 g/L was produced from 40 g/L substrate-based sugarcane bagasse hydrolysate (non-detoxified hydrolysate) at 40 °C by M. guilliermondii H1. These findings suggested that the newly isolated thermotolerant yeast M. guilliermondii H1 is a good candidate for ethanol production from agricultural wastes.