The following dichotomous key indicates how the genera discussed
above differ from each other:
- Vegetative reproduction by cross-wall formation followed by fission
—Schizosaccharomyces* - Vegetative reproduction by budding — 2
- Ascospores not formed —Candida
- Ascospores formed — 3
- Nitrate assimilated —Hansenula
- Nitrate not assimilated — 4
- Abundant true mycelium as well as budding — 5
- True mycelium scarce or absent — 6
- Asci formed exclusively on the true hyphae —Saccharomycopsis
- Asci not formed exclusively on the true hyphae —Pichia
- Asci dehiscent —Kluyveromyces
- Asci persistent — 7
- No conjugation preceding ascus formation —Saccharomyces
- Conjugation preceding ascus formation — 8
- Ascospores warty or with ridges —Debaryomyces
- Ascospores spherical and smooth —Zygosaccharomyces
*Schizosaccharomycesbelongs to the Archiascomycetes
9.3 Lactic acid Bacteria
The term lactic acid bacteria (LAB) has no strict taxonomic significance,
although the LAB have been shown by serological techniques and 16S
ribosomal RNA cataloguing to be phylogenetically related. They share a
number of common features: they are Gram-positive, non-sporeforming
rods or cocci; most are aerotolerant anaerobes which lack cytochromes
and porphyrins and are therefore catalase- and oxidase-negative. Some
do take up oxygen through the mediation of flavoprotein oxidases and
this is used to produce hydrogen peroxide and/or to re-oxidize NADH
produced during the dehydrogenation of sugars.
Cellular energy is derived from the fermentation of carbohydrate to
produce principally lactic acid. To do this, they use one of two different
314 Fermented and Microbial Foods