Novel strains of Moorella thermoacetica form unusually heat-resistant spores

Abstract

Two strains of Moorella thermoacetica, JW/B-2 and JW/DB-4, isolated as contaminants from autoclaved media for chemolithoautotrophic growth containing 0.1% (wt/vol) yeast extract, formed unusually heat-resistant spores. Spores of the two strains required heat activation at 100 degrees C of more than 2 min and up to 90 min for maximal percentage of germination. Kinetic analysis indicated the presence of two distinct subpopulations of heat-resistant spores. The decimal reduction time (D10-time=time of exposure to reduce viable spore counts by 90%) at 121 degrees C was determined for each strain using spores obtained under different conditions. For strains JW/DB-2 and JW/ DB-4, respectively, spores obtained at approximately 25 degrees C from cells grown chemolithoautotrophically had D10-times of 43 min and 23 min; spores obtained at 60 degrees C from cells grown chemoorganoheterotrophically had D10-times of 44 min and 38 min; spores obtained at 60 degrees C from cells grown chemolithoautotrophically had D10-times of 83 min and 111 min. The thickness of the cortex varied between 0.10 and 0.29 microm and the radius of the cytoplasm from 0.14 to 0.46 microm. These spores are amongst the most heat-resistant noted to date. Electron microscopy revealed structures within the exosporia of spores prior to full maturity that were assumed to be layers of the outer spore coat.

The Astrobiology Primer v2.0

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Physiology of the thermophilic acetogen Moorella thermoacetica

“…For those who have worked with M. thermoacetica, it is well known that glassware used to cultivate the organism is difficult to sterilize, mainly because its spores can survive autoclaving [41]. Indeed, M. thermoacetica has been isolated as a contaminant from autoclaved media [13]. The ability of M. thermoacetica spores to survive high temperatures demonstrates that this anaerobic bacterium can also survive standard commercial canning procedures.…”

“…For example, the spores of M. thermoacetica are among the most heat--resistant spores characterized. The decimal reduction time at 121 •C (i.e., the time required at 121 •C to achieve a 90% reduction of the viable population) for M. thermoacetica spores can be as long as 111 minutes [13]. For those who have worked with M. thermoacetica, it is well known that glassware used to cultivate the organism is difficult to sterilize, mainly because its spores can survive autoclaving [41].…”

Development of Polymerase Chain Reaction and Multiplex Polymerase Chain Reaction for Simple Identification of Thermoanaerobic Spore-forming Bacteria

“…In foods, however, many of these microbes exist in powdered raw materials manufactured by spray-dry processing or high-temperature extraction or reduction processing (Akutsu et al, 2008;Pollach et al, 2002;Sakurai et al, 2000). Bacteria contaminate sealed products through the raw materials and are able to survive under typical sterile conditions because of their high heat resistance (Tanaka et al, 1998;Enda et al, 1989;Byrer et al 2000). As a result, they survive in the product, continuing to grow during storage in vending machines exposed to high temperatures.…”