Special Edition: Alternative Proteins

Bacterial single cell protein shows benefits in salmon, shrimp diets: study

By Aerin Einstein-Curtis contact

- Last updated on GMT

© iStock/StrahilDimitrov
© iStock/StrahilDimitrov
A single cell protein from bacterium Methylobacterium extorquens show similar digestion and supported growth for farmed salmon and shrimp when replacing fishmeal, says researcher. 

Details of the research examining the use of the alternative protein for use in the feeds of Atlantic salmon, Pacific white shrimp and smallmouth grunt were published in the journal PeerJ​.

The single cell protein ingredient evaluated was that produced by US company, KnipBio. The Massachusetts-based firm has developed a series of naturally occurring microbes that convert low-cost feedstock into single-cell proteins with pigment-enhancing carotenoids, aimed at fish nutrition. A bacterial biomass is produced from the M. extorquens​, a leaf symbiont that grows rapidly on feedstock methanol.

The authors explained that they analysed white shrimp (Litopenaeus vannamei​) growth and consumer taste preference, smallmouth grunt (Haemulon chrysargyreum​) growth, survival, health and gut microbiota, and Atlantic salmon (Salmo salar​) digestibility when fed diets that substitute - the bacterium M. extorquens​ at a level of 30% (grunts), 100% (shrimp), or 55% (salmon) of the fishmeal in a compound feed.​ 

In each of these tests, the team found the animals performed equivalently when fed diets containing M. extorquens​ as when fed a standard aquaculture diet. "This transdisciplinary approach is a first validation of this bacterium as a potential SCP protein substitute in aquafeeds. Given the ease to produce this SCP through an aerobic fermentation process, the broad applicability for use in aquaculture indicates the promise of M. extorquens in leading toward greater food security in the future,"​ said the authors.

The species chosen for the study were were selected because of the size of the respective markets in the aquaculture sector, said Lawrence Feinberg, CEO of KnipBio, and corresponding author of the study. “Atlantic salmon farming alone is a $15bn per year industry,”​ he said.

“We face the potential of entering into a protein-short world as populations continue to grow and we are seeing the rise of a middle class in some of the planet's most populated and developing nations,”​ he told FeedNavigator. “With [about] 90% of our global fisheries at or beyond capacity, and many experiencing decline, we cannot look to natural marine resources to yield additional protein – terrestrial proteins have kept up to meet today's demand but arable land-use and unpredictable weather patterns are a real concern going forward.”

The company is working to scale up its production levels of the protein source from kilogram batches to tons, along with continuing research trials and is compiling an application for the product to be approved for use in the US, he said.

“The key takeaway from these first studies is that our SCP appears to be a suitable substitute already with no serious downsides - and we are only at the beginning of developing and optimizing this new alternative."

Single cell protein use

Unlike some alternative proteins used in aquaculture, only a small footprint is needed to generate single cell proteins (SCP), he said. The fermentation process needs little space, limited water use and no fertilizer.

Ongoing production means that new strains can be advanced more rapidly, he continued.

Although some results have been reported, research with the alternative protein is not completed, said Feinberg. And, some of the results have provoked follow-up inquires.

The research trials also used a version of the microbe that is about four years old, he said. The company has been working on advancing and updating the protein.

“Future investigations will be based on lineages of the single cell proteins that have been optimized for amino acid composition (including taurine), pigmenting carotenoids, higher protein content,” ​he​ said. “As additional new technologies come on line, the most promising candidates will continue to be tested.”  

Additionally, it can take years to move a novel protein from an idea to a practical feed ingredient, he said.

“Soy is heralded as an excellent, low-cost replacement to fishmeal,”​ he said. “However, it took [about] 15 years to get to where we are today, and serious concerns around stomach inflammation in carnivorous species like salmon [linked to soy usage] still remain.”

Study details

The single cell protein used was generated through an aerobic fermentation process and dried to create a flour designated as KnipBio Meal (KBM), said the researchers in the study.

The salmon diets were composed to examine the digestibility of KBM compared to other commercially available aquaculture diets, they said. Two diets were formulated for salmon, including a control using marine-based proteins and one with 30% of KBM.

Fecal matter was collected for the feeding trial on days two and four, they said. Both diets and feces were checked for organic matter, lipid content and energy and the apparent digestibility coefficients of for nutrients in the diet were determined.

Both the feeding trials for the shrimp and smallmouth grunt examined the use of the SCP-containing meal to replace differing amounts of fishmeal in the diet, said the researchers. The shrimp were then assessed for animal growth, health and survival rate.

Three diets for shrimp were generated including a control feed and to feed with 50% and 100% replacement of fishmeal with the SCP meal, they said. Shrimp were fed for 60 days and a selected group were raised for an additional 90 days.

They were checked for weight, length and flavor, said the researchers.  

For the grunt feeding trial, four diets were created, including a control diet, the control with added carotenoid, and fishmeal replacement at 10% and 50%, they said. Weight and length were tracked for 41 days and whole body amino acids, fatty acids and gut microbial DNA were analyzed. 

Research findings

The shrimp had similar levels of survival regardless of diet, said the researchers. The more replacement meal was in the diets the smaller the shrimp tended to be but the partial diet results were not significantly different from either end of the spectrum.

The grunt did not see differences in mortality, length, weight condition, specific growth rate or gut microbial community, they said. But, those on the fishmeal diet had higher levels of bodily protein.  

The feed conversion ratio was similar for the control diet and the partial fishmeal replacement diet, but the completely fishmeal free diet had a greater FCR, found the authors.

For the salmon, the diets had similar apparent digestibility coefficient (ADC) values, said the researchers. But the ADC specifically for protein was lower for the partial replacement diet and, the KBM diet had slightly better results for the majority of amino acids in the diet.

“It is certainly our hope that we can elevate inclusion levels and offset the use of increasingly limited marine resources,”​ said Feinberg of the trial diets.

“There are also strong indications from the literature that SCPs may help abate the stomach inflammation associated with soy and therefore can be a naturally complementing material to plant protein,”​ he said, regarding the salmon research. “Additionally, as a source of anti-oxidant containing carotenoids, we believe the health and immunity benefits should improve the overall welfare of the animal.”        

Source: PeerJ

Title: A transdisciplinary approach to the initial validation of a single cell protein as an alternative protein source for use in aquafeeds

DOI: doi.org/10.7717/peerj.3170

Authors: M. Tlusty, A. Rhyne, J. Szczebak, B. Bourque, J. Bowen, G. Burr, C. Marx, L. Feinberg

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