Corrigendum: Engineering strategies in microorganisms for the enhanced production of squalene: Advances, challenges and opportunities [Front. Bioeng. Biotechnol., 7, (2019) (50)] DOI: 10.3389/fbioe.2019.00050

Abstract

In the original article, there were mistakes in Tables 1, 3, and 4. From Table 1, all squalene values associated with Ryan et al. (2006) work (brazil nut, pecan, pistachio, cashew, and pine nut) have been deleted as the authors consider the values in their original article to be impractical. Also, the concentration of squalene in rape seed and wine lees were mentioned as 17 and 60 mg/100 g DCW, respectively, which has been corrected. For rape seed it is 43.7 mg/100 g and for wine lees it is 6,000 mg/100 g. In Table 3, some titer values (Mantzouridou et al., 2009; Chen et al., 2010; Fan et al., 2010) were mistakenly stated incorrectly following errors while converting units. In the case of Mantzouridou et al. (2009), the titers were incorrectly provided as "2.96*103 and 3.12*103 g/L" while they should be "2.96*10-3 and 3.12*10-3" g/L, respectively. As for Fan et al. (2010), the corrected titer value is "2.21*10-3" instead of "21.2 g/L." Additionally, the biomass weight was earlier stated as "No Data (ND)" but it was later found to be "0.37 mg/g" dry cell weight (DCW) when the glucose concentration was 30 g/L. Lastly, for Chen et al. (2010), the titer was incorrectly provided as "5.90 g/L" while it is "5.90*10-3 g/L." The work of Kaya et al. (2011) has been cited again in Table 3 (cited priorly in Table 2) pertaining to its fermentation parameter optimization. As for Table 4, the squalene biomass and yield values under Paramasivan and Mutturi's work 2017 have been corrected. Upon correction, the squalene biomass and yield in presence and absence of mitochondrial presequence have been labeled separately. The squalene biomass with the mitochondrial sequence happens to be 58.6 ± 1.43 mg/g DCW, while the yield is 28.4 ± 1.08 mg/L. Squalene biomass and yield without the mitochondrial presequence is 33.0 ± 2.96 mg/g DCW and 46.0 ± 4.08 mg/L, respectively. The corrected Tables 1, 3, and 4 appear below. Additionally, there were errors in the text. Following the deletion of Ryan et al.'s work from Table 1, paragraph 2 under "Squalene From Plants" has been reformed as follows: "Rice bran, a co-product of the rice milling process also contains a good amount (318.9-320 mg/100 g) of squalene (Rukmini and Raghuram, 1991; Pokkanta et al., 2019). Palm oil has just 20-50 mg/100 g of squalene (Goh et al., 1985; Lau et al., 2005) but because of its large-scale production, it can be considered as an acceptable source of the squalene overall. Apart from this, avocado (34-37 mg/100 g squalene) (Gutfinger and Letan, 1974) has also been reported to contain a meager amount of squalene. Some nuts also contain small amounts of squalene, including brazil nut (145.8 mg/100 g) (Derewiaka et al., 2014), peanut (27.4-132.9 mg/100 g) (Frega et al., 1992; Tuberoso et al., 2007; Pokkanta et al., 2019), hazelnut (9.3-39.2 mg/100 g) (Frega et al., 1992; Bada et al., 2004; Derewiaka et al., 2014), macadamia (7.2-38.3 mg/100 g) (Maguire et al., 2004; Wall, 2010; Derewiaka et al., 2014), pecan (20.8-29.8 mg/100 g) (Derewiaka et al., 2014; Fernandes et al., 2017), pistachio (5.5-22.6 mg/100 g) (Derewiaka et al., 2014; Salvo et al., 2017), cashew (11.6 mg/100 g) (Derewiaka et al., 2014), almond (1.3-9.6 mg/100 g) (Liu et al., 1976; Fernandes et al., 2017), and walnut (0.09-0.94 mg/100 g)." Following the correction in the concentration of squalene in rape seed in Table 1, the value of the same in the manuscript ("Squalene From Plants"; paragraph 3) been corrected as 43.7 mg of squalene per 100 gm DCW. Additionally, in paragraph 4, the following correction has been made: "Similarly, soybean, sunflower, canola, and palm fatty acid distillates encompass about 18-35, 43-45, 30-35, and 2-13 g/kg of squalene, respectively (Naziri et al., 2011b)" has been changed to "Similarly, soybean, sunflower, canola, and palm fatty acid distillates encompass about 18-55, 43-45, 30-35, and 2-13 g/kg of squalene, respectively (Dumont and Narine, 2007; Naziri et al., 2011b; Naz et al., 2014)." Two corrections have been made in "Fermentation Optimization for Squalene Production." In paragraph 2, "The maximum squalene production was noted to be 2.97 ± 0.12 and 3.13 ± 0.11 mg/L, whilst productivity of 0.10 ± 0.04 and 0.16 ± 0.05 mg/L/h was gained for S. cerevisiae BY4741 and EGY48, respectively (Mantzouridou et al., 2009)." has been changed to "The maximum squalene production was noted to be 2.97 ± 0.12 and 3.13 ± 0.11 mg/L, whilst productivity of 0.10 and 0.16 mg/L/h was gained for S. cerevisiae BY4741 and EGY48, respectively (Mantzouridou et al., 2009).". In paragraph 3, It was stated "In an experiment, squalene content was lifted to 21.2 g/L with a glucose concentration of 60 g/L." while it should be "In an experiment, squalene content was lifted to 2.21 mg/L with a glucose concentration of 30 g/L." In "Engineering Saccharomyces cerevisiae for Squalene Production", paragraph 2, "Additionally, this has been further improved to 250 mg/L by expressing the truncated HMGR (tHMGR) gene (Zhuang and Chappell, 2015)." has been changed to "Additionally, this has been further improved to 270 mg/L by expressing the truncated HMGR (tHMGR) gene (Zhuang and Chappell, 2015)". Additionally, in paragraph 3, "Eventually, the complete biosynthetic pathway for squalene was overexpressed and that obtained a yield reaching as high as 304.09 mg/L (Rasool et al., 2016a)." has been changed to "Eventually, the complete biosynthetic pathway for squalene was overexpressed and that obtained a yield reaching as high as 304.49 mg/L (Rasool et al., 2016a)." The authors apologize for these errors and state that this does not change the scientific conclusions of the article in any way. The original article has been updated.