Botulinum and tetanus neurotoxins, produced by Clostridium botulinum and Clostridium tetani, respectively, are the most poisonous poisons known to mankind. Although botulinum and tetanus neurotoxins share several characteristics, such as similar mol. wts, similar macrostructure, virtually identical mode of action, and a strong amino acid sequence homology, the two neurotoxins differ in one very significant way; only botulinum neurotoxin is a food poison. Factors responsible for the food poisoning potential of botulinum neurotoxins seem to be a group of complexing proteins that are also produced by C. botulinum, and are known to associate with the neurotoxin. Translation products of nucleotide sequences upstream to the neurotoxin genes of serotypes A, B, C, D, E and F botulinum neurotoxin reveal the location of genes for one of the complexing proteins that could be transcribed as polycistronic mRNA to include neurotoxin sequences. No such protein seems to be present in C. tetani, suggesting that the lack of complexing proteins might be responsible for tetanus not being a food poison.

The live and sedimentary components of the flat laminated microbial mat at Laguna Figueroa have been studied since the late sixties. This paper reports the observation and isolation of a variety of micro-organisms, both prokaryotes and eukaryotes. The microbes were taken from the flat laminated mats submerged under at least one meter of water due to the spring rains of 1979 and 1980. Both in situ and enrichment culture observations were made using light and electron microscopic techniques. New strains of the following microbes are reported here: Bacillus megaterium, Bacillus licheniformis, Arthrobacter simplex and Paratetramitus jugosus. Several pseudomonads were isolated, some of which form distinctive subsurface colonial structures. Regular distinctive colony morphologies and desiccation resistant cysts were often observed, several types of which grow to characteristically large sizes and resemble objects found in the pre-Phanerozoic fossil record. Some colonies of manganese oxidizing bacilli and other bacteria are reminiscent of microfossils of the 2 Ga-old Gunflint Iron formation such as Metallogenium, Eosphaera tyleri, Eoastrion and Huronispora. Some manganese oxidizing bacteria form colonial structures that might be mistaken for individual organisms in the tens to hundreds of microns size range. The diversity of microbial structures, including those with preservation potential, must be kept in mind when interpreting the microfossil record.