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The thermal resistance of fermenting microbes is a key characteristic of stable fermentation at high temperatures. Therefore, the effects of various metal ions on the growth of Zymomonas mobilis TISTR 548, a thermotolerant ethanologenic bacterium, at a critical high temperature (CHT) were examined. Addition of Mg 2+ and K + increased CHT by 1 • C, but the effects of the addition of Mn 2+ , Ni 2+ , Co 2+ , Al 3+ , Fe 3+ , and Zn 2+ on CHT were negligible. To understand the physiological functions associated with the addition of Mg 2+ or K + , cell morphology, intracellular reactive oxygen species (ROS) level, and ethanol productivity were investigated at 39 • C (i.e., above CHT). Cell elongation was repressed by Mg 2+ , but not by K + . Addition of both metals reduced intracellular ROS level, with only K + showing the highest reduction strength, followed by both metals and only Mg 2+ . Additionally, ethanol productivity was recovered with the addition of both metals. Moreover, the addition of Mg 2+ or K + at a non-permissive temperature in 26 thermosensitive, single gene-disrupted mutants of Z. mobilis TISTR 548 revealed that several mutants showed metal ion-specific growth improvement. Remarkably, K + repressed growth of two mutants. These results suggest that K + and Mg 2+ enhance cell growth at CHT via different mechanisms, which involve the maintenance of low intracellular ROS levels.

AbstrakTujuan penelitian ini untuk mengetahui pengendalian kualitas pengalengan jamur di PT Y. Penelitian menggunakan metode Six Sigma dibatasi tahap define, measure, analyze dan improve. Tahap improve menggunakan salah satu alat implementasi kaizen yaitu Five M Checklist untuk mengusulkan alternatif perbaikan pengalengan jamur. Hasil penelitian menunjukkan jenis cacat terbesar pengalengan adalah knocked down flange (KDF). Nilai sigma sebesar 3,46, final yield 97,5%, dan kapabilitas proses (Cp) sebesar 1,15. Penyebab KDF adalah pekerja kurang teliti, pekerja kurang memahami standard operational procedure (SOPs) produksi, kesalahan setting up mesin, mesin seamer tidak stabil, komponen mesin seamer aus, bahan kaleng kurang baik dan area produksi tidak nyaman. Alternatif perbaikan yang disarankan adalah memberi arahan dan SOPs training untuk pekerja, mengontrol dan merawat mesin lebih ketat, menjadwal penggantian komponen mesin, melatih dan mengawasi operator mesin, memeriksa bahan kaleng lebih ketat, serta menambah turbine ventilator di area produksi.

Thermotolerant genes, which are essential for survival at a high temperature, have been identified in three mesophilic microbes, including Zymomonas mobilis. Contrary to expectation, they include only a few genes for reactive oxygen species (ROS)scavenging enzymes and heat shock proteins, which are assumed to play key roles at a critical high temperature (CHT) as an upper limit of survival. We thus examined the effects of increased expression of these genes on the cell growth of Z. mobilis strains at its CHT. When overexpressed, most of the genes increased the CHT by about one degree, and some of them enhanced tolerance against acetic acid. These findings suggest that ROS-damaged molecules or unfolded proteins that prevent cell growth are accumulated in cells at the CHT.

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