Environmental Microbiology

Identification of novel bacteria isolated from mangrove soil

Mangrove sediment represents one of the most dynamic and diverse microbial habitats. Malaysian mangrove is the third largest mangrove in the Asia-Pacific region. However, microbial studies on Malaysian mangrove are still scarce. Accordingly, our group performed to isolate bacteria from mangrove sediment, mainly the Matang mangrove forest, Perak, Malaysia. Currently, we have isolated more than 250 strains and have found several candidates of new genus and species, as follows:

1. Mangrovimonas xylaniphaga ST2L12TThe 16S rRNA gene sequence of this strain showed 95.3% similarity to Mangrovimonas yuxiaonensis. ST2L12T exhibited degradation of xylan, casein and tween 80 while M. yuxiaonensis did not show the phenotypes.

2. Microbulbifer aggregans CCB-MM1TThe 16S rRNA gene sequence of this strain showed 98.12 %, 97.46 % and 97.33 % similarity with M. rhizosphaerae, M. maritimus and M. gwangyangensis, respectively. Interestingly, only this strain showed cell aggregation in stationary phase.

In addition, we are performing the characterization of new Catenovulum-like bacterium and Hahella sp.

Mechanism of bacterial predation in Aureispira sp. CCB-QB1

A diauxic growth of marine agarolytic bacterium Persicobacter sp. CCB-QB2

Diauxic growth is a two-phase growth response seen in the presence of two different substrates and is mainly observed in gut microbes. However, marine agarolytic bacterium Persicobacter sp. CCB-QB2 also exhibits diauxic growth in the presence of nitrogen source and agar in culture medium. Additionally, QB2 cells strongly produce agar degradation enzymes in the second growth phase. The diauxic growth may play an important role in the production of carbohydrate degradation enzymes, such as agarase, in marine bacteria.

A novel thermostable and detergent-tolerant β-agarase from Persicobacter sp. CCB-QB2

Agarolytic bacterium, Persicobacter sp. CCB-QB2 produced four agarolytic enzymes. One of them, PdAgaC, exhibited unique characters. PdAgaC showed thermostability at 50 °C and tolerance towards several detergents. In addition, the activity of PdAgaC after incubation with 0.1% of SDS and Triton X-100 increased approximately 1.2-fold. The agarolytic activity was outstandingly higher than that of many known agrases.

Generally, β-agarases produce neoagarobiose (dimer), neoagarotetraose (tetramer) and neoagarohexaose (hexamer) as its hydrolyzate, not monomeric sugar. Interestingly, although the major hydrolytic product of PdAgaC was neoagarobiose, monomeric sugar was also produced. This is the first report of an agarase which can produce monomeric sugar from agarose.

Screening of potential secondary metabolites

Bacteria, particularly actinomycetes, are great producers of bioactive compounds. In CCB, we have a culture collection known as Microbial Biodiversity Library (MBL). Research conducted in this group includes various assays to screen the presence of potential secondary metabolites from those microbes, such as anti-infective, anti-oxidant, anti-microbial, plant growth promoters, siderophore production, etc.

Anti-infective

Currently, a new potential anti-infective agent was successfully isolated and characterized from marine actinomycetes. Streptomyces sp. CCB-PSK 207 was found to rescue Caenorhabditis elegans from Pseudomonas aeruginosa infection through restitution of suppressed lysozyme 7 activities. A hexane partition of the extract from this isolate could promote the survival of PA14-infected worms to more than 60%. In addition, the partition was able to induce the expression of lysozyme 7, an important innate immunity defense molecule of C. elegans.

Antioxidant

Besides the anti-infective agent, we have identified and characterized anti-oxidant bioactive metabolites from mangrove Streptomyces. These Streptomyces also showed good anti-microbial activities against several human pathogens. Various assays were performed, including phosphomolybdate assay, DPPH (1, 1, diphenyl-2-picryl hydrazyl) scavenging activity assay, reducing power assay, Beta-carotene bleaching disc diffusion assay, etc. Further elucidation of the bioactive compound structures is currently in progress.

Antimicrobial & plant growth promoters

Recently, agriculture has been faced with destructive activities caused by numerous pests, including microbial pathogens, weeds and insects, which resulted in drastic decrease of crop yield. Screening of new biopesticide agents, plant growth promoters, as well as siderophore producers, will be definitely improving our future agriculture. Based on primary studies, few potential Streptomyces have been characterized. These isolates show the ability of plant growth promoters as well as anti-phytopathogenic producers. Partitioning of the extract and characterization of the bioactive molecules will be conducted to elucidate the structure of the active compound.

Presently, we are also actively screening the secondary metabolites from MBL for other research purposes.