Marine Metagenome and Supporting Technology 19.1 Bacteria and Marine Ecosystems 501
Part C | 19.2
known Cd accumulation proteins, metallothionein or
phytochelatin. Currently we are in the process of analyzing the characteristics and properties of this novel
protein.
Screening for Saline Tolerant Enzymes
Salt or saline tolerant enzymes have long been regarded as important enzymes required in industry, since
many industrial processes are highly dependent on conventional salt removal steps that result in high-energy
consumption. Thus, the isolation and use of salt-tolerant
enzymes in such processes may greatly contribute to
overcoming this problem. Several attempts have resulted in the isolation of salt-tolerant enzymes from
microorganisms found in high saline marine environments. Serine hydroxymethyltransferase (SMTH), for
example, commonly found in living organisms and
is a key enzyme in the cellular one-carbon pathway.
Waditee-Sirisattha et al. successfully identified this enzyme from the halotolerant cyanobacterium Aphanothece halophytica, expressed it in Escherichia coli and
further showed that enzyme activity was promoted in
the presence of high salinity [19.39]. Mai et al. on
the other hand, successfully cloned a ˇ-glucosidase
from a marine streptomycete showing that the enzyme
also showed remarkable activity enhancements under
saline conditions [19.40]. In addition, salt-tolerant enzymes such as general stress proteins, enoyl-CoA hydratase [19.41] and bacterial lipolytic enzymes [19.42]
have also been identified from metagenome library
screening.
In our efforts, we have also been successful in identifying a gene encoding for the FtsH protein from our
metagenome libraries. Upon comparison of the isolated
FtsH protein with that of Escherichia coli, our isolate
showed high saline resistant properties, suggesting the
possibility of it being a novel enzyme originating from
a marine bacterium. Although further functional analyses are in progress, the potential of this enzyme is
promising, since FtsH proteins are known to function as
crucial enzymes that play key roles in bacterial survival,
and it has been suggested that it participates in several
cellular processes, including protein assembly, export,
and degradation [19.43, 44]. Further studies may provide important insights to the function of FtsH proteins
in high salinity environments.
Potential of Marine Metagenomic
in Bioethanol Production
Bioethanol is a renewable energy that has received
much attention due to its potential in replacing current fossil fuel. Its production is dependent on biomass
resources such as starch-based biomasses (corn, sugarcane), cellulose or lignocellulose biomasses (wheat
grain), and marine biomasses (seaweed, microalgae).
Although conversion of sugar to ethanol is relatively
easy, starch-based biomasses conflict with the food
industry. Thus, the latter two types of biomasses
play a more important role in providing the resource for bioethanol production. Nevertheless, conversion of these biomasses to bioethanol is much
more challenging. In countries like Japan, providing
resources for land-cultivated biomasses is problematic
due to limited land resources, but marine biomasses
show greater potential. Marine biomasses grow relatively fast and produce a higher yield [19.45]. For
example, Laminaria japonica (brown algae) yields
six and a half times more than sugarcane. Nevertheless, although it has great potential, the conversion of marine biomasses to bioethanol is still
challenging.
Marine biomasses, seaweed in particular, are composed of polysaccharides such as ulvans (green algae), agarans and carrageenans (red algae), and alginates, fucans, and laminarin (brown algae), which
are required to be processed in order to be utilized [19.46]. Oligosaccharides from alginate, for instance, undergo saccharification by partial acid and
alkali hydrolysis. These saccharification processes are
complex and by-products can pose technical, environmental, and economic problems [19.47]. Thus, in
order to overcome this problem, the use of polysaccharide degrading enzymes extracted from the environment has received much attention. Recent reports
on the identification of novel genes encoding for enzymes such as porphyranases, agarases [19.48], ulvan
lyases [19.49], cellulase, alginate lyase, laminarinase,
and kelp-lyase [19.50] from various marine resources
have shown that microorganisms may, in fact, provide
an ideal source for the identification of highly active
algae degrading enzymes to assist in the processing of
marine biomasses.
Therefore, in order to attain highly active algae degrading enzymes, it is believed that the application of metagenomes from microorganisms can
be very useful. As described above, by implementing metagenomic research, these enzymes can
be fully exploited from both cultivable and uncultivable microorganisms. Furthermore, it is speculated that metagenomic research may play a major role and be of importance to this area of
research.
