## 1 Introduction  
The role of biohydrogen-producing bacteria in the selection of fermentation feedstock, bioprocess design, and final biohydrogen production yield is critical from the biotechnologyical processing perspective. There are numerous reports in the literature on biohydrogen fermentation using both mixed and pure cultures of wild-type strains [1; 2]. Accordingly, sludge, soil, wastewater, and compost have all been identified as natural habitats for such bacteria and have the potential to be excellent biocatalysts for biohydrogen fermentation [3]. Mixed cultures are generally preferred due to their ease of handling and the capability of utilizing a wider range of fermentation feedstocks. However, maintaining a stable biohydrogen-producing microbial community within mixed cultures remains a challenging task because of its dynamicity in evolving as fermentation operational parameters change [4]. Moreover, the threat of predominating non-hydrogen-producing bacteria such as methanogens, homoacetogens, and lactic acid bacteria must be taken into consideration when dealing with mixed cultures. A single culture of biohydrogen-producing bacterium, on the other hand, provides much-needed consistency in inoculum preparation, with higher, and consistent product yields. In order to minimize operational costs, the biohydrogen fermentation of a single culture inoculum must be performed without any medium sterilization [5; 6]. Several anaerobic organisms have been identified as biohydrogen producers. In general, biohydrogen-producing bacteria are classified as either obligate anaerobes (such as _Clostridia_) or facultative anaerobes (e.g., _Enteric_ bacteria) [7]. Obligate anaerobes are excellent biohydrogen producers, whereas facultative anaerobes have greater tolerance and durability when exposed to oxygen [8; 9]. _Clostridia_ sp. produces spores, so the first step in isolating bacterium from this genus is usually a pretreatment of inoculum. Pretreatment of inoculum, either chemically or thermally, results in an enrichment of spore-forming bacteria by removing potentially non-spore-forming biohydrogen producers [5; 6; 10]. Bacteria isolation procedures without seed inoculum pretreatment may result in a broader selection of biohydrogen producers. The ability to tolerate oxygen, on the other hand, is a major advantage of facultative anaerobes, such as _Enterobacteriaceae_, over obligate anaerobes, which simplifies process handling. Once oxygen is depleted in the fermentation medium, the enzyme activity involved in biohydrogen production can be rapidly restored. The genus can produce biohydrogen by metabolizing glucose via a mixed acid (primarily formic acid) or 2,3-butanediol fermentation pathway. Nevertheless, both types of bacterial genera have been shown to be capable of growing, consuming, and producing biohydrogen from a variety of waste and lignocellulosic materials, including oil palm biomass [11; 12; 13]. At the moment, Malaysia's palm oil mills generate ca. 95 million tons of oil palm fresh fruit bunches. Fresh fruit bunches are steam-sterilized after collection to inhibit lipid degrading enzymes and microbial action. The bunch's fruitlets are stripped, crushed, and digested for their oil content, leaving oil palm empty fruit bunches (OPEFB) as a major byproduct. Approximately 22-23% of the total mass of fresh fruit bunches, or nearly 20 million tons of solid biomass, is discharged as OPEFB. The OEPFB is composed of a main stalk (about 20-25% of total weight) and numerous spikelets with sharp spines at the tips. It is therefore critical to utilize OPEFB for purposes other than conventional mulching, soil conditioning, or pelletization for use as a fuel for boilers. These traditional methods are not sustainable because they either necessitate a large processing area or are harmful to the environment by emitting greenhouse gases into the atmosphere [14; 15; 16]. In this regard, creating value-added products from OPEFB generates additional profit, while at the same time addressing environmental issues.