Engineering membrane and cell-wall programs for tolerance to toxic chemicals: Beyond solo genes

Abstract

Metabolite toxicity in microbes, particularly at the membrane, remains a bottleneck in the production of fuels and chemicals. Under chemical stress, native adaptation mechanisms combat hyper-fluidization by modifying the phospholipids in the membrane. Recent work in fluxomics reveals the mechanism of how membrane damage negatively affects energy metabolism while lipidomic and transcriptomic analyses show that strains evolved to be tolerant maintain membrane fluidity under stress through a variety of mechanisms such as incorporation of cyclopropanated fatty acids, trans-unsaturated fatty acids, and upregulation of cell wall biosynthesis genes. Engineered strains with modifications made in the biosynthesis of fatty acids, peptidoglycan, and lipopolysaccharide have shown increased tolerance to exogenous stress as well as increased production of desired metabolites of industrial importance. We review recent advances in elucidation of mechanisms or toxicity and tolerance as well as efforts to engineer the bacterial membrane and cell wall.

Engineering Saccharomyces cerevisiae fatty acid composition for increased tolerance to octanoic acid

“…B). This has been linked to increased stability and rigidity of the membrane in bacteria (Sandoval and Papoutsakis, ) and has been reported in octanoic‐acid adapted S. cerevisiae cells (Liu et al, ). This increase in average lipid length was accompanied by an increase in total fatty acid content, as previously observed (Choi and Da Silva, ).…”

“…This decrease in order is accompanied by the insertion of a rigid element that diminishes the range of conformations available to an otherwise flexible chain, resulting in a bend in the aliphatic chain (Hazel and Williams, ; Marguet et al, ). In contrast, saturated fatty acids tend to form ordered structures with low permeability by packing tightly together through van der Waals interactions (Sandoval and Papoutsakis, ; Zhang and Rock, ). Therefore, an increase in the proportion of saturated fatty acid is expected to lead to higher stability and lower permeability of the membrane in the presence of octanoic acid.…”

“…Microbial production of short and medium chain fatty acids, such as octanoic acid, has the potential to functionally replace molecules derived from petroleum for synthesis of aliphatic alcohols (Gunukula et al, ) and high‐demand monomers for synthesis of polyolefins (Polyolefin Comonomers‐World Markets, 2005–2015). However, biological production of fatty acids such as octanoic acid (C8) is hindered by the toxic effects on the microbial cell factories (Jarboe et al, ; Sandoval and Papoutsakis, ).…”

“…In general, an increase in saturated fatty acids promotes membrane stability to solvents and high temperatures due to the establishment of more van der Waals interactions, while introduction of a cis ‐unsaturation impacts membrane fluidity. Longer chain length can provide higher stability and rigidity (Sandoval and Papoutsakis, ). Adding exogenous oleic acid (C18:1) to the media was shown to mitigate the toxic effects of octanoic acid (Liu et al, ) and acetaldehyde (Matsufuji et al, ) on the yeast cells.…”

Emerging tools, enabling technologies, and future opportunities for the bioproduction of aromatic chemicals

“…For instance, in addition to damaging cell membranes, p ‐coumaric acid is reported to also interact with DNA, negatively affecting replication and transcription . As has been done for other inhibitory bioproducts, progress is also being made towards engineering cell robustness towards aromatic bioproducts by modifying the cell envelope . In this review, we will discuss important cell envelope engineering strategies of general utility for increasing resistance to membrane disrupting compounds, particularly highlighting those studies specifically involving aromatic bioproducts.…”