Inhibition analysis of inhibitors derived from lignocellulose pretreatment on the metabolic activity of Zymomonas mobilis biofilm and planktonic cells and the proteomic responses

Lignocellulose pretreatment produces various toxic inhibitors that affect microbial growth, metabolism, and fermentation. Zymomonas mobilis is an ethanologenic microbe that has been demonstrated to have potential to be used in lignocellulose biorefineries for bioethanol production. Z. mobilis biofilm has previously exhibited high potential to enhance ethanol production by presenting a higher viable cell number and higher metabolic activity than planktonic cells or free cells when exposed to lignocellulosic hydrolysate containing toxic inhibitors. However, there has not yet been a systematic study on the tolerance level of Z. mobilis biofilm compared to planktonic cells against model toxic inhibitors derived from lignocellulosic material. We took the first insight into the concentration of toxic compound (formic acid, acetic acid, furfural, and 5‐HMF) required to reduce the metabolic activity of Z. mobilis biofilm and planktonic cells by 25% (IC₂₅), 50% (IC₅₀), 75% (IC₇₅), and 100% (IC₁₀₀). Z. mobilis strains ZM4 and TISTR 551 biofilm were two‐ to three fold more resistant to model toxic inhibitors than planktonic cells. Synergetic effects were found in the presence of formic acid, acetic acid, furfural, and 5‐HMF. The IC₂₅ of Z. mobilis ZM4 biofilm and TISTR 551 biofilm were 57 mm formic acid, 155 mm acetic acid, 37.5 mm furfural and 6.4 mm 5‐HMF, and 225 mm formic acid, 291 mm acetic acid, 51 mm furfural and 41 mm 5‐HMF, respectively. There was no significant difference found between proteomic analysis of the stress response to toxic inhibitors of Z. mobilis biofilm and planktonic cells on ZM4. However, TISTR 551 biofilms exhibited two proteins (molecular chaperone DnaK and 50S ribosomal protein L2) that were up‐regulated in the presence of toxic inhibitors. TISTR 551 planktonic cells possessed two types of protein in the group of 30S ribosomal proteins and motility proteins that were up‐regulated.     

Developing microbial biofilm as a robust biocatalyst and its challenges

Biocatalysts, such as bacteria, yeast, fungi and the enzymes they produce, have been used for many industrial applications since they function as effective and environmentally friendly tools. Whole cells have also been used in many sophisticated bioprocesses since a number of sequential reactions can be catalyzed within the cells. However, the use of whole cells in suspension in batch, fed-batch and continuous processes has some limitations. For instance, the cultures are non-reusable, they are sometimes sensitive to the toxicity of substrates or products, there can be issues with short-term stability, and each of these issues can impede biocatalyst regeneration, perturbing the downstream process and causing complexity in running large scale continuous culture. Recently, biofilms have emerged as a new generation of biocatalysts to solve these limitations in the production of many bio-based materials, including chemicals, antibiotics, enzymes, bioethanol, biohydrogen, and electricity production via microbial fuel cells. The establishment of industrial processes using biofilms has the potential for high benefit in terms of low-cost cell immobilization without the necessity of added polymers or chemicals. Many small-scale biofilm reactors have been developed for the production of value-added products, and it may be challenging to establish it on an industrial scale.     

Loss of flagellum-based motility by Listeria monocytogenes results in formation of hyperbiofilms

Biofilm formation by the gram-positive, motile, food-borne pathogen Listeria monocytogenes was demonstrated to occur by an ordered series of stages. Biofilm development involves flagellum-based motility, which when blocked decreases initial bacterial surface attachment but subsequently leads to the formation of hyperbiofilms, surface-attached communities reaching high density.     

Physiological studies of the Pediococcus pentosaceus biofilm

Pediococcus pentosaceus, a bacterium recently used in human and animal probiotics, was used in combination with supports made from polylactic acid composite soybean meal was used to study biofilm formation, and it was found that dense biofilms developed by Day 1. Proteomic comparison between planktonic and biofilm cultures of P. pentosaceus showed distinct expression patterns of intracellular and extracellular proteins. Type I glyceraldehyde-3-phosphate dehydrogenase was upregulated in biofilm cultures and mediated cell adhesion and encouraged biofilm production. GMP synthase, which regulates GMP synthesis and acts as an intracellular signal molecule to control cell mechanisms and has been exploited in the development of new therapeutic agents, was also upregulated in the biofilm mode of growth. The present work serves as a basis for future studies examining the complex network of systems that regulate lactic acid bacterial (LAB) biofilm formation and can serve as a framework for studies of production of therapeutic agents from LAB.