Analysis of the Life Cycle of the Soil Saprophyte Bacillus cereus in Liquid Soil Extract and in Soil

Abstract

Bacillus is commonly isolated from soils, with organisms of Bacillus cereus sensu lato being prevalent. Knowledge of the ecology of B. cereus and other Bacillus species in soil is far from complete. While the older literature favors a model of growth on soil-associated organic matter, the current paradigm is that B. cereus sensu lato germinates and grows in association with animals or plants, resulting in either symbiotic or pathogenic interactions. An in terra approach to study soil-associated bacteria is described, using filtersterilized soil-extracted soluble organic matter (SESOM) and artificial soil microcosms (ASM) saturated with SESOM. B. cereus ATCC 14579 displayed a life cycle, with the ability to germinate, grow, and subsequently sporulate in both the liquid SESOM extract and in ASM inserted into wells in agar medium. Cells grew in liquid SESOM without separating, forming multicellular structures that coalesced to form clumps and encasing the ensuing spores in an extracellular matrix. Bacillus was able to translocate from the point of inoculation through soil microcosms as shown by the emergence of outgrowths on the surrounding agar surface. Microscopic inspection revealed bundles of parallel chains inside the soil. The motility inhibitor L-ethionine failed to suppress outgrowth, ruling out translocation by a flagellar-mediated mechanism such as swimming or swarming. Bacillus subtilis subsp. subtilis Marburg and four Bacillus isolates taken at random from soils also displayed a life cycle in SESOM and ASM and were all able to translocate through ASM, even in presence of L-ethionine. These data indicate that B. cereus is a saprophytic bacterium that is able to grow in soil and furthermore that it is adapted to translocate by employing a multicellular mode of growth.

Integrated Management Strategies for Tomato Fusarium Wilt

“…B. cereus is mesophilic, and is capable of adapting to wide and varying environmental conditions, widely distributed in nature and commonly found in nature as a saprophyte. It grows optimally at temperatures between 20 and 40 Vilain et al, 2006 . Since it is a soil bacterium, it can easily enter different food plants or food made from animals eggs, meat, and dairy products as they feed on the plants.…”

The mechanism of Microcystis aeruginosa death upon exposure to Bacillus mycoides

“…It was very difficult to break these clumps except through ultrasonication. Some Bacillus species were reported to revert to spore formation, only germinating and becoming active once the external environment was conducive for growth (Villain et al, 2006). The spore formation state was not observed with B. mycoides B16 through the malachite test.…”

“…The bacteria surrounding to the Microcystis, presumably also released extracellular substances that interfered with the Microcystis photosynthesis system as indicated by the collapse in the plasmalemma and thylakoid membranes that was more evident after 24 h of bacteria treatment (Figures 4.10b and f). Burnham et al (1984) and Daft et al (1985) showed that Myxococcus fulvus BG02 exhibited polymorphism: spherules and myxospores, which showed lytic activity against B. mycoides B16 switched from single cell to a multicellularity phenotypes which is a characteristics of rhizodal phenotypes of B. mycoides species (Villain et al, 2006). The rhizoidal growth of B. mycoides through chain elongation over long distance may be viewed as translocation through the Microcystis algal blooms.…”

“…Thus the bacteria were able to derive nutrients from the lysis of Microcystis cells during the translocation process. Also the B. mycoides species formed clumps, possible as a survival strategy in the event of nutrient limitations (Villain et al, 2006). It was very difficult to break these clumps except through ultrasonication.…”

The Redox Regulator Fnr Is Required for Fermentative Growth and Enterotoxin Synthesis in Bacillus cereus F4430/73

“…Bacillus cereus is a facultatively anaerobic, spore-forming, opportunistic human pathogen (25,56). The majority of reported illnesses involving B. cereus are food-borne intoxications, classified as emetic and diarrheal syndromes (28,48).…”