Introduction
Microbial natural products represent an important reservoir for drug discovery and along with their (semi)synthetic derivatives, constitute a major component of the contemporary pharmaceutical arsenal. Their thusly validated utility is juxtaposed against the barriers to natural product discovery; high rediscovery rates, reliance on largely serendipitous response in bioactivity assays, and the resources and expertise required for their structure determination being the primary impediments . With this background, accessing biological sources that have not yet been extensively mined for natural product discovery is a promising route, one which, at the very least, promises to ameliorate the problem of continued rediscovery of known natural products. This review outlines the recent progress that has been realized using bacteria of the genus Microbulbifer. Together with the emerging field of natural product discovery from Microbulbifer bacteria, this genus of obligate marine bacteria is well validated to be a valuable source of biopolymer degrading enzymes. In this review, we outline the discovery of Microbulbifer enzymes that have substantial biocatalytic potential as it pertains to biopolymer degradation, followed by a description of natural product discovery from this genus.
Microbulbifer is a genus of rod-shaped, aerobic Gram-negative Alteromonadaceae family γ-proteobacteria. They are halophilic obligate marine bacteria that are frequently isolated from diverse marine holobionts such as sponges , sediments , algae , and corals using media that mimic the native salt water habitat. Strains of this genus are detected together with Pseudovibrio and Ruegeria strains that grow in identical culture conditions, and hence obtaining axenic Microbulbifer strains may require repeated rounds of serial enrichment. This genus was first described by Gonzales et al. in 1997 . More than 130 strains have been reported from regions of wide geographical dispersion (Table 1, Figure 1). Microbulbifer bacteria are well known for their capacity to degrade not only a wide variety of polysaccharides including cellulose, agar, chitin, alginate, and xylan , but also plastics . Progressing from their isolation and cultivation, natural product discovery from Microbulbifer bacteria is starting to gather steam . The major classes of natural products isolated from Microbulbifer to date include alkaloids , fatty acid and polyketides , and non-ribosomally synthesized peptides . These findings validate the potential for secondary metabolite discovery from Microbulbifer genus. This review will cover the distributions and origins of Microbulbifer bacteria strains, degradation enzymes, and secondary metabolite discoveries. A focus is placed on the novel chemical structures reported with reference to their biological activities and the biosynthetic studies they have inspired.
Table 1:
Summary of marine sources, geographical locations, and key characteristics of Microbulbifer strains reported in literature.
Origin
Location
Key characteristics
References
1
Microbulbifer hydrolyticus gen. nov.
marine pulp mill
USA
produces hydrolytic enzymes,
polyethylene degradation
2
Microbulbifer degradans. 2-40
salt marsh
USA
degrades polysaccharides,
polyserine linkers, chitinase
3
Microbulbifer salipaludis sp. nov.
salt marsh
Korea
–a
4
Microbulbifer arenaceous sp. nov.
red sandstone
Scotland
hydrolyzes chitin, esculin, gelatin, and starch
5
Microbulbifer elongates comb. nov.
–a
Germany
–a
6
Microbulbifer sp. JAMB-A7
sediment
Japan
β-agarase
7
Microbulbifer sp. JAMB-A94
sediment
Japan
β-agarase, ι-carrageenase
8
Microbulbifer sp. JAMB-A3
sediment
Japan
β-agarase
9
Microbulbifer maritimus sp. nov.
