Beginner’s Guide to Bacillus Use in Aquaculture
Bacillus is a genus of Gram-positive, rod-shaped, cylindrical bacteria that are widely found in soil, water, and air. This genus includes a variety of species – some or beneficial members of various terrestrial and aquatic ecosystems, while others are harmful to other organisms. Members of this genus are highly adaptable and quite hardy due to their ability to form endospores – structures that protect them from a wide range of negative environmental conditions, including extremely high and very low temperatures, extreme dryness, radiation and toxic chemicals. Bacillus can remain dormant for years in this form and activate again once the conditions are favorable. Aside from endospores, these incredible bacteria have a wide array of physiological abilities that help them to adapt to different environments and tolerate conditions that are deadly to many other organisms.
From Discovery to TodayThe genus Bacillus was discovered in 1835 by Christian Gottfried Ehrenberg, German naturalist and microscopist, who was a prolific researcher in the 19th century. Ehrenberg’s younger colleague, Ferdinand Julius Cohn, later named the genus Bacillus, after the shape of these bacteria (bacillus means “stick” in Latin). He also found that these bacteria have two different forms – one that is not resistant to heat, and the one that is. This was the discovery of endospores and their incredible ability to withstand unfavorable environmental conditions. Research continued in the following centuries, and as molecular methods improved, so did our knowledge of these versatile bacteria. Soon, it was discovered that some Bacillus species were able create useful metabolites and molecules that aid bioremediation of contaminated soils and water, as well as help plants and animals fight off pests and diseases – making them prime candidates for today’s aquaculture health industry. Bacillus in aquaculture A growing world population and environmental concerns have placed significant pressures on the global food producers to provide sufficient high-quality, cost-effective food. In aquaculture, higher stocking densities have increased food production but also contributed to a higher occurrence of diseases and need for feed. Aquaculture historically relied on the use of antibiotics to control the diseases and on fishmeal and fish oil (FMFO) feeds to meet these two challenges. However, studies are increasingly showing major problems with both antibiotic resistance and FMFO environmental effects. To solve these two problems, scientists have increasingly turned to the natural allies of almost all multicellular organisms – beneficial bacteria (commonly referred to as probiotics). Bacillus is a common beneficial bacteria for animal health applications due to four main characteristics:
- Remarkable durability (due to its endospore structure)
- Outstanding physiological abilities
- Prolific enzyme activity
- Rapid growth rate
- Improving water quality Intensive aquaculture industries are very prone to poor water quality due to the high stocking densities and excessive feeding rates. The resulting accumulation of organic waste, nitrogen, and phosphorus simultaneously creates stressful conditions for fish and shrimps (which weakens their immune systems) and creates favorable environment for pathogens to thrive.
- Direct Inhibition of Disease Some Bacillus species (for example, B. subtilis, B. mycoides,) are found naturally in the gut microbiome of some fish and can play an important role in fighting off pathogens.
- Immunostimulation / Indirect Inhibition of Disease Aside from inhibitors, Bacillus also produce compounds that can stimulate natural immune responses and indirectly prevent disease growth in the long term.
- Improving growth and feed utilization One of the most important tasks in aquaculture today is to reduce the use of FMFO.