Δ12 fatty acid desaturase gene from Geotrichum candidum in cheese: molecular cloning and functional characterization

Production of polyunsaturated fatty acids in pork backfat fermented by Mucor circinelloides

Pork backfat (PB) contains excessive saturated fatty acids (SFAs), but lacks polyunsaturated fatty acids (PUFAs). Excessive SFAs can be used as a substrate for the growth of certain microorganisms that convert them into PUFAs and monounsaturated fatty acids (MUFAs), and the added value of PB can be enhanced. In this study, Mucor circinelloides CBS 277.49 and Lactiplantacillus plantarum CGMCC 24189 were co-cultured for conversion of PB into fermented pork backfat (FPB) with high level of PUFAs. Our results showed that the content of γ-linolenic acid (GLA) and linoleic acid (LA) in the surface of FPB reached 9.04 ± 0.14 mg/g and 107.31 ± 5.16 mg/g for 7-day fermentation, respectively. To convert the internal SFAs of PB, ultrasound combined with papain was used to promote the penetrative growth of M. circinelloides into the internal PB, and the GLA level in the third layer of fat reached 2.58 ± 0.31 mg/g FPB. The internal growth of M. circinelloides in PB was promoted by adjusting the oxygen rate and ventilation rate through the wind velocity sensor. When the oxygen rate is 2 m/s and the ventilation rate is 18 m3/h, the GLA level in the third layer of fat reached 4.13 ± 1.01 mg/g FPB. To further improve the level of PUFAs in PB, FPB was produced by M. circinelloides at 18 °C. The GLA content on the surface of FPB reached 15.73 ± 1.13 mg/g FPB, and the GLA yield in the second and third layers of fat reached 8.68 ± 1.77 mg/g FPB and 6.13 ± 1.28 mg/g FPB, the LA yield in the second and third layers of fat reached 105.45 ± 5.01 mg/g FPB and 98.46 ± 4.14 mg/g FPB, respectively. These results suggested that excessive SFAs in PB can be converted into PUFAs and provided a new technique for improving PUFAs in FPB. KEY POINTS: • This article achieved the conversion of PUFAs in pork backfat by Mucor circinelloides CBS 277.49 and Lactiplantacillus plantarum CGMCC 24189. • This article solved the internal growth of M. circinelloides CBS277.49 in pork backfat by ultrasound combined with papain. • This article proposed an innovative of promoting the internal growth of M. circinelloides and increasing the PUFAs production by oxygen ventilation in pork backfat.

Linoleic acid enrichment of cheese by okara flour and Geotrichum candidum overexpressing Δ12 fatty acid desaturase

BACKGROUND

Mold-ripened cheeses have low levels of unsaturated fatty acids (UFAs). Geotrichum candidum is an adjunct culture for the development of Geotrichum-ripened cheese but has a low ability to produce high levels of UFAs. Δ12 fatty acid desaturase (FADS12) is a pivotal enzyme that converts oleic acid (OA) to linoleic acid (LA) and plays a vital role in UFA biosynthesis. By investigating FADS12 catalytic activity from various species with OA substrates, we found that FADS12 from Mucor circinelloides (McFADS12) had the highest catalytic activity for OA.

RESULTS

In the current study, a plasmid harboring McFADS12 was constructed and overexpressed in G. candidum. Our results showed that LA production increased to 31.1 ± 1.4% in engineered G. candidum - three times higher than that in wild-type G. candidum. To enhance LA production, an exogenous substrate (OA) was supplemented, and the yield of LA was increased to 154 ± 6 mg L^-1 in engineered G. candidum. Engineered G. candidum was used as an adjunct culture for Geotrichum-ripened cheese production. The LA level reached 74.3 ± 5.4 g kg^-1 cheese, whereas the level of saturated fatty acids (SFAs) decreased by 9.9 ± 0.5%. In addition, the soybean byproduct (okara) was introduced into the engineered G. candidum growth and the level of LA increased to 126 ± 4 g kg^-1 cheese and the percentage of UFAs:SFAs increased from 0.8:1 to 1.3:1.

CONCLUSION

This study offers a suitable technology for converting SFAs to UFAs in Geotrichum-ripened cheeses and provides a novel trend for converting soybean waste into a value-added product. © 2022 Society of Chemical Industry.

Uncovering the Biotechnological Importance of Geotrichum candidum

Fungi make a fundamental contribution to several biotechnological processes, including brewing, winemaking, and the production of enzymes, organic acids, alcohols, antibiotics, and pharmaceuticals. The present review explores the biotechnological importance of the filamentous yeast-like fungus Geotrichum candidum, a ubiquitous species known for its use as a starter in the dairy industry. To uncover G. candidum's biotechnological role, we performed a search for related work through the scientific indexing internet services, Web of Science and Google Scholar. The following query was used: Geotrichum candidum, producing about 6500 scientific papers from 2017 to 2022. From these, approximately 150 that were associated with industrial applications of G. candidum were selected. Our analysis revealed that apart from its role as a starter in the dairy and brewing industries, this species has been administered as a probiotic nutritional supplement in fish, indicating improvements in developmental and immunological parameters. Strains of this species produce a plethora of biotechnologically important enzymes, including cellulases, β-glucanases, xylanases, lipases, proteases, and α-amylases. Moreover, strains that produce antimicrobial compounds and that are capable of bioremediation were identified. The findings of the present review demonstrate the importance of G. candidum for agrifood- and bio-industries and provide further insights into its potential future biotechnological roles.

