Growth and physiological characteristics of Bacillus subtilis L-forms

Area of Science:

• Microbiology
• Cell Biology

Background:

• Bacillus subtilis can exist in cell-walled and cell-wall deficient (L-form) states.
• Understanding L-form growth dynamics is crucial for studying bacterial adaptation and evolution.

Purpose of the Study:

• To characterize the growth kinetics and key features of Bacillus subtilis L-forms.
• To compare the growth of B. subtilis L-forms with their cell-walled counterparts.

Main Methods:

• Growth rate determination using optical density (O.D.) and viable cell counts.
• Microscopic observation of cell morphology, including vacuole and granule presence.
• Analysis of DNA, protein content, and cell size over time.
• Assessment of sensitivity to osmotic shock and penicillin resistance.

Main Results:

• L-forms showed slower growth (mu = 0.127) by O.D. compared to cell-walled forms (mu = 0.219), but faster growth (mu = 0.288) by viable counts.
• L-form cell size increased significantly after cell division ceased, rendering O.D. measurements unreliable for growth assessment.
• Maximum viable cell numbers and DNA content were reached around 30h, preceding peak protein (46h) and O.D. (71h).
• L-forms were osmotically sensitive and penicillin-resistant, indicating peptidoglycan loss, yet retained antibiotic and protease production.

Conclusions:

• Optical density is an inaccurate metric for assessing Bacillus subtilis L-form growth due to post-division cell enlargement.
• L-forms display distinct growth patterns, including a lag in O.D. measurement compared to viable cell counts.
• Despite cell wall loss, B. subtilis L-forms maintain certain functional similarities to their cell-walled progenitors, such as producing antibiotics.