Distribution of putative spore germination genes in Clostridium species

Survival and persistence of Bacilli and Clostridia in the environment largely depends on their ability to produce spores which can germinate under favorable conditions. The process of spore germination is best understood in Bacilli. When a dormant spore senses an environment that can support the survival of a vegetative cell, germination of spores can be induced. Germination in response to nutrients is believed to be mediated by receptors that reside in the inner spore membrane, which are encoded by tricistronic so-called ger operons. Whereas ger family members are found in Bacillus and most Clostridia, the numbers of ger operons in Bacillus species tend to be higher than those found in Clostridia. Upon triggering of germination through the Ger receptor, full germination requires the removal of the sporecortex. Hydrolysis of the cortex in the genus Bacillus is likely performed by germination-specific cortex-lytic enzymes. Several of these cortex lytic enzymes from bacilli and clostridium have been characterized. In the present study, the occurrence of known and putative Bacillus germinationrelated genes in their anaerobic relatives was analyzed by a homology search of 34 sequenced Bacillus genomes and 24 Clostridium genomes. The presence of the various genes involved in germination in various species will be discussed, with a particular focus on the Clostridia.