Bacteria Are all simple single celled organisms, prokaryotes, that lack a cell nucleus along with other membrane bound organelles.  Prokaryotes are the most abundant organism on the Earth. Bacteria are found in different shapes cocci (round), bacilli (rod), and spirilla (spiral).  For many years the shape of a bacteria and its gram staining classified microorganisms. Now they compare the DNA and RNA sequencing. Firmicutes They are gram-positive bacteria, which means the cell wall is thicker due to the presence of Peptidoglycan. Peptidoglycan is composed of amino acid chains. Some of these organisms cause many diseases including Pneumonia, while others are beneficial to human health and used in antibiotics.  Not all of the bacteria in this phylum are gram- positive, some are gram-negative but share molecular similarities.  G-C (guanine-cytosine  content in the genetic make up is low Bacilli Cells are in a rod shape either straight or spiral, and can be found in pair or in a chain formation.  They are gram-positive. Lactobacillales They are known as lactic acid bacteria (LAB), because they produce lactic acid. Classification for this family is usually based on the metabolic characteristics. Can benefit the host, and are considered probiotic.  Other microorganisms can cause ailments. Lactobacillaceae They do not produce endospores. Endospores are a nonreproductive structures that help the bacteria survive when environmental conditions are stressful. Normally found in anaerobic environments. Lactobacillus Used in production of milk and dairy products, by converting lactose into lactic acid.  Make up most of the LAB, and starter cultures for food production. By looking at the genes that encode 16S or 23S rDNA molecules help microbiologists to split bacteria into their species.  delbrueckii All have closely related G - C sequences in 16S rRNA, but differ slightly from one another.  bulgaricus Rapid fermentation is essential in the production of yogurt, unlike lactis which is used in cheese and has a slower metabloism. Utilizes only lactose to ferment.