The paper by Ghiasi (2011) investigates lactic acid
bacteria (LAB), that represent a cross-over in marine and terrestrial environments:
they are found to inhabit fish intestines, as well as animal intestines. They
are said to benefit the host in terms of nutrient absorption and immunity,
specifically preventing the colonisation of pathogenic bacteria (for a fuller
list see the introduction). LAB are bacteria that produce lactate and acetate
upon fermentation of carbohydrates, leading to lactic acid, with a reliance on
vitamins. LAB are of importance for aquaculture due to their health benefits
suggested above, hence research into the natural occurrence such as this is
important.
Their composition is said to change seasonally, hence this paper considers their composition over one season: winter. Five adult silver carp (Hypophthalmichthys molitrix) were removed, once a month over the winter period, from Gheshlaghdam lake, Iran. They were transferred to indoor tanks with water temperatures matching the natural temperature. 1g digesta was homogenised with 9ml ‘normal saline’, from which a dilution series from 10-1 to 10-10 was created, and plated out onto agar. Anaerobic incubation occurred at 37°C for 48 – 72hours, before 20 well grown colonies were selected from each plate. The bacteria were identified by observing morphological characteristics and carrying out biochemical tests. The capability to ferment different sugars were tested. Once the bacteria were identified, the abundances of each species were compared.
The intestines of silver carp contained 3 species of LAB that fall into 2 genera: Lactobacillus plantarum, Lactobacillus raffinolactis and Lactococcus lactis (in order of dominance). They are relatively similar in that none hydrolyse urea, or produce indole, which results in harmful by-products. Their inability means they do not harm the host in this respect, reducing the potential for detrimental effects to occur to a host, which is important when including these bacteria as a feed additive. Also the test was negative for citrate, which is commonly a cause of food spoilage. These bacteria could potentially be used in delaying expiration, without harm to humans, as mentioned above.
One noticeable difference is that they vary the sugar they metabolise, which is no doubt a large advantage in terms of competition: they can exhibit similar traits without competing for nutrients, providing a unique niche for each species. It was interesting to see that only L. lactis can survive at 45oC, and the others survive only at 10oC. It would be interesting to see the ability of these bacteria to survive at intermediate temperatures, considering previous research. It seems that LAB thrive at higher temperatures as higher quantities being found during summer and almost absence counts were found in winter. The isolates found in silver carp are able to fill the niche of fish that inhabit cooler waters. It is possible for them to inhabit temperatures higher, since they inhabit organisms such as animals including humans (Kandler and Weiss, 1986)? And if they are capable, will they be outcompeted in terms of other bacteria that are more adapted to these higher temperatures, and is this why they have adapted to cooler temperatures?
Lactococcus sp. and Lactobacilli sp. are rarely found in the intestines of other fish, therefore the addition of them as probiotics to such fish species is likely to have a beneficial impact on nutrition and immunity.
This paper shows promise for the use of Lactobacillus plantarum, Lactobacillus raffinolactis and Lactococcus lactis, found in silver carp, in aquaculture and food preservation. These LAB are potentially of use as feed additives that control pathogenic colonisation in fish as alternatives to antibiotic use. If used in aquaculture, their reliance on vitamins may mean the inclusion of more in the fish feed.
Their composition is said to change seasonally, hence this paper considers their composition over one season: winter. Five adult silver carp (Hypophthalmichthys molitrix) were removed, once a month over the winter period, from Gheshlaghdam lake, Iran. They were transferred to indoor tanks with water temperatures matching the natural temperature. 1g digesta was homogenised with 9ml ‘normal saline’, from which a dilution series from 10-1 to 10-10 was created, and plated out onto agar. Anaerobic incubation occurred at 37°C for 48 – 72hours, before 20 well grown colonies were selected from each plate. The bacteria were identified by observing morphological characteristics and carrying out biochemical tests. The capability to ferment different sugars were tested. Once the bacteria were identified, the abundances of each species were compared.
The intestines of silver carp contained 3 species of LAB that fall into 2 genera: Lactobacillus plantarum, Lactobacillus raffinolactis and Lactococcus lactis (in order of dominance). They are relatively similar in that none hydrolyse urea, or produce indole, which results in harmful by-products. Their inability means they do not harm the host in this respect, reducing the potential for detrimental effects to occur to a host, which is important when including these bacteria as a feed additive. Also the test was negative for citrate, which is commonly a cause of food spoilage. These bacteria could potentially be used in delaying expiration, without harm to humans, as mentioned above.
One noticeable difference is that they vary the sugar they metabolise, which is no doubt a large advantage in terms of competition: they can exhibit similar traits without competing for nutrients, providing a unique niche for each species. It was interesting to see that only L. lactis can survive at 45oC, and the others survive only at 10oC. It would be interesting to see the ability of these bacteria to survive at intermediate temperatures, considering previous research. It seems that LAB thrive at higher temperatures as higher quantities being found during summer and almost absence counts were found in winter. The isolates found in silver carp are able to fill the niche of fish that inhabit cooler waters. It is possible for them to inhabit temperatures higher, since they inhabit organisms such as animals including humans (Kandler and Weiss, 1986)? And if they are capable, will they be outcompeted in terms of other bacteria that are more adapted to these higher temperatures, and is this why they have adapted to cooler temperatures?
Lactococcus sp. and Lactobacilli sp. are rarely found in the intestines of other fish, therefore the addition of them as probiotics to such fish species is likely to have a beneficial impact on nutrition and immunity.
This paper shows promise for the use of Lactobacillus plantarum, Lactobacillus raffinolactis and Lactococcus lactis, found in silver carp, in aquaculture and food preservation. These LAB are potentially of use as feed additives that control pathogenic colonisation in fish as alternatives to antibiotic use. If used in aquaculture, their reliance on vitamins may mean the inclusion of more in the fish feed.
Farzad Ghiasi, F (2011) Predominant lactic
acid bacteria isolated from the intestines of silver carp in low water
temperature, African Journal of
Biotechnology, 10(59):12717-12721
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