Functional diversity of Bisifusarium domesticum and the newly described Nectriaceae cheese-associated species

Bisifusarium domesticum is among the main molds used during cheese-making for its "anticollanti" property that prevents the sticky smear defect of some cheeses. Previously, numerous cheese rinds were sampled to create a working collection and not only did we isolate B. domesticum but we observed a completely unexpected diversity of "Fusarium-like" fungi belonging to the Nectriaceae family. Four novel cheese-associated species belonging to two genera were described: Bisifusarium allantoides, Bisifusarium penicilloides, Longinectria lagenoides, and Longinectria verticilliformis. In this study, we thus aimed at determining their potential functional impact during cheese-making by evaluating their lipolytic and proteolytic activities as well as their capacity to produce volatile (HS-Trap GC-MS) and non-volatile secondary metabolites (HPLC & LC-Q-TOF). While all isolates were proteolytic and lipolytic, higher activities were observed at 12 °C for several B. domesticum, B. penicilloides and L. lagenoides isolates, which is in agreement with typical cheese ripening conditions. Using volatilomics, we identified multiple cheese-related compounds, especially ketones and alcohols. B. domesticum and B. penicilloides isolates showed higher aromatic potential although compounds of interest were also produced by B. allantoides and L. lagenoides. These species were also lipid producers. Finally, an untargeted extrolite analysis suggested a safety status of these strains as no known mycotoxins were produced and revealed the production of potential novel secondary metabolites. Biopreservation tests performed with B. domesticum suggested that it may be an interesting candidate for biopreservation applications in the cheese industry in the future.

Catalytic mechanisms underlying fungal fatty acid desaturases activities

Polyunsaturated fatty acids (PUFAs) have beneficial roles in a variety of human pathologies and disorders. Owing to the limited source of PUFAs in animals and plants, microorganisms, especially fungi, have become a new source of PUFAs. In fungi, fatty acid desaturases (F-FADS) are the main enzymes that convert saturated fatty acids (SFAs) into PUFAs. Their catalytic activities and substrate specificities, which are directly dependent on the structure of the FADS proteins, determine their efficiency to convert SFAs to PUFAs. Catalytic mechanisms underlying F-FADS activities can be determined from the findings of the relationship between their structure and function. In this review, the advances made in the past decade in terms of catalytic activities and substrate specificities of the fungal FADS cluster are summarized. The relationship between the key domain(s) and site(s) in F-FADS proteins and their catalytic activity is highlighted, and the FADS cluster is analyzed phylogenetically. In addition, subcellular localization of F-FADS is discussed. Finally, we provide prospective crystal structures of F-FADSs. The findings may provide a reference for the resolution of the crystal structures of F-FADS proteins and facilitate the increase in fungal PUFA production for human health.

Autophagy and gastrointestinal cancers: the behind the scenes role of long non-coding RNAs in initiation, progression, and treatment resistance

Gastrointestinal (GI) cancers comprise a heterogeneous group of complex disorders that affect different organs, including esophagus, stomach, gallbladder, liver, biliary tract, pancreas, small intestine, colon, rectum, and anus. Recently, an explosion in nucleic acid-based technologies has led to the discovery of long non-coding RNAs (lncRNAs) that have been found to possess unique regulatory functions. This class of RNAs is >200 nucleotides in length, and is characterized by their lack of protein coding. LncRNAs exert regulatory effects in GI cancer development by affecting different functions such as the proliferation and metastasis of cancer cells, apoptosis, glycolysis and angiogenesis. Over the past few decades, considerable evidence has revealed the important role of autophagy in both GI cancer progression and suppression. In addition, recent studies have confirmed a significant correlation between lncRNAs and the regulation of autophagy. In this review, we summarize how lncRNAs play a behind the scenes role in the pathogenesis of GI cancers through regulation of autophagy.

Determination of allosteric and active sites responsible for catalytic activity of delta 12 fatty acid desaturase from Geotrichum candidum and Mortierella alpina by domain swapping

Cheese lacks essential fatty acids (EFAs). Delta 12 fatty acid desaturase (FADS12) is a critical enzyme required for EFA biosynthesis in fermentation of the predominant strains of cheese. Previously, we identified the FADS12 gene and characterized its function for the first time in Geotrichum candidum, a dominant strain used to manufacture soft cheese with white rind. In this study, we analyzed the molecular mechanism of FADS12 function by swapping domains from Mortierella alpina and G. candidum that had, respectively, high and low oleic acid conversion rates. The results revealed three regions that are essential to this process, including regions from the end of the second transmembrane domain to the beginning of the third transmembrane domain, from the end of the third transmembrane domain to the beginning of the fourth transmembrane domain, and from the 30-amino acid from the end of the sixth transmembrane domain to the C-terminal end region. Based on our domain swapping analyses, nine pairs of amino acids including H112, S118, H156, Q161, K301, R306, E307, A309 and S323 in MaFADS12 (K123, A129, N167, M172, T302, D307, I308, E310 and D324 in GcFADS12) were identified as having a significantly effect on FADS12 catalytic efficiency, and linoleic acid and its analogues (12,13-cyclopropenoid fatty acid) were found to inhibit the catalytic activity of FADS12 and related recombinant enzymes. Furthermore, the molecular mechanism of FADS12 inhibition was analyzed. The results revealed two allosteric domains, including one domain from the N-terminal region to the beginning of the first transmembrane domain and another from the 31^st amino acid from the end of the sixth transmembrane domain to the C terminus. Y4 and F398 amino acid residues from MaFADS12 and eight pairs of amino acids including G56, L60, L344, G10, Q13, S24, K326 and L344 in MaFADS12 (while Y66, F70, F345, F20, Y23, Y34, F327 and F345 in GcFADS12) played a pivotal role in FADS12 inhibition. Finally, we found that both allosteric and active sites were responsible for the catalytic activity of FADS12 at various temperatures, pH, and times. This study offers a solid theoretical basis to develop preconditioning methods to increase the rate at which GcFADS12 converts oleic and linoleic acids to produce higher levels of EFAs in cheese.