Nowadays, aquaculture not only as the fastest growing food-producing industry in the world, with an average annual growth with a rate of 8.9% since 1970, compared to the only 1.2% for capture fisheries but also an answer to ornamental industry. World aquaculture has grown significantly every year,the world needs a significant shift from wild fishing to aquaculture in order to prevent depleting our resources and to improve the aquaculture industry.
As a result of this significant shift, aquaculture development has accelerated throughout the years but due to the lack of new technologies, aquaculture sector still faces a lot of problems, the biggest being diseases.
These diseases are usually controlled by harmful chemicals, which not only put the pond’s health at stake, but can also harm the animals and pollute the water beyond repair. Diseases are listed as the primary constraint to a sustainable development of the aquaculture industry, which impedes both economic and social development in many places.
People nowadays also create a development plan based on the use of photosynthetic bacteria as a new technique to culture aquatic species.Through research, it has been discovered that Probiotics inhabit the growth and reduce pathogenic bacteria, at the same time they enhance the nutrition of the cultured species, improve the quality of water thus reducing the use of antibiotics and chemicals that harm our ecosystems.
In the early 90's some hatcheries in Taiwan and Thailand were promoting the use of probiotics, but these ideas were not readily accepted by the more scientific operations (Gomes, 1992). Today the concept of probiotics is reviewed by leading scientists (Verschuere et al, 2000). Verschuere et al defines aquaculture probiotics as "a live microbial adjunct which has a beneficial effect on the host by modifying the host-associated or ambient microbial community, by ensuring improved use of the feed or enhancing its nutritional value, by enhancing the host response towards disease, or by improving the quality of its ambient environment."
This bacteria was called PSB or Photosynthetic Bacteria because these bacteria showed movement towards light (phototactic) and growth is also induced by light. Purple bacteria or purple photosynthetic bacteria are proteobacteria that are phototrophic, that is, capable of producing their own food via photosynthesis D.A. Bryant (2006).They are pigmented with bacteriochlorophyll a or b, together with various carotenoids, which give them colours ranging between purple, red, brown, and orange. They may be divided into two groups – purple sulfur bacteria (Chromatiales, in part) and purple non-sulfur bacteria (Rhodospirillaceae).
S. Winogradsky, a German botanist observed that some purple bacteria can utilize hydrogen sulphide to sulphate with intracellular deposition of sulphur. C.B. Van Niel (1930) defined various metabolic versions of anoxygenic photosynthesis and demonstrated that it is the characteristic mode of energy yielding metabolism in both purple and green bacteria.
All the photosynthetic bacteria are divided into 35 groups. The group 10 contains anoxygenic phototrophic bacteria, while group 11 belongs to oxygenic phototrophic bacteria. Rhodobacter capsulatus belongs to anoxygenic (no evolution of oxygen) phototropic bacteria.
Like most other photosynthetic bacteria, purple bacteria do not produce oxygen (anoxygenic), because the reducing agent (electron donor) involved in photosynthesis is not water. In some, called purple sulfur bacteria, it is either sulfide or elemental sulfur. The others, called purple non-sulfur bacteria (aka PNSB), typically use hydrogen although some may use other compounds in small amounts.The anoxygenic group (no evolution of oxygen) has purple tad green bacteria, while oxygen evolving group has only cyanobacteria.
Rhodobacter capsulatus belongs to the anoxygenic photosynthesis and it depends on e– donors such as reduced sulphur compounds, molecular hydrogen or organic compounds. The ammonium salts are generally used as nitrogen source. Nitrogen fixation has been reported in some bacterial species.
It can grow chemo-auto-trophically under aerobic/micro-aerobic condition. Fatty acids, ethanol and organic acids serve as carbon sources. They are found in fresh water, brackish water, and marine and hyper-saline water.
The anoxygenic phototrophs grow under anaerobic conditions in the presence of light and do not use water as e-donor as in higher plants. The pigment synthesis is repressed by O2.
It grow auto-trophically with CO2 (C source) and hydrogen or reduced sulphur compounds act as e– donor. Photo-heterotrophy (i.e. light as energy source and an organic compound as a carbon source) also supports growth. Some purple bacteria also show chemo-organotrophy i.e. can grow in dark under similar conditions.
As a purple non sulphur bacteria, it deposit sulphur extracellularly. It grow anaerobically in the dark using fermentative metabolism, while the others can grow anaerobically in dark by respiration in which e– donor may be an organic compound/inorganic compound as H2. This group is most versatile energetically due to broad requirements and are photo-organotrophs i.e. use organic acids, amino acids, benzoate and ethanol.