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Summary: Lysophosphatidic acid acyltransferases (LPAATs) catalyze the formation of phosphatidic acid (PA), a central metabolite in both prokaryotic and eukaryotic organisms for glycerolipid biosynthesis. Phaeodactylum tricornutum contains at least two plastid‐localized LPAATs (ptATS2a and ptATS2b), but their roles in lipid synthesis remain unknown.Both ptATS2a and ptATS2b could complement the high temperature sensitivity of the bacterial plsC mutant deficient in LPAAT. In vitro enzyme assays showed that they prefer lysophosphatidic acid over other lysophospholipids.ptATS2a is localized in the plastid inner envelope membrane and CRISPR/Cas9‐generated ptATS2a mutants showed compromised cell growth, significantly changed plastid and extra‐plastidial membrane lipids at nitrogen‐replete condition and reduced triacylglycerols (TAGs) under nitrogen‐depleted condition. ptATS2b is localized in thylakoid membranes and its knockout led to reduced growth rate and TAG content but slightly altered molecular composition of membrane lipids.The changes in glycerolipid profiles are consistent with the role of both LPAATs in the sn‐2 acylation of sn‐1‐acyl‐glycerol‐3‐phosphate substrates harboring 20:5 at the sn‐1 position. Our findings suggest that both LPAATs are important for membrane lipids and TAG biosynthesis in P. tricornutum and further highlight that 20:5‐Lyso‐PA is likely involved in the massive import of 20:5 back to the plastid to feed plastid glycerolipid syntheses. [ABSTRACT FROM AUTHOR]

During maturation, heterocysts form an envelope layer of polysaccharide, called heterocyst envelope polysaecharide (HEP), whose synthesis depends on a cluster of genes, the HEP island, and on an additional, distant gene, hepB, or a gene immediately downstream from hepB. We show that HEP formation depends upon the predicted glycosyl transferase genes all4160 at a third locus and air3699, which is adjacent to hepB and is cotranscribed with it. Mutations in the histidine kinase genes hepN and hepK appear to silence the promoter of hepB and incompletely down-regulate all4160.

Acyl-CoA:lysophosphatidylcholine acyltransferase from the unicellular diatom Phaeodactylum tricornutum (PtLPCAT1) is involved in triacylglycerol and galactoglycerolipid synthesis and enhances eicosapentaenoic acid accumulation in recombinant oleaginous yeast Keywords: CRISPR/Cas9; eicosapentaenoic acid; LPCAT; Phaeodactylum tricornutum; Yarrowia lipolytica EN CRISPR/Cas9 eicosapentaenoic acid LPCAT Phaeodactylum tricornutum Yarrowia lipolytica 238 240 3 01/31/23 20230201 NES 230201 Dietary supplementation of omega-3 very long-chain polyunsaturated fatty acids (VLC-PUFAs), particularly eicosapentaenoic acid (EPA, C20: 5 SP 5,8,11,14,17 sp ) and docosahexaenoic acid (DHA, C22: 6 SP 4,7,10,13,16,19 sp ), is well known to have diverse health benefits. Recently, the biochemical properties of one I P. tricornutum i LPCAT (PtLPCAT1) were reported and it can esterify a 18: 3-, 18: 4- or 20: 4-CoA (n-3) moiety to lysoPC I in vitro i , the later acyl being available for further desaturation to synthesize EPA, contrasting with plant LPCATs (Polo'nska I et al i ., [2]). [Extracted from the article]

Summary: Long‐chain acyl‐CoA synthetases (LACS) play diverse and fundamentally important roles in lipid metabolism. While their functions have been well established in bacteria, yeast and plants, the mechanisms by which LACS isozymes regulate lipid metabolism in unicellular oil‐producing microalgae, including the diatom Phaeodactylum tricornutum, remain largely unknown.In P. tricornutum, a family of five genes (ptACSL1–ptACSL5) encodes LACS activities. We generated single lacs knockout/knockdown mutants using multiplexed CRISPR/Cas9 method, and determined their substrate specificities towards different fatty acids (FAs) and subcellular localisations.ptACSL3 is localised in the mitochondria and its disruption led to compromised growth and reduced triacylglycerol (TAG) content when cells were bubbled with air. The ptACSL3 mutants showed altered FA profiles in two galactoglycerolipids and phosphatidylcholine (PC) with significantly reduced distribution of 16:0 and 16:1. ptACSL5 is localised in the peroxisome and its knockdown resulted in reduced growth rate and altered molecular species of PC and TAG, indicating a role in controlling the composition of acyl‐CoAs for lipid synthesis.Our work demonstrates the potential of generating gene knockout mutants with the mutation of large fragment deletion using multiplexed CRISPR/Cas9 and provides insight into the functions of LACS isozymes in lipid metabolism in the oleaginous microalgae. [ABSTRACT FROM AUTHOR]

Summary: Fungal pretreatment is the most common strategy for improving the conversion of rapeseed meal (RSM) into value‐added microbial products. It was demonstrated that Bacillus amyloliquefaciens CX‐20 could directly use RSM as the sole source of all nutrients except the carbon source for iturin A fermentation with high productivity. However, whether fungal pretreatment has an impact on iturin A production is still unknown. In this study, the effects of fungal pretreatment and direct bio‐utilization of RSM for iturin A fermentation were comparatively analysed through screening suitable fungal species, and evaluating the relationships between iturin A production and the composition of solid fermented RSM and liquid hydrolysates. Three main unconventional adverse effects were identified. (1) Solid‐state fermentation by fungi resulted in a decrease of the total nitrogen for B. amyloliquefaciens CX‐20 growth and metabolism, which caused nitrogen waste from RSM. (2) The released free ammonium nitrogen in liquid hydrolysates by fungal pretreatment led to the reduction of iturin A. (3) The insoluble precipitates of hydrolysates, which were mostly ignored and wasted in previous studies, were found to have beneficial effects on producing iturin A. In conclusion, our study verifies the unconventional adverse effects of fungal pretreatment on iturin A production by B. amyloliquefaciens CX‐20 compared with direct bio‐utilization of RSM. [ABSTRACT FROM AUTHOR]