sediment
Korea
–a
10
Microbulbifer sp. A4B-17
ascidian
Palau
produces 4-HBA and
parabens
11
Microbulbifer sp. A4A-72
sponge
Palau
produces 4-HBA
12
Microbulbifer sp. V296
sponge
Yap
produces 4-HBA
13
Microbulbifer sp. A4B-20
algae
Palau
produces 4-HBA
14
Microbulbifer sp. A2C-113
sponge
Palau
produces 4-HBA
15
Microbulbifer sp. A4A-79
ascidian
Palau
produces 4-HBA
16
Microbulbifer sp. AM222
sediment
Palau
produces 4-HBA
17
Microbulbifer sp. AM292
sediment
Palau
produces 4-HBA
18
Microbulbifer sp. A4A-68
sponge
Palau
produces 4-HBA
19
Microbulbifer sp. A2D-17
sponge
Palau
produces 4-HBA
20
Microbulbifer sp. I1876
algae
Japan
produces 4-HBA
21
Microbulbifer sp. C91
algae
Yap
produces 4-HBA
22
Microbulbifer sp. HG111
sponge
Japan
produces 4-HBA
23
Microbulbifer sp. F-104
algae
Palau
produces 4-HBA
24
Microbulbifer sp. V32
sponge
Yap
produces 4-HBA
25
Microbulbifer sp. HG125
sponge
Japan
produces 4-HBA
26
Microbulbifer sp. A3G-2
ascidian
Palau
produces 4-HBA
27
Microbulbifer sp. A3P2-23-3-2
ascidian
Palau
produces 4-HBA
28
Microbulbifer sp. AM220
sediment
Japan
produces 4-HBA
29
Microbulbifer sp. YM3-0188
sponge
Palau
produces 4-HBA
30
Microbulbifer sp. A2D-15
sediment
Palau
produces 4-HBA
31
Microbulbifer sp. HG869
ascidian
Palau
produces 4-HBA
32
Microbulbifer sp. HG279
sponge
Japan
produces 4-HBA
33
Microbulbifer sp. ssthio04PA2-36a
sponge
Palau
produces 4-HBA
34
Microbulbifer celer sp. nov.
saltern
Korea
–a
35
Microbulbifer halophilus sp. nov.
saline soil
China
–a
36
Microbulbifer sp. CMC-5
seaweed
India
degrades polysaccharides,
β-agarase
37
Microbulbifer variabilis sp. nov.
algae
Japan
–a
38
Microbulbifer epialgicus sp. nov.
algae
Japan
–a
39
Microbulbifer sp. L4-n2
sponge
France
produces parabens
40
Microbulbifer donghaiensis sp. nov.
sediment
China
–a
41
Microbulbifer chitinilyticus sp. nov.
mangrove
Japan
chitin-degrading
42
Microbulbifer okinawensis sp. nov.
mangrove
Japan
chitin-degrading
43
Microbulbifer sp. SD-1
seawater
Korea
degrades agar
44
Microbulbifer sp. JAM-3301
sediment
Japan
inulinase producer
45
Microbulbifer maritimus
seaweed
India
agarase producer
46
Microbulbifer sp. 6532A
seaweed
Japan
alginate lyase producer
47
Microbulbifer marinus sp. nov.
sediment
China
–a
48
Microbulbifer yueqingensis sp. nov.
sediment
China
–a
49
Microbulbifer gwangyangensis sp. nov.
tidal flat
Korea
–a
50
Microbulbifer pacificus sp. nov.
sponge
Korea
–a
51
Microbulbifer mangrove sp. nov.
mangrove
India
polysaccharide-degrading
52
Microbulbifer elongatus HZ11
seawater
China
seaweed-degrading
53
Microbulbifer thermotolerans DAU221
sediment
Korea
produces carbohydrate esterase, α-amylase, esterase, chitinase, GH3
-glucosidase polysaccharide lyase
54
Microbulbifer elongatus sp. A13
seaweeds
India
agarase producer
55
Microbulbifer rhizosphaerae sp. nov.
halophytic plant
Spain
–a
56
Microbulbifer sp. ALW1
algae
China
produces alginate lyase, laminarinase, β-glucosidase, chondroitinase
57
Microbulbifer flavimaris sp. WRN-8
sediment
China
–a
58
Microbulbifer mangrovistrain DD-13
mangrove
India
degrades polysaccharides
59
Microbulbifer echini sp. AM134
sea urchin
Korea
–a
60
Microbulbifer aggregans sp. CCB-MM1
sediment
Malaysia
produces sulfite reductase
61
Microbulbifer aestuariivivens sp. GHTF-23
tidal flat
Korea
–a
62
Microbulbifer sp. Q7
sea cucumber
China
produces β-agarase, alginate lyases
63
Microbulbifer sp. 127CP7-12
sponge
Korea
produces violacein
64
Microbulbifer hydrolyticus IRE-31-192
chemical mutation
China
polyethylene degradation
65
Microbulbifer sp. GL-2
blackfish
Japan
cellulase
66
Microbulbifer agarilyticus. GP101
invertebrate turbo cornutus
Korea
–a
67
Microbulbifer sp. BN3
sediment
China
β-agarase, chitinase
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