Sinorhizobium meliloti is a soil bacterium, specifically nodulating alfa alfa, used from decades as soil/seed inoculants in agriculture to improve crop yield. In response to limiting oxygen conditions, we observed that S. meliloti 41 enters VBNC state in liquid microcosms. VBNC cells, unable to nodulate Medicago sativa, reduce CTC and maintain membrane integrity and Gram negative status up to nine months as demonstrated using fluorescent stainings. If VBNC status is a survival strategy of non differentiating bacteria to get through stress situations, they should be able to recover growth. When VBNC S. meliloti 41 is re-incubated in aerobic conditions an increase in colony counts is observed; however, overgrowth of residual still culturable cells present in microcosms generally interferes with the evaluation of the resuscitating fraction. The appropriate use of chloramphenicol enabled to unambiguously demonstrate that a consistent fraction of the VBNC population reverts to culturable state. This observation indicates that VBNC state for S. meliloti 41 is not a step to death but a complex physiological response to adverse transitory environmental conditions.
VBNC induction and resucitation of Sinorhizobium meliloti strain 41
CASELLA, SERGIO;POVOLO, SILVANA;BASAGLIA, MARINA
2001
Abstract
Sinorhizobium meliloti is a soil bacterium, specifically nodulating alfa alfa, used from decades as soil/seed inoculants in agriculture to improve crop yield. In response to limiting oxygen conditions, we observed that S. meliloti 41 enters VBNC state in liquid microcosms. VBNC cells, unable to nodulate Medicago sativa, reduce CTC and maintain membrane integrity and Gram negative status up to nine months as demonstrated using fluorescent stainings. If VBNC status is a survival strategy of non differentiating bacteria to get through stress situations, they should be able to recover growth. When VBNC S. meliloti 41 is re-incubated in aerobic conditions an increase in colony counts is observed; however, overgrowth of residual still culturable cells present in microcosms generally interferes with the evaluation of the resuscitating fraction. The appropriate use of chloramphenicol enabled to unambiguously demonstrate that a consistent fraction of the VBNC population reverts to culturable state. This observation indicates that VBNC state for S. meliloti 41 is not a step to death but a complex physiological response to adverse transitory environmental conditions.
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