handles environmental samples and the Organisation for Economic Co-operation and Development’s assay OECD 221, which was developed
for specific chemicals and compounds (ISO
2005; OECD 2006). Both are seven-day growth
rate tests, which use different media, to measure
the effective concentration of the substance, or
EC 50 , where the growth rate by frond count or
frond area is half of the control. These tests date
back to the 1970s and have surveyed the effects
of heavy metals, pharmaceuticals, various pesticides and organic compounds, and even
radioactivity on Lemna growth rate and health,
helping us quickly asses and monitor environmental safety.
In order to perform major gene function
studies, as well as to improve duckweed agronomic performance (Cao et al. 2016), it is
required to establish an efficient system for
genetic manipulation and transformation. Several
stable transformation protocols for Lemna
(Chhabra et al. 2011; Yamamoto et al. 2001),
Landoltia (Spirodela oligorrhiza; Vunsh et al.
2007), and Wolffia (Boehm et al. 2001; Khvatkov
et al. 2015) using either Agrobacterium-mediated
or biolistic gene transfer together with a recent
gene-silencing platform in L. minor (Cantó-Pastor et al. 2015) have been described, providing
the means to further develop gene/genome-edited
duckweed as a powerful biomanufacturing
platform.
1.2 Current State
of Duckweed-Based
Applications
1.2.1 Historical
For centuries, people have seen the role duckweed
can play in their food production. Perhaps by
observing their livestock consume duckweed
species, small-scale farmers in Southern Asia
started feeding duckweed, often fresh as a portion
of the diet, to their fish, ducks, chickens, pigs, and
goats. In addition to animal feed, the people of
Thailand, Laos, and Cambodia have consumed
wild harvested and farmed Wolffia, mainly
globosa, rinsed, and then incorporated into soups,
salads, sauces, and a wide variety of foods
(Bhanthumnavin and Mcgarry 1971). If the
Wolffia is not cooked in with other ingredients, it
is generally briefly boiled, thereby selecting a
duckweed species without harmful calcium oxalate crystals and killing potential pathogens.
Recently, farmer education programs in Guatemala, Indonesia, and across the globe have
improved the use of duckweed to treat manure
while using it as a fertilizer and expanded the
practice within Asia and around the world, especially in Central America where a consortium of
*200 small-scale farmers grows duckweed and
tilapia. It is estimated by the executive director of
the International Lemna Association that the
thousands of small-scale farmers collecting wild
duckweed or growing it on site for human or
animal consumption are currently a greater part of
the duckweed applications by volume than the
large-scale, higher tech companies.
1.2.2 Water Treatment
As global population rises, so does demand in
clean water supply and wastewater treatment
systems. While developed nations have often
relied on a combination of aerobic bacteria
degradation and chemical treatment in activated
sludge systems, a variety of natural treatment
systems have been growing in popularity for
their often 50% lower capital and operating costs,
ability to recapture nitrogen, phosphorous, and
other valuable nutrients, and in some cases convert them into appropriate products. The main
downsides of these natural treatment systems are
their larger land requirements (up to 5 m
2 /person), poorer performance at cold temperatures,
and the requirement of knowledgeable and diligent staff to manage ecosystems through toxic
wastewater streams, harsh weather, etc. All this
indicates that natural treatment systems such as
constructed wetlands are ideal in rural locations,
especially of tropical countries, precisely where
many of the 2.5 billion people without access to
sanitary wastewater treatment live (Zhang et al.
2014b).
4
P. Fourounjian et al.
for specific chemicals and compounds (ISO
2005; OECD 2006). Both are seven-day growth
rate tests, which use different media, to measure
the effective concentration of the substance, or
EC 50 , where the growth rate by frond count or
frond area is half of the control. These tests date
back to the 1970s and have surveyed the effects
of heavy metals, pharmaceuticals, various pesticides and organic compounds, and even
radioactivity on Lemna growth rate and health,
helping us quickly asses and monitor environmental safety.
In order to perform major gene function
studies, as well as to improve duckweed agronomic performance (Cao et al. 2016), it is
required to establish an efficient system for
genetic manipulation and transformation. Several
stable transformation protocols for Lemna
(Chhabra et al. 2011; Yamamoto et al. 2001),
Landoltia (Spirodela oligorrhiza; Vunsh et al.
2007), and Wolffia (Boehm et al. 2001; Khvatkov
et al. 2015) using either Agrobacterium-mediated
or biolistic gene transfer together with a recent
gene-silencing platform in L. minor (Cantó-Pastor et al. 2015) have been described, providing
the means to further develop gene/genome-edited
duckweed as a powerful biomanufacturing
platform.
1.2 Current State
of Duckweed-Based
Applications
1.2.1 Historical
For centuries, people have seen the role duckweed
can play in their food production. Perhaps by
observing their livestock consume duckweed
species, small-scale farmers in Southern Asia
started feeding duckweed, often fresh as a portion
of the diet, to their fish, ducks, chickens, pigs, and
goats. In addition to animal feed, the people of
Thailand, Laos, and Cambodia have consumed
wild harvested and farmed Wolffia, mainly
globosa, rinsed, and then incorporated into soups,
salads, sauces, and a wide variety of foods
(Bhanthumnavin and Mcgarry 1971). If the
Wolffia is not cooked in with other ingredients, it
is generally briefly boiled, thereby selecting a
duckweed species without harmful calcium oxalate crystals and killing potential pathogens.
Recently, farmer education programs in Guatemala, Indonesia, and across the globe have
improved the use of duckweed to treat manure
while using it as a fertilizer and expanded the
practice within Asia and around the world, especially in Central America where a consortium of
*200 small-scale farmers grows duckweed and
tilapia. It is estimated by the executive director of
the International Lemna Association that the
thousands of small-scale farmers collecting wild
duckweed or growing it on site for human or
animal consumption are currently a greater part of
the duckweed applications by volume than the
large-scale, higher tech companies.
1.2.2 Water Treatment
As global population rises, so does demand in
clean water supply and wastewater treatment
systems. While developed nations have often
relied on a combination of aerobic bacteria
degradation and chemical treatment in activated
sludge systems, a variety of natural treatment
systems have been growing in popularity for
their often 50% lower capital and operating costs,
ability to recapture nitrogen, phosphorous, and
other valuable nutrients, and in some cases convert them into appropriate products. The main
downsides of these natural treatment systems are
their larger land requirements (up to 5 m
2 /person), poorer performance at cold temperatures,
and the requirement of knowledgeable and diligent staff to manage ecosystems through toxic
wastewater streams, harsh weather, etc. All this
indicates that natural treatment systems such as
constructed wetlands are ideal in rural locations,
especially of tropical countries, precisely where
many of the 2.5 billion people without access to
sanitary wastewater treatment live (Zhang et al.
2014b).
4
P. Fourounjian et al.