Importance character of low and high G+C gram-positive bacteria

Bacteria were first observed by the Dutch microscopist Antonie van Leeuwenhoek in 1676, using a single-lens microscope of his own design. He then published his observations in a series of letters to the Royal Society of London. Bacteria were Leeuwenhoek's most remarkable microscopic discovery. They were just at the limit of what his simple lenses could make out and, in one of the most striking hiatuses in the history of science, no one else would see them again for over a century.
Only then were his by-then-largely-forgotten observations of bacteria — as opposed to his famous "animalcules" (spermatozoa) — taken seriously. In most bacteria, a cell wall is present on the outside of the cytoplasmic membrane. The plasma membrane and cell wall comprise the cell envelope. A common bacterial cell wall material is peptidoglycan (called "murein" in older sources), which is made from polysaccharide chains cross-linked by peptides containing D-amino acids. Bacterial cell walls are different from the cell walls of plants and fungi, which are made of cellulose and chitin, respectively. Gram-positive bacteria possess a thick cell wall containing many layers of peptidoglycan and teichoic acids. In contrast, Gram-negative bacteria have a relatively thin cell wall consisting of a few layers of peptidoglycan surrounded by a second lipid membrane containing lipopolysaccharides and lipoproteins. Lipopolysaccharides, also called endotoxins, are composed of polysaccharides and lipid A that is responsible for much of the toxicity of Gram-negative bacteria. Most bacteria have the Gram-negative cell wall, and only the Firmicutes and Actinobacteria have the alternative Gram-positive arrangement. These two groups were previously known as the low G+C and high G+C Gram-positive bacteria, respectively. These differences in structure can produce differences in antibiotic susceptibility; for instance, vancomycin can kill only Gram-positive bacteria and is ineffective against Gram-negative pathogens, such as Haemophilus influenzae or Pseudomonas aeruginosa.

Low G+C gram-positive bacteria

This group includes the gram positive Bacteria with low G+C content in their DNA. Most of the members are heterotrophic and gram positive. Because of low G+-C content, the mycoplasams are also included in this groups though they lack cell wall and are Gram negative in nature. Many are endospore forming. They show variation in morphology such as cocci, roods and mycoplasams  are pleomorphic. 

Important character

1. Shape of the member of this group varies from cocci, rods, ring shaped to filamentous or without any particular shape. 
2. Diameter of the cells varies from 0.15 to 0.3micrometre, thereby considered as smallest free living bacteria. 
3. Cells are surrounded by a triple-layered double membrane containing sterols. 
4. Due to absence of cell wall, they are highly plastic and pleomorphic. 
5. They are gram-positive in nature. 
6. G+C content of DNA varies between 23 and 40 moles %.

High G+C gram-positive bacteria

This group includes the member with diverse morphological assemblage having pathogenic and economical important member. The important character giving bellow:

1. Morphology they are of various types ranging from cocci, rods with rudimentary branching to elaborate mycelia forms. 
2. They are of gram-positive types. 
3. G+C content of DNA is moles % or more, designated as high G+C group.

The phylum includes both useful and harmful bacteria.

Useful member:

1. Many species of Streptomyces are useful in the commercial production of antibiotic. 
2. Propiniobacterium and Brevibacterium are useful in diary industry. 
3. Frankia spp.are able to infect many non-leguminous plants like Casuarina, Myrica, Alnus, Coriaria, and produce nitrogen-fixing root nodules.

Harmful bacteria:

1. Mycobacterium leprae causes leprosy. 
2. Corynebacterium diphtheria causes diphtheria in humans. 
3. Actinomyces israelii  causes abscesses of connective tissue in man.