Part C | 19.2
known Cd accumulation proteins, metallothionein or
phytochelatin. Currently we are in the process of analyzing the characteristics and properties of this novel
protein.
Screening for Saline Tolerant Enzymes
Salt or saline tolerant enzymes have long been regarded as important enzymes required in industry, since
many industrial processes are highly dependent on conventional salt removal steps that result in high-energy
consumption. Thus, the isolation and use of salt-tolerant
enzymes in such processes may greatly contribute to
overcoming this problem. Several attempts have resulted in the isolation of salt-tolerant enzymes from
microorganisms found in high saline marine environments. Serine hydroxymethyltransferase (SMTH), for
example, commonly found in living organisms and
is a key enzyme in the cellular one-carbon pathway.
Waditee-Sirisattha et al. successfully identified this enzyme from the halotolerant cyanobacterium Aphanothece halophytica, expressed it in Escherichia coli and
further showed that enzyme activity was promoted in
the presence of high salinity [19.39]. Mai et al. on
the other hand, successfully cloned a ˇ-glucosidase
from a marine streptomycete showing that the enzyme
also showed remarkable activity enhancements under
saline conditions [19.40]. In addition, salt-tolerant enzymes such as general stress proteins, enoyl-CoA hydratase [19.41] and bacterial lipolytic enzymes [19.42]
have also been identified from metagenome library
screening.
In our efforts, we have also been successful in identifying a gene encoding for the FtsH protein from our
metagenome libraries. Upon comparison of the isolated
FtsH protein with that of Escherichia coli, our isolate
showed high saline resistant properties, suggesting the
possibility of it being a novel enzyme originating from
a marine bacterium. Although further functional analyses are in progress, the potential of this enzyme is
promising, since FtsH proteins are known to function as
crucial enzymes that play key roles in bacterial survival,
and it has been suggested that it participates in several
cellular processes, including protein assembly, export,
and degradation [19.43, 44]. Further studies may provide important insights to the function of FtsH proteins
in high salinity environments.
Potential of Marine Metagenomic
in Bioethanol Production
Bioethanol is a renewable energy that has received
much attention due to its potential in replacing current fossil fuel. Its production is dependent on biomass
resources such as starch-based biomasses (corn, sugarcane), cellulose or lignocellulose biomasses (wheat
grain), and marine biomasses (seaweed, microalgae).
Although conversion of sugar to ethanol is relatively
easy, starch-based biomasses conflict with the food
industry. Thus, the latter two types of biomasses
play a more important role in providing the resource for bioethanol production. Nevertheless, conversion of these biomasses to bioethanol is much
more challenging. In countries like Japan, providing
resources for land-cultivated biomasses is problematic
due to limited land resources, but marine biomasses
show greater potential. Marine biomasses grow relatively fast and produce a higher yield [19.45]. For
example, Laminaria japonica (brown algae) yields
six and a half times more than sugarcane. Nevertheless, although it has great potential, the conversion of marine biomasses to bioethanol is still
challenging.
Marine biomasses, seaweed in particular, are composed of polysaccharides such as ulvans (green algae), agarans and carrageenans (red algae), and alginates, fucans, and laminarin (brown algae), which
are required to be processed in order to be utilized [19.46]. Oligosaccharides from alginate, for instance, undergo saccharification by partial acid and
alkali hydrolysis. These saccharification processes are
complex and by-products can pose technical, environmental, and economic problems [19.47]. Thus, in
order to overcome this problem, the use of polysaccharide degrading enzymes extracted from the environment has received much attention. Recent reports
on the identification of novel genes encoding for enzymes such as porphyranases, agarases [19.48], ulvan
lyases [19.49], cellulase, alginate lyase, laminarinase,
and kelp-lyase [19.50] from various marine resources
have shown that microorganisms may, in fact, provide
an ideal source for the identification of highly active
algae degrading enzymes to assist in the processing of
marine biomasses.
Therefore, in order to attain highly active algae degrading enzymes, it is believed that the application of metagenomes from microorganisms can
be very useful. As described above, by implementing metagenomic research, these enzymes can
be fully exploited from both cultivable and uncultivable microorganisms. Furthermore, it is speculated that metagenomic research may play a major role and be of importance to this area of
research.